Alaska Airlines MD-83 plane crash

The aircraft was on a passenger flight from Puerto Vallarta, Mexico to San Francisco, California, when the crew reported that they were encountering problems with the stabilizer trim. At 28,000 feet, the crew reported that they were unable to control the pitch of the aircraft. Descending through 23,000 feet, the crew reported that they had regained control, declared an emergency, and received vectors to land at Los Angeles International Airport. The last radio contact with the crew came as the aircraft passed 17,000 feet at an unusually slow speed of 119 knots. A park ranger, along with the pilots of a nearby aircraft, reported seeing the aircraft plummet into the Pacific Ocean in an inverted flight attitude.

The probable cause is the loss of airplane pitch control resulting from the in-flight failure of the horizontal stabilizer trim system jackscrew assembly's acme nut threads. The thread failure was caused by excessive wear resulting from Alaska Airlines' insufficient lubrication of the jackscrew assembly.