On July 27, 1995, a Hughes 269C (registration N747MK) was involved in an aviation accident near Redlands, CA. Investigators recorded the probable cause as: The pilot's failure to ensure the landing gear actuators were fully charged after a field repair, which resulted in ground resonance and subsequent rollover. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter experienced ground resonance during cooldown after landing, rolling onto its side because engine and rotor RPM were too low for corrective action. Investigation found landing gear actuators were not fully charged due to a missing baffle from a prior field repair.
What happened
The helicopter encountered ground resonance while in the cool-down period following a landing. During this phase, the aircraft subsequently rolled over onto its side. The pilot was unable to effect a corrective liftoff because the engine and main rotor revolutions per minute (RPM) were insufficient for such an action.
The investigation
An examination of the helicopter's landing gear actuators disclosed that they were not fully charged. Further inspection revealed that one actuator's required baffle had not been reinstalled after a previous field repair.
Findings
The primary contributing factor was the incomplete reassembly of the landing gear system, specifically the missing baffle on one actuator, which prevented proper charging and left the aircraft vulnerable to ground resonance effects during the post-landing cooldown period.
Probable cause
The pilot's failure to ensure the landing gear actuators were fully charged after a field repair, which resulted in ground resonance and subsequent rollover.