Altimeter Troubleshooting - Piper PA-44-180 SEMINOLE Maintenance Manual

ALTIMETER.
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 corner 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.
Trouble
Excessive scale error.
Excessive pointer oscil-
lation.
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.
Dull or discolored markings.
Barometric scale and ref-
erence markers out of syn-
chronism with pointers.
Altimeter sticks at altitude
or does not change with
change of altitude.
PIPER AIRCRAFT
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
CHART 3402. TROUBLESHOOTING (ALTIMETER)
Cause
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.
Age.
Drift in mechanism.
Water or restriction in static
line.
Replace instrument.
Replace instrument.
Eliminate leak in static
pressure system and check
alignment of sensor.
Replace instrument.
Replace instrument.
Tighten instrument screw, if
Loose. Replace screw. if missing.
Replace or repair instrument.
Replace or repair instrument.
Refer to latest revision
of AC 43.13-1.
Remove static lines from all
instruments, blow line clear
from cockpit to sensor.
2I22
Remedy
3 4 - 1 2 - 0 0
Page 34-04
Revised: May 15, 1989