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How does a 737 engine start?
The vanes connect to a shaft that also spins the turbine’s compressor. The electric motor spins the main shaft until there is enough air blowing through the compressor and the combustion chamber to light the engine. Fuel starts flowing and an igniter similar to a spark plug ignites the fuel.
Is the APU always on?
Crews normally run the APU before flight for electrical power, air conditioning and engine start. After landing, the APU is started so engines can be shut down as soon as the aircraft arrives at the gate. If the APU is needed during flight, it can be started in about a minute.
Can aircraft fly without APU?
Without an APU an aircraft would depend on GSE only for starting one engine with pressurized ground supplied air. Aircraft are allowed in general to fly without an APU. Exceptions are flights with two-engined aircraft and long routes over water or terrain without an alternate airport – so called ETOPS flights.
When is the engine bleed air, Apu and packs turned off?
APU Bleed air is usually turned on while starting the engine to supply them with enough pressure. After the engines have started, Engine Bleed is turned on an APU Bleed air is turned off as it’s not needed anymore and the APU is being shut down. For takeoff you can decide whether you keep the Engine Bleeds on or not.
Where does the bleed air pack come from?
The pack can be fed from the left engine, the right engine, or both. The bleed air mode thus maps to the isolation valves: left bleed air means left isol valve open, right bleed means right isol valve open, bleed both or auto mean both isolation valves open.
What does two pack operation on Apu mean?
Bleed Pack Operation: The number of packs to use on the ground. APU’s which should run both packs have load compressors to supply bleed air. So two pack operation gives both cooler turbine wheel temperatures and a lower fuel burn. Main Engine Start (MES) to APU shutdown: The cool-down time to allow after main engine start.
What’s the difference between bleed air and auto?
The bleed air mode thus maps to the isolation valves: left bleed air means left isol valve open, right bleed means right isol valve open, bleed both or auto mean both isolation valves open. If an APU was installed, it would feed into the center duct regardless of the isolation valve settings, controlled by the APU valve, just like the GPU. 3.