MH370 and Other Investigations

More precise tracking data has recently become available that gives new insights about how MH370 was flown just before the transponder was disabled near the waypoint IGARI. The data was broadcast by the aircraft and received by a Malaysian ATC receiver at Terengganu. It is similar to the data that has been previously available from the aircraft tracking site FlightRadar24, except that the spacing between data points is shorter, and the data are the raw values that were actually broadcast by the aircraft. As a result, more details about the flight can be extracted.

The new tracking data was transmitted by the aircraft’s Automatic Dependent Surveillance – Broadcast (ADS-B) system, which broadcasts the GPS-derived position and altitude, as well as other parameters, as often as about every one-half of a second. Because of the inherent accuracy of GPS, the ADS-B position is more accurate than the traditional radar systems, which derive the position from the timing and angular direction of received signals from the aircraft using a rotating antenna.

A file containing the ADS-B data for MH370 is available here.

Path Near IGARI

The figure below shows that the aircraft was on a track to pass over waypoint IGARI. However, before reaching IGARI, the aircraft began to turn towards waypoint BITOD. The radius of the turn indicates that the bank angle was around 15°. The start of the turn before reaching the waypoint and the bank angle are both consistent with the aircraft following an automated route in “LNAV” mode in which the flight computers were programmed to fly “direct” to IGARI and then to BITOD. (IGARI is a compulsory “flyby” waypoint.) This suggests that at the time the transponder was disabled after 17:20:34.55, the autopilot was still engaged and the aircraft was flying in accordance with the flight plan. (The Safety Investigation Report states that the Mode S symbol dropped off the radar display at 17:20:36, which is close in timing to the last ADS-B point.) This is evidence that the deviation from the flight plan occurred after the transponder was disabled.

Comparison with Military Radar Data

The radar data that we have after the transponder was disabled consists of “primary surveillance radar” (PSR) data from civilian and military sources. Although the civilian radar data sets from the Kota Bharu and Butterworth radar sites have become available through unofficial channels, the range of the civilian primary radar sites is much less than the military primary radar sites, so that after the transponder was disabled near IGARI, only military radar captured the turnback to Malaysia. (The range of the Kota Bharu ATC radar is nominally 60 NM. IGARI is about 90 NM from Kota Bharu, and therefore not visible to the Kota Bharu ATC radar.)

Unfortunately, after many requests, the raw military data of MH370 has never been released by the Malaysian authorities. What we do have are low resolution images from official reports that depict the path of the aircraft. We also have filtered speed and track data that has been digitized from graphical data presented in a report from Australian authorities. Neither of these data sets provides the level of resolution and accuracy that would allow us to independently study the details of the path after passing IGARI, including the details of the turnback.

The figure below shows the military radar data (fuzzy yellow line) that was officially released in a low-resolution image, and enlarged here to show the path near IGARI. In the image, the bulls-eye was labeled “Last secondary radar data 1722”. For reference, the waypoints IGARI and BITOD were added to the image, as well as the ADS-B data (red) and the IGARI-BITOD route leg (black). The box (orange) around IGARI represents the much smaller area shown in the previous image.

There are some obvious discrepancies between the military data shown above and the ADS-B data shown in the previous figure. For one, the military data shows the turn towards BITOD starting after passing over IGARI. This “flyover” of IGARI is not consistent with how an aircraft following an automated path during the cruise part of the flight would turn between waypoints. If this path was actually flown, it would suggest that the navigational mode was not LNAV near IGARI.

The location of the last ATC radar point (the bulls-eye) is also different in this image from what the ADS-B data suggests. The ADS-B data shows that the transponder was disabled when MH370 was abeam IGARI. However, the image above shows the last ATC radar point occurring after the turn towards BITOD was completed. This could be because what is shown was extrapolated from the final transponder reply in what is referred to as “coasting”.

The military data also shows an impossibly sharp turn to the left occurred. Despite numerous requests, Malaysian officials have never provided an explanation for the false depiction of this turn.

These discrepancies indicate that the military data near the turnback should be used with caution. It’s possible that the radar installation that captured the turnback was Western Hill on Penang Island, and the turnback was near the maximum range of the radar site. (IGARI is about 220 NM from Western Hill.) If so, the inaccuracies might be from limitations of the military radar coverage this area. As such, the path depicted in the image may have been extrapolated from missing or inaccurate data, and should be assigned an appropriate level of uncertainty.

Finally, shown in the figure are the “entry and exit waypoints” of the turn that were supplied by the military and used by Malaysian safety investigators to study how the aircraft was flown after IGARI. As described in the Safety Investigation Report, simulations performed by the Malaysian investigative team matched the timing and position of the entry and exit waypoints of the turn only when the aircraft was manually flown with a steep bank angle of around 35°. However, considering the suspected inaccuracies in the military data, the conclusion that the turnback was manually flown should be re-visited. For instance, if the turn was begun prior to the entry waypoint, it would be possible to reach the exit waypoint at the proper time with a bank angle of 25°, which is a selectable bank angle when either of the autopilot modes “Heading Select” or “Track Select” is chosen.

Timing of Events Near IGARI

According to the Safety Investigation Report, the final radio transmission from MH370 occurred at 17:19:30. The following list shows the timing of this event along with the timing of the last three ADS-B points:

17:19:30 Last radio transmission (“Good night Malaysian Three Seven Zero”)
17:20:33.61 Last ADS-B point with altitude reported
17:20:34.15 First ADS-B point with no altitude reported
17:20:34.55 Last ADS-B point, no altitude reported

In a Boeing 777, the transponder may be disabled in the cockpit with a mode selector switch located on the pedestal between the left and right seats. The selector switch for the transponder, shown below with the label (1), would be set to standby (STBY):

During the time that the transponder was operating with altitudes reported, it was either in the switch position designated “TA/RA” for full functionality, or “TA ONLY” to suppress Resolution Alerts, or “ALT ON” to suppress both Traffic and Resolution Advisories. (TAs and RAs are part of the aircraft’s traffic collision avoidance system.) In order to select STBY from one of these three positions, it’s required to pass the intermediary position labeled “ALT OFF”. In this position, the transponder is replying to interrogations and is transmitting ADS-B data. However, there is no altitude data included in the replies and broadcasts.

Looking at the final ADS-B messages, we see that the altitude is missing for the last two messages, spanning a time of less than one-half of a second. This could mean that the intermediate switch position ALT OFF was captured as the selector switch was rotated to the standby position.

The time interval between the last radio transmission from the crew and the first message with no altitude reporting is 64 seconds. If the diversion from the flight path was caused by a third party forcing their way into the cockpit and taking control, those events would have to have occurred in 64 seconds or less. It is very unlikely that this could have been achieved by a third party in such a short amount of time.

Summary

New tracking data that has only recently become available gives us new insights as to how MH370 was flown before it disappeared from ATC radar:

• At the time the transponder was disabled near IGARI, the ADS-B data shows a path that is consistent with normal automated flight in LNAV mode following a programmed route from IGARI to BITOD.
• Discrepancies near IGARI between the ADS-B data and the military radar data suggest that the radar data has inaccuracies possibly because of the range limits of the radar installation on Western Hill on Penang Island.
• The Malaysian investigators’ conclusion that the turnback after IGARI was manually flown should be re-visited in light of the demonstrated limited accuracy of the military radar data near IGARI.
• The final ADS-B points may have captured an intermediate switch position as the transponder’s selector switch was rotated towards the standby position.
• After the last radio transmission from MH370, the maximum time available to disable the transponder and divert the aircraft was 64 seconds. That leaves an impractically small amount of time for a third party to enter the cockpit and take control.

We now have better ADS-B data for understanding how MH370 was flown up to the point that the transponder was disabled at 17:20:35. This complements the primary radar data from Kota Bharu that starts at 17:30:33. However, we are still missing the military radar data that would cover the 10-minute gap between these two data sets. That gap includes the left turn at the start of the diversion that put MH370 on a course back over Malaysia.

It is important for Malaysia to release this closely-held military radar data so that other investigators that are working to solve this mystery can perform independent analyses of how the aircraft was flown during the turn back to Malaysia. Whatever strategic reasons there might have originally been for withholding the military data are no longer relevant more than 5 years after the disappearance.

Fellow IG members Mike Exner and Don Thompson have provided valuable comments to this article.

Narendran (Naren) KS, who lost his wife Chandrika on MH370, on Twitter says: Yes, give us the truth. Not too many people we know are convinced that 459 pages of the 2018 report is the sum total of all that is known regarding the disappearance of MH370. The following note accompanies his Tweet.

Friends,

My family and friends in India send you their greetings.

Unlike previous years, I have been ambivalent about making this trip. I have searched hard to understand this. It is almost 5 years since I saw off my wife, Chandrika, and the last we heard from Malaysia Airlines flight MH370, the flight she boarded en route to Mongolia.

It has been a long haul dealing with loss and rebuilding a life, a task that remains incomplete. What became clear is that lately the cloud of sorrow and despair, the listlessness with life in general, and the restlessness with the MH370 search and investigation has become less intense.

What remains is the solidarity with the MH families, their loss and struggles to cope, to envision a future and reconstruct their lives. This only grows as each nuance in a shared language of loss, grief and reconstruction becomes more widely shared and understood.

5 years is a long time.

Among the MH families, the old have grown older. Some whose will to live was broken by irreconcilable loss believe they have nothing left to live for.

Among the young, some have by now moved on to pursue studies, take up jobs, moved home, find partners, have babies, … Somethings to cheer about and remind ourselves that winter is not the only season, each day isn’t always drab, and the sky isn’t only grey.

However, many among us continue to struggle while applying ourselves to the chores of daily existence. For all of us, knowing what happened to MH370 remains the key to unlock a part of our lives, our energies.

Our prayers have remained unchanged: Find the plane. Find the passengers. Give us answers to ‘what’, ‘why’, ‘how’ and if it comes to it, ‘who’.

Give us the truth.

Yes, give us the truth. Not too many people we know are convinced that 459 pages of the 2018 report is the sum total of all that is known regarding the disappearance of MH370. Those who know more but have chosen silence, if indeed there are some, will eventually die a thousand deaths each day, for guilt is a latecomer but an unforgiving squatter. It is the order of things and not what we would wish for them.

In this search for the truth, there isn’t a Malaysian truth, an Australian truth, a British truth or an American one. Or (even) an Indian and a Chinese one. There were 239 passengers from 14 countries. An international mix of nationalities. A Boeing 777, an American company’s product. The incident is believed to have occurred in the Indian Ocean, in international waters. The investigation is governed by the conventions written in by the International Civil Aviation Organization. Experts from across the world when consulted or otherwise, have weighed in with their analysis and recommendations regarding the search. It is an event that concerns, every airline, every passenger and perhaps almost every family across the world exposed to civil aviation.

To suggest as some do that it should be left to Malaysians to script the story and the end game does not cut ice. If anything, the fact that it was a Malaysian airline’s flight under Malaysian air traffic control and Malaysia’s leadership of the investigation places an unshakable burden of responsibility to the world at large….to persist, to mobilize the funds necessary, and to hunt for the credible evidence for further search that it never tires of reminding us as being a requirement. It also has responsibility to test the claims of those who proclaim new knowledge, new evidence and fresh coordinates, and offer a public, transparent well-argued refutation if indeed that is what will end misguided or false narratives.

The best tribute we can offer to those we have lost is through demonstrating the will to find credible answers, fix the issues and assure the world that more lives will not lost in future to similar incidents.

A new Malaysia under this new Government has been the source of new fledgling hope.

To those who have fallen silent travelling on MH370, we remain respectful and eternally indebted for the time they shared with us. To those who have offered silent support, those who have lent their voice and those who have sent their prayers, we remain grateful. We draw strength from your little acts of kindness, words of solidarity, and your quest for the truth – whichever corner of the earth you seek it from.

Questions have a way of persisting and even outliving you and me till satisfactorily answered. I go back to pick up the threads of my life in Chennai secure and with faith that one day we will know.

Thank you.

Introduction

The civilian radar data for MH370 that became publicly available in April 2018 provides insights as to how MH370 was flown after the transponder was disabled around 17:20:31 UTC. After flying by waypoint IGARI and turning back, the aircraft passed to the north of Kota Bharu Airport, crossed the Malaysian peninsula in a southwest direction, passed to the south of Penang Island, turned to the northwest, and flew over the Malacca Strait. Here, we look more closely at the flight path as it flew towards, around, and away from Penang.

In order better understand the sequence of inputs to the flight control system, we created a simulation using the PMDG 777 model in Microsoft Flight Simulator. In particular, we studied whether the aircraft might have been flown with the pilot providing inputs to the autopilot, and what those inputs might have been.

Although we can calculate the groundspeed from the radar data, the altitude of this portion of the flight is not known. In the simulation, the flight segment near Penang was flown with the assumption of a level flight at FL340 and at Mach 0.84, and with representative meteorological data. These assumptions are consistent with the observed groundspeeds of around 510 knots. Within a reasonable range, the assumptions about altitude, Mach number, and atmospheric conditions do not materially change our observations and conclusions for this portion of the flight.

Simulation

A flight simulation with the autopilot engaged was created in the following manner:

1. In the Flight Management Computer (FMC), Penang Airport (WMKP) was set as the destination, and the procedure for an arrival to the ILS04 Runway via the BIDM1A standard terminal arrival route (STAR) was selected. The waypoints for this complete route would be BIDMO- PUKAR-ENDOR-MEKAT-KENDI-CF04-FF04-RW04. The final three waypoints are the final approach course fix, the final approach fix, and the runway threshold, in that order, for an ILS approach to Runway 04.
2. Of these waypoints, all are deleted from the route except ENDOR and FF04. VAMPI is added after FF04.
3. The aircraft approaches ENDOR with the autopilot engaged and LNAV selected. After passing ENDOR, the aircraft automatically turns towards FF04.
4. About 2 NM before FF04, TRK SEL is chosen and the pilot turns the selection knob to steer towards OPOVI using the map in the navigational display (ND) as a guide. The aircraft passes FF04 about 0.4 NM to the right. (If the autopilot had remained in LNAV, the aircraft would not have flown exactly over FF04, as the aircraft would have “cut the corner” as it turned towards VAMPI.)
5. After passing near OPOVI, TRK SEL of 300° is dialed with a maximum bank angle of 15°. This initiates a turn to the right at 15°. When the track of 300° is approached, the aircraft automatically rolls out of the turn and maintains this track.
6. Once established on a track of 300°, LNAV mode is selected as the next mode.
7. At this track angle, the aircraft path converges towards the route leg defined by the waypoints FF04-VAMPI. At about 30 NM from FF04, as the aircraft approaches this leg, the autopilot mode automatically changes from TRK SEL to LNAV, and the route leg is captured.
8. The plane proceeds in LNAV mode past Pulau Perak and towards VAMPI on the path defined by FF04-VAMPI.

The next figure shows how the waypoints and route legs would appear in the navigation display (ND) in the cockpit after the aircraft had just passed ENDOR and with the route configured as ENDOR-FF04-VAMPI. The route (magenta line) shows the path the aircraft would have followed if the autopilot remained in LNAV mode as the aircraft rounded Penang Island. By comparing the preceding figure with the one below, it is clear that the autopilot changed to a different mode before FF04 and changed back to LNAV mode when the path converged on the LNAV route about 30 NM from FF04.

Observations

There are some interesting observations about this path:

1. The agreement between the simulated flight path and the civilian radar data is very good, including the intercept and capture of the route leg to the northwest and towards VAMPI. This suggests that this portion of the flight path was flown in autopilot, although it is nearly impossible to prove that the aircraft was not manually flown.
2. The final civilian radar targets fall close to the path defined by FF04-VAMPI. This suggests that VAMPI was selected as a waypoint before reaching FF04, which further implies that there was an intention to fly northwest over the Malacca Strait and to intercept VAMPI even when the aircraft was near Penang. (The distance between FF04 and VAMPI is 166 NM.)
3. While in the vicinity of Penang Island, the high measured speed, the implied high altitude, and the selection of VAMPI as a waypoint suggest that there was no true intention to land at Penang Airport.
4. The selection of VAMPI as a waypoint while in the vicinity of Penang is consistent with the unverified military radar data that was shown to the MH370 family members at the Lido Hotel in Beijing on March 21, 2014. That radar data shows an aircraft that intercepted airway N571 at VAMPI.
5. Although there was no true intention to land at Penang Airport, the flight path may have been chosen to deceive radar operators into believing there was an intention to land.

Possible Deception to Land at Penang

In the figure below, the flight path from MH370 is plotted together with two recent Air Hong Kong flights (both LD561) for the route Ho Chi Minh City to Penang. These flight paths are representative of arrivals to Penang from the northeast. The LD561 paths do not follow the BIDM1A approach route and bear little resemblance to MH370’s path. Likely, the flight crews received vectors from Butterworth Approach to intercept and establish the final approach on the localizer for Runway 04. One of the flights was established at the final approach course fix (CF04) and the other was established only 3 NM from threshold. In the both cases, the intercept with the final approach course required a turn less than 90°. On the other hand, if MH370 had intercepted the localizer, it would have required a turn of about 135°, which would have been a very sharp turn.

Airline pilot Juanda Ismail noticed that MH370’s crossing of the ILS approach occurs at a similar location and similar intercept angle to what would be flown in the course reversal procedure for ILS04. The procedure is shown in the figure below, and consists of an outbound leg to 7 NM from the threshold of the runway at a track of 222°, a 45° right turn to a track of 267°, a straight leg, a 180° left turn to a track of 87°, a straight leg, followed by a 45° left turn to intercept the inbound approach course on a track of 42°. In the figure above, this same course reversal procedure is represented by the black curve with the arrow.

In the course reversal procedure, the straight leg at 267° is similar to part of the path that MH370 flew. However, in comparing MH370’s path to the course reversal procedure, it is missing the outbound leg, the 180° turn, and the final intercept. As the altitude for capturing to the glide slope is 2500 ft at FF04 (shown as D7.8 IPG in the figure), clearly there was no intention on the part of the pilot to actually perform the procedure and to land. However, it is possible that by flying an element of the course reversal procedure, there was a deliberate attempt to deceive radar operators into believing that MH370 had an intention to land.

With waypoints ENDOR-FF04-VAMPI selected as the route, there is a question as to why the pilot chose to not remain in LNAV mode when approaching FF04, as this would have turned the aircraft and put it on a direct northwest path to VAMPI without the need for pilot intervention. One explanation is that once a turn to the northwest towards VAMPI occurred, it would be clear to the air traffic controllers at Butterworth that there was no intention to land. Entering TRK SEL mode and steering the plane towards OPOVI before tracking back towards the FF04-VAMPI leg delayed that discovery and also positioned the aircraft to initiate the turn further from Butterworth.

It is also noteworthy that once a northwest track was established, the aircraft was tracking to pass through the restricted area designated WMD-412A. This would be expected to draw the attention of the military air traffic controllers at Butterworth. The relationship between the military and civilian ATC is described in this section from the Factual Information released in March 2015:

Provision of approach control service (within lateral limits of Butterworth Control Zone: 5,500 ft. altitude – FL245. (elsewhere 2,500 ft. altitude – FL245). Air traffic to/from the civilian Penang International Airport (PIA) is provided by military ATCOs who have been licensed by the ATI Division develops and establishes the ANS safety standards and performs safety oversight and to ensure the provision of services to civil traffic. The rationale for such an arrangement is based on the military activities at Butterworth Military Airport (BMA) which is in close proximity to PIA, and other military activities carried out over the high seas in danger areas WMD 412A and WMD 413A (permanently established). Furthermore, the final approach segments of both the PIA and the BMA intersect. No major incident has been recorded with the present arrangement/delegation of authority.

Conclusions

1. MH370’s flight path near Penang can be replicated with the autopilot engaged.
2. The flight path near Penang is consistent with a navigation system that is fully operational.
3. It is likely that waypoint VAMPI was entered in flight computers before crossing the approach path to runway ILS04, some 166 NM away.
4. The flight path near Penang is consistent with the image of the military radar data in the Malacca Strait that was never officially released.
5. It is very unlikely that there was an intention to land at Penang Airport.
6. It is possible that the elements of the flight path near Penang were chosen to deceive radar operators into believing that the aircraft had an intention to land.

Acknowledgement

I gratefully acknowledge the helpful comments and suggestions offered by fellow IG members Don Thompson, Richard Godfrey, and Mike Exner.

 

Today Blaine Gibson and other MH370 family members delivered to Malaysian authorities five new pieces of debris that are believed to be from the missing aircraft. The parts were found as a result of a campaign led by Blaine and the families to make the residents of Madagascar more aware of debris from MH370 that has drifted across the Indian Ocean and continues to land on the shores of East Africa.

Blaine has provided photographs and descriptions of the five parts, which are made available here in a zipped file. More recent high-resolution photographs are available here. The most recently discovered part (Part 5), pictured above, was found by a local fisherman this past August.

One piece of debris (Part 3) was identified by MH370 Independent Group (IG) member Don Thompson as a shattered piece of the interior floorboard of a Boeing 777. The part’s location in the B777 and the nature of the damage is consistent with a high speed impact, and therefore has probative value.

Identification of the Floorboard Piece

IG members Don Thompson and Mike Exner assisted Blaine in identifying the floorboard piece, and Don documented his findings in a report. An important clue was the piece contained a portion of a placard with the identifying characters WPPS61. Don was able to determine that the full placard number is BAC27WPPS61. This type of placard is affixed to high strength panels of material specification BMS4-20, which is used as flooring  material in passenger compartments of commercial aircraft, including the Boeing 777-200ER. Amazingly, Don was able to find a similar placard affixed to the floorboard of wreckage from MH17, which was also a Boeing 777-200ER. This leaves little doubt that the piece recovered from Madagascar is from MH370.

Discussion

The new debris gives us additional insight about where and how the aircraft impacted the sea. In light of the past efforts to find the aircraft, there are three main possibilities that remain:

1. The aircraft impacted the ocean relatively close to the 7th arc, but at a latitude further north than the area previously searched.
2. The aircraft impacted the ocean at a latitude previously searched, but farther from the 7th arc than previously assumed.
3. The aircraft debris field was in the subsea area previously scanned by sonar, but was either missed or misidentified.

Sources close to the previous search effort believe (3) is very unlikely, as there was a thorough review of the sonar data by multiple parties with high levels of experience, and because any “points of interest” were scanned multiple times to ensure the resolution was adequate to make a determination with a high level of confidence.

When considering the satellite data, the final two BFO values at 00:19 UTC are consistent with an aircraft at an increasingly high rate of descent. The new debris and some of the previously recovered debris also suggest that the aircraft impacted the ocean at high speed. That means that (2) is possible only if the aircraft first was in a rapid descent (producing the final BFO values), and then the pilot skillfully recovered from the rapid descent and glided some distance away from the 7th arc beyond the width of the subsea search, and then later the aircraft again descended at high speed and impacted the sea (producing the shattered debris). This sequence of dive-glide-dive is considered by many to be a very unlikely sequence of events, although it cannot be completed dismissed.

What is left is possibility (1). This suggests future subsea search efforts should proceed along the 7th arc, starting where the last search ended near 25S latitude, and continuing farther north. (In a previous blog post, I showed that an automated flight ending along the 7th arc at 22S latitude is possible.)

The part recovered in Madagascar in August 2018 was the latest in a series of finds that began with the discovery of the flaperon on Reunion Island in July 2015. Because of the wide range of discovery times, and because there is an undefinable delay between when a part arrives on a beach and when it is discovered, it is difficult to use the timing and location of debris discoveries to precisely pinpoint where to search for MH370.

Finally, the new debris finds illustrate the critical role of independent investigators in the search for MH370, and one investigator in particular. The local communications campaign to educate residents of Madagascar about debris washing ashore was spearheaded by Blaine Gibson with the help of some of the MH370 families. Blaine has also done a commendable job of developing a local network to help recover the debris after discovery. We have to wonder if additional debris is sitting on the shores of other countries like Tanzania, Kenya, and Somalia, where there were no similar campaigns to alert and organize the residents.

Links in this article:

Photographs and description of debris provided by Blaine Gibson

Additional high resolution photographs of debris

Identification of the piece of floorboard by Don Thompson

Reconstructed path ending near 22S latitude by Victor Iannello

About one year after its disappearance, one of Ocean Infinity’s (OI’s) autonomous underwater vehicles (AUVs) has detected the remains of the missing Argentine submarine, the ARA San Juan. From Ocean Infinity’s website:

Ocean Infinity, the seabed exploration company, confirms that it has found ARA San Juan, the Argentine Navy submarine which was lost on 15 November 2017.

In the early hours of 17 November, after two months of seabed search, Ocean Infinity located what has now been confirmed as the wreckage of the ARA San Juan. The submarine was found in a ravine in 920m of water, approximately 600 km east of Comodoro Rivadavia in the Atlantic Ocean.

Oliver Plunkett, Ocean Infinity’s CEO, said:

“Our thoughts are with the many families affected by this terrible tragedy. We sincerely hope that locating the resting place of the ARA San Juan will be of some comfort to them at what must be a profoundly difficult time. Furthermore, we hope our work will lead to their questions being answered and lessons learned which help to prevent anything similar from happening again.

We have received a huge amount of help from many parties who we would like to thank. We are particularly grateful to the Argentinian Navy whose constant support and encouragement was invaluable. In addition, the United Kingdom’s Royal Navy, via the UK Ambassador in Buenos Aires, made a very significant contribution. Numerous others, including the US Navy’s Supervisor of Salvage and Diving, have supported us with expert opinion and analysis. Finally, I would like to extend a special thank you to the whole Ocean Infinity team, especially those offshore as well as our project leaders Andy Sherrell and Nick Lambert, who have all worked tirelessly for this result.”

Ocean Infinity used five Autonomous Underwater Vehicles (AUVs) to carry out the search, which was conducted by a team of approximately 60 crew members on board Seabed Constructor. In addition, three officers of the Argentine Navy and four family members of the crew of the ARA San Juan joined Seabed Constructor to observe the search operation.

Ocean Infinity had committed to conduct the search operation for up to sixty days, and to take on the economic risk of the search, only receiving payment if the submarine was found.

Position Estimates from Acoustic Measurements

The debris field is centered at (-45.9499,-59.7730). Meanwhile, after analyzing the hydro-acoustic data from CTBTO sensors that was collected on Nov 15, 2017, the hot-spot was estimated to be centered at (-46.12,-59.69). That’s a distance of only 20 km, which is an impressive demonstration of the capabilities of the hydro-acoustic analysis.

There was a test explosion on Dec 1, 2017, that was used to calibrate and verify the position estimation model. The position error of the test explosion was 37 km. Therefore, the position error for the debris field was well within what was expected based on the test explosion.

An interesting description of the CTBTO’s hydro-acoustic analysis is presented here.

Implications for the Search of MH370

Unfortunately, the acoustics generated by the impact of MH370 on the ocean surface would not propagate along the “deep sound channel” (DSC) the way an underwater acoustic event does, so the impact likely was not detected by CTBTO sensors.

The San Juan’s debris field was detected earlier this month only after an AUV mission was conducted in a deep trench that was previously scanned from a higher altitude in September. The ability to skim about 100 meters above the challenging surface contour allowed the side scan sonar sensors in the AUV to collect data at the proper altitude to achieve the required image resolution. Because of its limited ability to glide above steep slopes, this resolution would have been very difficult to achieve using a “towfish”, which is a cable-towed underwater vehicle that is similarly equipped with side scan sonar sensors, but is much more limited in maneuverability than an AUV.

The initial seabed search for MH370 was conducted by the vessels Fugro Discovery, Fugro Equator, and GO Phoenix, each using a towfish. These vessels scanned about 120,000 square kilometers of seabed using this technology. Based on the failure of OI to detect the San Juan’s debris field until an AUV mission was conducted in a trench, we have to at least consider the possibility that that the debris field for MH370 was passed over in the initial search but was not detected due to challenging terrain.

In the coming weeks, we’ll learn more about what worked and didn’t work in the search for the San Juan. That knowledge should be applied to MH370 to determine if we can confidently eliminate all of the seabed that has been previously searched.

Update on November 18, 2018

The ATSB did provide statistics for estimating the confidence of detecting MH370 in the 120,000 square kilometers that were initially scanned primarily by towfish. Those statistics are presented in the figure below. About 97.4% of the total area had a detection confidence of 95%, based on the ability to detect a debris field with dimensions of 100 meters by 100 meters. About 2.1% of the area had a detection confidence of 70%, mostly due to difficult terrain, environmental conditions, or degraded data. About 0.5% of the area had no data. The aggregate probability to detect MH370 in the 120,000 square kilometers is therefore about 94%. Although this is high, it is not 100%.

Don Thompson and Mike Exner provided helpful comments for this article.

Lion Air flight JT610, with 181 passengers and 8 crew, was climbing out of Jakarta on a flight to Pangkal Pinang (Indonesia) when control was lost at around 5,000 ft. Soon after, the Boeing 737-MAX 8 aircraft crashed into the Java Sea northeast of Jakarta. Although we don’t know the cause of the crash, there were some anomalies noted on the previous flight related to sensor disagreements for speed and altitude which required maintenance. Some suspect that these previous issues might have been related to the crash. Luckily, the flight data recorder (FDR), commonly known as a “black box”, was recovered, and the approximate location is known for the cockpit voice recorder (CVR), the other “black box”, so there is a good probability that the cause of the crash can be determined.

Investigators are now claiming they have recovered 69 hours of data from the FDR, which would be sufficient to analyze JT610 as well as the preceding flight which had the anomalous behavior.

The last ADS-B data that we have from Flightradar24 has the aircraft at an altitude of 425 ft, a groundspeed of about 360 knots, and a descent rate of 30,976 fpm. That translates to an approximate true airspeed of 472 knots and a descent angle of about 40 deg. That suggests the aircraft impacted the sea with very high energy. Similarly, the final BFO values for MH370 suggest a downward acceleration of about 0.7g over 8 seconds, reaching a descent rate of about 15,000 fpm. Unless a pilot was at the controls and skillfully recovered from this descent, MH370 also impacted the sea with high energy. Therefore, the debris produced from the JT610 crash gives us some indication of the types of debris probably produced from the crash of MH370.

Indonesia’s National Search and Rescue Agency (BASARNAS) is in charge of the rescue and recovery operation for JT610, which is in water about 100 feet deep, with efforts reportedly hampered by strong underwater currents and limited visibility. Already one volunteer diver has lost his life while recovering body parts.

The video at the top shows floating debris for JT610. If the objects shown are truly representative of the main field of floating debris, it is evidence that a high speed impact produces only small floating parts spread over a fairly limited area. Now admittedly, a B777 is considerably larger than a B737, and the floating debris field should be easier to find. However, the surface search for MH370 in the Southern Indian Ocean (SIO) from the air began weeks after the disappearance, and the dispersive effects of waves and currents in the SIO are strong. The combination of a dispersed field and small parts might explain the failure for the air search to detect floating objects along the 7th arc. The small size of the floating parts might also explain why satellite images along the 7th arc have not spotted aircraft debris.

Despite the likelihood of small floating debris, the underwater searchers for MH370 expect to find a fairly substantial debris field (bigger than 100 m) and substantial, distinguishable objects such as the landing gear and engines, consistent with the debris field of Air France 447. This is also consistent with the parts of JT610 that have already been found on the seabed. For instance, the picture below shows an engine and part of the landing gear of JT610.

To locate parts on the seabed, BASARNAS is using a combination of technologies, such as multi-beam echo sounders (MBES), side-scan sonar (SSS), magnetometers, and remotely-operated vehicles (ROV). The SSS technology has been the workhorse for the subsea search of MH370, used in both the towed vehicles and the underwater drones.

The video below shows divers helping to retrieve debris from the seabed.

The debris recovered from the crash of JT610 helps explain why no MH370 floating debris was spotted by air and by satellite along the 7th arc, and why we remain hopeful that it will be detected on the seabed with sonar sensors once the correct search area is selected.

Update on November 13, 2018

Here’s a Wall Street Journal story that discusses the stall-protection system that likely led to the crash of JT610.

Boeing Withheld Information on 737 Model, According to Safety Experts and Others

Data related to a new flight-control feature suspected of playing a role in crash in Indonesia

By Andy Pasztor and Andrew Tangel
Nov. 12, 2018 11:16 p.m. ET

Boeing Co. withheld information about potential hazards associated with a new flight-control feature suspected of playing a role in last month’s fatal Lion Air jet crash, according to safety experts involved in the investigation, as well as midlevel FAA officials and airline pilots.

The automated stall-prevention system on Boeing 737 MAX 8 and MAX 9 models—intended to help cockpit crews avoid mistakenly raising a plane’s nose dangerously high—under unusual conditions can push it down unexpectedly and so strongly that flight crews can’t pull it back up. Such a scenario, Boeing told airlines in a world-wide safety bulletin roughly a week after the accident, can result in a steep dive or crash—even if pilots are manually flying the jetliner and don’t expect flight-control computers to kick in.

That warning came as a surprise to many pilots who fly the latest models for U.S carriers. Safety experts involved in and tracking the investigation said that at U.S. carriers, neither airline managers nor pilots had been told such a system had been added to the latest 737 variant—and therefore aviators typically weren’t prepared to cope with the possible risks.

“It’s pretty asinine for them to put a system on an airplane and not tell the pilots who are operating the airplane, especially when it deals with flight controls,” said Capt. Mike Michaelis, chairman of the safety committee for the Allied Pilots Association, which represents about 15,000 American Airlines pilots. “Why weren’t they trained on it?”

One Federal Aviation Administration manager familiar with the details said the new flight-control systems weren’t highlighted in any training materials or during lengthy discussions between carriers and regulators about phasing in the latest 737 derivatives.

Boeing declined to immediately answer specific questions Monday. “We are taking every measure to fully understand all aspects of this incident, working closely with the investigating team and all regulatory authorities involved,” the company said in a statement. “We are confident in the safety of the 737 MAX.”

On Monday, an FAA statement reiterated that the agency had mandated flight manual changes to emphasize proper pilot responses to the new flight-control systems. “The FAA will take further action if findings from the accident investigation warrant,” the statement noted, but declined to comment further.

Boeing marketed the MAX 8 partly by telling customers it wouldn’t need pilots to undergo additional simulator training beyond that already required for older versions, according to industry and government officials. One high-ranking Boeing official said the company had decided against disclosing more details to cockpit crews due to concerns about inundating average pilots with too much information—and significantly more technical data—than they needed or could digest.

Minutes after takeoff from Jakarta in good weather, Lion Air Flight 610 experienced problems with airspeed indicators and a related system that feeds data to computers about the angle of the nose. The crash killed all 189 people on board.

Investigators haven’t described the precise sequence of events that caused the twin-engine jet to plummet into the Java Sea at a steep angle and high speed. But Indonesian authorities already have called for stepped-up pilot training and suggested they are delving into design issues. In the U.S. at least, substantial training changes will have to wait until new flight simulators are delivered to carriers.

The focus of the probe is shifting away from its early emphasis on individual system malfunctions and suspected pilot mistakes, according to people tracking developments.

Instead, these people said, U.S. and Indonesian crash investigators increasingly are delving into the way the MAX 8’s automated flight-control systems interact with each other, and how rigorously the FAA and Boeing analyzed potential hazards in the event some of them malfunction and feed incorrect or unreliable data to the plane’s computers. Swiftly turning off the automated feature is the solution in such cases.

Earlier 737 versions have different stall-protection systems, that don’t automatically drive down the nose even when other functions of the plane’s autopilot are turned off.

Yet operation of those older systems was highlighted in training over the years, and pilots had to memorize steps to counteract potentially dangerous unintended consequences. MAX 8 training materials don’t include a requirement to memorize the steps to turn off the stall-protection system.

Stepped-up scrutiny of the latest 737 MAX features applies to more than 200 of the models that have been delivered to customers around the world, including Southwest Airlines , American Airlines and United Airlines. Boeing’s 737 factory near Seattle currently churns out 52 planes a month.

“We’re pissed that Boeing didn’t tell the companies and the pilots didn’t get notice obviously, as well,” said Capt. Jon Weaks, president of Southwest Airlines Co.’s pilot union. “But what we need now is…to make sure there is nothing else Boeing has not told the companies or the pilots.”

Like Mr. Weaks, some FAA managers and industry officials aren’t satisfied with what they contend is Boeing’s belated candor.

Boeing is working on a software fix, according to industry and government officials, that would likely mitigate risks. On Saturday, the company went further than before in spelling out dangers pilots can face if they misinterpret or respond too slowly to counter automated commands.

In a message sent to all 737 operators, and reviewed by The Wall Street Journal, the Chicago plane maker explained in painstaking detail the engineering principles and operational parameters behind the latest automation.

That message was more detailed than the bulletin Boeing voluntarily issued earlier, alerting pilots about the potential hazard—and touching off debate over the stall-prevention system’s design. Within hours, the FAA followed up with its emergency directive mandating changes in flight manuals.

Such interim efforts “are very appropriate in the near term to increase pilot awareness,” said John Cox, a former 737 pilot and ex-crash investigator for North America’s largest pilots union who now consults on safety for carriers and business aviation.

Boeing’s latest communications with airlines prompted American’s union to alert its members. “This is the first description you, as 737 pilots, have seen,” the union pointedly told pilots in a memo, referring to the 737 MAX stall-prevention system. Noting the system wasn’t mentioned in American Airlines’ or Boeing manuals, the union memo added: “It will be soon.”

The ultimate way to counteract dangerous automated nose-down commands is basically the same for old and new systems, though checklists and procedures for the 737 MAX 8 entail more steps and take more time. Investigators and safety experts are convinced that as the emergency worsened, the Lion Air crew had barely seconds in which they could have diagnosed the problem and taken action to save the aircraft.

Shortly before the plane crashed, according to local Indonesian media reports, one of the pilots told air-traffic controllers about difficulties controlling the plane.

The article that follows, translated from French, appeared on the website 20 Minutes with AFP:

While all other countries have stopped investigating, France is not giving up. The investigators in charge of the case of the disappearance of flight MH370 of Malaysia Airlines hope to soon go to the United States where crucial investigations must move forward, Ghyslain Wattrelos, who lost four family members in the disaster, announced Thursday.

On March 8, 2014, 239 people disappeared after taking off from Kuala Lumpur aboard a Boeing bound for Beijing. Other than some debris that seem to belong to it were recovered in the Indian Ocean, no trace of the 239 passengers has ever been found. Ghyslain Wattrelos has notably lost his wife and two of his children in the plane’s disappearance.

On Thursday, he was received with his lawyer Marie Dosé by the judge of instruction in charge of the judicial inquiry opened in France, to take stock of the investigations and the avenues to explore by the investigators.

Questions for the FBI and Boeing

Among the priorities that mobilize the investigators, a trip to the United States is “back on the agenda”.  A previous trip was cancelled in September, even though it was part of an international rogatory commission launched in October 2017, they announced at a press conference Thursday. According to Dosé, this trip had to be canceled, as the US authorities opposed “confidentiality clauses” and then the “industrial secret” of the manufacturer Boeing.

“We are a little angry and now we want to say stop, it is time that the United States really cooperate on this issue,” responded Ghyslain Wattrelos. “It is necessary to go there because there are three entities that hold important information for understanding what happened on this flight,” he continued. Starting with Boeing and the FBI, even if the investigators seem to have obtained assurances from the intelligence agency that they could be received, he said.

A hacking of Satcom?

But attention is now also focused on a third entity, a company uncovered by investigators. The challenge, according to Ghyslain Wattrelos, is whether it sells software capable of reprogramming or even hacking the Satcom, the antenna that communicates to the Inmarsat satellite signal from the aircraft. “The essential trail is the Inmarsat data. Either they are wrong or they have been hacked,” he says. However, these satellite data are essential to better understand the trajectory of the aircraft.”

The release of the Malaysian investigation report in July had dampened Ghyslain Wattrelos’ hopes, but since then French investigators have suggested new theories to explore. In particular, the investigators found “inconsistencies” in the Malaysian investigation’s official report, and the presence of “curious” passengers,  whom “we should continue to investigate”. Among them is a Malaysian traveler with a troubling profile: he was seated under the Satcom module, and proved to be an expert in aeronautics, according to Ghyslain Wattrelos and his lawyer.

[End of story]

It’s not clear what additional information the French investigators expect to obtain while in the US. Boeing has cooperated with the Annex 13 investigation team, and is unlikely to provide private French investigators with data that has not already been made public. Meanwhile, the FBI is unlikely to release information on matters related to ongoing or past investigations.

The mysterious “third entity” referred to by Mr Wattrelos that might be selling software capable of maliciously altering SATCOM data is also unknown, although there are a handful of companies in the US and Canada that supply hardware and software for designing, building, and testing parts of the Inmarsat network.

Independent investigators that are studying this mystery are at an impasse. Although the overwhelming consensus is that MH370 did indeed crash in the Southern Indian Ocean, the considerable efforts of official and private investigators have not succeeded in locating the debris field on the seabed. The data we have, notably the satellite data, is imprecise, so additional data is needed to reconstruct the trajectory of the plane.

There is always the chance that during Mr Wattrelos’ visit to the US, some new evidence or insights will be uncovered that help us to better understand the disappearance and to find the plane.

More likely, the existence of helpful new information will be found in Malaysia.

Update on October 23, 2018

The following article, translated from French, was published in the L’Essor, which is the [unofficial, self-described] French journal for the military police.

MH370: Gendarmes waiting for a green light for a trip to the United States

The investigators of the research section (SR) of the Gendarmerie Air Transport (GTA) are waiting for the green light from US authorities to travel to the United States related to the case of the disappearance of the flight MH370 Malaysia airlines, more than four years ago.

The SR of the GTA is responsible for the judicial inquiry, opened in France, on the death of 239 people, including four French, aboard the Boeing who disappeared on March 8, 2014 after taking off from Kuala Lumpur for Beijing. Debris likely to belong to the aircraft have been discovered in the Indian Ocean but no trace of the 239 passengers has ever been found.

The gendarmes work within the framework of an international rogatory commission launched in October 2017 by the French justice. A trip to the United States, scheduled for September, had to be canceled and French investigators are waiting for the green light from the US authorities.

The investigators want to check overseas if a US company sells software capable of reprogramming or even hacking the Satcom. This system is used by airlines to transmit messages about the state of the aircraft in flight and its communications.

[End of story]

This story, if true, suggests that the French judiciary system, and in turn the military police that are assigned to the case, are seriously considering whether the Inmarsat data was corrupted by a malicious intrusion into the SATCOM onboard MH370. Considering that the Inmarsat data is consistent with the aircraft crashing in the SIO near the 7th arc, and that the timing and location of the recovered parts from the aircraft also suggest that the aircraft crashed in the SIO, to doubt the Inmarsat data implies doubting the veracity of the recovered parts. This is the first time a government investigative body is known to be seriously considering a hack of the SATCOM combined with planting of debris.

To say the least, most private investigators believe there are more productive avenues to pursue. However, an honest, competent investigation of any type is to be welcomed, and there is always the chance some new evidence or insights will be uncovered that help us to better understand the disappearance and to find the plane.

Today, Malaysia’s Ministry of Transport quietly released the full ACARS message log for MH370. The new log confirms that the traffic logs presented in previous reports were incomplete and edited, as asserted in a previous blog article. This release comes on the heels of a strong denial from Malaysia Airlines stating that it has “provided full cooperation and assistance to all respective authorities”.

Notably, the new log contains an additional ACARS message that was sent from MAS Operations Dispatch Center (ODC) and destined for MH370 over the VHF link. The message was sent at 18:38:51 and was intended to be displayed in the cockpit on a Control Display Unit (CDU), which a pilot uses to perform tasks such as programming the flight computers. The message was not received by MH370, and was re-sent by MAS ODC at 18:39:52, 18:40:42, and 18:41:52, failing each time. The text of the message was:

DEAR MH370. PLS ACK TEST MSG. RGDS/OC.

The new log confirms that there was a renewed attempt to initiate communications with MH370 using ACARS over the VHF link at 18:38:51. The error messages that were generated confirm that the VHF link was not available at that time, likely because MH370 was not logged into ARINC’s server. ARINC was MAS’ service provider for ACARS over VHF.

Also of note is the new ACARS message was sent about a minute before an attempted telephone call over the satellite link at 18:39:56, suggesting an increase in activity at MAS ODC at this time.

The new log contains other traffic between MAS ODC and other ground computers. This data is under examination for additional clues. The new log also confirms that the name of the MAS ODC employee that sent the ACARS messages was redacted from the message logs in previous reports.

Fellow MH370 Independent Group members Don Thompson and Richard Godfrey have found some anomalies in the message logs that were included in Factual Information (FI) released by Malaysia on March 8, 2015, and the Safety Investigation Report (SIR) released by Malaysia on July 30, 2018. The logs from these two reports document the communication between MAS Operations Dispatch Center (ODC) and service providers that route messages over SATCOM and VHF paths, as part of the Aircraft Communications Addressing and Reporting System (ACARS). The anomalies suggest the traffic logs appearing in the reports are not complete, and what appears in the reports has been modified.

A simplified schematic of the ACARS is shown in the figure. For MAS, the service provider for satellite communications is SITA using the Inmarsat network and the service provider for VHF communications is ARINC using a network of ground stations.

Missing Messages Between 18:15:23 and 18:43:33

According to text in both the FI and the SIR, an urgent message from MAS ODC was submitted at 18:03 and then re-transmitted multiple times:

The first message sent to the aircraft cockpit printer from the MAS ODC was at 1803:23 UTC. The ACARS message requested the crew to contact the HCM ACC immediately. The incoming downlink message at 1803:24 UTC showed the message failed to reach the aircraft. Messages are auto transmitted every 2 minutes and the message was retransmitted until 1843:33 UTC but all messages failed to get a response. Automated downlink message by ACARS showed ‘failed’. 

However, the last message from MAS ODC that was shown in both the FI and SIR traffic logs occurred at 18:15:23, and not the 18:43:33 stated in the text. This means that either the explanatory text is wrong, or the traffic logs do not contain all the message traffic.

VHF Messages Not Included

The missing messages could be explained if they were routed via the VHF link. For the ACARS traffic log in the FI, the filter parameters used to extract the message records included only SATCOM traffic for the time period 12:48:00 to 20:00:00, so that if any VHF messages were exchanged, those messages would not be included in the traffic log. (The filter parameters appear at the top of each page of the traffic log in Appendix 1.9A.)

The facts surrounding the ACARS traffic log in the SIR (also Appendix 1.9A) are more suspicious. For Page 1 of the log, the filter parameters did not limit the messages to only SATCOM messages. In fact, at 15:54:31, there is a message submitted by MAS ODC over the VHF link that requests personnel on the aircraft to re-configure the center VHF radio so that future messages would be exchanged via SATCOM. However, starting with Page 2 of the report, the filter parameters used to generate the remaining pages of the report were changed so that VHF messages, if any occurred, were excluded.

The change in filter parameters after Page 1 is unexplained. Two messages received by MAS ODC at 15:54:41 and 15:54:53 appearing at the bottom of Page 1 are repeated at the top of Page 2. The change in filter parameters and the repeated messages are clear evidence that the traffic log in the SIR is actually two reports that were pieced together and presented as a single report.

Edited Text

As it appears in the ACARS traffic log in the SIR, the text message that was sent by MAS ODC at 18:03:23 is:

URGET [sic] REQUEST
PLS CONTACT HO CHI MING [sic] ATC ASAP
THEY COMPLAIN CANNOT TRACK YOU ON THEIR RADAR
I RECEIVED CALL FROM SUBANG CENTRE
PLS ACK THESE MSG
REGARDS

However, the last line of the message appears to have been edited. By examining the ASCII characters embedded in the PDF version of Appendix 1.9A, the following text can be extracted:

REGARDS
MXXXXX

where MXXXXX is an actual name with six letters beginning with M.

There is also a misplaced © symbol on the bottom of the page that appears after the report page number on Pages 2 and later, but properly appears before the name “SITA” on Page 1. This is yet another indication that the traffic log in the SIR was edited.

Request for Complete, Unmodified ACARS Logs

It is disappointing that more than four years after MH370’s disappearance, we are still asking Malaysia to release withheld data. The military radar data is another example of a data set that has never been released in full despite its significance in providing information about how the aircraft was flown after the diversion from the flight plan.

It is important that Malaysia provide a complete, unmodified log of all ACARS communications on SATCOM, VHF, and HF paths for the period between 12:48 and 20:00 on March 7, 2014. This is particularly significant in light of questions surrounding the delayed response of Malaysian authorities after MH370 went missing.

Update on Sept 4, 2018

The Daily Star reports that it has received a statement from Malaysia Airlines about the anomalies in the traffic data logs that were reported in the article above:

A spokesman told Daily Star Online: “Malaysian Airline System Berhad (Administrator Appointed) (“MAS) is aware of the recent media reports alleging anomalies to the traffic data logs in the Safety Investigation Report published by the Malaysian ICAO Annex 13 Safety Investigation Team for MH370. 

“MAS wishes to state that MAS has provided full cooperation and assistance to all respective authorities on the investigation for MH370, including the submission of relevant documents necessary for the investigation.

MAS will continue to cooperate with the Authorities and if necessary, provide any information to them in line with international requirements and applicable laws.” 

Conspicuously absent is an explanation for the missing messages and the edited logs.

Introduction

With the failure of the recent search by Ocean Infinity to locate the debris field along the 7th arc at latitudes as far north as 25S and at widths equal to or exceeding +/- 22 NM, we consider whether it is possible that with the assumption of uncontrolled flight, the plane could have impacted the ocean farther than 22 NM from the 7th arc, and was missed because the search along the arc was too narrow.

At each phase in the subsea search for MH370, the search area was defined by following parameters:

• A range of latitudes along the 7th arc
• A width inwards and outwards from the 7th arc

The range of latitudes for the search was determined by analysis of the satellite data, aircraft performance, and drift models. Collectively, these data sets constrain the position that MH370 crossed the 7th arc. Unfortunately, due to the imprecise nature of these data sets, official and independent investigators have proposed a fairly large range of latitudes, and this continues to be the subject of debate.

In a parallel effort by the ATSB, the width inwards and outwards from the arc was estimated by the distance the aircraft could have glided after fuel exhaustion. With the assumption that there were no pilot inputs after fuel exhaustion, this distance was determined by end-of-flight simulations conducted by Boeing based on aircraft conditions requested by the ATSB. The simulations were completed in Boeing’s engineering simulator, which offers high fidelity of the aircraft’s performance. Some of the results of these simulations were presented in an ATSB report entitled MH370 Search and Debris Update, released in November 2016.

Simulation Results

Because of the importance of the simulations in establishing the search width, I asked the ATSB for more details about the conditions modeled and the results of the ten simulations. (Because Boeing conducted the simulations based on conditions requested by the ATSB in support of the search, they are an ATSB product.) Although legal restrictions prevent the ATSB from providing specific details about each of the ten simulations (referred to as Cases 1-10), the ATSB did reveal that the initial speeds varied between M0.75 and M0.83, the starting altitudes were either FL350 or FL400, the initial headings were either 178°, 184° or 190°, and turbulence was either light or moderate. Winds at various altitudes were included in the simulations.

In addition to these general descriptions, the ATSB did provide me with numerical results of the ten simulation runs in the form of X, Y, and altitude in one second increments, where X is the E-W position in NM, Y is the N-S position in NM, and the altitude is in feet. (The ATSB deliberately did not include the latitude and longitude values in these files so that there was no association with a particular crossing of the 7th arc.) The ATSB has permitted me to share these results on this blog so that a broader group of investigators can independently analyze the results. To my knowledge, this is the first time these results have been released to the public.

Although not included in the files, derived quantities such as groundspeed, Mach number, track, vertical speed, vertical acceleration, bank angle, and wing loading are all calculable, although some parameters such as Mach number and calibrated airspeed need assumptions about the wind and temperature fields.

A presentation of the detailed technical analyses of all the simulations would be lengthy and not appropriate for a blog post. However, some generalized observations and results are summarized below:

• There were two groups of simulations. In the first group (Cases 1,2,5,7,8,9), the autopilot was lost after the flameout of the second (left) engine, which corresponds to a “normal” configuration of the electrical system.
• In the second group (Cases 3,4,6,10), the electrical configuration was in an “alternate” configuration in which the left generator and left backup generator were isolated with switches in the overhead panel. In this case, when the right engine is running, power is supplied to the left bus from the right bus through the bus tie breaker. However, after the first (right) engine flames out, both main AC busses and both transfer busses lose power, which causes the flight control mode to transition to “secondary” and the autopilot and autothrottle disengage, even as the left engine continues to provide thrust.
• The SATCOM’s log-on request at 00:19 is assumed to occur two minutes after the loss of the autopilot. (The two minute interval assumes the APU would take one minute to start supplying power, and the SDU would subsequently take one minute to power up and request a log-on to the satellite.) The ATSB has adjusted this position in all the simulations so that the two-minute mark occurs at the same X,Y values, and the paths can be compared. The two-minute mark serves as a reference position (labeled with “2 mins” in the figure above).
• For all ten simulations, the paths stay within a distance of 32 NM from the reference position. However, since all paths are curved, the farthest impact point from the 7th arc is only about 15 NM, and depends on the track angle between the initial path and the arc tangent.
• There were five simulations (Cases 3,4,5,6,10) in which the rate of descent exceeded 15,000 fpm and the downward acceleration exceeded 0.67g, which are the values indicated by the two final values of BFO. This included all four cases with the “alternate” electrical configuration, and one with normal configuration. The maximum downward acceleration for these cases ranged between 0.87g and 1.30g.
• For the five simulations (Cases 3,4,5,6,10) with high descent rates, the impact occurs within 14 NM from the reference position, and about the same distance from the 7th arc, depending on the track angle between the initial path and the arc tangent.
• For the five simulations (Cases 3,4,5,6,10) with high descent rates, the descent rate of 15,000 fpm and the downward acceleration of 0.67g occur at different times, and are not predicted to occur at the time of the log-on. If the impact distance is measured from the point at which the descent rate first exceeds 15,000 fpm, the distance ranges between 4.7 NM and 7.9 NM.
• In none of the simulations did the plane fly straight with level wings after the autopilot was disengaged. Ultimately, the magnitude and direction of the bank that develops is the net effect of a many factors, including thrust asymmetry, TAC, manual rudder input, weight imbalance, aerodynamic asymmetry, and turbulence, with the dihedral effect of the wings and center-of-mass tending to restore the bank to zero.

Simulation of Alternate Electrical Configuration

The four simulations (Cases 3,4,6,10) with the alternate electrical configuration are interesting because in all cases, the descent rates and downwards accelerations exceeded the values suggested by the final BFOs, and the high speed descent is achieved within minutes of loss of the autopilot. To further illustrate the sequence of events, we consider Case 6, with initial conditions of a groundspeed of 425 knots at an altitude of 35,000 ft, and shown in the figure above.

When there is no more fuel in the right tank, the right engine coasts down and the left engine speed increases to full thrust. The loss of AC power causes a transition to secondary control mode, and the autopilot and the autothrust are disengaged. As the right engine coasts down, the automatic thrust asymmetry compensation (TAC) will apply left rudder, but the amount of rudder does not change after the flight control mode degrades to secondary.

After the right engine flames out, there is a slight turn to the right, which means the rudder position does not completely balance the yaw from the resulting thrust asymmetry. It is possible that the transition to secondary control mode occurs before the TAC can apply sufficient rudder input to fully compensate for the thrust asymmetry of no right engine thrust and full thrust of the left.

At some point, the remaining fuel in the left tank is exhausted, and the left engine shuts down. With both engines producing no thrust, the left rudder position now causes a steep turn to the left, and the plane descends. At the point it reaches 27,000 ft, the descent rate is 15,000 fpm, and it has achieved a downward acceleration of 0.3g over the preceding eight seconds. The plane levels off at about 19,000 ft, and then begins to again rapidly descend, reaching a descent rate of 15,000 fpm at about 18,000 ft, and impacting the sea about 3.3 NM from this point. The impact distance from the earlier point of reaching a descent rate of 15,000 fpm is about 7.9 NM.

Discussion

[Phrases in italics were added on Aug 21, 2018 for clarity.]

If we consider that the end-of-flight Boeing simulations were representative of the actual conditions of MH370, we have three possibilities:

1. If the flight was uncontrolled after fuel exhaustion, and if we ignore the final BFO values, the plane impacted no farther than about 15 NM from the 7th arc.
2. If the flight was uncontrolled after fuel exhaustion, and if the descent rates suggested by the final BFO values are valid, then the aircraft impacted no more than about 8 NM from the 7th arc.
3. If the flight was controlled after fuel exhaustion, an efficient, stable glide starting at about 40,000 ft could have achieved a distance of 120+ NM from the 7th arc.

Possibilities (1) and (2) suggest the next search should occur along the 7th arc north of 25S latitude at a width of about +/-25 NM.  The +/-25 NM is an estimate that includes uncertainty in the simulation models and uncertainty in the final BTO values. 

Because possibility (3) requires pilot inputs after fuel exhaustion, if this occurred, we have to assume that pilot inputs also occurred during the powered part of the flight after 19:41. As such, there would be no reason to believe that paths reconstructed with the assumption of automated flight with no pilot inputs are representative of the path actually flown. The large width (+/- 120 NM) and the difficulty in objectively constraining the crossing latitude of the 7th arc would make it difficult to define a manageable search area without additional information.

Until additional information or insights become available, it will be difficult to establish a new search area.