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of the battery, there may be sufficient power available for
45 minutes of flight—or for only a matter of minutes. Pilots
should also know which systems on the aircraft are electric and
those that continue to operate without electrical power. Pilots
can attempt to troubleshoot alternator failure by following
the established alternator failure procedure published in the
POH/AFM. If the alternator cannot be reset, advise ATC of
the situation and inform them of the impending electrical
failure.
Analog Instrument Failure
A warning indicator or an inconsistency between indications
on the attitude indicator and the supporting performance
11-7
Figure 11-7. Emergency Instrumentation Available to the Pilot on Electronic Flight Instrumented Aircraft.
instruments usually identifies system or instrument failure.
Aircraft control must be maintained while identifying the
failed component(s). Expedite the cross-check and include
all flight instruments. The problem may be individual
instrument failure or a system failure affecting multiple
instruments.
One method of identification involves an immediate
comparison of the attitude indicator with the rate-of-turn
indicator and vertical speed indicator (VSI). Along with
providing pitch-and-bank information, this technique
compares the static system with the suction or pressure system
and the electrical system. Identify the failed component(s)
and use the remaining functional instruments to maintain
aircraft control.
Attempt to restore the inoperative component(s) by checking
the appropriate power source, changing to a backup or
alternate system, and resetting the instrument if possible.
Covering the failed instrument(s) may enhance a pilot’s
ability to maintain aircraft control and navigate the aircraft.
Usually, the next step is to advise ATC of the problem and,
if necessary, declare an emergency before the situation
deteriorates beyond the pilot’s ability to recover.
Pneumatic System Failure
One possible cause of instrument failure is a loss of the
suction or pressure source. This pressure or suction is
supplied by a vacuum pump mechanically driven off the
engine. Occasionally these pumps fail, leaving the pilot with
inoperative attitude and heading indicators.
Figure 11-8 illustrates inoperative vacuum driven attitude
and heading indicators which can fail progressively. As the
gyroscopes slow down they may wander, which, if connected
to the autopilot and/or flight director, can cause incorrect
movement or erroneous indications. In Figure 11-8, the
aircraft is actually level and at 2,000 feet MSL. It is not in
a turn to the left which the pilot may misinterpret if he or
she fails to see the off or failed flags. If that occurs, the pilot
may transform a normally benign situation into a hazardous
situation. Again, good decision-making by the pilot only
occurs after a careful analysis of systems.
Many small aircraft are not equipped with a warning system
for vacuum failure; therefore, the pilot should monitor the
system’s vacuum/pressure gauge. This can be a hazardous
situation with the potential to lead the unsuspecting pilot into
a dangerous unusual attitude which would require a partial
panel recovery. It is important that pilots practice instrument
flight without reference to the attitude and heading indicators
in preparation for such a failure.
Pitot/Static System Failure
A pitot or static system failure can also cause erratic and
unreliable instrument indications. When a static system
11-8
Figure 11-8. Vacuum Failure.
problem occurs, it affects the ASI, altimeter, and the VSI.
In most aircraft, provisions have been made for the pilot to
select an alternate static source. Check the POH/AFM for
the location and operation of the alternate static source. In
the absence of an alternate static source, in an unpressurized
aircraft, the pilot could break the glass on the VSI. The VSI
is not required for instrument flight, and breaking the glass
provides the altimeter and the ASI a source of static pressure.
This procedure could cause additional instrument errors.
Communication/Navigation System
Malfunction
Avionics equipment has become very reliable, and the
likelihood of a complete communications failure is remote.
However, each IFR flight should be planned and executed in
anticipation of a two-way radio failure. At any given point
during a flight, the pilot must know exactly what route to fly,
what altitude to fly, and when to continue beyond a clearance
limit. Title 14 of the Code of Federal Regulations (14 CFR)
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Instrument Flying Handbook仪表飞行手册下(92)
