What happened
On 4 July 2018, a Britten-Norman BN-2B-21 Islander, registration VP-AEJ, was performing a commercial passenger flight from F. D. Roosevelt Airport in Saint Eustatius to Robert L. Bradshaw International Airport in Saint Kitts. Shortly after departure, the pilot observed that the aircraft's ailerons felt sluggish while performing a right-hand turn.
Given the short duration of the flight, which was estimated to last only 10 to 12 minutes, the pilot continued to the destination. The aircraft landed safely at Saint Kitts with no injuries to the 4 passengers or the crew. During a post-flight walk-around inspection, the pilot discovered that the drive rod for the right aileron had snapped.
The investigation
Investigators examined the aircraft's aileron drive mechanism and identified that the rod had experienced an overload fracture approximately 70 mm from the rod end. The investigation established that a spherical bearing at the end of the rod had suffered heavy corrosion, which caused the component to seize.
Environmental factors were also scrutinized. The maintenance organisation noted that the region had recently experienced significant storms and hurricanes. Additionally, the decomposition of large amounts of Sargassum seaweed along the Caribbean coastline had released hydrogen sulphide into the atmosphere, potentially accelerating the corrosion process.
Findings
- The primary cause of the failure was the seizure of a spherical bearing due to heavy corrosion.
- This seizure caused the aileron drive rod to fracture when subjected to standard operational loads.
- The local environment, characterized by high levels of hydrogen sulphide from decomposing seaweed and recent severe weather, likely accelerated the degradation of the component.
- The existing maintenance programme required lubrication of the rod ends every 1,000 hours, which proved insufficient for the specific environmental conditions encountered.
Safety action
Following the incident, the following actions were implemented:
- The aircraft manufacturer issued Service Letter SL127 to remind operators of proper greasing procedures and to collect data on bearing corrosion.
- The maintenance organisation reduced the lubrication interval for aileron drive rod bearings from 1,000 hours to 100 hours.
- A fleet-wide inspection of all drive rods and bearings was initiated by the maintenance organisation to detect further corrosion.