Piper SEMINOLE PA-44-180, Maintenance Manual

Page: 494 / 881

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.
CHART 3402. TROUBLESHOOTING (ALTIMETER)
Trouble Cause Remedy
Excessive scale error. Improper calibration Replace instrument.
adjustment.
Excessive pointer oscil- Defective mechanism. Replace instrument.
lation.
High or low reading. Improper venting. Eliminate leak in static
pressure system and check
alignment of sensor.
Setting knob is hard to Wrong lubrication or lack Replace instrument.
turn. of lubrication.
Inner reference marker fails Out of engagement. Replace instrument.
to move when setting knob
is rotated.
Setting knob set screw Not tight when altimeter Tighten instrument screw, if
loose or missing. was reset. Loose. Replace screw. if missing.
Cracked or loose cover glass. Case gasket hardened. Replace or repair instrument.
Dull or discolored markings. Age. Replace or repair instrument.
Barometric scale and ref- Drift in mechanism. Refer to latest revision
erence markers out of syn- of AC 43.13-1.
chronism with pointers.
Altimeter sticks at altitude Water or restriction in static Remove static lines from all
or does not change with line. instruments, blow line clear
change of altitude. from cockpit to sensor.
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
3 4 - 1 2 - 0 0
Page 34-04
Revised: May 15, 1989
2I22
PIPER AIRCRAFT