A slow decompression may have occurred onboard Malaysia Airlines flight MH370 and knocked its occupants, including its crew members, unconscious as the plane continued to fly on autopilot.
The decompression might have been caused by cracking or corrosion on the aircraft's fuselage skin, which might have also disabled communication.
These explanations are contained in a blog article titled "MH370 – what happened".
The article, however, does not carry the name of the writer who has come up with the "plausible explanation" on what happened to the Malaysia Airlines Boeing 777-200ER passenger jet and why it was missing.
The author said the United States' Federal Aviation Administration (FAA) Airworthiness Directive (AD) for Boeing 777 aircraft could be a clue for investigators.
According to the directive issued in September last year, the FAA had proposed the adoption of a new AD for certain Boeing 777 aircraft. This followed a report of cracking in the fuselage skin underneath the satellite communication (Satcom) antenna adapter.
The AD requires repetitive inspections of the visible fuselage skin and doubler, if installed, for cracking, corrosion, and any indication of contact of a certain fastener to a bonding jumper, and repair if necessary.
Cracking and corrosion in the fuselage skin can lead to rapid decompression and loss of structural integrity of the airplane.
The nameless author said it was plausible that a fuselage section near the Satcom antenna adapter failed. It would then disable the satellite-based GPS (global positioning system), ACARS (aircraft communications addressing and reporting system), and ADS-B/C (automatic dependent surveillance-broadcast/contract) communications, and leading to a slow decompression that left all occupants unconscious.
The writer said if such decompression left the aircraft intact, the autopilot would have flown on the planned route or maintained its direction or altitude until it runs out of fuel.
A slow decompression, from a golf-ball-sized hole for instance, would have gradually impaired and confused the pilots before cabin altitude (pressure) warnings sounded.
The writer offered a chain of events that could have happened onboard MH370.
"Likely fuselage failure near Satcom antenna adapter disabled some or all of GPS, ACARS, ADS-B, and ADS-C antennas and systems.
"Thus, only primary radars would detect the plane. Primary radar range is usually less than 100nm (nautical miles) and is generally ineffective at high altitudes.
"If the decompression was slow enough, it’s possible the pilots did not realise to put on oxygen masks until it was too late." The writer said oxygen masks would not deploy until cabin altitude reaches 13,500m and the passengers were likely already unconscious by then.
Since it was also a red-eye flight, most passengers would had been sleeping and perhaps unaware of oxygen deprivation.
"No confirmed debris has been found anywhere near the search area, consistent with the plane having flown for hours after it lost radar contact."
The writer said another pilot flying 30 minutes ahead of MH370 heard "mumbling" from the missing plane.
It was because very high frequency (VHF) communication would be unaffected by Satcom equipment failure, he said. It was reported earlier this week that another Boeing 777 pilot, who was flying to Narita, Japan, had established contact with MH370 just after 1.30am on Saturday around the time the plane went off the radar.
The pilot was asked by Vietnamese air traffic control to use his plane's emergency frequency to ask MH370 to establish its position after the authorities lost contact with the MAS jet.
The pilot had reported that there was a lot of interference and static, as well as mumbling before he lost contact with MH370.
On how relatives got through the mobile phones of the missing MH370 passengers, the writer said the plane was equipped with cellular communication hardware, supplied by AeroMobile, to provide GSM services via satellite.
The hardware is, however, an aftermarket product, which is not connected through Satcom to the writer's knowledge.
"This explains why 19 families signed a statement alleging they were able to call the MH370 passengers and hear their phones to ring, but with no response.
"When Malaysia Airlines tried to call the phone numbers a day later, the phones did not ring. By this time, fuel would have been exhausted."
The writer also agreed with some early reports that an “explosive decompression” or “inflight disintegration” was unlikely.
"This was likely a slow decompression that gradually deprived all crew and passengers of oxygen, leaving the autopilot to continue along the route autonomously.
"The aircraft may be at the floor of the East China Sea, Sea of Japan, or the Pacific Ocean thousands of miles northeast from the current search zone."
The author also offered some "sensible and low-cost recommendations to best aid recovery efforts". Investigators, the writer said, should obtain data logs from primary radars throughout mainland China that would have been along the planned route because they may be the best clue as to the trajectory of the aircraft.
"Per the latest reported news, the Strait of Malacca is a possibility. Investigators should also obtain all passengers’ cell phone log and location data.
"The timing of the last successful cellular connection (ring/SMS/data-packet) can predict how long the plane was in the air. iPhone/iOS location (GPS) data may be available from Apple if subpoenaed. Android location data may be available from Google.
"Add a secondary search space to include a 300nm radius around Beijing, focusing on surrounding bodies of water. Using planned routing trajectory, known autopilot logics, fuel quantities, and weather patterns, it may be possible to define a smaller 50nm x 50nm search space. Consider running the above scenario in the MH’s 777-200ER full flight simulator.
"Boeing should provide expertise about the Satcom antenna schematics and autopilot/navigation logic, so as to help plot this second search space."
The author added that an email with the recommendations had been sent to the National Transportation Safety Board's media relations.
MH370 left the Kuala Lumpur International Airport at a 12.41am on Saturday with 227 passengers and an all-Malaysian crew of 12.
The plane was supposed to land in Beijing at 6.30am the same day but it never showed.
According to reports, all contact with the plane was lost about 1.30am. Search and rescue operations around the South China Sea, the Strait of Malacca and the Andaman Sea have yet to yield any results. – March 12, 2014.