It’s been more than six months since MH370 vanished, and in some ways we know no more now than we did in late March: no new clues have emerged, no more data has been discovered. In a sense, though, we have come a very long way. For one thing, we now understand how many of the “breaking news” developments that occurred in the early days were actually untrue. (There were no wild altitude swings, no “fighter plane-like” maneuvering, and probably no cell-tower connection with the first officer’s phone.) What’s more, thanks no doubt to a drumbeat of public pressure, the authorities have released a tremendous amount of data and provided useful explanations of how that data is being interpreted. And finally, a spontaneous collaboration between technical experts and enthusiasts around the world has provided a trove of insight into avionics, aerodynamics, satellite communications, and a whole host of other topics that collectively shed light on what might and what might not have taken place on the night of March 7/8, 2014.
While a great deal of information has become available, it has not always been easy to find; much of it, for instance, has been exchanged via email chains and Dropbox accounts. For my part, I often find myself rummaging through emails and folders looking for information that I’m pretty sure I’ve seen, but can’t remember where. So what I’d like to do with this post is try to aggregate some of the most basic facts — a set of canonical values, if you will, of the basic data on MH370. Necessarily, some of this data comes with implicit assumptions attached, so as far as possible I’ll try to make these assumptions explicit.
Okay, on to the data. What we know now:
The bedrock data. In the wake of MH370’s data, there were numerous news reports concerning information leaked by anonymous sources from within the investigation and elsewhere that have subsequently been either disproven or inadequately verified. For the purposes of the present discussion, the following are considered the bedrock sources of information upon which our understanding of the incident can be built — the “Holy Trinity” of MH370 data:
- Up to 17:21: radio communications, ACARS, transponder, ADS-B
- 17:22-18:22: military radar track. This information is of uncertain provenance but has been endorsed by the governments of both Malaysia and Australia. Furthermore, it plausibly connects the prior and following data sets.
- 18:25-0:19: Inmarsat data, especially BFO and BTO values. There is some discussion as to how this data is best interpreted, but the numbers themselves are assumed to have been received and recorded by Inmarsat from MH370 via their 3F-1 satellite. The “ping rings” in particular are derived through relatively simple mathematics and should be regarded as established fact unless someone comes up with a specific mechanism by which some other result could be obtained.
Timeline. Courtesy of Richard Godfrey and Don Thompson, here is a basic timeline of MH370’s disappearance (all times UTC):
- 16:41:43 MH370 departs runway at KUL runway 32R
- 17:01:14 MH370 flight crew report top of climb at 35,000 feeet
- 17:07:48.907 Last acknowledged DATA-2 ACARS message sent from plane
- 17:19:29 Last radio voice transmission
- 17:21:04 Plane passes over IGARI waypoint
- 17:21:13 MH370 disappears from air traffic control (secondary) radar screens
- 18:22 Last primary radar fix
- 18:25:27 Inmarsat log-on request initiated by aircraft
- 0:19 Final transmission from aircraft to satellite
A more complete table of values, including the location of the plane at each point in time, can be found here, courtesy of the inimitable Paul Sladen. And Don Thompson has created an impressively detailed breakdown of the sequence of events, with a special focus on radio communications between the aircraft, ground, and satellite, here.
More stuff after the jump…
Physical characteristics. MH370 was a Boeing 777-200ER. Its “zero fuel mass” (ZFM) was 174,000 kg. With 49,200 kg of fuel aboard, its takeoff weight was 223,200 kg. (We know the fuel aboard on takeoff at 16:41 thanks to Paul Sladen’s deciphering of ACARS data shown briefly onscreen during a CNN segment. Note that in a press statement Malaysia Airlines indicated that the fuel load on takeoff was 49,100 kg.) UPDATE: Thanks to the October ATSB report, we now know that the fuel remaining at 17:07 was 43,800 kg.
UPDATE 2: Don Thompson has rounded up four publications which contain a wealth of 777 technical information: Boeing 777 Flight Management System Pilot’s Guide, Qatar Airways 777 Flight Crew Operations Manual, United Airlines 777 Aircraft Maintenance Manual/Satcom System, and Honeywell Multi-Channel SATCOM System Description, Installation, and Maintenance Manual.
Communications. In addition to a traditional transponder for use with ATC secondary radar, MH370 was equipped with ADS-B equipment that was operational the night it disappeared. The plane was equipped with VHF and HF radios for voice and data communication, which could also be sent and received via a satcom system that relied on one low-gain and two high-gain antennae mounted near the rear of the aircraft. (Specs, courtesty of Don Thompson, here.) These antennae were connected to a Honeywell/Thales MCS6000 satellite communications system located in the ceiling beneath them; this unit received location and velocity information needed to aim the high-gain antenna and to precompensate the transmission frequency via ARINC cable from the Inertial Reference System in the E/E bay. After the plane disappeared from primary radar, Malaysia Airlines made three attempts to reach its crew via satphone, but the calls did not go through; Don’s signal analysis of the three attempted phone calls suggests that the high-gain antenna might not have been working properly, perhaps because the antenna was not steered correctly.
Wind speed and temperature aloft. Stare at this for a while if you want to. If you like your data a bit rawer, you can find historical radiosonde data at the website of the University of Wyoming. For a more granular idea of what the weather was doing on the night in question, Barry Martin has compiled a large table of reanalyzed weather-model data from NOAA here.
Speed. As part of his paper detailing his estimate of where MH370 might have gone, Dr. Bobby Ullich has produced an impressive analysis of MH370’s speed before it disappeared from radar. While I’m agnostic as to the correctness of Bobby’s conclusions, I think he makes an excellent point with regard to the plane’s speed, which is that it clearly accelerated after the diversion at IGARI. The ground speed before the turn was about 470-474 knots, after, it was around 505-515 knots. Given that the winds aloft at the time were somewhere around 20 knots from the east-northeast, this would be broadly consistant either with an acceleration in airspeed or with a steady airspeed in the range of 490-495 knots.
In his ongoing analysis of MH370’s performance, Barry Martin points out that a likely speed for the plane to fly would be “Long Range Cruise,” or LRC, which can be selected through the flight management system. LRC is faster than the Maximum Range Cruise speed and 1 percent less fuel efficient. To quote a Boeing manual: “This speed… is neither the speed for minimum fuel consumption nor the speed for minimum trip time but instead is a compromise speed somewhere in between. It offers good fuel mileage but is faster than the maximum range cruise speed.” LRC is given as a Mach number, and varies with weight. At MH370’s takeoff weight, LRC at 35,000 feet would be Mach 0.84, which translates to 481 knots in a standard atmosphere. At the time, however, the temperature was 11 deg C higher than that of a standard atmosphere, so its true airspeed would be 494 knots.
It’s worth noting as well that Brian Anderson has devised an entirely different means of calculating airspeed, based on the observation that between 19:40 and 20:40 the plane reached its point of closest approach to the satellite; by calculating this distance, and estimating the time at which it occured, one comes up with a groundspeed that turns out to be, by Brian’s (and other’s) reckoning to be in the neighborhood of 494 knots. Brian observes that “by removing the wind vector, the answer becomes about 486 knots TAS.”
Richard Godfrey has run the numbers for the early part of the flight and come up with slightly different figures from Bobby Ullich.
The last ADS-B data shows a speeds around 471 to 474 knots. Last calculated Ground Speed was 474.3 knots. The average Ground Speed required to follow this path from the turn back point and get to Pulau Perak by 18:02:37 for the start of the Beijing Radar Trace is 510.7 knots. The difference between 474.3 and 510.7 is accounted for by an 18 knot head wind that becomes an 18 knot tail wind after turn back. The wind in the area was around 18 knots at the time. This would make the Air Speed 492.5 knots. The Ground Speed required to get from the start to the end of the Beijing Radar Trace by 18:22:12 is 503.6 knots.
The major turns and turn back flight path occur at borders between Malaysia, Vietnam, Singapore, Thailand and India. Indonesian Airspace is carefully avoided in the Malacca Strait. The major turns are just out of range of the Malaysian, Thai and Vietnam radars. The Satcom Login at 18:25:27 is just 14 seconds after reaching NILAM which represents the point just out of range of the Malaysian and Thai radars.
Performance. As the plane flew along, it burned fuel, and thus became lighter. As a consequence its optimum altitude — that is to say, the altitude at which it would experience the greatest fuel efficiency — became higher, and its LRC at a given altitude would become lower. Additionally, as the plane moved to higher latitudes, the air would have gotten colder, which would reduce its true airspeed for a given Mach number. All these factors would tend to gradually reduce the measured ground speed of the plane, which is indeed what we see geometrically for straight-line flight through the ping rings. For more on aircraft performance, see Barry Martin’s excellent Analytic Fuel Flow Analysis.
The Satellite. From 18:25 onward the sole evidence we have of MH370’s fate comes from the analysis of a handful of electronic exchanges between the plane and Inmarsat satellite 3F-1, which occupies a geosynchronous orbit above the equator at 64.5 degrees east longitude. Its position was not fixed; two years before, due to the fact that its hydrazine thrusters were getting low on fuel, Inmarsat had begun to let its inclination slowly increase. By March 7/8, it had reached an inclination of 1.7 degrees. Paul Sladen has published a table of ephemera. Here is a chart produced by Duncan Steel, showing the progression of the subsatellite point during the course of MH370’s final hours (click to enlarge):
The Search. Via Don Thompson: As announced at a JACC press conference 28th April, on the occasion of the end of surface search, “Australia has been coordinating the search for 41 of the 52 days since MH370 went missing. In this period, more than 4.5 million square kilometres of ocean has been searched. There have been 334 search flights conducted, an average of eight a day for a total of over 3000 hours.”
On September 24, 2014, the ATSB announced that “over 106,000 square kilometres of the wide search area have been [bathymetric] surveyed.”
Inmarsat Raw Data and ATSB report. For two months after MH370 disappeared, members of the press and the general public begged and pleaded for the authorities to release the raw data logs of transmissions between Inmarsat and the missing plane. On May 27, 2014, they finally did.
In June, the Australian Transport Safety Board released a report (later updated) that provided even more useful information, this time explaining how the raw data had been interpreted. More recently, Inmarsat’s Chris Ashton was the lead author of a paper in the Journal of Navigation explaining how the company conducted its analysis.
Thanks to these documents, we now have a much better understanding of what transpired, and have the wherewithal to undertake a critical assessment of the official investigation–which, as I described in my last post, seems to be paying off.
Burst Frequency Offset is a measure of how the signal received by the satellite from the airplane has been shifted by various factors. You can measure how closely a prospective route matches the values recorded from MH370’s actual flight by using Yap’s BFO calculator.
End of the flight. The BFO data associated with the final “half ping” at 0:19 is anomalous in comparison to the preceding pings; it values that could not be generated by any combination of speed, location or heading that is physically possible for a 777. The data is compatible with a steep descent into the ocean at an acceleration of 0.7 g, which Mike Exner, Victor Iannello and others have interpreted as a spiral dive resulting from the fuel tanks running dry. There is some dispute at present as to whether fuel exhaustion would result in such a dramatic maneuver. While plans to enlist a professional-grade simulator are underway, John Fiorentino reports that he has already researched such an experiment, and says that the plane did not spiral dive but instead descended wings-level in a phugoid oscillation, that is to say, with the plane pitching down and gaining speed, then pitching up and losing speed, then pitching down and gaining speed, and so on. I’ve excerpted his report here.
More to come…