Event Summary
On Sunday, 3 May 2009, at 10:15 local time, a Robinson R-44 helicopter, registration G-KPAO, departed from Ampuria Brava (LEAP) airport in Gerona for Castellon airport (LECN) with the pilot and two passengers. En route, the pilot notified LEAP of a frequency change and received instructions to proceed to the Bagur VOR. Approximately 3 nautical miles past the VOR, the engine lost power. The pilot declared an emergency, entered autorotation, and landed in a nearby olive grove. During touchdown, the vertical stabilizer struck a tree, causing damage to its lower section. The occupants were uninjured and exited the aircraft unassisted before reporting their position.
Aircraft and Crew Details
The helicopter was a Robinson R-44 (serial number 0382) powered by a single Lycoming O-540-F1B5 engine. It held a valid airworthiness certificate and had passed all scheduled inspections, including those specified in manufacturer service bulletins. The pilot, aged 55, held a valid commercial helicopter pilot license (CPL(H)) issued by the English authority and a current medical certificate. He had 2,200 flight hours, of which 2,000 were on type.
Post-Accident Inspection
Examination of the engine revealed a broken pushrod and bent external guide on the number 2 cylinder exhaust valve. The cap and tappet were disassembled, showing damage to the tappet. Clearances between the rod and guide were measured on all cylinders against specifications in Service Bulletin 338 C (allowable range: 0.015 to 0.030 inches): No. 1 and 3 cylinders had 0.300 inches; No. 4 had 0.027 inches; No. 5 had 0.017 inches; No. 6 had 0.028 inches. Two cylinders were at the upper limit, two were close to the maximum but within limits, and one was near the minimum, also within limits. The tail cone was disassembled to check for structural damage, and the upper vertical stabilizer was inspected with liquid penetrants, revealing no cracks.
Findings
Analysis of the clearance measurements indicated that all cylinders were near the limits, making it likely that the maximum allowed clearance was exceeded on the number 2 cylinder. Excessive clearance can cause the guide to not be perfectly straight, increasing friction and allowing oil to pass through and solidify, potentially limiting valve movement. The incident occurred because the number 2 cylinder exhaust valve became blocked in the closed position, leading to the broken pushrod and bent guide. This resulted in a loss of engine power, forcing the pilot to perform an emergency landing.