During a normal Auxiliary Power Unit start, the Electronic Control Unit has energized ignition and the starter-generator. At what point does the system first introduce fuel for combustion, and why is that sequencing significant?, Fuel is introduced at 30 percent speed after oil pressure has been established, preventing a wet start., Fuel is introduced at approximately 7 percent speed after initial shaft rotation has been established by the starter-generator., Fuel is introduced at 60 percent speed simultaneously with ignition-system de-energization., During flight, the Auxiliary Power Unit is shut down by a fire condition rather than by normal crew selection. How does the shutdown sequence differ from a normal shutdown?, The normal 60-second cooldown continues, but the bleed-air valve and generator are disconnected immediately., The inlet guide vanes remain open to provide cooling airflow until the Auxiliary Power Unit falls below 30 percent speed., The fuel solenoid valve closes immediately and the normal 60-second cooldown cycle is bypassed., During Auxiliary Power Unit operation, electrical control logic fails but the flight crew pulls the Auxiliary Power Unit fire switch. What design feature helps ensure that the fuel shutoff valve can still close?, The Auxiliary Power Unit fire switch has a direct electrical path through the Electronic Control Unit to the fuel shutoff valve output, with additional closing power available from the hot battery bus or emergency fuel shutoff battery., The fire switch mechanically drives the fuel shutoff valve closed through the air inlet door linkage., The Start Converter Unit supplies an independent 270-volt direct-current closing signal to the fuel shutoff valve., During Auxiliary Power Unit start, why is the Fuel Flow Divider solenoid energized closed between approximately 7 and 30 percent speed?, To maintain constant differential pressure across the fuel metering valve during acceleration., To prevent primary manifold pressure from exceeding the fuel-nozzle opening pressure., To prevent premature filling of the secondary fuel manifold, which could reduce primary manifold pressure enough to cause flameout or underspeed., The aircraft is performing an Auxiliary Power Unit start from battery power because 115-volt alternating-current transfer bus 1 is unavailable. How is the required starter-generator power produced?, The Start Converter Unit converts battery power directly to three-phase alternating current without using the Start Power Unit., The Start Power Unit converts the battery’s direct-current input to approximately 270 volts direct current, and the Start Converter Unit then converts that power to synchronized three-phase alternating current for the starter-generator., The Auxiliary Power Unit Generator Control Unit excites the starter-generator directly from the battery until 70 percent speed., Corrected airflow through the Auxiliary Power Unit load compressor decreases below the calculated surge-margin setpoint. What control response is expected?, The Electronic Control Unit commands the Surge Control Valve open so additional compressor airflow is discharged into the exhaust and minimum compressor flow is maintained., The Electronic Control Unit closes the Surge Control Valve to force all load-compressor airflow into the aircraft pneumatic manifold., Vanes, Auxiliary Power Unit oil temperature is below 140 degrees Fahrenheit. What path does the lubrication system command, and what separate condition can produce the same bypass even when oil is hot?, All oil is forced through the oil cooler; bypass occurs only if oil pressure falls below 50 pounds per square inch differential., Oil bypasses the cooler below approximately 140 degrees Fahrenheit, and it can also bypass if differential pressure across the bypass valve exceeds approximately 50 pounds per square inch differential., The Temperature Control Valve blocks oil flow entirely until the oil reaches 170 degrees Fahrenheit., Why is the air-oil separator required in the Auxiliary Power Unit scavenge system rather than simply returning the complete scavenge mixture directly to the gearbox reservoir?, It removes magnetic particles from the oil before the oil enters the gearbox reservoir., It regulates scavenge oil pressure to the starter-generator and turbine bearing compartment., It separates entrained air from scavenge oil by centrifugal action, returns the oil to the gearbox sump and vents the separated air overboard through the exhaust duct., During a protective shutdown, load-compressor airflow falls to approximately zero. Why does the Electronic Control Unit command the Bleed Air Valve closed after about one second even though reverse-flow shutdown logic requires approximately six seconds of near-zero flow?, Closing the Bleed Air Valve early isolates the aircraft pneumatic manifold and prevents reverse airflow toward the load compressor, thereby preventing many reverse-flow shutdowns from progressing to the six-second threshold., The Bleed Air Valve closure is required to increase compressor differential pressure so the Surge Control Valve can close., The early closure allows the Auxiliary Power Unit to remain supplying pneumatic power while the Electronic Control Unit confirms the pressure-sensor fault., A protective shutdown has produced a start inhibit while the aircraft is on the ground. After correcting the originating fault, what is required before another Auxiliary Power Unit start can be attempted?, Cycling the battery switch automatically clears every start-inhibit condition stored by the Electronic Control Unit., The Limited Restart function in the Onboard Maintenance Function must be used to reset the Electronic Control Unit start-inhibit logic., The Data Memory Module must be removed and reinstalled to clear the protective-shutdown record.

ATA 49

by
Print
Embed

Leaderboard

Visual style

Options

Switch template

Continue editing: ?