Gremline Flight Safety Report: Eurocopter AS350 Squirrel Fatal Accident

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the gremline digest — eurocopter AS350  squirrel accident

Eurocopter AS350 Squirrel Fatal Accident
A Eurocopter AS350 Squirrel been flown by a pilot whose licence and Type Rating had both expired crashed into trees while engaged in low-level high-speed flight close to the pilot’s home. The pilot and his three passengers died on impact.
      The accident resulted in an exhaustive investigation by The Air Accidents Investigation Branch and the publication of the AAIB findings in their Report EW/C2007/09/06 that is included in AAIB Bulletin 2/2009. This Report covers 32 pages in the Bulletin and contains a wealth of information that is of vital interest to all owners and operators of the Eurocopter AS350 and similar helicopters.



The following comments and opinions are those of the Gremline Technical Editor and do not seek to represent those of AAIB or anyone else. They are based on the findings of the AAIB Report, which source is gratefully acknowledged.
      The AAIB Report highlights a characteristic of the Eurocopter AS350 flight control system that may not be fully understood by all pilots and operators, and this lack of understanding may have led to the accident that caused the death of two adults and two children. There are other possibly contributing factors covered in the Report that deserve careful attention from all aircraft pilots, particularly from helicopter pilots, dealing with the hazards of low flying by pilots who have not had the benefit of specific specialist instruction in this very demanding skill.
The AAIB Report provides a detailed explanation of the “Flight control servo transparency phenomenon” with particular reference to the AS350 series of helicopters. This phenomenon is also sometime known as “jack stall” but is termed “servo transparency” or “control reversibility” by Eurocopter. No matter what it is called it is of the utmost importance that all AS350 pilots fully understand how this phenomenon may occur, what immediate action is demanded and how best to avoid entering that corner of the flight envelope where the phenomenon may be encountered. The topic of “servo transparency” does not lend itself to being précised so no attempt to do so will be made here.



It appears from eyewitness evidence and from a video recording recovered from the wreckage that the helicopter was been flown in what I would describe as an exuberant manner at very low level immediately before the impact. It seems likely that the pilot lost control at a height and attitude that made recovery impossible. He probably lost control because he encountered “servo transparency.” Eurocopter had issued Service Letter SL 1648-29-03 and Rush Revision 3A to the AS350B2 Flight Manual providing owners and operators with more information about servo transparency. The Flight Manual for the accident aircraft did not include Rush Revision 3A, issued in 2004. The revisions, and other information, are also available directly from Eurocopter via their internet site. Owners and operators may register to receive this material without charge. The pilot of the accident aircraft had not used this facility.
     The fact that the pilot’s licence and Type Rating had both expired may have no bearing on the accident. He also failed to keep the required up-to-date records of his flying hours. These lapses may have been oversights or may reflect an attitude towards regulations.
The AAIB Report includes remarks about helicopter low flying that are repeated here as sound advice to ALL helicopter pilots.


Helicopter low flying
Aviation is a complex and often unforgiving activity that demands not only skill and knowledge, but also discipline and sound judgement. Low level flying is inherently high risk, increasing the aircraft’s exposure to hazards and reducing the pilot’s options in the event of an aircraft malfunction. An engine failure at low height in a wooded valley would leave the pilot of a single-engined helicopter (like the accident aircraft) with little or no chance of landing safely. The risks associated with low level operations are well known by agencies like the military, who are required to operate there. To address and minimise the risks, military pilots are subject to rigorous selection, and extensive training in low level flying techniques, and are required to maintain currency in the environment.
      There are also sensitive environmental issues concerning helicopter operations, particularly as helicopters often operate closer to the general public than many other aircraft types. Military and commercial operators place great emphasis on lessening the environmental impact of low level helicopter operations. The CAA produced a leaflet in their ‘Safety Sense’ series covering many aspects of helicopter airmanship, including environmental considerations. Readers of the leaflet are urged to read the ‘Codes of Conduct’ produced by the British Helicopter Advisory Board (BHAB) and available on their website.
      The BHAB’s main objective is to promote the use of helicopters throughout the country and to bring to the attention of potential users the advantages of using or owning a helicopter. It is also concerned that helicopter operations are conducted safely and responsibly, and proper attention is paid to environmental issues. The first point in the BHAB’s Code of Conduct is:
ALWAYS FLY AS HIGH AS POSSIBLE consistent with the weather and other factors. This will reduce your projected noise at ground level, and also give you more scope to find a suitable landing site in the event of an emergency.’”




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