I don't have FSX installed, but IIRC the controls have a "repeat" slider next to them, have you tried moving that to the right?
Alternatively, you can have VoiceAttack press the key repeatedly:
Start Loop : Repeat 10 Times
Press F2 key and hold for 0,06 seconds and release
Pause 0,01 seconds
End Loop
This is the "simple" solution, where the key is pressed a set number of times. You can adjust the key down and pause timing so that each press will be registered correctly by FSX, or add more presses than you need to compensate for those that are lost(if you're moving a control to the maximum/minimum value).
You could also use a loop to repeat the key for a certain amount of time:
Set decimal [~timeStart] value to the converted value of {DATETICKS}
Start Loop While : [{EXP: {DATETICKS} >= {DEC:~timeStart} + 10000000}] Equals '0'
Press A key and hold for 0,06 seconds and release
End Loop
Again, you can adjust the key hold down time(likely reduce it, as 60ms is longer than many applications require). The amount of times the key is pressed in the given timespan depends on how long it's held down each time.
You can adjust the total repeat time by changing 10,000,000(which is one second in ticks), to another number.