ALERTS NAV1108.00 113.00 NAV2108.00 110.60 134.000 118.000 COM1 123.800 118.000 COM2 $_{WPT }$______$_{ DIS }$__._ $_{NM DTK }$___$_{° TRK 360°}$ N-S  E-W  Figure 11-7. The stand-by instrumentation a vailable to the pilot on Electronic Flight Instrumented Aircraft.  Figure 11-7. Emergency instrumentation available to the pilot on electronic flight instrumented aircraft. 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. 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.  Many small aircraft are not equipped with a warning system  for vacuum failure; therefore, the pilot should monitor the  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. 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.  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 Analog Instrument Failure 11-7