BOMBARDIER INC DHC-8-402 — Houston, TX, USA, 2012-04-07

NTSB summary

After take-off from the departure airport, the crew observed a master caution, an amber nose gear open advisory light, a landing gear inoperative caution light, and they noticed a different than normal airflow noise During the flight, the crew heard a "thump" and noted that the previously observed caution lights had extinguished indicating that the nose gear was retracted and the nose gear doors were closed.  In accordance with abnormal procedures checklists, and guidance from the company, the crew elected to use the Alternate Landing Gear Extension checklist to prepare for landing at the destination After pulling the main gear release handle and the nose gear release handle the crew observed that the main landing gear indicated down and locked with green indicator lights, the nose landing gear did not indicate down and locked, and the red Nose Gear Unsafe light was illuminated.  The crew landed the airplane with the main landing gear down and the nose landing gear retracted, and the airplane came to rest on the main gear and forward fuselage on the runway. Post-accident, the nose gear was successfully extended multiple times using the alternate extension handle and the landing gear was also extended multiple times under hydraulic power with no anomalies noted.  Testing of landing gear system components did not reveal any failures that should have prevented the gear from extending via the alternate extension method.  The pull force required to extend the nose gear alternate release handle to a position where the nose gear released from the up and locked position was measured at approximately 72 lbs. According to manufacturer's design requirements, the pull length on the alternate release handle should be approximately 11 inches with a force of 90 pounds. A post-accident review of the alternate gear extension procedures was conducted in a full flight simulator by the investigation group with the participation of the accident flight crew.  The pull force required and the pull length required to extend the nose gear using the alternate extension handle was determined to be significantly lower in the flight simulator as compared to the aircraft. There was no guidance contained in the alternate landing gear extension procedure specifying required pull forces when using the alternate extension handle. Subsequent to the accident, the manufacturer added details to the alternate landing gear extension procedure in the Airplane Flight Manual regarding the maximum pull forces that a pilot may experience when the alternate extension handle is pulled.

Probable cause

the nose landing gear alternate release handle was not pulled with sufficient enough force or distance to release the uplocks and allow extension of the nose landing gear. Contributing to the accident was the dissimilar pull force and pull length set on the flight simulator that was used for flight crew training of alternate landing gear extension procedures and the lack of information available to crew members advising of the dissimilar pull force.

Sequence of events (FDR factual report)

Recorder documents in the docket

Docket: data.ntsb.gov/Docket/?NTSBNumber=DCA12FA058. This brief is an analytical aid assembled from public records; it is not an investigative finding.