The pilot of a Piedmont jetliner that dropped its right engine shortly after takeoff from O'Hare International Airport last week was apparently unaware the engine had fallen off until he landed about 4 minutes later, according to cockpit tapes released Tuesday.

"What happened to it," the unidentified pilot calmly asked after the tower informed him the 737 had lost the engine."Piedmont 1480, it looks like you've lost the engine. Can you make a right turn back for (runway) 32R?," a tense air traffic controller asked.

The pilot was aware he had lost thrust from his right engine, but it wasn't until 4 minutes later after he had landed safely that the pilot confirmed the engine was gone.