Aviation occurrence briefs

Loss of control involving a Robinson R44 helicopter, Townsville Airport, Qld, on 23 April 2020

Number:
AB-2020-015
Status: Completed
Investigation completed

Brief

Occurrence Briefs are concise reports that detail the facts surrounding a transport safety occurrence, as received in the initial notification and any follow-up enquiries. They provide an opportunity to share safety messages in the absence of an investigation.

What happened

On 23 April 2020, the student pilot of a Robinson R44 helicopter was returning to Townsville Airport, Queensland, from a solo training navigation exercise.

As the pilot returned the helicopter to the parking position near the hangar and was in the process of landing from the hover, he momentarily lost directional yaw control. At this time, one of the helicopter’s skids was in contact with the ground while the collective[1] was in a raised position. This resulted in an unstable airframe that commenced a roll about the skid.

Despite the efforts of the pilot to recover, the helicopter continued to rollover and came to rest on its side resulting in substantial damage. The pilot was uninjured in the accident.

Figure 1: Helicopter post-accident

Figure 1: Helicopter post-accident.
Source: Townsville Airport

Source: Townsville Airport

Figure 2: Helicopter’s bent tail boom and broken main rotor blade

Figure 2: Helicopter’s bent tail boom and broken main rotor blade.
Source: Townsville Airport

Source: Townsville Airport

Helicopter static and dynamic rollovers

Static rollover occurs when a helicopter is pivoted about one of its landing skids or wheels and the helicopter’s centre of gravity passes outside the in-contact skid or wheel. Once in this position, removal of the original force that raised the helicopter to that angle will not stop the helicopter from rolling further. This angle is termed the ‘static rollover angle.’

A rotors-running helicopter resting with one landing skid or wheel on the ground may, without appropriate pilot input, commence rolling. Under certain circumstances, this roll cannot be controlled and the helicopter rolls over. This condition is known as ‘dynamic rollover’ and is a function of the interaction between the:

  • horizontal component of the total rotor thrust (or lift) acting about the point of ground contact
  • weight of the aircraft, initially acting between the helicopter’s skid landing gear or wheels. This second, counter-rolling moment decreases the greater the roll.

Recovery from dynamic rollover is by smoothly lowering the collective lever while controlling any tendency to roll in the opposite direction with cyclic[2] to re-establish the helicopter’s weight evenly on the ground. In general, the application of smooth collective inputs is more effective in avoiding rollover issues than using the cyclic control.

Safety message

This accident highlights the importance of smooth and controlled flight control inputs in the critical phases of flight. While a helicopter is in contact with the ground and before its full weight is applied to the landing gear, it is subject to various influences such as the possibility of a rollover. A thorough understanding of the principles of, and contributing factors to, both static and dynamic rollover and the recovery methods are essential to conducting safe helicopter lift-offs and landings.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

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  1. Collective: a primary helicopter flight control that simultaneously affects the pitch of all blades of a lifting rotor. Collective input is the main control for vertical velocity.
  2. Cyclic: a primary helicopter flight control that is similar to an aircraft control column. Cyclic input tilts the main rotor disc, varying the attitude of the helicopter and hence the lateral direction.
General details
Date: 23 April 2020   Investigation status: Completed  
Time: 0943 EST    
Location   (show map): Townsville Airport    
State: Queensland    
Release Date: 09 June 2020   Occurrence category: Serious Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer Robinson Helicopter Co  
Aircraft model R44 II  
Type of operation Flying Training  
Sector Helicopter  
Damage to aircraft Substantial  
Destination Townsville Airport, Queensland  
Last update 09 June 2020