B2/2003L Aircraft accident at Enontekiö on June 25,2003

On 25 June 2003, at 12.30LT there was an accident at Lake Ounasjärvi, Hetta, Enontekiö. A float-equipped Cessna A185F aircraft, owned by Polar Lento Ltd and registered OH-CVT, collided with water during take off. The aircraft was carrying a pilot and two passengers. The pilot and the passenger in the middle row survived with minor injuries but the passenger in the front right seat drowned. The purpose of the flight was a reindeer industry flight. The pilot intended to take the passengers from Lake Ounasjärvi to Lake Kalkujärvi, approximately 40 km Northeast.

30 June 2003, The Accident Investigation Board Finland appointed an investigation commission B 2/2003 L. The investigator-in-charge was chief air accident investigator Esko Lähteenmäki and members were MSc Ville Hamalainen and airline pilot Timo Wahe. The commission nominated professor emeritus Seppo Laine and meteorologist Tapio Tourula as experts to the investigation.

The pilot started the take off towards east along the lake. The head wind was approximately three knots. The waves were approximately 10 cm high. The pilot had trimmed the longitudinal trim in such way that the aircraft lifted off by itself from the float step and continued to climb. As the aircraft was climbing at a height of approximately 15 m, it suddenly rolled and yawed to the right. The pilot used full opposite aileron and full left rudder. The counter control measures were ineffective and the aircraft collided with water at an almost right angle. The aircraft nose had yawed more than 90º to the right. The aircraft capsized but remained afloat. The passenger on the middle row right-hand seat escaped onto the float. The pilot tried to unbuckle the seatbelt of the passenger next to him but was unable to locate the buckle. Finally he had to dive to the surface. The rescuers were able to get the passenger up from the aircraft two hours after the accident.

The investigators investigated the take off procedure used and the effect of the installed Robertson STOL (R/STOL) kit on the take off performance of the aircraft. In the R/STOL kit the aileron mechanism is mechanically connected to the trailing edge flap mechanism and the ailerons, for example, turn 13 down with a flap setting of 20. The properties of the wing and aircraft were studied with aerodynamic aerofoil and flight mechanics calculations as well as with test flights. The test flight was flown with a flow indicator wool strings attached to the aircraft fuselage, vertical stabiliser, rudder and upper right wing surface. The movements of the strings were videotaped. The test flight was flown with the same type of aircraft as the accident aircraft with a similar modification and equipment status.

The investigation commission stated that the cause of the accident was the pilot’s procedure to climb above the ground effect without reducing the pitch angle. The aileron and flap connection of the R/STOL kit of the aircraft combined with the aileron type caused the right wing to tip stall in take off configuration. The pilot did not recognise the stall and did not act in the required sense to recover.

The investigation commission recommended that the appropriate authority should take measures to inform pilots as comprehensively as possible about the stall behaviour of the Robertson STOL Cessna 185 aircraft. The aircraft flight manual supplement should also contain a warning of this. The commission also recommended that the Finnish Flight Safety Authority would revise the regulations OPS M3-6 and AIR M11-2 so that all persons on board must always wear a life vest during water operations.

B2/2003L Report (pdf, 0.23 Mt)

VIDEOCLIPS FROM A TEST FLIGHT ON JULY 1, 2004

Aircraft accident at Enontekio on June 25, 2003, B 2/2003 L

Videoclips from a test flight on July 1, 2004:

Stall with the aircraft in clean configuration. The stall speed was approximately 51 knots. The flow separates first from the wing root area and the stall was safe.

B2_2003L_1.wmv (wmv, 1.89 Mt) B2_2003L_2.wmv (wmv, 4.02 Mt)

Stall with the aircraft in take-off configuration. The stall speed was approximately 55 knots. The flow separates first from the wing tip area and the aircraft rolled to the right.

B2_2003L_3.wmv (wmv, 1.9 Mt) B2_2003L_4.wmv (wmv, 1.9 Mt)