234 APU Condensed Flashcards
(21 cards)
Type of APU in the 234
Solar T62-T2-C, single stage gas turbine.
95 SHP
Self-governing with automatic over-temp and overspeed protection.
Provides hydraulic and electrical auxiliary power during ground operations and provides hydraulic power for main engine start.
What is the ESU
Electronic Sequencing Unit
Electronic brain of the APU
Has BITE detection system to determine causes of APU failure
APU fuel supply
Airframe mounted DC boost pump/fuel valve
Fuel from LH main tank
Fuel flow rate: 115 lb/hr loaded
EPUSHA
Electric Pump Utility System Hydraulic Accumulator
Used to pressurize the 200 inch accumulator for APU start
200 inch accumulator
1400 psi nitrogen pre-charge
Used to store 3125 psi hydraulic pressure for APU start
APU Lubrication
Self lubricated with Exxon 2380 via 4 jets. 3 to the drives and gears and 1 creates an air/oil mist down the shaft of the compressor.
APU oil pressure switch
Located in the drive gear housing and monitored by the ESU
APU Fire Detection
Wire around APU filled with gas that expands when heated.
Triggers a light on the flight deck panel
Pushing the APU FIRE button discharges fire bottle
Testing APU fire detection system with the APU running will shut the APU down
APU Start Procedure
RUN for 3 seconds, START for 3 seconds, springs back to RUN
When switch is placed in the START position the hydraulic start valve opens, AGB valve opens and the utility isolation valve closes. At 5% start fuel is introduced and ignited, 14% main fuel is introduced, 70% start fuel and ignition are turned off. At 90%, APU light comes on, hydraulic start valve and AGB valve close.
Generators on as soon as possible.
APU Limitations
APU during taxi and flight is provided.
200” Accumulator
Used to store 3125psi hydraulic pressure for starting the APU
Has 1400psi nitrogen pre-charge
ESU
Electronic Sequencing Unit
Acts as the brains of the APU. Sends and receives DC signals to/from APU systems
Has a failure detection system used for troubleshooting APU failures. The detection system is cleared when APU switch set to OFF
APU Lube System
Self lubricated with EXXON 2380 via 3 jets to drives and gears and 1 jet misting oil down the shaft of the compressor/turbine
APU Oil Pressure Switch
ESU will shut down the APU if oil pressure drops below operating range
APU Electrical System
28 VDC from HOT BATT bus. Controlled through the ESU
APU Fire Protection
Fire Detection
- Wires filled with gas are routed around APU compartment. When heated during a fire, the gas expands, triggering a light and audible warning on the fire detection panel in the flight deck
Fire Suppression
- Pushing the APU FIRE button on the FIRE EMERG panel will discharge Monobromotrifloromethane into the APU compartment
Testing the APU fire detection system while the APU is running will shutdown the APU.
APU Start Procedure
APU Switch to:
RUN for 3 seconds, No. 1 Flight Boost Pump Solenoid drops Hyd pressure to about 500psi, power is applied to ESU and APU system, fuel boost pump valve is opened
APU Switch to:
START for 3 seconds, Hyd start valve opens, AGB valve opens, utility iso valve closes, motor/pump acts as start until 90% APU rpm
At 90%:
APU ON light illuminates (within 1.5 seconds), Hyd start valve closes, AGB valve closes, utility iso valve opens, turn GENs and TRs on as soon as possible.
Green APU ON Light
APU at full speed
Amber APU ON Light
APU is running and one or both ECLs are in FLY
Do not taxi or takeoff
APU Limitations
Operation of the APU during taxi or in flight is prohibited
APU Overspeed and Overtemp
Monitored and controlled by the ESU
