Pilot Debrief

MESSERSCHMITT-BOLKOW-BLOHM BK 117 B-2 near Sheboygan, WI — 2018-03-05

Final reportCEN18LA115
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Date
2018-03-05
Location
Sheboygan, WI, USA
Airport
SBM
Aircraft
MESSERSCHMITT-BOLKOW-BLOHM BK 117 B-2
Registration
N1174U
Category
Helicopter
Highest injury
None
Fatalities
0
Phase of flight
Descent

Probable cause

The restricted cyclic control movement for reasons that could not be determined because postaccident examination and testing of the cyclic control system did not reveal any evidence of mechanical malfunctions or failures that would have precluded normal operation.

NTSB narrative

Before departure on the air ambulance flight, standard flight control and hydraulic transfer checks were performed with no anomalies noted with the flight controls. The helicopter’s hover, departure, and cruise were normal. During his approach to the hospital, the pilot started a slow descent using the collective and performed the before landing checks; all systems were normal. However, when attempting to decelerate from cruise speed, the pilot noticed restricted cyclic control movement, about 1 inch in any direction, with normal collective and yaw control movement. He then chose to abort the descent and execute a precautionary landing at a nearby airport. During the short flight to the airport, the pilot cycled the hydraulic test switch twice with no change noted to his flight controls. During the approach to land, the pilot held the cyclic trim switch aft in an attempt to gain additional aft cyclic authority. With continuous cyclic pressure against the aft stop, the pilot was able to slow the helicopter to 80 knots on final approach. The helicopter touched down near the runway centerline, skidded about 500 ft, exited the runway surface, and came to rest upright. The helicopter sustained substantial damage to the main rotor blades and fuselage structure. Postaccident examination of the helicopter’s flight control system, including the trim system, did not reveal any evidence of malfunctions or failures that would have precluded normal operations. The cyclic trim was found in the full forward and left position. The flight control dual hydraulic pack was functionally tested on the helicopter and at a repair facility with no anomalies noted. Thus, the reason for the restricted cyclic control movement could not be determined.

Analysis

Primary failure mode
Human factors
First missed decision gate
Pilot should not have cycled hydraulic test switch in-flight as per manual.

NTSB coding

Evidence available

  • Photos
  • 9 docket documents
View NTSB final reportView NTSB docket

Docket documents9

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