What Happened to Transponder?
If the power to the electrical system operating the plane’s transponder had not been suddenly cut, the transponder would have kept sending signals about the aircraft’s position and altitude to radar screens on the ground, which would have shown it losing altitude as it fell. Among the kinds of things that might have suddenly cut power would be a bomb, an explosive decompression caused by a structural weakness, or a decompression caused by a midair collision. Mr. Kriendler said there was no indication of an explosion and that Pan Am had not received any threats. He said that 30-mile-an-hour winds were reported at about 4,000 feet when the aircraft took off, but there was no information of how strong the winds were at 31,000 feet, the plane’s cruising altitude before it apparently lost power. The 747 was a relatively old plane, the 15th such aircraft built, and had been involved in one previous accident, according to National Transportation Safety Board records. That was in 1970, when it
