San Diego

Investigators have determined that the loss of an engine from an American Airlines Boeing 727 en route to San Diego on April 17 was not caused by any mechanical problem in the engine or the aircraft.

A foreign substance entering the engine while the plane was in flight, causing the engine to jam and rip away from the tail section, is now being considered as the most likely cause of the incident, according to National Transportation Safety Board investigator Al Crawford.

“There was no fault in the aircraft that could have permitted the engine just to fall off,” Crawford said. “Whether or not something could have entered the engine is not known at this point.”

American Airlines Flight 199 lost its No. 3 engine while flying at 35,000 feet over New Mexico, making the plane shudder violently and forcing the pilot to drop 9,000 feet as a safety precaution. The plane, with its two remaining functioning engines, proceeded to a safe landing at Lindbergh Field 45 minutes after the incident. There were no injuries reported among the 81 passengers and nine crew members aboard.

Search crews found the engine in a remote area near Deming, N.M., and transported it to the airline’s maintenance headquarters in Tulsa, Okla., where it was examined by safety board investigators.

American Airlines spokeswoman Linda Johnson said the aircraft has been repaired and returned to service.

The investigation of the incident is continuing, Crawford said.