Six months after Malaysian Airlines Flight MH370 disappeared the reason it disappeared remains the most frustrating mystery in aviation history. Still nothing can explain it. And that is the point:. The science of air crash investigation – and it is a very mature science – abhors mystery. There were supposed to be no mysteries left.
The passing of six months has more significance than simply a point on a calendar. It really is startling that not one fragment of an airplane that weighed 250 tons has yet turned up.
No airplane this large sinks whole to the bottom of the ocean. Some parts are too buoyant to ever sink. Which should mean that somewhere out there in the expanse of ocean between Australia and the Antarctic there are traces of Flight 370 – albeit very small pieces.
What would be the most likely pattern of wreckage in this case? To provide some perspective, I have looked at five cases where large commercial airplanes have crashed into the sea in order to determine how much wreckage was left on the surface and how soon it was located:
June 1985: An Air India Boeing 747 with 329 people aboard flying from Montreal to London is destroyed by a bomb in a suitcase as it nears the coast of Ireland. The airplane falls into deep water but because traffic controllers immediately see its disappearance a search begins, and within two hours some wreckage and bodies are located on the surface.
November 1987: A South African Airways 747 en route from Taiwan to Johannesburg with 159 people aboard reports a serious fire in its cargo hold and crashes into the Indian Ocean off the coast of Mauritius. Within 12 hours an oil slick is spotted, along with some wreckage.
September 1998: A Swissair MD-11 flying from JFK to Geneva with 229 people aboard reports a fire in the cabin that spreads to the cockpit as it approaches Canadian air space. The fire overcomes the pilots and the airplane hits the ocean at 345 m.p.h. There is a huge impact that disintegrates it into thousands of pieces, most of which sinks, but some of it floats and more washes up on the nearby coast.
October 1999: An Egypt Air Boeing 767 on a flight from JFK to Cairo with 217 people aboard suddenly plunges into the Atlantic soon after reaching cruise altitude, finally diving 14,000 feet in 36 seconds before hitting the ocean with extreme force. An oil slick and some wreckage is spotted five hours later.
June 2009: An Air France Airbus A330 on a flight from Rio to Paris with 228 people aboard disappears over the South Atlantic. Within three days floating wreckage is spotted, and within two weeks 640 pieces of debris and 50 bodies are recovered.
These examples show how no two accidents are ever alike. Two were caused by human action, terrorism in the case of Air India and pilot suicide in the case of Egypt Air (though the Egyptians have never accepted the investigators’ conclusion).
Two have something in common with Flight 370: The South African 747 and the Air France A330 both ended up in very deep water. Indeed, the search for the South African 747 involved going to a depth of more than 16,000 feet, at least 2,000 feet deeper than the search for the Air France A330.
But what actually determines the amount of wreckage left floating on the surface?
The two most violent impacts involved airplanes hitting the water at high speed in a steep dive, the Swissair MD-11 and the Egypt Air 767. There were no large pieces of floating debris left.
The impact of the Air France A330 was the least violent: it hit the water in an attitude very much like a final approach to a landing, except that its landing gear was not down, with its wings level and its nose slightly up and a downward speed of 11,000 feet per minute. There was one very large and easily identifiable piece of debris floating, the vertical stabilizer.
We know nothing of how Flight 370’s Boeing 777 hit the water. The most accepted theory is that it was flying normally at cruise height until it ran out of gas.
Opinions differ, though, on what then happened. Some believe that if the two engines died simultaneously the 777 would have flown on in a stable but unpowered glide until it hit water, similar to the way the Air France A330 did. Others believe (as I do) that one engine would have died before the other and that the unbalanced power tipped the airplane over into a dive and an impact as violent as that of Egypt Air 767.
My confidence in the second theory is reinforced by the fact that the Malaysian 777 had three emergency locator transmitters that should send distress signals after the impact of a crash in water, including two in a life raft, and none was heard from, suggesting a violent impact – and, therefore, that any floating wreckage would be in very small pieces.
The resources being devoted to the search underline the hard fact that, in the absence of any wreckage, the investigation is stalled. At a press conference in Canberra, Australia last week the Malaysian transport minister, Liow Tiong Lai, said bluntly: “The investigation cannot continue without the search result.”
The investigators are being led by Kok Soo Chon, a former head of Malaysia’s Department of Civil Aviation. Experts from the United States, Europe, Asia and Australia are involved. So too are engineers from the airplane’s maker, Boeing, and Rolls Royce, whose engines powered the 777. They all are split into three groups, one dealing with the structure and systems of the 777, one with the airline’s operations and one with human factors including the crew’s psychological history.
Although nothing has been revealed of their work, it would be very surprising if the investigators were just sitting on their hands. Several experts have pointed out to me that in the absence of physical evidence, the technology exists to run computer simulations that are able to replicate the known behavior of the 777 in its last hours.
Some hint of this came at a news conference in Canberra in June. Martin Dolan, the chief commissioner of the Australian Transport Safety Bureau (the country’s highly respected equivalent of the NTSB), confirmed that all the available evidence suggested that the 777, once it headed out over the Indian Ocean, maintained its normal cruise altitude and speed until it ran out of fuel – in other words, validating the “zombie flight” theory.
He refuted earlier assertions by the Malaysian authorities that the airplane had made extreme changes of altitude, climbing to 45,000 feet before diving to 23,000 feet. Dolan said that the autopilot had been flying the 777 for its final six hours or so with all its systems functioning normally – except that there were no signs of life in the cockpit and no human communications.
The Australians posited that this could be explained by a situation in which the crew had been overcome by oxygen deprivation, the condition called hypoxia. The autopilot would be used throughout a normal flight because the 777, like all large airliners, is difficult to fly manually.
This scenario could serve as a model for what could be programed into a virtual simulation. Investigators would then go deep into the 777’s systems and try to arrive at a trigger point: What sequence of events would end with the airplane able to fly normally without any human intervention or capacity to communicate?
The techniques used for such an analysis are long established. They were developed in 1962 by Bell Telephone Laboratories to diagnose faults in the U.S. Air Force’s Minuteman missile system. This method, called fault tree analysis, was then taken up by Boeing and has been extensively used to test the reliability of many systems.
A technical document setting out the principles says: “It is a deductive procedure for determining the various combinations of hardware and software failures and human errors that could result in the occurrence of specified undesired events.” With today’s computer power available, the diagnosis can include numerous alternative scenarios.
At the perplexing heart of the Flight 370 riddle lies one critical moment: the airplane’s sudden silence. At 1:19 am local time on March 9 the last communication from the flight deck was received, spoken by either the pilot or copilot: “Good night Malaysian three seven zero.”
A few minutes later the 777’s transponder, constantly transmitting its position to the ground, stopped working. Its other umbilical link to the ground (ACARS) that sends bursts of data about the condition of its systems every 30 minutes, also failed to transmit.
Several top airline executives believe that these two systems were manually turned off during some kind of human intervention on the flight deck. The most specific of these executives was Tim Clark, the boss of Emirates Airlines based in Dubai, which operates a large fleet of 777s. He said he believed that the airplane’s links to the ground were expertly terminated by somebody with a far deeper knowledge of its systems than any of his own pilots.
But that analysis can be turned on its head: if the skills required were so rare and arcane, who would have them? By Clark’s measure it would have to be somebody with extremely specialized experience and knowledge, and so far the list of passengers has not produced a suspect with those credentials. (The criminal part of the investigation is being handled separately by the Malaysian police.)
In fact, transponders are known to be vulnerable to power outages. An electrical systems failure could also have taken out the ACARS. Both the transponder and the ACARS transmit via external antennas, two for the transponder and one for ACARS, and it is just possible that the antennas could have been damaged, though how that could happen is far from clear.
However, there is another crucial part of the 777’s systems that would be have to be diagnosed as part of a simulated test: its Airplane Information Management System, AIMS, which sits in the electronics bay beneath the flight deck and forward of a cargo hold. The introduction of AIMS in the 777 changed the architecture of the avionics on Boeing airliners. To make maintenance simpler and speedier, AIMS combined functions previously handled through separate, discrete computer units into two cabinets, each with four removable processors.
This made AIMS the gateway for all communications to and from the flight deck. It is the 777’s brain stem. AIMS handles the management of the flight itself, how the airplane is flown in real time, as well as the cockpit information displays, monitoring all of its conditions including the cabin climate and—saliently in this case—the receipt and dispatch of data.
Ultimately, then, the purpose of a fault tree analysis of MH370 would be to find out what combination of events could lead to the known and mystifying outcome of the airplane being left to fly itself for so long.
There might well be more than one path to that outcome. One is that the communications systems were disabled by some kind of power failure. Another is that there was a structural failure or an event that produced a slow decompression and loss of oxygen, leaving the pilots incapacitated while the autopilot remained able to fly the airplane. And another is, of course, that there was a deliberate human intervention – although no motive for that has ever been declared or discovered.
Last week the area now to be searched was shifted slightly further south as a result of calculations made by analyzing a call made to the 777 from a satellite phone soon after controllers lost track of it—the existence of this call had not previously been disclosed. It seems typical of the way Malaysia has handled information that something as vital as this somehow did not get immediately to the people who needed it.
The satellite phone data indicates that Flight 370 turned left into its final southern flight path sooner than previously believed. As well as implying that the 777 flew into the ocean further south before crashing, this information has another implication – instead of crossing the western tip of Indonesia over Banda Aceh, the flight crossed over a more populated part of Indonesia further east – apparently without being noticed.
Planning the next phase of the search has required creating a body of new scientific knowledge about the southern oceans. The target zone is so remote that before the disappearance of Flight 370 nobody saw cause to explore or map it – underlining the fact that our planet still includes quite a bit of terra incognita, albeit under water, for the good reason that it is normally too fearsome to approach.
More than 23,000 square miles have been mapped by a pair of survey ships, one Dutch and one Chinese. What they found is akin to an underwater Himalayas. “There are volcanoes down there we’ve found which were unknown before” Paul Kennedy, one of the scientists involved in the mapping, told BBC News. The deepest parts are nearly four miles down, with huge valleys between mountain ranges. Even the shallowest parts are more than 3,000 feet deep.
As forbidding as this terrain is, there is another force at work on the ocean surface – the Antarctic Circumpolar Current. This is a giant rotating flow of water moving like a continuous belt, clockwise, between Antarctica and Australia, connecting the waters of the Atlantic, Pacific and Indian oceans, driven by strong westerly winds part of which were known to mariners in the days of the old Clipper ships as the roaring forties because they were to be found between the latitudes of 40 and 50 degrees. By the time the first air and sea search began in March, any floating remnants of wreckage could have been carried into this current and lost forever.
In any event, the coming search will have nothing like the precision that was possible in the search for the debris field of Air France 447 in the South Atlantic. Because the Airbus 330’s last known position had been calculated from data streamed from the airplane the search was narrowed down to a radius of 40 miles. Even then, it took two years to find the wreckage and the flight data recorders. In contrast, the area to be searched for Flight MH370 is 17,500 square miles, an unprecedented challenge.
Beginning this month, Dutch vessel Fugro Survey has been contracted for a year to direct the search, expected to cost nearly $50 million (that’s in addition to at least $55 million spent on the first air and sea search). It will deploy three specialized underwater vehicles including side-scan sonar, multi-beam echo sounders, video cameras, and a chemical sensor that can detect jet fuel in water in as little a concentration as a few parts per billion.
Any air crash investigation has one primary and urgent purpose: to understand and explain the cause – and that includes looking for a vulnerability in the airplane that has not shown itself before. This 777 was vulnerable in some way, human or mechanical, not anticipated by its makers or its operators. That, at least, is incontrovertible. And one thing not to be forgotten in this mystery of mysteries is the fate of the 227 passengers. Although the first priority in the investigation is the pilots’ condition, the greater riddle is, what was the condition of so many passengers for six or more hours as the 777 flew toward the great dark deep?