by Iain Maciver
Having some experience of using air traffic control systems, albeit some time ago, it is difficult for me to accept the current theory advanced by experts, on Sky News particularly, that the Malaysian airliner suddenly depressurised. Then, they reckon, the pilots would have turned back to Kuala Lumpur but would soon after have lapsed into unconsciousness and the plane would have carried on in autopilot mode until it ran out of fuel and dropped into the Indian Ocean. I don’t buy that.
In that otherwise reasoned theory lies a big flaw. Flight MH370 also stopped showing on civil radar an hour into the flight when they say that depressurisation must have happened. Even a sudden drop in pressure would not have caused the radar return signal to disappear. It certainly did not happen in other sudden depressurisations including the Helios Airways Flight 522 crash in Greece in 2005. That was put down to wrongly-set flightdeck controls but problems with badly-fitting or torn door seals have caused depressurisation before. It was too high for a bird strike.
Ill-informed media speculation about why the Malaysian military say they saw it many miles off track suggests the flight must have been monitored as a spy target or terrorist threat. No evidence exists for that at all, as the briefings are public set-pieces. From my own years in RAF air traffic control I can tell you that the civil authorities would have relied on Secondary Surveillance Radar (SSR), the more hi-tech radar system which gives a readout on the controller’s screen showing callsign, height and direction of travel. That readout is known as a squawk.
However, military units everywhere also use old-fashioned but still useful long-range Primary Radar, which merely shows a plane as a blip on the screen among other shadows and all kinds of fixed obstacles and weather. A vital difference between the two systems is that SSR needs a signal to be sent back from a box on board. That equipment, technically a transponder but known as a squawk box, is interrogated and then sends data back to the ground. Primary Radar, by comparison, is basic and needs only a reflected beam of energy to show the plane as a blip on the screen. Primary also shows flocks of birds and storm clouds. Malaysian Air Force controllers could see MH370 wandering off its flight plan but the civilian controllers with SSR could not. If the squawk box was switched off, the civilian ground controller would see nothing. Crucially, they should still hear them though.
Whatever caused MH370 to deviate from its course is unlikely to have been depressurisation. I suspect either someone switched off the SSR transponder or it was damaged in an incident on board. Spilt tea has caused planes to stop squawking or to show an incorrect squawk. Even if that happened, why did the radio two-way communications also completely stop? There would have been time to get a Mayday message out. In the case of the Greek crash, the pilots panicked but they got several Maydays out. Unfortunately, they were on the wrong frequency. When they eventually passed out, a flight attendant with pilot training then took to the radio but he too did not check the frequency.
Because we now know it diverted well off its planned course, and was tracked towards the Malacca Strait where the search has now moved, there was no catastrophic mid-air explosion on the Boeing 777. At least not south of Vietnam, where it suddenly disappeared off SSR. A clued-up hijacker may have switched off or disabled the squawk box to stop the crew dialling up 7500, the international hijack alert code. He may also have ordered them not to communicate or may have snipped their microphone wires. That is one possible explanation which, I have to say, fits what we now know.
Yet there is no ransom demand, no political grandstanding, no fundamentalist flag-waving and not even a glimpse of the plane which would normally lead us to believe the worst had already happened. What little information we do have already puts this mystery in a class of its own. The truth, when it eventually emerges, may be stranger than fiction. Sadly, as time marches on, it is also increasingly likely to be nothing less than utterly tragic for the 239 souls who went on board that plane on Friday evening.