What happened
On 25 November 2010, a Bombardier Dash 8 Q400, registration G-FLBE, was performing a commercial passenger flight when the crew observed an indication that the right main landing gear was not in the down and locked position. Following the selection of the landing gear to the down position, the crew performed emergency checklist items and subsequently initiated a go-around. After the crew declared a MAYDAY, the aircraft entered a holding pattern.
Following the completion of emergency procedures, the crew shut down the right engine and performed an emergency landing at Paris Charles de locating de Gaulle Airport. The aircraft came to a halt on the runway, and passengers were evacuated. There were no injuries to the 4 crew members or 60 passengers on board, and the aircraft sustained no damage.
The investigation
Engineers from the operator arrived at the scene to investigate the landing gear mechanism. They confirmed that the right landing gear locking mechanism had failed to engage fully. The investigation identified that a grease nipple had become lodged on the eye end of the landing gear downlock actuator. This obstruction prevented the actuator from completing its full range of travel, which triggered the unsafe gear warning.
Further inspection revealed that the grease nipple had detached from the right main landing gear lock link assembly. Additionally, the investigation found that the landing gear locking pins had not been correctly inserted by airport rescue and fire services (AFRS) during their attempt to secure the gear. The examination also noted that the grease nipple was a push-fit type, which is installed using liquid nitrogen and an adhesive coating on the shank.
Findings
- A grease nipple released from the right main landing gear lock link assembly and became stuck in the downlock actuator.
- The presence of this nipple prevented the landing gear from fully locking.
- A fleet-wide inspection by the operator revealed that 50% of the aircraft had at least one missing grease nipple, and 84% of the fleet showed evidence of excessive grease around the fittings.
- The investigation noted that 500 such nipples had been issued to the fleet in 2010, compared to 450 in 2009.
Safety action
- The operator has implemented a fleet-wide inspection of landing gear assemblies to ensure all grease nipples are present.
- New maintenance practices have been introduced to prevent the use of high-pressure grease guns during lubrication.
- Procedures now require the removal of excess grease from nipples and gear components, and any loose nipples must be replaced and recorded in the technical log.
- The operator is consulting with manufacturers regarding potential improvements to installation procedures, including the possible introduction of threaded grease nipples.