Memorandum by the the Aerospace Medical
In the first decades of the 20th Century, when
aviation was in its early days, aeronautical engineers and aviation
medicine practitioners explored the question of what would constitute
an acceptable cabin altitude. Although there are no precise records
of their deliberations, the literature does indicate that the
agreed maximum cabin altitude of 8,000 feet was a compromise taking
into consideration aircraft design, operational requirements,
and human performance. Practically every regulatory agency and
airline in the world has accepted this compromise.
In recent decades, some experts have advocated
lowering the maximum cabin altitude from 8,000 feet to 6,000 feet
presuming this would enhance cockpit and cabin crew performance
and protect the health of the passengers. But is there evidence
Recommendations to lower cabin altitude are
based upon the reasonable assumption that a higher ambient pressure
and the resulting improved pO2 would lessen the risk of exacerbation
of pre-existing illness (particularly cardiopulmonary) and barotrauma.
Although there have been a number of articles published in the
literature describing inflight medical events, including death,
we have been unable to find a correlation of these events with
cabin altitudes below about 10,000 feet.
On the other hand, we know that some passengers
develop a broad array of nonspecific symptoms during flight including
anorexia, nausea, fatigue, headache, and insomnia. We do not know
the cause of these symptoms although, for the most part, they
are relatively minor and resolve quite rapidly postflight.
Anecdotal evidence seems to suggest that some
cabin crew (flight attendants) may similarly experience such transient
symptoms which may be aggravated by the nature of their work,
which can be quite physically demanding at times. While it would
be physiologically plausible for this to happen, there are however,
no studies documenting the relationship especially with regard
to an "acceptable" cabin altitude where these effects
are significantly minimised. It is a known fact that exercise
can aggravate symptoms of hypoxia especially in cardiorespiratory
compromised individuals. This would happen at any altitude above
sea level and would be increasingly severe, the higher the altitude.
Again, the question of an "acceptable" altitude remains
unanswered. From an occupational health standpoint, workers who
are not reasonably fit for the environmental conditions expected
within an aircraft cabin, may need to be redeployed.
Regarding performance of cockpit crew, McFarland
and Barach did a number of seminal studies some years ago to determine
if there is a decrement in cockpit performance with increasing
It was observed that there is, in some cases, a small but not
a significant decrement in vision and psychomotor skills until
one reaches a cabin altitude above 10,000 feet, well beyond the
prescribed 8,000 feet cabin altitude. Likewise, Denison et al
reported small decrements in response time during orientation
tasks at 8,000 feet relative to 5,000 feet and at both altitudes
relative to sea level performance. It is reasonable to assume
that there is no added threat to civil flying safety due to performance
decrement with an 8,000 feet cabin altitude.
In summary, we could find no evidence that lowering
the cabin altitude would prevent significant adverse health effects
on reasonably healthy passengers and cabin crew nor significantly
enhance performance by cockpit crew. One can only presume that
a lower cabin altitude might be more conducive to preventing illness
in flight, but this is only conjectural.
Therefore, the Aerospace Medical Association
cannot, at this point, recommend a lowered cabin altitude based
solely upon health and cockpit performance considerations. The
Aerospace Medical Association would encourage more research to
be done into this area.
30 May 2007
1 McFarland R Human Factors in Air Transportation.
New York, McGraw-Hill Book Co Inc. 1953. Back
Barach AL, McFarland RA, Seitz CP. The effects of oxygen deprivation
on complex mental functions. J Av Med-1937; 8 ( 4): 197-207. Back
Denison DM, Ledwith F, Poulton EC. Complex reaction times at simulated
cabin altitudes of 5,000 feet and 8,000 feet. Aerospace Med
1996; 10: 1010-1013 Back