Sensitive Altimeter; Altimeter Troubleshooting - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
10-37. SENSITIVE ALTIMETER.
10-38. GENERAL. The altimeter indicates altitude in feet above sea level. The indicator has three pointers
and a dial scale, the long pointer is read in hundreds of feet, the middle pointer in thousandths of feet and
the short pointer in ten thousandths of feet. A barometric pressure window is located on the right side of
the indicator dial and is set by the knob located on the lower left comer of the instrument. The altimeter
consists of a sealed diaphragm that is connected to the pointers through a mechanical linkage. The
instrument case is vented to the static air system and as static air pressure decreases, the diaphragm
expands, causing the pointers to move through the mechanical linkage to indicate a higher altitude.
10-39. TROUBLESHOOTING.
TABLE X-V. ALTIMETER
Trouble
Cause
Remedy
Excessive scale error.
Excessive pointer
oscillation.
High or low reading.
Setting knob is hard
to turn.
Inner reference
marker fails to
move when setting
knob is rotated.
Setting knob set
screw loose or
missing.
Cracked or loose
cover glass.
Improper calibration
adjustment.
Defective mechanism.
Improper venting.
Wrong lubrication or
lack of lubrication.
Out of engagement.
Not tight when
altimeter was reset.
Case gasket hardened.
Replace instrument.
Replace instrument.
Eliminate leak in
static pressure system
and check alignment of
sensor.
Replace instrument.
Replace instrument.
Tighten instrument
screw, if loose. Re-
place screw, if
missing.
Replace or repair
instrument.
Dull or discolored
markings.
Age. Replace or repair
instrument.
Barometric scale and
reference markers
out of synchronism
with pointers.
Drift in mechanism.
Refer to latest
revision of AC43.13-1.
Revised: 9/24/81
INSTRUMENTS
3B12