What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
The certified flight instructor had worked approximately an 11 hour duty day starting at 5:00 am local time before the accident flight, performing ground instruction and flight instruction duties.
The weather observation at 4:00 pm indicated visual meteorological conditions with clear skies, winds from 210 degrees at 13 knots with gusts up to 21, and 10 miles of visibility. The temperature was 32 celsius, dew point was 5 celsius, and altimeter setting was 30.03 in hg, resulting in a density altitude of approximately 8000 feet.
The helicopter was holding short of runway 21L at taxiway C4 after a training flight. The ground controller issued a crossing clearance ?universal 18 cross runway 21L? And the instructor began a hover taxi directly to parking. Approximately ten seconds later the ground controller issued traffic advisory and the taxi clearance again with specific instructions ?universal 18 taxi behind company to parking, cross the runway C4 to D4, and then taxi behind company.? Fearing a runway incursion violation by the FAA, the instructor immediately attempted to comply with the instruction by slowing and turning left to return to the taxiway D4 that was included in the second clearance. The helicopter turned downwind and the crew reported a low rotor warning light. The helicopter settled into the ground and subsequently bounced. Upon contact with the ground the second time, the helicopter rolled onto its left side and sustained substantial damage. One crew member sustained minor injuries. There were no mechanical irregularities reported by the crew.
The helicopter was performing near maximum power during this hover taxi in part due to the density altitude of 8,000 feet. In the moments leading up to the accident, the helicopter was slowed down and a left turn was initiated. The reduction in airspeed and turn downwind from the prevailing winds resulted in a reduction in translational lift, effectively requiring a higher angle of attack from the main rotor blades to maintain the hover, which resulted in an increase in power required from the engine. Additionally, a left turn in this type of helicopter requires an increase in angle of attack and more thrust production from the tail rotor, also resulting in more power required from the engine. The lack of available power led to the low rotor RPM and subsequent loss of lift.
As the FAA filed it
THE CERTIFIED FLIGHT INSTRUCTOR HAD WORKED APPROXIMATELY AN 11 HOUR DUTY DAY STARTING AT 5:00 AM LOCAL TIME BEFORE THE ACCIDENT FLIGHT, PERFORMING GROUND INSTRUCTION AND FLIGHT INSTRUCTION DUTIES.
THE WEATHER OBSERVATION AT 4:00 PM INDICATED VISUAL METEOROLOGICAL CONDITIONS WITH CLEAR SKIES, WINDS FROM 210 DEGREES AT 13 KNOTS WITH GUSTS UP TO 21, AND 10 MILES OF VISIBILITY. THE TEMPERATURE WAS 32 CELSIUS, DEW POINT WAS 5 CELSIUS, AND ALTIMETER SETTING WAS 30.03 IN HG, RESULTING IN A DENSITY ALTITUDE OF APPROXIMATELY 8000 FEET.
THE HELICOPTER WAS HOLDING SHORT OF RUNWAY 21L AT TAXIWAY C4 AFTER A TRAINING FLIGHT. THE GROUND CONTROLLER ISSUED A CROSSING CLEARANCE ?UNIVERSAL 18 CROSS RUNWAY 21L? AND THE INSTRUCTOR BEGAN A HOVER TAXI DIRECTLY TO PARKING. APPROXIMATELY TEN SECONDS LATER THE GROUND CONTROLLER ISSUED TRAFFIC ADVISORY AND THE TAXI CLEARANCE AGAIN WITH SPECIFIC INSTRUCTIONS ?UNIVERSAL 18 TAXI BEHIND COMPANY TO PARKING, CROSS THE RUNWAY C4 TO D4, AND THEN TAXI BEHIND COMPANY.? FEARING A RUNWAY INCURSION VIOLATION BY THE FAA, THE INSTRUCTOR IMMEDIATELY ATTEMPTED TO COMPLY WITH THE INSTRUCTION BY SLOWING AND TURNING LEFT TO RETURN TO THE TAXIWAY D4 THAT WAS INCLUDED IN THE SECOND CLEARANCE. THE HELICOPTER TURNED DOWNWIND AND THE CREW REPORTED A LOW ROTOR WARNING LIGHT. THE HELICOPTER SETTLED INTO THE GROUND AND SUBSEQUENTLY BOUNCED. UPON CONTACT WITH THE GROUND THE SECOND TIME, THE HELICOPTER ROLLED ONTO ITS LEFT SIDE AND SUSTAINED SUBSTANTIAL DAMAGE. ONE CREW MEMBER SUSTAINED MINOR INJURIES. THERE WERE NO MECHANICAL IRREGULARITIES REPORTED BY THE CREW.
THE HELICOPTER WAS PERFORMING NEAR MAXIMUM POWER DURING THIS HOVER TAXI IN PART DUE TO THE DENSITY ALTITUDE OF 8,000 FEET. IN THE MOMENTS LEADING UP TO THE ACCIDENT, THE HELICOPTER WAS SLOWED DOWN AND A LEFT TURN WAS INITIATED. THE REDUCTION IN AIRSPEED AND TURN DOWNWIND FROM THE PREVAILING WINDS RESULTED IN A REDUCTION IN TRANSLATIONAL LIFT, EFFECTIVELY REQUIRING A HIGHER ANGLE OF ATTACK FROM THE MAIN ROTOR BLADES TO MAINTAIN THE HOVER, WHICH RESULTED IN AN INCREASE IN POWER REQUIRED FROM THE ENGINE. ADDITIONALLY, A LEFT TURN IN THIS TYPE OF HELICOPTER REQUIRES AN INCREASE IN ANGLE OF ATTACK AND MORE THRUST PRODUCTION FROM THE TAIL ROTOR, ALSO RESULTING IN MORE POWER REQUIRED FROM THE ENGINE. THE LACK OF AVAILABLE POWER LED TO THE LOW ROTOR RPM AND SUBSEQUENT LOSS OF LIFT.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.