Power Loss During Climb and Emergency Landing in a Robin DR 400-125

Incident Overview On 11 June 2011 at 17:00 local time, a Robin DR 400-125 registered F-BVCY, operated by a flying club, experienced an engine power loss during a training climb. The aircraft departed from runway 26 at Moulins Montbeugny Aerodrome with an instructor and a student on board. ## Sequence of Events At approximately 2,900 feet altitude (2,000 feet above ground level), about 2 nautical miles from the aerodrome, the instructor noticed abnormal noise and vibrations followed by a loss of engine power. The instructor took control, turned the aircraft around, and made an emergency landing on the same runway from which it had departed. ## Technical Findings Initial observations showed that the Lycoming O-235 J2A engine was properly supplied with fuel and that the magnetos were functioning normally. The engine had accumulated 809 hours since its 2009 overhaul at an approved facility, during which new cylinder blocks were installed. These blocks included modifications required by EASA SIB 2009-24 following cracks found on some engines at the cylinder bases. A further examination revealed a significant crack in the left crankcase half near the base of cylinder number 2. This crack caused an oil leak. No cylinder base was cracked. Signs of “fretting” were visible on the internal bearing surfaces of the crankcase at the crankshaft bearings. ## Contributing Factors The report explains that fretting is the result of friction between the contact surfaces of the two crankcase halves. It can be caused by insufficient tightening of the through-bolts during maintenance operations, such as cylinder replacement. ## Meteorological and Human Factors The weather conditions were: wind 270° at 5 knots, CAVOK, temperature 19°C, and QNH 1018 hPa. The instructor had 5,000 total flight hours, including 3,000 on type, 170 hours in the previous three months (100 on type), and 3 hours in the previous 24 hours (all on type). The student had 120 total flight hours, including 11 hours in the previous three months (all on type), and none in the previous 24 hours. ## Conclusion The deterioration of the crankcase near the base of cylinder number 2 caused vibrations and a loss of engine power. The observed damage could correspond to a defect in the tightening of the through-bolts. The instructor’s prompt response limited the consequences of the failure in flight.