Bombardier DHC8 N934HA accident near Newark, New Jersey

Probable cause

the frozen left main landing gear (MLG) uplock roller due to lack of lubrication and the uplock latch that had worn beyond acceptable tolerances, which prevented the flight crew from extending the left MLG using the alternate extension system. Contributing to the accident were the operator's improper maintenance practices, which did not detect the lubrication issue with the roller and the wear of the latch.

NTSB analysis

While on an instrument approach to the airport, when the flight crew attempted to lower the landing gear, they received an unsafe indication on the left main landing gear (MLG). They conducted a fly by of the airport control tower, and the controller verified that the left MLG was only partially extended. The flight crew performed the alternate landing gear extension procedure and worked with company maintenance to troubleshoot the failure, however, the left MLG would not extend after multiple attempts. Although the first officer indicated that he became confused after the sixth step of the alternate landing gear extension procedure, post accident testing determined that this did not have any effect on the outcome Because the left MLG would not extend, the captain elected to conduct the landing with all gear retracted to minimize the likelihood of a loss of directional control after touchdown. All passengers and crew successfully evacuated after the airplane came to a rest on the runway.

Postaccident testing confirmed that the left MLG would not deploy using the normal or alternate gear extension systems. Examination of the landing gear components found that the left MLG uplock roller was seized and the groove on the left uplock latch was out of tolerance. The seized uplock roller and worn latch caused the forces to exceed the crews capability to release the landing gear by use of the alternate gear extension system.

Examination of the operators maintenance records indicated that the uplock rollers were to be inspected every 220 flight hours and that they were to be lubricated only on condition. The accident airplanes left MLG uplock was inspected 11 times in year prior to the accident. In all instances, the inspection paperwork indicated that the roller rotated freely and did not require lubrication for the last. Further, the uplock latches were to be visually inspected every 440 flight hours. The latches were not required to be measured and were replaced only on condition. The last measurement of the left MLG latch on the accident airplane occurred 10 years prior to the accident. After the accident, the operator modified the maintenance procedures to include regular lubrication of the rollers and to measure the wear of the uplock latch.

Text from the NTSB. Open the NTSB docket for DCA13FA094 for the full record.