TM 1–1520–238–T–1
3–18
3–3
APU – OPERATING INSTRUCTIONS (cont)
3–3
When the APU turbine rotor has achieved
95 percent or greater of normal revolutions
per minute (rpm), the APU ON indicator on
the pilot caution/warning panel lights.
11. Initiate APU start–up as specified in the following
procedures.
a. On APU/FIRE TEST panel, set START/RUN/OFF
switch to RUN – hold for 5 seconds.
b. Transition START/RUN/OFF switch to START for 1 to
2 seconds, then return to RUN.
c. Verify APU ON indicator on pilot caution/warning
panel is lit.
CAUTION
On the ground, the APU may be restarted
after roll down (compressor comes to a
complete stop). Wait 30 seconds for fuel to
drain. The PTO clutch duty cycle shall be
observed. The clutch duty cycle allows two
consecutive start attempts and then a
20–minute delay before the next start
attempt. No more than three starts shall be
allowed in a 1–hour period. Start attempts in
which the clutch does not engage do not
apply. Failure to comply could result in
damage to the PTO clutch.
NOTE
The APU is hydraulically started. If the APU
fails to start and there are no reported
NO/GOs, check the utility hydraulic
accumulator pressure for a minimum of 2600
psig. Manual compression (pumping) of the
hydraulic pressure to 3000 psig may be
necessary before attempting another APU
start.
If external power is to be used concurrently
with the APU, bypass procedural step 12.
12. Select test generator 1 (GEN 1) and generator 2 (GEN 2)
as specified in following procedures.
