TM 55-151 O-221 -10
placards and locate exits. An inertia switch, when
ORIDE OFF - RESET - AUTO - TEST. Should the
subjected to a 2 G shock, will illuminate interior lights in
system accidentally actuate, the emergency lights will
the cockpit, forward and aft cabin areas, and exterior
illuminate. Placing the switch in the momentary OFF
lights aft of the emergency exit and aft of the cabin door.
RESET position will extinguish the lights. To test the
The battery power source is automatically recharged by
system, place the switch in the TEST position. The
the aircraft electrical system.
lights should illuminate. Moving the switch to the OFF
- RESET position will turn the system off and reset it.
b. Operation. An emergency lights override switch,
located on the overhead control panel (fig. 2-12), is
provided to turn the system off if it is accidentally
actuated. The switch is placarded EMERG LIGHTS
Section Xl. FLIGHT INSTRUMENTS
PITOT AND STATlC SYSTEM.
a. Description, The pitot and static system (fig.
2-28) supplies static pressure to two airspeed indicators,
the copilot altimeter, the air data computer (ADC), two
vertical velocity indicators, and also ram air to the
airspeed indicators and the ADC. This system consists
of two pitot masts (one located on each side of the lower
portion of the nose), static air pressure ports in the
aircrafts exterior skin on each side of the aft fuselage,
and associated system plumbing. The pitot mast is
protected from ice formation by internal electric heating
b. Alternate Static Air Source. An alternate static
air line, which terminates just aft of the rear pressure
bulkhead, provides a source of static air for the pilots
instruments in the event of source failure from the pilots
static air line. A control on the pilots subpanel placarded
PILOTS STATIC AIR SOURCE, may be actuated to
select either the NORMAL or ALTERNATE air source by
a two position selector valve. The valve is secured in the
NORMAL position by a spring clip. Refer to Chapter 7
for airspeed indicator and altimeter calibration
information when using the alternate air source.
2-80. TURN-AND-SLIP INDICATORS.
Turn-and-slip indicators are installed separately on
the pilot and copilot sides of the instrument panel (fig.
2-29). These indicators are gyroscopically operated.
They use DC power and are protected by 5-ampere
circuit breakers placarded TURN & SLIP PILOT or
COPILOT on the overhead circuit breaker panel (fig.
2-81. AIRSPEED INDICATORS.
Airspeed indicators are installed separately on the
pilot and copilot sides of the instrument panel (fig. 2-29).
These indicators require no electrical power for
operation, The indicator dials are calibrated in knots
from 40 to 300. A striped pointer automatically displays
the maximum allowable airspeed at the aircrafts
2-82. COPILOTS ENCODING ALTIMETER.
The copilots altimeter on the upper right side of the
instrument panel (fig. 2-29) is a self-contained unit
consisting of a precision pneumatic altimeter combined
with an altitude encoder. The display face indicates
while, simultaneously, the encoder transmits pressure
altitude information to the INS and GPS. Altitude is
displayed by a 10,000 foot counter, a 1000 foot counter, a
100 foot counter, and a single needle pointer which
indicates hundreds of feet on a circular scale in 20 foot
intervals. The needle pointer is also coupled to the 100
foot drum counter so that both move at the same time.
Below an altitude of 10,000 feet, a diagonal striped
symbol will appear on the 10,000 foot counter. A
barometric pressure setting knob is provided to insert
the desired altimeter setting in inches Hg or millibars. If
AC power to the altitude encoder is lost, an OFF flag will
appear in the upper center portion of the instrument face
to indicate that the encoder is inoperative and the
system is not reporting altitude to ground stations.
2-83. PILOTS ALTlMETER INDICATOR.
The pilots altimeter, on the upper left side of the
instrument panel (fig. 2-29), is a servoed unit under
control of the Air Data Computer and is part of the Flight
Director/Autopilot System. It lacks encoding capability,
but displays altitude as described for the copilots
instrument. Operating instructions are provided in
chapter 3. When the BAR0 knob is adjusted to ground
supplied instructions, the updated altitude pressure is
routed to the Air Data Computer. The ADC recomputes
all data on hand, sends corrected altitude pressure
information to the Flight Director and autopilot, sends
servo commands to correct the display on the pilots