Almost three years after Malaysian Airlines flight MH370 disappeared while traveling between Kuala Lumpur and Beijing, the search for the plane and its 239 passengers and crew has been called off. The anguish of the relatives of those who died on the Boeing 777-200ER and their anger that the quest to find the wreckage has been abandoned is understandable. There are strong grounds for the Australian and Malaysian authorities to call a halt to an investigation that has involved a high technology underwater search of no less than 120,000 square km of the Indian Ocean. Yet the recent suggestion by the Australian Transport Safety Bureau that the airliner was more likely to be in a 25,000 square km area to the north of the current search area clearly frustrates all those who do not want the probe to stop. They are asking why the larger southern area was the focus of the deep-sea search and why the investigation cannot now be moved to the relatively smaller area to the north. This is, however, to ignore one of the basic truths of all search and rescue operations, which is that even when nothing is found, something is discovered. A fruitless search proves the negative. That which is looked for is not there, so it must be somewhere else. In normal circumstances resources can be directed more intensely to other areas where statistically the likelihood of a find has been increased. But these are calculations in an ideal world. The immense area and the complexity of the subsea terrain involved in the search for MH370 make this a task of almost unbelievable difficulty. Moreover, there is one factor which has been given little publicity as the deep water probes scoured the ocean floor. In every search, for instance by highly-trained mountain and wild country search teams, there is an element called "Probability of Detection" (POD). This is a calculation which combines the nature of the area just searched with the speed at which it was searched and the number of people, drones or aircraft that have been deployed. Feed the figures into the formula and out comes the likelihood that the object or person searched for has in fact been missed. Depending on the outcome, search managers will reassign priority areas that need to be searched again. There is hardly ever a POD of 100 percent. The POD for the scouring of this vast area of the seabed has not been made clear by the Australians who have led the investigation. And there is one more key detail with MH370 that has made this search extremely difficult. Normally on land, those in charge need to know the point at which their subject was last seen. For MH370 this was to the west of Malaysia. Thereafter, it was a calculation based on some meager automated engine reporting data, the fuel load and remaining range of the Boeing. One good development to emerge from the hunt for this airliner is the pressing need for airlines to fit transponders that cannot be deactivated from within the aircraft itself. The International Civil Aviation Organization, which began to address the challenge following the 2009 loss of Air France Flight 447 in the Atlantic, is now mandating the measure along with aircraft design changes by 2020 which will allow flight recorders to be ejected on impact.
