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The lessons are clear. The first is that loss of a pneumatic system in actual instrument
conditions, without a back-up system, is an emergency that may become life-threatening
unless the airplane can be flown by partial panel into visual weather conditions. It may
not be possible to do so, either due to weather conditions or lack of pilot practice with
partial panel flying.
An airplane with a single pneumatic system with no back-up system, or back-up instruments,
should not be flown in any IFR conditions that do not provide for quick access to
VFR conditions. IFR flight "on top" of cloud layers with good ceiling underneath
should create minimal problems with pneumatic system failure, but flying in actual
IFR with low ceilings and visibilities underneath sets the stage for serious difficulties.
The second lesson is that any airplane used regularly in IFR weather should be equipped
with either a back-up power source, such as dual pneumatic systems, or back-up
electrically powered gyroscope instruments. Although it is legal to fly single
engine aircraft without dual power sources for gyroscope instruments, and the exposure
rate to accidents due to pneumatic system failure while in actual instrument weather
is low (1 accident for each 40-50,000 general aviation instrument flight plans filed),
prudence suggests that a back-up power source is good insurance against being forced
to fly partial panel in adverse weather without sufficient practice.
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