TM 55-1520-240-23-7
9-60
LIGHTING SYSTEMS
(Continued)
9-60
SECONDARY COCKPIT LIGHT SYSTEM WITHOUT
17
Description
The secondary cockpit lighting system provides lighting
for the overhead panel, instrument panel, and console.
The lighting system consists of 10 floodlights, two relays,
three toggle switches, and a dimming control. Two of
the floodlights provide lighting for the overhead panel,
and eight provide lighting for the instrument panel, and
console. The instrument panel and console floodlights
are located under the glareshield. The system also
includes an interlock circuit for pilot’s and copilot’s turn
and slip indicator lights. The interlock circuit provides 28
vdc, instead of 26 vac, if No. 1 ac bus or No. 1 dc bus
is not powered. The secondary cockpit lighting system
operates from the 28 volt essential dc bus.
Operation
1.
When INSTR FLOODLIGHTING circuit breaker
is closed, 28 vdc power from the essential dc bus
is connected to FLOOD LTS control. When the
control is turned from OFF, power is connected
through the control to pins 2 of INST PNL switch,
CONSOLE switch, and OVHD PNL switch.
When any switch is set to ON, power is applied
to the respective floodlights. FLOOD LTS control
provides on-off and brightness control of all the
secondary cockpit lights.
2.
During normal operation transfer relay K1 is
operated when 115 vac is available from the No.
1 ac bus. Floodlight relay K2 is operated from
the 28 volt No. 1 dc bus through NO. 1 DC BUS
CONT circuit breaker and contacts of relay K1.
This circuit provides 26 vac to the pilot’s and
copilot’s turn and slip indicator lights.
3.
If 28 vdc is lost from the No. 1 dc bus, relay K2
releases. If 115 vac is lost from the No. 1 ac bus
relay, K1 releases, causing relay K2 to release.
With relay K2 released, the pilot’s and copilot’s
turn and slip indicator lights are connected to
the 28 volt essential dc bus. This connection is
made through contacts of relay K2 and a switch
on PILOTS FLT INST LTS control if PILOTS
FLT INST LTS control is not positioned at OFF.
Contacts of relay K2 also provide an alternate
circuit for the instrument panel and overhead
panel floodlights. This circuit is through the
switch on control 121R1 and contacts of the
relay. The circuit bypasses FLOOD LTS control,
INST PNL switch, and OVHD PNL switch which
will illuminate all secondary cockpit lighting.
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