Robinson Helicopter R44 N288L accident near Myrtle Beach, South Carolina

Probable cause

Vibration in the airframe and flight controls for reasons that could not be determined based on the available evidence.

NTSB analysis

The pilot and three passengers departed for a short sightseeing tour after the helicopter had flown about 40 preceding tours on the day of the accident. The pilot reported that after takeoff about 500-700 ft above ground level (agl), he experienced a “violent shutter and shaking” of the helicopter flight controls. The pilot described the vibration as “very violent, like a brick in a [clothes] dryer, but three times more violent.” He stated that he noticed the erratic movement of the rpm on the tachometer and that the helicopter was no longer climbing. The pilot entered an autorotation to make an emergency landing in a parking lot. The vibration continued throughout the autorotation all the way to the ground; however, the pilot reported no unusual resistance, binding, or other issues with the flight controls.

During the approach, he flared the helicopter and pulled the collective to cushion the landing; the helicopter landed on its skids and slid on the pavement before impacting a mound of dirt and rolling on its left side. The pilot and passengers were not injured and the helicopter sustained substantial damage to the tail boom and fuselage.

A postaccident examination of the flight controls and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation. The examination of the engine included four successful test runs of the engine. The engine manufacturer had issued a mandatory service bulletin to mitigate an issue with sticking valves. While a stuck valve could not be ruled out, all valves moved freely during the two post-accident examinations, subsequent compression tests were not consistent with an open/stuck valve, and the maintenance records indicated that the manufacturer’s related service bulletin instructions were performed regularly. A “slight” engine vibration was reported during engine warm-up, but it smoothed out during the third and fourth engine runs.

The pilot stated that he noted that the helicopter stopped climbing, which would normally associated with a loss of power. However, it’s also possible that when the violent vibrations occurred initially, the pilot inadvertently lowered the collective slightly as he tried to ascertain the reason for the vibrations and the erratic movement of the rpm on the tachometer. He likely interpreted the leveling of the helicopter’s altitude as a loss of power as he entered the autorotation due to the violent vibrations. Based on available evidence, the reason for the vibrations described by the pilot could not be determined.

Text from the NTSB. Open the NTSB docket for ERA22LA168 for the full record.