The US FAA on Thursday will issue an airworthiness directive calling on operators of Bombardier CRJ700 and CRJ900 regional twinjets to check for and replace faulty bearings in the aircraft's horizontal stabilizer trim system.
The problem stems from installation of incorrect ball bearings in the some of the twinjet's Sagem-built horizontal stabilizer trim actuator (HSTA) units during maintenance at an unnamed facility.
"The material of these discrepant balls has lower wear characteristics and as such, has a shorter expected life," says the FAA in the final airworthiness directive (AD).
Transport Canada issued the same directive in July, following the release of a non-mandatory Bombardier service bulletin on the issue in June. "If not corrected, this condition can result in the HSTA jam leading to difficulties in controlling the aircraft," the FAA says.
Operators will be required within 500 flight cycles to determine if defective parts are installed, and if so, change out the HSTA within a certain number of flight cycles, depending on the in-service time of the unit.
Bombardier could not be immediately reached for comment.