Comedian Jay Leno didn't know while taping his "Tonight Show" monologue for Monday night's broadcast that his gags about a USAir Boeing 737 dropping an engine in Philadelphia on Saturday would air right after KNBC-TV Channel 4's extended news broadcast on Monday's crash of a PSA commuter plane. USAir is the parent company of PSA. "A woman from (NBC) Standards and Practices came in when we were three-quarters of the way through taping to say there had been a crash," said Leno's manager and attorney Jerrold Kushnik, who added that Leno was not told of the crash until taping was over. "There was nothing we could do." Following a half-hour of discussion with Leno and "Tonight Show" personnel, NBC decided to air the monologue but scrambled the name "USAir."