What happened
On 27 November 2017, an AW109SP Grand New, registration G-IWFC, was conducting maintenance flight checks at Sywell Aerodrome, Northamptonshire. The flight was part of a series of intermittent maintenance tasks that had been delayed by heavy rain.
Prior to the flight, the pilot and a team had been performing rotor blade checks in a hover. During this process, a warning light indicated a hot oil cap issue on the No 1 engine. Following the alert, an engineer inspected the engine by opening the engine cowl. After this inspection, the helicopter departed again to continue the scheduled maintenance flight.
During the flight, the occupants noticed a slight, unusual vibration. The pilot decided to return to the airfield to land. As the aircraft approached the runway, the vibration intensified significantly, becoming very heavy. The pilot executed a run-on landing to manage the instability, after which no further issues occurred.
The investigation
Investigators examined the aircraft following the incident. The inspection of the airframe revealed that the engine cowl had physically contacted the main rotor blades. This contact resulted in impact damage to both the engine cowl and two of the rotor blades.
Findings
- The primary cause of the vibration and subsequent damage was that the engine cowl had not been correctly latched shut during the preceding engine inspection.
- The vibration was initially subtle but escalated into a severe event during the landing approach.