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magnitude), but there are mitigating circumstances in the air with some studies showing that older, more
experienced, pilots have fewer accidents. In accidents attributable to incapacitation of the pilot there are
important differences between single-pilot and multi-pilot operations: in those aircraft in which there is
only one crew member, the rate of complete incapacitation will approach the accident rate. Subtle
incapacitation will also erode safety. In multi-crew operations, an incapacitating cardiovascular event,
like an engine failure, should be containable in all but the most adverse circumstances. There is a strong
case, therefore, to demand a higher standard of fitness for pilots engaged in single-crew operations. This
is the basis of the OML restriction (see above).
During the 1960s, civil air-transportation accidents in which cardiovascular incapacitation was a
contributory factor occurred on a worldwide basis at the rate of approximately one every 18 months,
culminating in the loss of a British European Airways (BEA) Trident 1 at Staines near London Heathrow
Airport in June 1972. There were, however, major aircrew training and operational differences at that
time when compared with modern airline operations and less was understood about the multi-factorial
nature of accident causality. In the near one billion multi-crew jet hours flown since 1974, when an ICAO
requirement for experience in procedures for crew incapacitation — "incapacitation training" — was
adopted (see Annex 1, 2.1.5.2.a)), hull loss accidents caused by pilot cardiovascular incapacitation has
been all but eliminated. There have, however, been a small number of significant incidents with safety
degradation, and cardiovascular deaths continue to occur whilst pilots are on duty, varying at a recorded
rate of two to four per annum worldwide.
ICAO Preliminary Unedited Version — October 2008 III-1-4
Early cardiovascular-cause accident experience led to reports by certain “expert” groups which were not
commissioned by any Licensing Authority. These recommended, inter alia, that exercise
electrocardiography, still in its early days, might be helpful in the detection of occult coronary artery
disease. This was at a time when resting electrocardiography had only relatively recently been made
mandatory by ICAO (1963). A better understanding of probability theory in populations with a low
prevalence of disease led to the rejection of this suggestion at the ICAO cardiovascular study group in
Montreal in 1980.
The “1% Rule”
A seminal contribution to regulatory judgement was made by the suggestion that there was symmetry
between the cardiovascular event rate in aircrew and the accident rate of aircraft. From this beginning
emerged what has become known as the “1% Rule”. This is a mathematical model of accident probability
based on the epidemiology of coronary artery disease. It may, however, be applied to other medical
conditions as well (see Part 1, Chapters 2 and 3). In cardiology, it is easier to apply to those cardiac
conditions for which event rates can be reasonably predicted, such as the coronary syndromes, rather than
to the more capricious problems, such as atrial fibrillation. Inevitably such predictions apply to groups of
individuals rather than the individual himself.
It calculates that provided the predicted cardiovascular mortality of an individual does not exceed
approximately one per cent per annum (that of a Western male aged 70 years), the probability of an
accident to a multi-crew aircraft from cardiovascular incapacitation of the pilot should be “very remote”,
i.e. no more than 1:109 (one per one billion) flying hours.
In spite of the rule being predicated on the basis of cardiovascular mortality, confusion continues in
distinguishing this from the non-fatal cardiovascular event rate. Every coronary death will be clustered
with perhaps three to four non-fatal co-morbid events but in aviation the population will have been
factored, as some of the co-morbid events will have brought about the earlier removal (because of a
regulatory “unfit” assessment) of higher-risk pilots. In regulatory terms, the cardiovascular death rate thus
approximates to the cardiovascular incapacitation rate.
The “1% Rule” is only one of several means of defining regulatory cut-off points. The rule has been
reviewed comprehensively recently and some Contracting States have found a two per cent cut-off point
to be justified.
Cardiovascular causes of incapacitation
Incapacitation due to cardiovascular disease may be insidious or sudden in onset, and subtle or obvious in
its manifestation. The coronary syndromes are not infrequent in aircrew in the Western world or the
　
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