Accident Details
On March 4, 2018, at approximately 2324 central standard time, a Messerschmitt-Bolkow-Blohm BK 117 B-2 helicopter, registration N1174U, operated by Air Methods Corporation, sustained substantial damage during a hard landing at Sheboygan County Memorial Airport (SBM) in Sheboygan, Wisconsin. The flight was conducted under Title 14 Code of Federal Regulations Part 135 as a helicopter air ambulance. Night visual meteorological conditions prevailed at the time, and no flight plan was filed. The helicopter had departed Fond du Lac, Wisconsin, about 2257, and was destined for HSHS St. Nicholas Hospital in Sheboygan. The commercial pilot, flight nurse, and flight paramedic aboard were not injured.
Flight Sequence
According to the pilot, standard flight control and hydraulic transfer checks were performed prior to departure with no anomalies noted. The pilot, wearing night vision goggles, climbed to 2,500 ft above ground level and accelerated to 125 knots indicated airspeed. Approaching the hospital, the pilot began a slow descent using the collective and performed before-landing checks, with all systems normal. When attempting to decelerate from cruise speed, the pilot noticed restricted cyclic control movement, about 1 inch in any direction, while collective and yaw controls remained normal. The pilot aborted the descent and elected to make a precautionary landing at SBM, about 6 miles west of the hospital.
Control Issue
During the flight to SBM, the pilot cycled the hydraulic test switch twice from the overhead panel, with no change to the flight controls. The flight paramedic in the left seat checked for popped circuit breakers, confirmed systems were within normal ranges, and noted no caution or advisory lights illuminated. All circuit breakers and systems were normal.
The pilot initially approached runway 22 but, being too high and fast, circled to land on runway 13 for a more favorable quartering headwind. During these approaches, the pilot held the cyclic trim switch aft to gain additional aft cyclic authority. With continuous cyclic pressure against the aft stop, the helicopter slowed to 80 knots on final approach.
Landing and Damage
The helicopter touched down near the runway centerline, skidded about 500 ft, exited the runway surface, and came to rest upright. The top wire strike protection system separated due to contact by the main rotor blades. The landing gear skids partially collapsed. One main rotor blade had a portion of its skin and core separated, and all blades sustained leading edge damage.
Postaccident Examination
Postaccident examination revealed the cyclic trim position was in the full forward and left position. Examination of the flight control system, including the trim system, found no anomalies that would have precluded normal operations. The dual hydraulic pack was functionally tested on the helicopter with no anomalies, then removed for further testing.
On April 5, 2018, under FAA supervision, the cyclic control trim system switch and motors were tested about 50 times in each direction of full travel and from neutral positions; no anomalies were noted. On April 16, 2018, under FAA supervision, the dual hydraulic pack was tested in accordance with repair manual procedure REM 401-04-22 Dual Hyd-Pack Final Work/Test; no anomalies were found during examination or testing.
A review of the aircraft maintenance logbook revealed no reports of control problems or recent maintenance to the flight control system.
According to the helicopter flight manual, the hydraulic test switch should not be operated in-flight if a hydraulic system caution light illuminates; it should remain in the normal position.