AUXILIARY POWER UNIT (APU) 1. GENERAL ¡ APU is a single shaft gas turbine located in the unpressurized tailcone ¡ Fuel for the APU normally comes from the Left Main Tank - Left FWD AC fuel boost pump is used when AC ground service power is available - APU DC fuel pump is used when no AC power is available.
2. LIMITS ¡ Maximum 3 starts within 60 minutes. ¡ BLEED until 17500 ft ¡ ELECTRICAL until 43100 ft (has always priority on Bleed air) Electrical + 2 Packs on ground
3. START ¡ On ground, APU and Airplane batteries are required. ¡ APU battery supplies power to :
- starter - air inlet door - APU control circuitry
¡ Aircraft battery supplies power to : - Fire Protection - APU fuel valve - DC fuel pump - APU control circuitry when heavy starter load ¡ Sequence :
RUN
- Selector to start - APU fuel valve opens ( FAULT and RUN light flashes during ops > SELF TEST) - APU inlet door starts to open - DC pumps starts in left tank - Electric starter engages - Acceleration to normal speed
(white) = APU is at operating speed (available for electrical & bleed)
4. SHUTDOWN Switch OFF :
- BLEED valve closes (if OPEN) - Time delay feature for cooling = 60 seconds after bleed valve has been closed (between 0 and 120 ") - Inadvertent shutdown with RUN remaining ON = resume back to normal by momentarily selecting START - RUN light extinguishes and FAULT light momentarily ON indicating APU fuel valve closure - Resets FAULT circuitry
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BOEING 767 SYSTEMS REVIEW
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5. PROTECTION Battery Switch OFF : - On ground = shutdown with delay protection but without FIRE DETECTION - In flight = no result FAULT
(amber) + EICAS APU FAULT + auto shut-down = Fault or Fire sensed (inhibited when APU selector is OFF)
OR FAULT
(amber) + EICAS APU FUEL VAL + auto shut-down = Fuel valve not in correct position
6. NICE TO KNOW ¡ Average APU fuel consumption = 115 kg / h (ground) & 90 kg / h (flight) ¡ No Fire system test required before starting the APU. ¡ When rotating APU selector ON (for start), always verify APU FAULT LIGHT cycles ON then OFF, then rotate APU selector to START and let it spring back to ON.
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BOEING 767 SYSTEMS REVIEW
APU DIAGRAM
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BOEING 767 SYSTEMS REVIEW
APU FIRE DETECTION Copyright Smartcockpit.com Ludovic ANDRE / version 00
