Reports/The Operational Search for MH370/PIC Simulator
Other search area considerations
During the course of the underwater search for MH370 the ATSB actively sought any information or analysis from credible sources which may have assisted in better understanding where the aircraft may be located. A range of information from disparate sources was carefully considered in the context of defining the most probable underwater search area. While some information and analysis did not yield any new insights or was considered and discounted on the basis of new or existing evidence or analysis, it was important to exhaust every avenue which could improve the chance of locating the aircraft.
Pilot in Command’s flight simulator
Data from the Pilot-in-Command’s (PIC) home flight simulator was recovered and analysed in March/April 2014. This information was provided to the ATSB on 19 April 2014, during the surface search and was subsequently also analysed for relevance to the underwater search.
The simulator data was a partial reconstruction of a flight simulator session from 2 February 2014. It comprised four complete and two partial data captures of various aircraft and simulator parameters at discrete points during the simulation. The aircraft simulated was a B777-200LR. Information on the data points is summarised below:
- The initial data point indicated an aircraft at Kuala Lumpur airport.
- No useful location or aircraft information apart from simulator time was able to be recovered for the second data point.
- The next two data points indicated an aircraft tracking to the northwest along the Strait of Malacca.
- The aircraft had climbed to an altitude of 40,000 ft by the fourth data point and was in a 20° left bank, 4° nose down, on a heading of 255°.
- The final two data points were close together in the southern Indian Ocean, 820 NM southwest of Cape Leeuwin. The data indicated that the simulated aircraft had exhausted its fuel. The fifth data point was at an altitude of 37,651 ft, the aircraft was in an 11° right bank and heading almost due south at 178°.
- The data for the sixth data point was incomplete. It was 2.5 NM from the previous data point and the aircraft right bank had reduced to 3°.The aircraft was pitched nose down 5° and was on a heading of 193°. At this time there was also a user input of an altitude of 4,000 ft.
The aircraft track from the simulator data points is shown in Figure 74. The track shows the aircraft flying up the Strait of Malacca before a left turn into the southern Indian Ocean. The aircraft then tracks southeast to the fifth data point (assuming that there is no intermediate data point not captured) to fuel exhaustion at the final point. By the last data point the aircraft had flown approximately 4,200 NM. This was further than was possible with the fuel loaded on board the aircraft for flight MH370. Similarly, the simulated aircraft track was not consistent with the aircraft tracks modelled using the MH370 satellite communications metadata.
Figure 74: Simulator data indicative track (and 7th arc)
Source: Google Earth, annotated by ATSB
On the day the simulation was conducted the PIC was on a rostered day of leave. The following day the PIC was rostered to fly from Kuala Lumpur to Denpasar, Bali and return the same day. On 4 February 2014 the PIC was rostered to fly from Kuala Lumpur to Jeddah, Saudi Arabia. The first three data points recovered from the simulator were consistent with the route from Kuala Lumpur to Jeddah. In the weeks between the Jeddah flight and the accident flight the PIC was rostered to fly return flights from Kuala Lumpur to; Denpasar, Beijing, Melbourne and then Denpasar again.
Six weeks before the accident flight the PIC had used his simulator to fly a route, initially similar to part of the route flown by MH370 up the Strait of Malacca, with a left-hand turn and track into the southern Indian Ocean. There were enough similarities to the flight path of MH370 for the ATSB to carefully consider the possible implications for the underwater search area. These considerations included the impact on the search area if the aircraft had been either glided after fuel exhaustion or ditched under power prior to fuel exhaustion with active control of the aircraft from the cockpit.
Controlled glide or ditching
The B777 aircraft can theoretically achieve an unpowered glide ratio of approximately 17:1. That is, for every 1,000 ft of altitude lost in an unpowered glide the aircraft can travel a distance of approximately 2.8 NM. If MH370 was at an altitude of 40,000 ft at the point of fuel exhaustion, the aircraft could be glided more than 100 NM with an average rate of descent between 2,500 and 3,000 ft/min. Simulations conducted in a B777 simulator early in the search, confirmed these results which were included in the ATSB’s MH370-Definition of Underwater Search Areas report released in June 2014.
The possibility of a controlled ditching was carefully considered. Something occurred on board MH370 just before it reached the 7th arc which interrupted the power supply to the satellite data unit (SDU), (it takes a minute for the SDU to reboot after a short interruption of power). Since early in the search, analysis of the aircraft’s fuel consumption and endurance, and the characteristics of the final series of SATCOM transmissions had yielded fuel exhaustion as the most likely explanation for the power interruption. However, it was considered that the SDU reboot could be explained in other ways, much less likely, if there was someone active in the cockpit and preparing the aircraft for a controlled ditching.
If the aircraft was being actively controlled during the final segment of the flight south into the Indian Ocean, a series of step climbs[1] (which must be initiated by someone active in the cockpit) could have resulted in enough fuel at the end of flight to perform a controlled ditching under power rather than an unpowered glide. At the time the 7th arc was generated by the aircraft logging back onto the SATCOM system, the aircraft could have been descending in a ‘normal’ landing configuration including full instrumentation and full hydraulic power available for all flight control surfaces including slats and flaps.
At normal rates of descent (around 2,000 ft/min) the aircraft could have flown approximately 120 NM from the top of descent (an assumed altitude of approximately 40,000 ft) to sea level. If the Boeing ditching procedure were being followed there would have been turns at lower altitudes, firstly to the southwest into the prevailing wind and finally a turn close to sea level to land the aircraft parallel to the prevailing seas.
On 8 March 2014 the sun was 6 degrees above the horizon at 0019:30 UTC as the aircraft reached the 7th arc. Sunrise had been 24.5 minutes earlier, at 2355 UTC. The surface of the ocean would have been visible in order to judge the touchdown on the sea surface. In addition, at the time the aircraft was close to fuel exhaustion, the lightest state it could be, and therefore it was possible to make a controlled ditching with the lowest possible approach speed, with flaps extended in accordance with the Boeing ditching procedure.
The most likely aircraft tracks (after the turn at the tip of Sumatra) derived from the DST Group modelling (summarised in the ATSB’s MH370-Definition of Underwater Search Areas report released in December 2015) were considered at the time with a controlled descent starting just before the 7th arc, indicatively the areas of priority for searching to cover a controlled ditching (or a controlled glide) at the end of flight, as it was considered at the time, are shown in Figure 75.
Figure 75: Indicative controlled ditch scenario search areas at July 2016 (not included here)
By June 2016 many pieces of aircraft debris (see following section on Aircraft debris) confirmed or very likely from MH370, had been recovered from east African shorelines. Some items were from within the fuselage. While no firm conclusions could be drawn given the limited amount of debris, the type, size and origin on the aircraft of these items generally indicated that there was a significant amount of energy at the time the aircraft impacted the water, not consistent with a successful controlled ditching.
Critically, a section of right outboard main flap (Figure 81) was found near Tanzania on 20 June 2016. The item was shipped to the ATSB for analysis. This analysis indicated that the flaps were most likely in a retracted position at the time they separated from the aircraft making a controlled ditching scenario very unlikely.
The ATSB’s MH370-Search and Debris Examination Update on the flap analysis also contained the summary of the analysis The Use of Burst Frequency Offsets in the Search for MH370 performed by DST Group scientists on the final two satellite transmissions from the aircraft. This work quantified the range of possible rates of descent based on the burst frequency offsets of the SATCOM transmissions. In summary, the analysis concluded that the aircraft was descending at a rate of between 2,900 ft/min and 15,200 ft/min when the 7th arc was crossed. Eight seconds later the rate of descent had increased to between 13,800 ft/min and 25,300 ft/min[2] . These rates of descent ruled out a controlled unpowered glide with the intent to extend range.
Notes
- ↑ A step climb in aviation is a series of altitude gains that improve fuel economy by moving into thinner air as an aircraft becomes lighter (when fuel is burnt during the flight) and becomes capable of faster, more economical flight.
- ↑ It should be noted that these descent rates were derived assuming the SDU was still receiving valid track and speed labels from the ADIRU at 0019:37 UTC for use in its doppler pre-compensation algorithm.
Source: The Operational Search for MH370, Australian Transport Safety Bureau, 3 October 2017
https://www.atsb.gov.au/publications/investigation_reports/2014/aair/ae-2014-054/
Extracts from The Operational Search for MH370 have been included here for reference purposes, particularly the sections which relate to the history of the flight; times and events; the aircraft's satellite data unit (SDU); and the Pilot in Command’s flight simulator.