A3 Sentry Aircraft?
I think the poor chap means Boeing E3 Sentry aircraft?
The A3 was surely the US Navy version of the Douglas B-66 Sky Warrior. One of my old co-pilots used to fly the A3D version. He reckoned that if the gear collapsed during a carrier landing this stood for All 3 Dead!
Anyway, I just thought I would join in the thread-drift frenzy before the whole lot gets shifted to the Spotters Forum which is where it should have been in the first place!