What happened
On 30 March 2004, an MD 902 Explorer (NOTAR), registration G-HPOL, was conducting a public transport flight near Worksop, Nottinghamshire. The aircraft was returning to Leconfield, Humberside, following the completion of an annual check at Staverton, Gloucestershire.
During the cruise phase of the flight, a passenger seated in the rear of the cabin reported hearing an unusual noise originating from the area above and behind them. The sound was described as being similar to the movement of a seat. No other cockpit or cabin indications of abnormality were noted at that time. Approximately ten minutes after the noise was first heard, the Integrated Instrument Display System (IIDS) issued a 'CHECK NOTAR BALANCE' advisory warning. In response to this alert, the pilot performed a precautionary landing at Lecon and Leconfield.
The investigation
Following the landing, technicians performed three separate tests to assess the balance of the anti-torque NOTAR fan. All three tests confirmed that the fan was unbalanced and significantly exceeded the permitted operational limits.
Upon removing an access panel from the tail boom to inspect the hardware, investigators discovered that nine of the thirteen fan blades had sustained damage. Additionally, the inspection revealed damage to the fan liner. A thorough examination of the interior of the tail boom was conducted to search for foreign object debris (FOD), but no such objects were found. Furthermore, a comprehensive check of the entire helicopter confirmed that no fasteners, panels, or other components were missing or could have been ingested into the tail boom fan duct area.
Findings
- The primary cause of the incident was the damage to nine fan blades and the associated fan liner.
- No evidence was found of foreign object ingestion or missing aircraft components that could have caused the damage.
- At the time of the report, there was no evidence of an inherent manufacturing defect in the fan assembly.