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those that continue to operate without electrical power. Pilo ts can attempt to troubleshoot alternator failure by following t he established alternator failure procedure published in the PO H/ AFM. If the alternator cannot be reset, advise ATC of t he situation and inform them of the impending electrical failur e. 

## Analog Instrument Failure 

A warning indicator, or an inconsistency between indicatio ns on the attitude indicator and the supporting performan ce 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 that 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 mean sea level (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 

