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Instrument Flying Handbook
Emergency Operations
Analog Instrument Failure
Pneumatic System Failure

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Instrument Flying


Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Using an Electronic Flight

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency

Figure 11-7. Emergency Instrumentation Available to the Pilot on Electronic Flight Instrumented Aircraft.

Analog Instrument Failure

A warning indicator or an inconsistency between indications
on the attitude indicator and the supporting performance
instruments usually identify system or instrument failure.
Aircraft control must be maintained while identifying the
failed component(s). Expedite the crosscheck and include
all flight instruments. The problem may be individual
instrument failure or a system failure-affecting multiple

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.