What happened
On 12 September 2007, a Schweizer 300CBi helicopter, registration G-CDTK, was performing a local flight near Clonshanny, Co. Offaly. The flight, which included the pilot and one passenger, was part of a series of local movements following a trip to Cork Airport. While returning to the base at an altitude of approximately 1,000 feet, the engine suddenly lost power.
In response to the engine failure, the pilot initiated an auto-rotation procedure. However, the pilot flared the aircraft too high during the maneuver, which led to a heavy vertical impact with the ground. The landing occurred without forward speed, causing the skid undercarriage to collapse and resulting in extensive damage to the airframe. The passenger sustained serious spinal injuries, while the pilot suffered less severe injuries.
The investigation
The AAIU investigation focused on the sudden loss of engine power and the circumstances leading to the fuel depletion. Investigators examined the fuel system and found that the tank contained only a negligible amount of fuel at the time of the crash. Testing at the AAIU facility confirmed that the engine was mechanically sound and that no leaks were present in the fuel system.
Crucially, the investigation identified a failure in the low fuel warning system. Although the aircraft was equipped with a capacitance-type warning light, the light failed to illuminate when fuel levels reached a critical point. This was traced to a physically damaged contact within the bulb holder, likely caused by frequent or heavy-handed use of the press-to-test function. Additionally, the investigation looked into the pilot's fuel management, noting that the pilot was uncertain regarding the exact fuel consumption rate and the conversion between liters and U.S. gallons.
Findings
- The primary cause of the engine stoppage was that the fuel tank had been completely depleted.
- The severity of the impact and the resulting injuries were due to the pilot flaring the helicopter too high during the auto-rotation.
- The low fuel warning light failed to function because of a distorted central contact in the bulb holder.
- The pilot's management of fuel levels was inadequate, partly due to a lack of familiarity with the specific fuel consumption and the failure of the warning system.
- The aircraft was being maintained under a program that incorrectly applied an 80% multiplier to hourmeter readings, meaning several scheduled inspections were overdue and the Certificate of Airworthiness was likely invalid.
Safety action
- The AAIU recommended that the Irish Aviation Authority (IAA) implement educational programs for helicopter owners regarding the risks of using general aviation aircraft for business purposes.
- A recommendation was made to the UK CAA to ensure maintenance organizations do not use arbitrary factors when calculating maintenance intervals for this aircraft type.
- The report highlighted the need for EASA to review regulations concerning corporate aviation activities in Europe.