FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 12. Aircraft Avionics Systems | 3. Ground Operational Checks for Avionics Equipment (Non-Electrical) | 12-38. Pneumatic Gyros
9/27/01
AC 43.13-1B CHG 1
FIGURE 12-2. Instrument vacuum system using a wet-type vacuum pump.
from the cabin where there is usually a good
deal of dust and very often tobacco smoke.
Unless all of the solid contaminants are re-
moved from the air before it enters the instru-
ment, they will accumulate, usually in the rotor
bearings, and slow the rotor. This causes an
inaccurate indication of the instrument and
will definitely shorten its service life. Dry air
pumps are also subject to damage from in-
gested contaminants, and all of the filters in
the system must be replaced on the schedule
recommended by the aircraft manufacturer,
and more often if the aircraft is operated under
particularly dusty conditions, especially if the
occupants of the aircraft regularly smoke while
flying. (See figures 12-3 and 12-4.)
Par 12-38
Page 12-17