Originally Posted by The Joker
What do you mean could have? He didn't say anything about it. That's the point. It wasn't mentioned to fool people into thinking he had died. The question asked was why didn't he tell Selina about the auto pilot in the first place.
Batman told Selina that the Bat had no Auto pilot (as far as I can remember, I've seen the movie only two times.)
Here is what the Official novelization says -
Batman: "Two minutes, I can fly it out over the bay."
Catwoman:"Rig it to fly over the water, then bail..."
he shook his head.
Batman: "No autopilot."
To me it sounds as if he was not entirely sure that autopilot would work, so he wanted to fly the Bat himself (to get rid of the nuke), but then he was not sure that he would survive the blast, so he lied about the whole autopilot thing, just so that Selina should not have a false hope of seeing him again.
That he wanted he to believe that he was going to die when he was fully confident that he will escape the blast radius.He wanted everyone to believe that he died.
Personally speaking, I prefer the first reason.