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ASN Wikibase Occurrence # 197098
Last updated: 15 July 2019
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Date:02-AUG-2017
Time:07:20
Type:Sikorsky S-97 Raider
Owner/operator:Sikorsky Aircraft Corp.
Registration: N971SK
C/n / msn: 0001
Fatalities:Fatalities: 0 / Occupants: 2
Other fatalities:0
Aircraft damage: Substantial
Category:Accident
Location:William P Gwinn Airport, Palm Beach County, FL -   United States of America
Phase: Manoeuvring (airshow, firefighting, ag.ops.)
Nature:Test
Departure airport:Jupiter, FL (06FA)
Destination airport:Jupiter, FL (06FA)
Investigating agency: NTSB
Narrative:
The airline transport pilot of the experimental, fly-by-wire-equipped helicopter was taxiing to the runway for a test flight. During the taxi, he had commanded a high collective pitch and a slight forward cyclic pitch stick, and the helicopter was light on its wheels; as a result, the flight control computer transitioned from ground mode to flight mode. The slight forward pitch stick in combination with flight control mode resulted in a nose down pitch rate. The pilot took corrective action, inputting aft cyclic stick. The initial pitch axis correction led to a small initial left roll. The pilot countered the small left roll rate with an appropriate magnitude right stick input. In conjunction with the right stick input, the pilot raised the collective to increase the helicopter's altitude. The helicopter’s right roll response to the right stick input was larger than expected, and the pilot countered with a large left stick input. The helicopter’s left roll response was also larger than expected. The helicopter bank angles quickly increased, and the pilot rapidly lowered the collective to land the helicopter. The rapid left and right rolls resulted in upper and lower rotor contact, which damaged all rotor blades. The investigation determined that the larger-than-expected roll response to the pilot’s cyclic stick input was the unintended result of a flight control system design change that resulted in an increase in cyclic stick sensitivity in the roll axis during the transition from ground control mode to flight mode.


Probable Cause: A design change in the helicopter's fly-by-wire control system that resulted in an increase in the sensitivity of the cyclic stick while transitioning from ground to flight mode, magnifying the pilot's control inputs, which resulted in unintentional over control in the roll axis, upper and lower main rotor contact, and damage to the rotor blades.

Sources:

NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20170802X24925&key=1
FAA register: http://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?NNumbertxt=N971SK

Accident investigation:
cover
  
Investigating agency: NTSB
Status: Investigation completed
Duration: 1 year and 11 months
Download report: Final report


Revision history:

Date/timeContributorUpdates
02-Aug-2017 21:58 Iceman 29 Added
02-Aug-2017 22:26 Aerossurance Updated [Aircraft type, Location, Embed code]
03-Aug-2017 05:28 Aerossurance Updated [Time]
03-Aug-2017 10:47 Iceman 29 Updated [Registration, Source, Embed code]
11-Sep-2017 17:57 Aerossurance Updated [Time, Registration, Cn, Location, Phase, Departure airport, Destination airport, Source, Damage, Narrative]
11-Sep-2017 18:01 Aerossurance Updated [Location, Narrative]
11-Sep-2017 21:18 Aerossurance Updated [Source, Narrative]
01-May-2019 15:43 Aerossurance Updated [Source, Narrative]
15-Jul-2019 18:03 ASN Update Bot Updated [Time, Cn, Operator, Nature, Departure airport, Destination airport, Source, Embed code, Narrative, Accident report, ]
15-Jul-2019 18:36 harro Updated [Nature, Source, Embed code, Narrative, Accident report, ]
15-Jul-2019 18:36 harro Updated [Operator]

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