Couple of problems with the airfield theory:
1) as already mentioned, the survivors have no idea and no way to find out the condition of the airstrip at
Fort Irwin, therefore making a landing potentially impossible, something
the Tower couldn't afford.
2) Forget about landing for a second. How would they take off?
LAX has been described as a wreck and even if they had a clear strip, they would have to find a plane that works and is gassed up (something that they could probably do, but the wrecked airfield is still a problem).
3) Flying an airplane is a lot more difficult than flying a helicopter.
Kalani is the only qualified pilot they have and if they couldn't get an airplane big enough to fit everyone, it'd be very risky for the survivors to fly with whoever is the second pilot.
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