AAIB Bulletin No: 4/2004

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1 Cessna F177RG Cardinal, G-BFIV AAIB Bulletin No: 4/2004 Ref: EW/G2003/09/06 Category: 1.3 Aircraft Type and Registration: Cessna F177RG Cardinal, G- BFIV No & Type of Engines: 1 Lycoming IO-360-A1B6D piston engine Year of Manufacture: 1977 Date & Time (UTC): 5 September 2003 at 1632 hrs Location: Blackbushe Airport, Camberley, Surrey Type of Flight: Private Persons on Board: Crew - 1 Passengers - 1 Injuries: Crew - None Passengers - None Nature of Damage: Damage to propeller blades and fuselage belly Commander's Licence: Private Pilot's Licence Commander's Age: 60 years Commander's Flying Experience: 2,031 hours (of which 1,600 were on type) Last 90 days - 27 hours Last 28 days - 7 hours Information Source: Aircraft Accident Report Form submitted by the pilot and further enquiries by the AAIB History of the flight The aircraft departed Blackbushe Airport for a return flight to Henstridge Airfield. On the downwind leg at Henstridge the pilot selected the landing gear down. He was then surprised by the sound of a mechanical 'graunching' noise from the rear of the aircraft. It became apparent that the main gear had not locked down and that it was partially extended, trailing aft in the slipstream but the nose gear had locked down. The pilot selected the landing gear up and then down again but the main gear remained hanging in trail. No 'graunching' sound was heard on this second attempt at extension. At this point the pilot decided to return to Blackbushe. During the return journey the pilot tried to persuade the main gear to lock down by manoeuvring at high and low 'g' and by flying very slowly whilst operating the landing gear emergency hand pump. When the hand pump was operated the pilot could feel the hydraulic pressure increasing and he was aware that the nose gear was extending properly. The pilot concluded from these perceptions that the main gear must have been jammed. During a fly-by of the tower at Blackbushe Airport the air traffic controller was able to confirm to the pilot that the main gear was trailing aft in the slipstream. Cessna F177RG Cardinal, G-BFIV 2 At this point the pilot realised that he was committed to an abnormal landing with resulting damage to the aircraft. There is no light aircraft maintenance facility at Blackbushe Airport so the pilot's passenger, who was also a licensed pilot, called Blackbushe Information and requested a diversion to Wycombe Air Park where the aircraft was maintained. However, Wycombe Air Park denied the aircraft permission to land there. The pilot then flew in circles to the north of Blackbushe for approximately 40 minutes to allow Blackbushe based aircraft to return to the airport before the runway was inevitably blocked by G-BFIV. During this period the pilot and his passenger decided on a plan of action for their emergency landing. They had the option of landing with the nose gear extended or retracted. The pilot considered that landing with the nose gear extended would possibly avoid damage to the propeller, engine and forward fuselage, but could result in large bending loads within the fuselage centre if the aircraft's weight was supported only at the nose and rear fuselage. He also thought that a wing would be more likely to drop after touchdown as the aircraft slowed down with the nose gear extended, than if the aircraft were sliding flat on its belly. For these reasons he decided to land on the aircraft's belly with the nose gear retracted. On final approach at approximately 50 feet agl the pilot and his passenger unlatched the doors, turned the master switch to 'OFF', set the mixture to 'IDLE CUTOFF', turned the fuel selector to 'OFF' and set the propeller pitch to coarse. The aircraft touched down and gradually slid to a stop with, in the pilot's words, "no real drama" apart from the noise. The pilot and his passenger exited the aircraft via the cabin doors. The fire and rescue service arrived quickly on the scene but there was no fire. Description of the landing gear system The Cessna 177RG's retractable landing gear is hydraulically actuated. The nose landing gear, which has its own hydraulic actuator, retracts rearwards beneath the engine and the main gear legs retract rearwards into open wheel wells in the aft fuselage. The main gear legs are mechanically linked and move as one unit; they are actuated by a single hydraulic actuator that is attached to the gear by an eye-shaped rod end. The actuator rod is fully extended when the gear is retracted. The rod retracts and pulls on the main gear attachment to extend the gear until the gear engages a lock in the down position. When hydraulic pressure is lost, the gear can free fall but it will not rotate forwards into the locked position by gravity alone. The aircraft has an emergency hand pump to provide hydraulic pressure to fully extend the gear. Aircraft examination Following the gear-up landing the aircraft was lifted with air bags. It was then discovered that the main gear could be pulled down by hand until it locked in the down position. An investigation by maintenance engineers revealed that the main gear hydraulic actuator rod end had failed. The actuator was no longer connected to the main gear and so it could not actuate the gear into the extended position. Actuator rod end examination The failed actuator rod end (see Figure 1) was sent to the AAIB for examination. The rod end appeared to have failed first at the greasing hole (surface A) and then the remaining attached strap had elongated plastically until it had failed in tensile overload (surface B). The rod end was taken to a metallurgist for further examination. The metallurgist confirmed that the strap fracture at surface B had failed due to overload. He also reported that the fracture surface at A did not show signs of a classical fatigue failure but it was possible that a very low cycle, high-stress fatigue mechanism had