Pilot Incapacitation: Debate on Assessment, 1% Rule etc.

Reuters reported on 15 February 2012 that the captain of a Czech Airlines plane collapsed and died in flight from Warsaw to Prague. The plane carrying 46 passengers made a safe landing with the co-pilot on controls [1]. In another case, a Qatar Airways captain passed away in October 2010 on a flight from Manila, Philippines to Doha, Qatar [2]. Still earlier in 2009, the 60 year old captain of a Continental Airlines flight from Brussels to Newark died in mid-flight [3]. Such news items may be a cause of concern for the flying passengers despite of stringent periodic medical assessment instituted by the aviation regulators. But, it is more important to note that all those flights landed safely, thus proving the wisdom of allowing multi crew composition in commercial aviation while effectively applying Evidence Based Medicine in the Aeromedical Decision Making (ADM) while determining the medical fitness of pilots by the regulatory medical authorities.

The medical assessment of commercial pilots is undertaken to ascertain their functional ability as well as physical capacity to safely exercise the privileges of their professional licenses during routine and emergency situations in flight. Additionally, it allows a reasonable assessment of “risk of incapacitation during the period of validity of the medical certificate” [4].

The acceptable 1% level of risk of incapacitation in a multi-crew environment of commercial operations, the so-called ‘1% Rule’, has stood the test of time thus far. This rule, devised to consider the failure of the human component, in terms of mechanical system reliability to be at par with the airworthiness requirements of airliners. Thus as a reasonably acceptable but ‘extremely remote’ failure rate for any aircraft sub-system, including the human component – pilot error or pilot incapacitation is to be less than one in 100 million flying hours. So also the risk of failure of the human component due to medical reasons, should be less than one in 1000 million flying hours or less [5, 6, 7]. This rule, initially proposed for cardiovascular mortality rate which increases exponentially with age, works out to one per cent per annum for the males in England and Wales [8].

Most of the regulatory medical authorities now use this broad rule – an acceptable rate of ‘one per cent per annum’ (approximately equal to one in 1 million flying hours) for pilot incapacitation due to medical reasons to assess fitness of the pilots. The vital mitigating factor: presence of another healthy pilot on a serviceable commercial aircraft allows for acceptable risk of pilot incapacitation by a factor of 1000 from 1000 million flying hours to a more reasonable1 million flying hours [8]. The veracity of this rule was substantiated by simulator studies showing that in case one pilot has sudden incapacitation in a critical phase of flight, 399 times out of 400 the second pilot could take over the control and continue the flight safely [9], thus providing the proof of risk mitigation in the multi-crew environment of commercial aviation. This has been further refined to a modest assumption that the second pilot can continue the safe flight in 99 occasions out of 100 in actual flight [6].


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Acknowledgement   Image courtesy Freedigitalphotos.net

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