I got yelled at a couple of times but there is a knack. Be set up and ready to shoot before setting foot on the apron and mentally be prepared to stop, shoot and walk on smiling innocently like an excited tourist.
I know staff are not supposed to shoot on aprons but many do, I got yelled at by BA groundstaff boarding the last Air Southwest out of LGW and told "no photos". I didn't argue even though I had seen a camera crew from the TV there a moment ago. In JFK last month, I had a seven foot tall black rampir get borderline frightening with his gestures. I had dared to shoot an American B757 at the gate, he actually started running towards me at one point and I though he was going to come inside! 9-11 casts a long shadow indeed.