1. Altitude Alert (ALT) Annunciator
2. Pointer Display
4. Baro Knob
5. Altitude Pointer
6. Counter Drum Display
Figure 3B-19. Pilot's Altimeter
b. Controls and Functions.
(1) Altitude Alert (ALT) Annunciator. The
altitude alert annunciator illuminates to provide a visual
indication when the aircraft is within 1000 feet of the
preselected altitude during the capture maneuver and
extinguishes when the aircraft is within 250 feet of the
preselected altitude. After capture, the annunciator
will illuminate if the aircraft departs more than 250 feet
from the selected altitude, and extinguish when the
aircraft has departed more than 1000 feet from the
between 1000-foot levels with 20-foot graduations.
In the event of a total ac and dc electrical
power loss, the warning flag will be in view,
the altimeter will be inoperative, and the
indicated altitude will remain as existed at
the time of failure.
(3) Barometric Pressure and MILLIBARS
Counter. The barometric pressure and MILLIBARS
counter, set with the baro knob, displays barometric
pressure in inches of mercury and millibars.
(4) Baro Knob. The baro knob is used to set
the barometric pressure and MILLIBARS counter.
(5) Altitude Pointer. The altitude pointer
points to the altitude on the pointer display between
1000-foot levels, in 20-foot increments.
(6) Counter Drum Display. The counter
drum displays altitude and is marked in 20-foot
annunciated by a black and white crosshatch on the
left-hand digit position of the counter display.
A failure warning flag in view indicates the
altitude information is unreliable; however,
the Mode C information may be valid.
c. Operating Procedure.
1. Barometric set knob Set desired
altimeter setting in IN HG window.
2. Warning flag Check not visible.
3. Needle indicator Check operation.
If the altimeter does not read within 70 feet
of field elevation when the correct local
barometric setting is used, the altimeter
needs calibration or internal failure has
occurred. An error of greater than 70 feet
also nullifies use of the altimeter for IFR