The A key works for me....
And I found this somewhere:
Startup is simple, all commands to ground crew must have the canopy open.
1. Call up the Ground Crew and order Ground Power On (Default: 1. \ 2. F8 3. F2 4. F1)
Ground Crew will respond "Copy... Ground Power is now On"
2. Press the Start button just aft of the throttle.
This will begin the startup cycle, you have a limited time to execute the following commands;
3. When engine RPM reaches 5% RIGHT CLICK the Throttle
4. When engine RPM reaches 15% RIGHT CLICK the Throttle again.
Failure to complete these two steps before 20% RPM will result in a failed start and the engine will cycle down, forcing you to wait to attempt the start cycle from the beginning. If this occurs mid way through startup, retard throttles to Idle and LEFT CLICK on the throttle until it is back in starting position, then go back to step 2.
5. Call up the Ground Crew and order Ground Power Off (Default: 1. \ 2. F8 3. F2 4. F2)
Ground Crew will respond "Copy... Ground Power is now Off"
You may now close your canopy and complete whatever other take off preparations you would like to, such as warming up the Radar and Nav computer.