Beech 90, N46BM, 18 May 2011

8 © Crown copyright 2012 AAIB Bulletin: 2/2012 N46BM EW/C2011/05/03 ACCIDENT Aircraft Type and Registration: Beech 90, N46BM No & Type of Engines: 2 Pratt &Whitney PT6A-28 turboprop engines Year of Manufacture: 1978 Date & Time (UTC): 18 May 2011 at 1131 hrs Location: Kinson Manor Farm, Bournemouth Type of Flight: Private Persons on Board: Crew - 1 Passengers - 1 Injuries: Crew - None Passengers - None Nature of Damage: Substantial damage to airframe and powerplants; landing gear collapsed Commander’s Licence: FAA Commercial Pilot’s Licence Commander’s Age: 47 years Commander’s Flying Experience: 800 hours (of which 660 hours were on type) Last 90 days - 13 hours Last 28 days - 6 hours Information Source: AAIB Field Investigation Synopsis The aircraft’s climb rate was lower than expected after takeoff and it was subsequently unable to maintain altitude. The pilot made a forced landing into a field. The cause of the apparent power loss was not determined. History of the flight The pilot had planned to fly from Bournemouth Airport to Manchester Airport operating the flight as a single pilot, with a passenger seated in the co-pilot’s seat. He arrived at the airport approximately one hour before the planned departure time of 1130 hrs, completed his pre‑flight activities and went to the aircraft at approximately 1110 hrs. The 1120 hrs ATIS gave the weather at the airport as: surface wind from 230° at 10 kt, visibility 10 km or greater, few clouds at 1,000 ft, broken cloud at 1,200 ft and at 2,000 ft, temperature 16°C, dew point 12°C and QNH 1015 hPa. After starting the engines, the pilot was cleared to taxi to holding point ‘N’ for a departure from Runway 26 and he was given clearance to take off at 1127 hrs. At 1129:45 hrs, approximately 55 seconds after the aircraft became airborne, the aerodrome controller transmitted “four six bravo mike do you ha ve a problem? ” because he believed the aircraft was not climbing normally. The pilot replied “november four six bravo going around” and, shortly afterwards, “four six bravo requesting immediate return ”. The 9 © Crown copyright 2012 AAIB Bulletin: 2/2012 N46BM EW/C2011/05/03 controller cleared the pilot to use either runway to land back at the airport but received no reply. The pilot carried out a forced landing into a field 1.7 nm west of the Runway 08 threshold at Bournemouth Airport and neither he nor his passenger was hurt. Information from the pilot The pilot reported that both engines started normally and the propeller checks that he carried out at the holding point before takeoff were satisfactory (see the section ‘Propeller checks’ below). He was given takeoff clearance while lining up on the runway and did not bring the aircraft to a halt before applying power. The pilot believed that, if he selected the propeller levers fully forward (high rpm) and then moved the power levers forward to the torque limit 1 , the propellers would exceed the 2,200 rpm limit during the takeoff run. Consequently, he normally took off with the propeller levers approximately half an inch aft of the fully forward position. He used this takeoff technique on the accident flight and recalled that the takeoff seemed normal with no tendency for the aircraft to drift either left or right. There was little crosswind and so he held the ailerons neutral during the takeoff roll and rotated the aircraft at an indicated airspeed of 104 kt. Immediately after leaving the ground, the pilot “dabbed” the brakes and selected the landing gear to up. Shortly afterwards he noticed that the aircraft had drifted slightly to the left of the runway centreline, although he had not felt a marked swing that would have accompanied an engine failure. He also recalled that the aircraft’s heading was still very close to the runway heading. After raising the landing gear, he put his hand back on to the power levers and Footnote 1 The torque limit the pilot used was marked by a solid red line on the torque gauge. See the later section on engine power. noticed that the left lever was approximately “half an inch” behind the right lever. He rebalanced the left lever and thought that the imbalance might have caused the aircraft to drift left. The pilot sensed that the aircraft’s rate of climb was not normal although he did not recall the actual rate of climb. He checked the primary engine indications 2 and stated that they “seemed normal”. No right rudder was required to keep the aircraft balanced and the pilot did not believe that the left engine had failed. He confirmed that the landing gear and flap were retracted (the takeoff had been made without flap), pushed the power levers forward to increase power and moved the propeller levers aft slightly, believing this would prevent the propellers from exceeding 2,200 rpm. The aircraft was climbing “but not well” and the pilot asked the controller whether he could return to the airport. He began a right turn intending to fly a circuit to the right and land back on Runway 26. The engine instruments still seemed to the pilot to be indicating normally, and the master warning system generated no warnings or cautions, but he had to lower the nose to maintain the speed above 88 kt, which was the Minimum Single Engine Control speed, V m c a . Shortly afterwards, the pilot realised that the aircraft was no longer climbing and decided to turn left to position for a return to Runway 08. As he began the turn, the EGPWS generated a sink rate warning indicating that the aircraft was descending. The pilot levelled the wings and, realising that the aircraft was still descending, decided to land in a field ahead. The pilot selected the landing gear down as the aircraft neared the field and moved the power levers to idle as the aircraft clipped some trees at the field boundary. Footnote 2 Torque, rpm, and Interstage Turbine Temperature (ITT). 10 © Crown copyright 2012 AAIB Bulletin: 2/2012 N46BM EW/C2011/05/03 After the aircraft came to a halt, he turned off the fuel and master switches and vacated the aircraft. Neither he nor the passenger was injured. The pilot stressed that his operating technique on this takeoff was no different than on any other. He could not understand at the time, or subsequently, why the aircraft had performed so differently on this occasion. Accident site details The aircraft landed in a large field approximately two miles west of Bournemouth Airport, having flown through some young trees on the southern bank of the River Stour at a height of approximately 10 ft and on a track of around 207º(M). It touched down heavily on all three landing gears in a slightly nose-down attitude. The nose leg detached and was found approximately 50 m from the trees together with additional small items of debris, mainly from the underside of the engine nacelles. Between approximately 90 and 100 m from the trees, coincident with a shallow dip in the surface of the field, ground marks suggested that the aircraft became airborne momentarily. Subsequently, the main landing gear collapsed/retracted and the aircraft slid along on its belly, rotated to the left and came to a halt approximately 180 m from the trees on a heading of 112º(M). The aircraft remained intact through the impact sequence although the main spar outboard of the left engine broke at some point. There was some creasing in the rear fuselage and there were numerous areas of damage on the leading edges of the wing and horizontal stabiliser caused by contact with the trees. The radome suffered significant damage and the radar antenna dish became detached. There was no fire. Propeller ground marks There was a short sequence of propeller blade ‘chop marks’ in the area of the initial touchdown point. The marks reflected the slight nose-down attitude at impact, which was probably accompanied by significant airframe and landing gear deflections. The distances between successive marks were approximately 60 cm and 56

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Beech 90, N46BM, 18 May 2011

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