On / Off Switch?

Sat Oct 21, 2000 1:17 am

How do you 'start' a big commercial jet like a 757 or A330? Do they have ignition keys? Is there a master on / off switch? Do the doors have keys? Or if someone were to scale a fence, pop the door, get in the cockpit, and just turn it on could they grab one?

I don't have anything approaching the means or knowledge to do this, but I've often wondered if they are "locked" when they're sitting in the airport at 3 AM... Or whether they ever "lose the key" (wouldn't that be embarrassing - "ladies and gentlemen, on behalf of Delta I'd like to apologize for the delay in our departure from Atlanta. Our pilot today thought the first officer had the ignition key, and the first officer could have sworn he put it on his key chain when he left the hotel, but no one seems to be able to find it..")
Posts: 220
Joined: Sat Oct 21, 2000 4:57 am

RE: On / Off Switch?

Sat Oct 21, 2000 5:38 am

If the aircraft has an APU, it is started first. Electrical and pneumatics then are used to start the engines. On the DC-9, bleed air is extracted from the APU and that air pressure (35psi min) is sent through a start valve and gets N2 spinning(high pressure section of the engine). Oil pumps and hydraulic pumps are connected to N2 so oil pressure and hydraulic pressure indications begin to rise almost immediately during engine start. At 20% N2 RPM, The fuel control lever is placed on. This is a two hand operation beacuse the start switch is on the overhead pannel and the fuel control is on the center console, between the pilots. Once N2 RPM reaches 35%, the starter is released and the engine continues to accelerate to idle power(aprox 50% N2). Rarely, too much fuel enters during start (hot start) or the engine fails to accelerate to idle(hung start) or the start valve does not close after being released. The engine is immediately shut down for any of those conditions. To answer some of your questions, there is no Master switch but there is a Battery switch which must be on in order to get the APU running. No ignition keys, just a cockpit key. At night the Jetway is pulled away from the aircraft for security reasons. Smaller turbo-prop engines have an electric starter, much like an automobile starter. It gets everything truning to a specific RPM and then the fuel is added. Once the engine reaches another specific RPM, the starter dis-engages and the engine turns on it own. Hope this helps. Keep the greasy side down.