Loss of Control During Hover Taxi in Westland Scout AH1

Casualties unknown • Near Barn Farm, Ruddington, Nottinghamshire, GB

A Westland Scout AH1 experienced an uncommanded nose-up pitch during a hover taxi near Ruddington, resulting in a heavy landing and significant aircraft damage.

What happened

On 29 December 2015, a Westland Scout AH1, registration G-BYRX, was performing a private flight near Ruddington, Nottinghamshire. While the pilot was hover taxiing for takeoff in approximately 11-knot winds, the aircraft suddenly experienced a significant loss of control. The pilot attempted to yaw the helicopter to the left to position into the wind, but the aircraft failed to respond to the inputs. Instead, the nose pitched up sharply to an angle between 45 and 60 degrees, and the cyclic stick became stuck in the aft position.

In an attempt to manage the situation, the pilot lowered the collective, causing the helicopter to descend rapidly. The aircraft struck the ground tail-first before rolling onto its right side. The impact caused the tail boom and skids to break away, and both the main and tail rotor blades were destroyed. While the engine remained running following the impact, the aircraft was damaged beyond economic repair. There were no fatalities, though one passenger sustained minor injuries.

The investigation

An AAIB field investigation examined the wreckage at the pilot's farm complex and later conducted a detailed analysis of the control systems. Investigators found that the hydraulic system and the centralized warning system were functioning normally, and no hydraulic leaks were identified prior to the accident. The engine and rotor systems were found to have been under power at the moment of impact.

Detailed laboratory examination of the servo-jacks by the 1710 Naval Air Squadron revealed the presence of fine black deposits within all three jacks. Additionally, longitudinal wear marks were observed on the large pistons of two jacks, suggesting potential misalignment between the piston and cylinder. While some light surface oxidation was found on the control valves, it was not deemed significant enough to impede operation. Analysis of the hydraulic fluid showed it was of the correct grade, though gas chromatography indicated some level of degradation.

Findings

  • The aircraft experienced an uncommanded nose-up pitch during a low-level hover.
  • The pilot was unable to maintain control due to the cyclic stick becoming fixed in the aft position.
  • A temporary restriction in a servo-jack control valve may have caused the loss of control by significantly increasing the physical force required to manipulate the flying controls.
  • The presence of black deposits in the servo-jacks suggests that debris may have intermittently blocked a control valve.

Probable cause

The investigation could not definitively prove a mechanical failure, but the loss of control was likely caused by a temporary restriction in one of the servo-jack control valves, potentially due to debris, which necessitated much higher control forces than the pilot could manage during the hover.

Frequently asked questions

What happened in the 2015-12-29 Westland Scout AH1 accident near Near Barn Farm, Ruddington, Nottinghamshire, GB?

A Westland Scout AH1 experienced an uncommanded nose-up pitch during a hover taxi near Ruddington, resulting in a heavy landing and significant aircraft damage.

What aircraft was involved and where did it happen?

The accident on 2015-12-29 involved a Westland Scout AH1, registration G-BYRX , at Near Barn Farm, Ruddington, Nottinghamshire, GB.

What was the probable cause of the accident?

The investigation could not definitively prove a mechanical failure, but the loss of control was likely caused by a temporary restriction in one of the servo-jack control valves, potentially due to debris, which necessitated much higher control forces than the pilot could manage during the hover.

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