On 11 January 2010, a British Aerospace ATP being operated by West Air Sweden on a cargo flight from Helsinki to Copenhagen with only the two operating flight crew on board at night could not be rotated for take off on runway 22R. The ensuing rejected take off in normal ground visibility was achieved within the available runway length and the aircraft was undamaged and returned to the apron.
An Investigation into the incident was carried out by the Swedish Accident Investigation Board (SHK) following delegation of responsibility by the AIB Finland because the Swedish-domiciled operator of the aircraft involved was also the largest single operator of the aircraft type. The Investigation determined that the issues involved in the investigated incident had been seen beyond the specific aircraft type involved and whilst the Investigation remained focused on the aircraft type involved, it was judged as a result of extensive testing and analysis, that similar issues relating to the use of thickened ground de/anti icing fluids were also relevant to other aircraft types and the eventual Safety Recommendations made were therefore generic.
It was established that the incident aircraft had undergone a normal two step ground de/anti icing procedure prior to departure and noted that this had involved an initial application of hot water mixed with Type I fluid followed by an application of thickened fluid, in this case Type IV, the exact product used being “Clariant Safewing MP IV Launch". The aircraft commander had been the designated PF.
It was noted that the BAe ATP had been tested in 1991 for the use of Type II fluid and these tests had shown that increased stick force was needed on rotation after application of the fluid used in the test. The aircraft was certified for use with Type II, and in 1998 was also certified for use with Type IV fluids. However, the Type IV testing was not carried out on the ATP, but on a different type of aircraft, the Jetstream 41, because this type was “considered to be more critically sensitive to effects arising from Type IV fluid”.
The AIB noted that once their Investigation commenced, “it was discovered that several similar incidents involving the same type of aircraft and similar conditions had occurred [...] which had all involved deicing with thickened fluids [...] combined with too narrow a gap between the stabiliser and elevator”. A number of common factors were identified in most of these incidents:
- the elevator movement was restricted and/or felt very stiff to manoeuvre in connection with takeoff rotation
- the problems arose at speeds around Vr
- the incidents were often accompanied by "Standby Controls" and/or "Split" Warnings
- all the occurrences took place during winter conditions
- the aircraft had been deiced in preparation for flying
- (thickened) fluid of Type II or Type IV had been applied
- full elevator travel had been confirmed in rudder checks before and after the incidents
- no known balance problems had played a part in the occurrences
- no technical/mechanical faults could be identified in the aircraft
- the fault differed in character depending on whether the pilot performing take-off was seated on the right-hand or left-hand side
The Investigation noted that the process for drawing up specifications and requirements for deicing fluids is to a certain extent controlled by trade organisations (coordinated through SAE) and that “at present no monitoring or specific inspection activities relating to these fluids are carried out by any pan-European aviation safety body”. It was also noted that there is no regulatory authorisation process or any established certification rules to control which types of aircraft can use different types of deicing fluids.
The formal Conclusion of the Investigation was that the investigated incident and other similar ones which had involved the same aircraft type had been caused by:
“a phenomenon which, for unknown reasons, occurs following the use of anti-icing fluids containing thickening agents, on individual aircraft where the stabiliser and elevator are too close together”
and that one Contributory Factor was that:
“there were shortcomings in that part of the aircraft's type certification exercises that concerned anti-icing.”
Safety Action taken during the Investigation by the ATP Type Certificate Holder, BAE Systems and by EASA, which issued an AD based on procedures and` requirements developed by BAE Systems on 17 December 2010
As a result of the Investigation, and the Safety Action achieved in respect of the specific aircraft type involved, four generic Safety Recommendations were made in respect of all aircraft types:
- That EASA should work for an extension of EASA’s remit to include certification of fluids used for ground de- and antiicing of aircraft. (RL 2011: 16e R1)
- That EASA should investigate the possibility of tightening requirements on aircraft design organizations in terms of demonstrating that the aircraft has full manoeuvrability during all phases of the takeoff procedure after the application of de- and anti-icing fluids. (RL 2011: 16e R2)
- That EASA should actively consider the value of a wider use of Type III fluids (or corresponding fluids), within the field of European Civil Aviation. (RL 2011:16e R3)
- That ICAO should, within the international flight safety community, work to ensure that in the future, the issuing of requirements, specifications and definition of areas of use, aircraft de- and anti-icing fluids are made the responsibility of airworthiness authorities. (RL 2011:16e R4)
The Final Report of the Investigation RL 2011:16e was published on 23 November 2011.
Note: Although the AEA ceased to exist in 2016, the most recent of their publications still contain some pertinent information. Readers are cautioned to validate the recommendations of these guidebook using more current information sources.