Atlas Air 767 down/Texas

[Old Boeing Driver]

@ FDR Thanks for your response.

Here is the "proposed AD

" ....in 2000"On January 31, 2000, there was an accident involving a McDonnell Douglas Model DC-9-83 (MD-83) airplane. The National Transportation Safety Board (NTSB) determined that the probable cause of this accident was a loss of airplane pitch control resulting from the in-flight failure of the acme nut threads of the jackscrew assembly of the horizontal stabilizer trim system.
The NTSB concluded that the thread failure was caused by excessive wear, resulting from insufficient lubrication of the jackscrew assembly.Start Printed Page 58621The drive mechanism of the horizontal stabilizer on McDonnell Douglas Model DC-9-83 (MD-83) airplanes has a jackscrew assembly with an acme screw.
The drive mechanism of the horizontal stabilizer on Boeing Model 767 airplanes uses a ballscrew. Acme screws and ballscrews have some differences in design, but perform similar functions and have the same airplane level effect following failure. The manufacturer's safety analysis of the 767 drive mechanism found no safety problems with the configuration of the drive mechanism, but showed that changes to the maintenance procedures and maintenance intervals are required to keep the drive mechanism properly maintained and operating as designed.
We have received a report indicating that the ballscrew in the drive mechanism of the horizontal stabilizer on a Boeing Model 757 series airplane showed extensive corrosion, which could lead to excessive wear. The ballscrew on Boeing Model 757 airplanes is similar to that on Boeing Model 767 airplanes that are the subject of this proposed AD. Therefore, both of these airplane models could have the same unsafe condition.
We are considering separate action for the Boeing Model 757 series airplanes and other similar Boeing airplanes.Extensive corrosion of the ballscrew in the drive mechanism of the horizontal stabilizer, if not corrected, could cause an undetected failure of the primary load path for the ballscrew and subsequent wear and failure of the secondary load path, which could lead to loss of control of the horizontal stabilizer and consequent loss of control of the airplane."