AAIB Bulletin: 7/2009 G-RVRG EW/C2008/07/03

were no apparent defects with the pitot-static system. The engine was examined externally. The rocker covers were then removed to check valve gear operation whilst the engine was rotated by hand. The spark plugs were removed to allow a borescope inspection of the pistons, cylinders, valve heads and valve seats. No defects were noted and the condition of the components examined was consistent with normal operation and with the life of the engine. Fuel samples were taken from both the left and right tanks. Preliminary visual examination found them to be satisfactory and free of contamination. Sixty litres of fuel were recovered from the tanks. Initial inspection by the Fire Service indicated the fuel selector valve was in the off position, but a later more detailed inspection confirmed the valve was selected to the left position. The fuel selector is a rotary valve that has left, right and off positions. To prevent inadvertent selection, a spring-loaded pawl needs to be moved away before off can be selected. The valve is located near the base of the firewall and is connected to the selector lever at the base of the centre instrument panel by an extension rod. When interviewed afterwards, the passenger, perhaps as a result of the briefing she received from the instructor in a similar type aircraft, demonstrated a good understanding of the function and location of the various cockpit controls. She stated that she did not recall the fuel selector being moved by either occupant before or after the accident. The valve body may have been displaced in the impact which in turn displaced the selector lever, leading to the misleading indication. Performance A loadsheet produced after the accident indicated that the aircraft was within weight and balance limits, with a fuel load of 78 litres and a takeoff weight of 1,658 lb. The Pilot’s Operating Handbook (POH), produced by the manufacturer, indicated that at the maximum takeoff weight of 1,670 lb the stall speed of the aircraft in standard atmospheric conditions would be 53 kt. At this weight, and in the conditions reported at the time of the accident, the takeoff run would be approximately 250 metres. The manufacturer notes that published data are based on flight tests of a new aircraft in standard configuration and do not allow for physical deterioration, pilot technique or runway surface. High humidity also has a detrimental effect on the performance of normally aspirated piston engines for which no consideration is made in the POH. Nevertheless, continued successful operation of this aircraft type at Barton indicates that it is capable of achieving satisfactory performance for takeoff from Runway 09R. Aerodrome information Barton Aerodrome (City Airport Manchester) is situated on the western edge of Manchester and bordered to the east by a contiguous built-up area. It has four licensed grass runways, two of which are aligned east-west. One of these, Runway 09R, has a takeoff run available of 621 metres. The aerodrome is susceptible to waterlogging and has several notable humps which are locally known to be sufficient to cause aircraft close to takeoff speed to become momentarily airborne. The aerodrome operator has an ongoing program of works that attempt to maintain the manoeuvring areas in satisfactory condition. 31 © Crown copyright 2009 AAIB Bulletin: 7/2009 G-RVRG EW/C2008/07/03 An accident1 in which a similar aircraft failed to become airborne safely from Runway 09L at Barton was found to have resulted from an excessive nose-up pitch input and not from inadvertent launch from one of these humps. Aircraft routinely operate from Barton without incident and there is no evidence that the presence of such humps is unduly troublesome. Aerodrome standards Civil Aviation Publication (CAP) 168 – ‘Licensing of Aerodromes’ gives guidance to licence holders on the procedures for the issue and continuation of or variation to an aerodrome licence and indicates the licensing requirements used for assessing a variation or application. The section relating to unpaved surfaces (including grass runways) states, in part: ‘Natural surfaces of unpaved runways should be prepared or treated to remove irregularities which might adversely affect the directional control, braking or riding characteristics of an aeroplane.’ and, ‘A simple method of assessing the evenness of a natural surface is to drive over it in a Land Rover or similar vehicle at 30 mph. If the surface is acceptably even, this test should be accomplished without discomfort to the vehicle occupants.’ Operator procedures The instructor, who most frequently flew from the operator’s base at Liverpool Airport, had been briefed on procedures for flying at Barton and had been assessed on his ability to follow them by the operator’s Chief Footnote 1 AAIB reference EW/G2006/09/13 published in the Bulletin 2/2007 Flying Instructor. The aircraft operator has also issued written orders to its instructors concerning operation at Barton. In particular, it requires that aircraft contain no more than 78 litres of fuel prior to departure in order to restrict maximum takeoff weight and reminds pilots to ensure that ‘rotate speed and climb speed’ are achieved before allowing the aircraft to become airborne. Discussion Based on information published in the POH and the continued successful operation of the type at Barton, it is likely that the aircraft was capable of taking off from Runway 09R in the prevailing conditions. Despite containing undulations, which are known to cause aircraft to become airborne before intended by their pilots, there is no evidence that the surface of Runway 09R has caused similar accidents to this one. When an aircraft becomes airborne at its stall speed there is no performance margin and a change in flight path or control input may result in development of the stall. Aircraft of this type generally have insufficient power to accelerate away from the stall whilst climbing. Conclusion The aircraft was in an airworthy condition and operating normally immediately prior to the accident, which occurred when the aircraft failed to achieve the proper takeoff speed before becoming airborne and stalled during the attempted forced landing.