Weight & Balance for Cessna 404 Titan

The aircraft was subjected to severe vibration. Some 2 to 4 seconds later, the oscillation of the control column ceased; it was observed that the right aileron had also partially detached and was trailing from the wing. The pilot managed to correct a slight bank to the right with left rudder, and then ordered the parachutists to leave the aircraft. This they did, with alacrity, at a height of approximately 2,500 feet, whilst the aircraft was still in cloud. They fell clear of the cloud at about 2,000 feet and landed safely in nearby fields. After the parachutists had left the aircraft in the vicinity of Wansford, 7 miles due west of Peterborough, the pilot headed south towards the aerodrome, roughly following the course of the River Nene. He reports that at this stage the aircraft began progressively banking to the right, despite the application of left rudder, until the aircraft remained banked at an angle of 45° to the right against full left rudder. Subsequently the aircraft entered an uncontrollable right turn which progressively tightened until the aircraft was heading and descending towards the village of Yarwell. At this stage, the pilot applied power to maintain a height sufficient to overfly the houses in the village; his airspeed was then in the region of 100 knots. The pilot further described how, after the application of power, the bank angle increased to approximately 60° to the right, still against full left rudder. After clearing the houses, he therefore decided that the only course of action open to him was to continue the descent and force-land before all further control was lost. Observers saw the aircraft in a right turn, descending into a field, where the right wing and right main landing gear struck the ground and became partially detached. The aircraft then pivoted to the right through 180° and came to rest upright, but in a 30° right wing low attitude. * For definition see 1.6.6 2 The pilot evacuated the aircraft by the right-hand main door, having sustained minor injuries and fuel burns to the skin. The burns had been caused by a massive fuel leak from the left wing as a result of the impact. There was no fire. 1.2 Injuries to persons Injuries Crew Passengers Others Fatal 0 0 0 Serious 0 0 0 Minor/none 1 8 1.3 Damage to aircraft The ailerons, right outer wing together with the right fixed gear, and engine became detached. The fuselage and tail assembly were buckled; the aircraft was damaged beyond economic repair. 1.4 Other damage Some fuel contamination to an unsown ploughed field. 1.5 Personnel information Pilot: Licence: Ratings: Medical Certificate: Certificate of Test: Total pilot hours: Total hours on type: British Parachute Association authority to drop parachutists: 3 Male, aged 25 years Commercial Pilot's Licence containing Groups A and B. The pilot was exercising the private privileges of his licence, which he is entitled to do under the Exemption to Article 39(2) of the Air Navigation Order. Part I Pilot-in-command, Gulfstream American series AA-1 and AA-5; Piper Twin Comanche series PA30, and PA39; Pilatus Turbo Porter PC-6 B2-H2. Last medical examination 29 January 1982, Class 1 with no restrictions. 29 September 1983 2,500 hours 700 hours of which 15 were acquired during the preceding 28 days. Initial authorisation was issued to the pilot on 28 April 1978. The then current authorisation issued on 29 April 1982, specified the Pilatus PC-6, Cessna 182, and Cessna 206 aircraft. 1.6 1.6.1 1.6.2 Aircraft information A general view of the aircraft is shown at Appendix 1. Leading particulars Type: Registration: Manufacturer: Date of Manufacture: Manufacturer's Serial No: Certificate of Airworthiness (C of A): Category: Issued: Valid to: Registered Owner: Engine: Propeller: Engine cycles: Total airframe hours: Maintenance: Last 100 hour check: Last 50 hour check: Aircraft weight and balance Maximum authorised weight: Pilatus PC-6/B2-H2 Turbo Porter G-BIZP Pilatus Flugzeugwerke AG, Switzerland 1981 812 Private 10 August 1981 9 August 1984 Peterborough Parachute Centre Ltd One Pratt and Whitney PT6A-27 Turboprop Hartzell HC-B3TN-3D 1,303 999.45 hours The aircraft was maintained to the Approved Maintenance Schedule No CAA/LAMS/FW/ 1978 30 August 1983 at 917.40 hours (coincident with annual check) 30 October 1983 at 972.20 airframe hours. 4,850 lb (2200 kg) Estimated take-off weight: 4,842 lb (2196 kg) Estimated accident weight: 4,770 lb (2164 kg) Estimated weight less 8 parachutists: Centre of Gravity limits @ 4,850 lbs: Calculated Centre of Gravity at take-off: 3,282 lb (1489 kg) 18.7 ins to 25.44 ins aft of datum (AOD), or 25% to 34% of Mean Aerodynamic Cord (MAC) 22.9 ins AOD, 30.6% MAC 4 1.6.3 Fuel Type: Quantity at time of accident: 1.6.4 Flight Manual airspeed limitations Jet A-1 (Avtur) approximately 58 US gallons (219 litres) 1.6.5 The Flight Manual ‘airspeed limits' are quoted in knots, calibrated airspeed (CAS), and correspond to the 'attention airspeeds' which are in knots IAS and marked on the face of the airspeed indicator (ASI). The relevant speeds are: (i) Never exceed (VNE) 151 kt (ii) Structural cruising (VC) 118 kt (iii) Manoeuvering (VA) 106 kt The ASI is marked with a green arc from 52 kt (flaps up speed) to 118 kt (VC). The arc from 118 kt to 151 kt (VNE) is yellow, and is known as the cautionary range. The VNE speed is marked by a red radial line. The normal operating speed (VNO) as defined in the British Civil Airworthiness Requirements (BCAR's) is, in this case, coincident with the Flight Manual VC of 118 kt. Effect on wing loading of varying bank angle and all-up weight Estimated wing loading, level flight, accident weight 15.48 lb/ft² Estimated wing loading, level flight, accident weight less 8 parachutists Estimated wing loading, 45° bank, accident weight 1.6.6 Operating procedures 10.72 lb/ft² 21.89 lb/ft² The following extracts from the PC-6 Airplane Flight Manual outline the operation of propeller pitch and power controls in the Beta range. "Propeller speed is kept constant at any pre-selected propeller control position by the propeller governor, except in the beta range where the maximum propeller speed is controlled by the pneumatic section of the propeller governor. Beta Range Beta mode operation of the propeller is used in flight to effect fast deceleration and high rates of descent. In the beta range, the propeller blades are set at a very low positive pitch angle to provide a braking effect for steep controlled descents. When operating in the beta mode, the propeller pitch angle is controlled by power lever movement between the lift detent and the point where constant speed operation becomes effective. NOTE: For optimum BETA MODE operation reduce airspeed to 100 mph or below." 5 1.6.7 1.6.8 1.7 The manufacturer's normally recommended technique for use in parachute operations is to descend at an IAS of 118 kt with beta mode selected. This technique is used by the operator of the only other aircraft of the same type on the UK register. However, because operation in the beta mode produces a considerably enhanced noise level compared with operation outside this mode, the manufacturer recommends operators in noise sensitive areas to descend at 140 kt with a torque setting of 10 psi (ie, outside the beta range). Aileron installation (see Appendix 2) The flaps and aileron control surfaces are similar in construction, the main difference being that the flaps have a slat attached to their leading edges. The outboard attachment of the flap to the wing (at mid semi-span) is shared with the inboard end of the aileron. The outboard end of each aileron is attached by means of a small triangular bracket on the wing tip fairing. An attachment at the mid span positions of the flaps and ailerons is similar in design to the shared flap aileron attachment. In each case, the control surface is attached to a mounting bracket which is secured to the wing underside by means of four bolts. The bolts are grouped in forward and rear pairs and located into anchor nuts which are riveted to the horizontal flange of an angle bracket inside the wing structure. The vertical flange of the angle bracket is riveted to the diaphragm that forms part of the structure of the wing. The manufacturer has stated that the rear angle bracket installation has been stressed to a design load of 4598 Newtons. The attachment is hidden from view by the lower surface wing skin, which has an average thickness of 0.58 mm. Each aileron consists of two halves joined at the mid span point, in line with the central mounting bracket on the wing. The joint is effected by means of the control horn which is linked to the aileron push-pull rod emerging from the wing, and the mounting bracket. The flanks of the control horn are also riveted to the abutting end ribs of the two aileron halves. The two halves are further linked at the trailing edges by a 'Flettner tab', which is a servo tab operated, when the aileron is deflected, by means of a rod attached to the mounting bracket. PC-6 fleet history Since the first flight of a piston engined PC-6 in 1959, some 440 aircraft have been built, including licensed production by Fairchild in the USA. The majority of these aircraft were turboprop variants, and production continues at the rate of 10 per year. Pilatus estimate that the world-wide fleet has accumulated in excess of 4 million flying hours, with high time aircraft having achieved more than 15,000 flying hours each. The aircraft is operated in a wide range of roles across the spectrum of climatic conditions. The aileron support installation has remained unchanged until revised by Service Bulletin (SB) 138 issued in December 1982 (see 1.17.2). Meteorological information Meteorological information was obtained from an assessment made by the pilot and an aftercast compiled by the Meteorological Office, Bracknell. Weather observations are not routinely made at Peterborough Sibson aerodrome, nor are they required to be. 6 Pilot's observation Surface wind: Visibility: Temperature: Cloud: south south-easterly 15 kt more than 10 km 14-15°C 7-8 oktas at 3,000-4,000 feet Aftercast Wind above 2,000 feet above mean sea level (amsl): Visibility: Height of 0°C isotherm: Cloud: Warning and remarks: 150° true, 30-35 kt 8-15 km 3,000 feet 1-5 oktas of stratus base 1,000-1,500 feet, tops 2,000 feet 4-7 oktas of stratocumulus layers between 3,500 feet and 6,000 feet moderate low level turbulence Statements by the pilot and parachutists do not, however, indicate that any significant turbulence was encountered. The accident occurred in daylight. 1.8 Aids to navigation 1.9 1.10 Not relevant. Communications The pilot was in RTF contact with the PPC on their own Air/Ground frequency of 129.9 MHz, and was able to inform them of the mishap to the ailerons. No other distress call was made. Aerodrome and ground facilities Peterborough (Sibson) aerodrome is operated by the Peterborough Aero Club, and has two grass runways: runway 07/25, 703 metres long and 30 metres wide; and runway 15/33, 551 metres long and 18 metres wide. The aerodrome is 100 feet amsl. There is an Air/Ground radio service, with call-sign 'Sibson Radio', on 122.3 MHz. The PPC is based at, and principally operates from, Sibson. 1.11 Flight recorders The aircraft was not equipped with a flight data recorder or cockpit voice recorder, nor were these required to be installed. 7 1.12 1.12.1 Wreckage and impact information On site examination The activities of recovery vehicles in the area around the wreckage had completely obliterated the ground marks caused by the aircraft at impact. Accordingly, it was not possible to verify the impact parameters as described by the pilot and witnesses. Nevertheless, the detachment of the right-hand main gear, plus the damage to the outboard section of the right wing and to the nose area, was clear evidence of a significant angle of bank to the right at impact. It became apparent that one half of each aileron was missing from the wreckage. The outboard half of the right aileron, complete with mass balance, was discovered 1.6 miles north-east of the accident site. The inboard half of the left aileron was found in a field approximately 0.5 miles north-west of the right aileron portion, 1.7 miles from the accident site. Prior to recovery of the wreckage, the wings had been removed from the fuselage. This operation was carried out by the chief engineer of the company which maintained the aircraft, and he had verified that there had been no pre-impact disconnection to any of the flying controls running through the wing root area. 1.12.2 Subsequent detailed examination The wreckage was removed to a hangar at Sibson aerodrome, where an examination of the flying controls revealed no evidence of a pre-impact failure or disconnect in the aileron circuit upstream of the aileron push-pull rods. The rudder, elevator and flap systems were all intact and it was evident that, at the moment of impact, the flaps had been retracted. As found, the position of the rudder trim indicated 2 units (out of 6) right rudder trim selected. The pitot system was checked for freedom from obstruction and the airspeed indicator was subjected to a calibration check, which proved satisfactory. Subsequently the wings and aileron fragments were removed to the AIB facility at the Royal Aircraft Establishment at Farnborough for detailed examination. It was found that both left and right ailerons had become detached in an identical manner, the initial failure occurring at the central of the three attachments. In each case, the mounting bracket had pulled out of the wing undersurface, causing the centre portion of the aileron to be no longer restrained in the vertical plane. The resulting motion had caused each aileron push-pull rod to be 'guillotined' at the point where it passes through a span-wise stringer in the rear of the wing. The position at which the rods had been severed indicated that the ailerons had been approximately neutral at the time of the occurrence. Following the failure of the central attachment, each half aileron would have been tenuously joined to its neighbour by the aileron control horn and the trailing edge Flettner tab. After these had failed, it was evident from examination of the inboard and outboard attachments that each aileron half had drooped downwards and rearwards. In both cases, the aileron mounting bracket had remained with the inboard half. The left aileron inboard attachment to the shared flap/aileron mounting bracket and the right aileron outboard attachment had both failed in the air, with the resultant 8 1.13 detachment of the two half ailerons. It was clear that impact forces had caused the final failure of the attachments of the aileron sections that had remained with the aircraft. Despite the loads to which the shared flap/aileron attachment must have been subjected, both mounting brackets had remained attached and bore no external signs of distress. Examination of the central aileron attachments revealed that separation was caused by failure of the angle brackets within the wing into which the mounting brackets are bolted. In the case of the left wing, both forward and rear angle brackets had failed in the radius between the vertical and horizontal flanges. In the right wing, the rear angle bracket had failed in the radius whereas the forward bracket had been pulled intact from the wing, due to failure of the rivets attaching it to the diaphragm. A metallurgical examination revealed the presence of fatigue in each of the rear angle brackets. Damage to the fracture faces precluded any assessment of crack propagation rate; however, it was established that the cracks had resulted from the coalescence of a number of origins along a line coincident with the bases of the anchor nuts located on the horizontal flange of each angle bracket. Photographs of the failed brackets are presented at Appendix 3a and 3b and it can be seen that the fractures follow the outline of the anchor nut bases along part of their length. In particular, it was noted that fatigue had extended along 20 mm and 42 mm respectively of the total length of the fractures on the left and right wing angle brackets. The metallurgical examination revealed no defects in the material specifications of the angle brackets. The aileron stops, which are located on the bellcrank that is attached to the forward end of the aileron operating rod, bore no signs of excessive impact that might have been indicative of high amplitude control surface oscillation. In the structurally intact left wing, the control cables that link the wing root bellcrank with the aileron operating bellcrank were still intact. No significant wear was observed in the Flettner tab operating mechanism or hinges that might have contributed to aileron instability. Medical and pathological information Not relevant. 1.14 Fire There was no fire. 1.15 Survival aspects The pilot and the eight parachutists survived the accident. The parachutists were fully equipped, and had been ready to jump; on the advice of the pilot, they abandoned the aircraft. All were well experienced and jumped at a height well above the minimum of 500 feet agl recommended in the British Parachute Association's Parachuting Pilot's Brief. All eight landed safely. 9