Robinson Helicopter R44 N828RD accident near Myrtle Beach, South Carolina

Probable cause

A loss of available power to the main rotor due to a fractured exhaust pushrod and housing, which allowed engine oil to coat the V-belts. Contributing to the accident was the pilot's decision to continue the tour and his failure to maintain adequate rotor rpm during the landing, which resulted in a hard landing.

NTSB analysis

The commercial pilot and two passengers departed in the helicopter for a commercial air tour flight. The pilot reported that, shortly after takeoff, the helicopter started shaking like a "minor kick," which he thought might be due to a stuck engine valve. He immediately radioed the operator and requested that maintenance personnel meet the flight after the tour ended. He chose to continue the tour and attempted to maintain about 70 knots with the engine operating at 25 inches manifold pressure, which resulted in a descent rate of 300 ft per minute. When the helicopter was near the helipad location, company personnel reported seeing white smoke trailing from the helicopter, and the pilot noted that the alternator light was on. When the pilot started to slow the descent, the low rotor rpm horn sounded, and the engine rpm spiked. After realizing the helicopter would not be able to reach the helipad, the pilot turned the helicopter parallel to the slope of an adjacent field and fully pulled the collective pitch to cushion the landing, but the helicopter landed hard.

Postaccident examination of the engine revealed that the No. 5 cylinder exhaust valve pushrod and housing were fractured, which allowed about 2.5 quarts of engine oil to drain from the engine; the oil had coated the V-belts that transmitted power from the engine to the main rotor system. The pushrod and housing likely failed due to a stuck exhaust valve that occurred at engine startup and then became unstuck once the engine was warmed up. The subsequent release of oil onto the V-belts, of which the pilot was unaware, likely resulted in the V-belts slipping and the main rotor rpm decreasing. A service bulletin recommending a procedure every 300 hours or earlier to determine exhaust valve and guide condition was last accomplished on the helicopter 298.3 hours since overhaul.

Text from the NTSB. Open the NTSB docket for ERA17LA257 for the full record.