It is now nearly two years since Malaysian Airlines flight MH370 disappeared somewhere over the Indian Ocean. Apart from the trailing-edge flaperon that washed up on Reunion Island and was discovered last July, there has been no trace of the Boeing 777 or its 239 passengers and crew. It remains among the world’s most enigmatic aviation mysteries.

A search of the southern Indian Ocean, led by the Australian Transport and Safety Bureau (ATSB), continues in an area defined by a complicated set of calculations derived from five “handshakes” and five other communications events between the aircraft, the Inmarsat 3F1 satellite and a ground station in Perth, Western Australia. Two key parameters associated with the signals from MH370 over a seven-hour, 40-minute period were used in the analysis: Burst Timing Offset (BTO) and Burst Frequency Offset (BFO).

Inmarsat led the effort, assisted by other members of a Flight Path Reconstruction Group (FPRG), including Australian defense scientists, British air accident investigators, U.S. NTSB officials, Boeing, Honeywell, Thales UK and two specialist ground-station contractors, SED and Square Peg Communications. Four Inmarsat employees described the work in detail for the journal of the Royal Institute of Navigation in October 2014, including the reasons for revising the search area after a few months.

A 15-strong “Independent Group” of current and retired aerospace and communication industry professionals have voluntarily investigated the disappearance and corresponded with the relatives. The group’s spokesman is a former Thales flight simulation engineer, Don Thompson. He told AIN that “the challenge of finding MH370 is immense. The revised search area is equivalent to the land area of Switzerland and Austria with some similar mountainous [underwater] terrain.”

The Independent Group has questioned some of the FPRG’s assumptions. It has published its findings on the website www.duncansteel.com. In a recent post, they write that the longer the aircraft remains undiscovered, the more likely the possibility of a fundamental conceptual error. For instance, the BTO and BFO data might fit alternative calculations of the MH370 fuel burn, a much earlier descent, and a more northerly end point. The conclusion by the FPRG that one engine flamed out, followed within minutes by the other, is important to the search area calculation. It has been tested in the Boeing engineering simulator, based on historic data from MH370’s engines.

Others have disagreed more fundamentally with the search strategy. Aron Gingis, an Australian environmentalist specializing in cloud microphysics, told the ATSB that it should be possible to analyze archived satellite imagery for cloud changes generated by MH370’s vapor trails. He told AIN that “Inmarsat’s modeling and calculations have been largely approximate and possibly wrong.” The ATSB declined his assistance. A Ukrainian scientist claimed that acoustic and seismic data could be brought to bear. Australian scientists disagreed.

At the end of last November, five scientists from the Australian Defence Science and Technology Group (DSTG) published the draft results of their revisiting of all the available data, and their new modeling. As a result, the ATSB again slightly revised its calculation of the likely seabed location of MH370. The DST Group examined ocean drift data and said that discovery of the flaperon on Reunion was not inconsistent with the designated search area.

The Independent Group commented that the Bayesian approach used by the DSTG team has a pronounced bias favoring straight flight paths, and higher speeds. They also noted that assumptions about the 777’s autopilot roll mode affect the potential end point of the flight. 

Three specialist vessels have now searched more than 80,000 sq km of the seabed. Two of them use deep-tow sonar, while a third deploys an autonomous underwater vehicle (AUV) that surveys the most difficult terrain–of which there is plenty. The project director for Fugro, the maritime survey specialists contracted for the search, has described volcanic cones, fracture zones running for 100 km, and 70-degree cliff faces. If the aircraft broke into small pieces upon impact with the water, above such a zone, could sonar ever find it?

The governments of Australia, Malaysia and China have committed to searching a further 40,000 sq km, which should take until the middle of this year. That will be the end of the search, “unless credible new information leads to a specific location of the aircraft,” they say. 

Various theories on the cause of the disappearance continue to circulate. Last month, an Australian media article revived the pilot hijack theory. It repeated a report that the flaperon broke off the aircraft in an extended position, and suggested that MH370 made a controlled ditching. The ATSB stated last month that no conclusions had yet been reached on the flaperon. Further, it noted that “for search purposes, the relevant facts and analysis most closely match a scenario in which there was no pilot intervening in the latter stages of the flight.”

Earlier in the flight is another matter. There are no convincing explanations as to why the aircraft should have made three big turns–the initial 180-degree reversal over the South China Sea, another one to the northwest over Penang towards the Andaman Sea, and a final one to the south near the northern tip of Sumatra. These turns are assumed from the primary radar traces that were analyzed post-flight, after Malaysian air defense and ATC controllers failed to identify and track the errant airliner in real time. Those turns don’t make any sense in an emergency situation, and neither does continued navigation without communication from the flight deck.