The pilot of the Sikorsky S76 helicopter reported that while approaching Barrow Island and immediately after he reduced the helicopter's airspeed for landing gear extension, he found that the cyclic could not be moved aft. He also found that with any further forward movement of the cyclic stick, the stick then could not be moved aft of the new position. The pilot froze the cyclic longitudinal position and the helicopter stabilised in a level pitch attitude at about 85 kts indicated airspeed. Using only lateral cyclic movements to manoeuvre the helicopter, the pilot conducted an 80-kt run-on landing on the runway at Barrow Island.
The subsequent maintenance inspection found a panhead type screw at the base of the cyclic stick. The screw had lodged between the lower protrusion on the casting on the end of the cyclic stick torque tube and the lugs on a support bracket. The lodgement of the screw in that location had caused the cyclic restriction experienced by the pilot.
The cyclic stick base hardware was accommodated in a tub-like area formed by the cabin structure supports. A leather boot mounted at the base of the cyclic normally prevented foreign objects from entering the tub. The subsequent maintenance inspection found the leather boot on this helicopter to be intact. With the boot in place, the only possible entry points where a screw could be inserted was through a rigging pin hole in the aft mid-height position of the boot-halves joint, or vertically through an opening provided for the cyclic stick electrical wiring loom. Due to the unlikelihood that a screw could enter the tub area when the boot was fitted, the screw was probably introduced to the area during prior maintenance while the boot was removed.
Operator safety action
The operator issued an alert message for its fleet of S76 helicopters to undergo an inspection of the subject area. A defect report was also submitted to the Civil Aviation Safety Authority.
Manufacturer safety action
As a result of this incident and a similar incident experienced by another Australian S76 operator in 1995, and following consultation between the operator, helicopter manufacturer and BASI; the manufacturer conducted a design engineering review of the cyclic stick base hardware to determine if it was possible to reduce the effect of foreign object entry to the tub area.
Following the review, the manufacturer advised that a field modification of the pilot's side bracket was being prepared to increase the gap between the torque tube rig boss and the bracket foot. On 28 August 1999, the manufacturer also advised of its intention to issue an Alert Service Bulletin, in due course, to address the results of the engineering review.
BASI safety action
BASI will monitor the progress of this manufacturer's proposed safety action.
|Date:||04 August 1999||Investigation status:||Completed|
|Time:||1000 hours WST|
|Location:||Barrow Island , Aero.|
|State:||Western Australia||Occurrence type:||Control - Other|
|Release date:||20 October 1999||Occurrence category:||Incident|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||Sikorsky Aircraft|
|Type of operation||Charter|
|Damage to aircraft||Nil|
|Departure point||Cossack Pioneer, WA|
|Destination||Barrow Island, WA|
|Role||Class of licence||Hours on type||Hours total|