Safety Matters and Safety Briefs are based on the AAIB Bulletin UK Airprox Board reports, with additional material from the US National Transportation Safety Board
Slingsby spin fatalities, a cliff-hanger, and a Chinook close encounter
Wrong spin recovery action?
Aircraft Type: Slingsby T67M MKII Firefly Date & Time: 30 April 2016 at 0938 Commander’s Flying Experience: PPL, 215 hours, three on type Last 90 days: 34 hours Last 28 days: 14 hours The pilot and passenger were students on the Tucano phase of their RAF flying training, having flown Grob Tutors during their initial training. After takeoff from Full Sutton they tracked towards the Castle Howard estate, where witnesses saw the T67 perform a loop. On the downward half of the manoeuvre the aircraft appeared to enter a spin, during which the engine was initially heard to cut out, then seemed to restart before cutting out again. The witnesses lost sight of the aircraft as it descended behind the roof of an outbuilding, then heard the sound of an impact.
Other witnesses reported a ‘corkscrewing’ motion before the Firefly crashed into a ploughed field in a steep nose-down attitude. It had come to rest upright. The engine was partially buried, at an angle around 50º to the horizontal. There was severe disruption to its structure. Both wings had suffered severe leading edge damage, and their left and right fuel tanks had split open, with no fuel left in either. The fatally injured pilot and passenger were each found to be holding the top part of their respective control columns, which had broken off in their hands. The pilot was holding his stick with both hands, the passenger with just his right hand.
The Ppl-rated pilot had started flying in November 2009, and flew Grob Tutors until November 2012. In July 2014 he started training as a RAF student pilot, completing his basic course on Tutors in February 2015 after accumulating 152 hours, during which time specific spin training was undertaken. In November 2015 he started training on the Shorts Tucano and had completed 63 hours in the aircraft, 21 hours in a flight simulator, and had carried out spin training in the Tucano in the early stages of his course. He had recorded four flights in the T67 — two dual check flights and two as PIC. The instructor who cleared him to fly the T67 in January 2016 had not carried out spin training, so the pilot had not been taught type-specific spin recovery on the aircraft.
The passenger started basic training in August 2015 as a RAF student, accumulating 59 hours on the Tutor during which he would have carried out spinning and spin recovery training. He had logged 5.7 hours on the Tucano, but had not yet carried out spin training on that type. He did not hold a civilian licence.
Three months prior to the accident the pilot and another student pilot had flown together in a T67 and recorded their manoeuvres on camera. The footage showed them sharing the flying and performing aerobatics. This colleague recalled that, following a reverse stall turn that was obviously not going to be completed, the accident pilot took the recovery action of ‘throttle to idle and control column centralised’. He then put the throttle to full power and the engine
returned to full power quickly, but not smoothly. After the flight, the pilot remarked that the reason he used full throttle was that he realised that for an incipient (spin) recovery he should have left the throttle at full power. Closing the throttle was part of the incipient spin recovery action for the Tucano on which he was then training.
When compared with the spin recovery action for the Grob Tutor and Tucano, the Slingsby T67 differs in that the control column must be moved progressively forward to effect spin recovery. Initially on moving the stick forward the rate of spin rotation will increase before coming out of the spin. Application of Tutor or Tucano spin recovery technique by placing the stick in a central position is not the correct recovery action for the Slingsby.
The AAIB report concludes: ‘Despite the extensive damage to the aircraft it can be determined that there had been no structural failure or loss of control surfaces in flight. The ground marks and damage to the aircraft suggest the outer portion of the right wing leading edge hit the ground simultaneously with the propeller spinner, suggesting a slight left yaw. The clear imprint made by the right and left wing leading edges on the ground at impact showed no evidence of rolling or spinning of the aircraft at this point. Examination has found that there was continuity and operation in the correct sense of the flying control system and that there was no pre-accident fault or control failure of the aileron, rudder or elevators.
‘From witness evidence, the aircraft appears to have inadvertently entered a spin from some form of looping manoeuvre shortly after the apex of that manoeuvre. From the recorded radar data, the altitude at that point was probably between 3,500 and 4,000ft, which should have provided sufficient height for the spin to have been stopped and the aircraft pulled out of the dive if spin recovery action had been taken correctly and promptly. The same witness also described hearing the engine faltering during the descent but no physical evidence has been found to suggest an engine problem. It is possible the witness was hearing the effect of rapid opening or closing of the throttle, coupled with the masking effect on the engine sound as the aircraft rotated during the spin. Both pilot and passenger had been taught spin recovery in the Grob Tutor. The pilot had undergone a Slingsby T67 check flight… with the club CFI which was a single circuit and did not cover aerobatics or spin recovery.
‘The spin recovery action in the Grob Tutor, and in the Tucano, requires that following the application of opposite rudder, the control stick is centralised. This is taught by using both hands in the Tucano and there is no requirement to move the control stick forward. In the Slingsby T67, the control stick should be moved progressively forward until the spin stops and with an aft centre of gravity the flight manual emphasises that the pilot must be prepared to move the control stick fully forward. As the stick is moved forward the spin’s rate of rotation initially increases.
‘The aircraft appeared to have descended in a spin. However, aircraft attitude and ground marks at impact suggest that it had started to recover, albeit too late to avoid hitting the ground. An instructor who regularly spins this aircraft type states that if the correct recovery action is taken, the aircraft will come out of the spin. Given that the aircraft may have been in the process of recovering from the spin in the very last moments of the descent, it is possible that an incorrect spin recovery technique was used, as the requirement to move the control stick progressively forward is a critical element of the spin recovery action in the Slingsby T67. This was not a requirement for spin recovery in the Tutor or Tucano, aircraft on which the pilot had previously received spin training. It is possible that if the pilot initially adopted the technique applicable to those aircraft, the spin recovery would have been delayed.’
Unexplained turn on takeoff
Aircraft Type: Zenair CH 601 XL Zodiac Date & Time: 22 August 2015 at 0820 Commander’s Flying Experience: French ULM Pilot Certificate, 670 hours, 64 on type Last 90 days: 40 hours Last 28 days: 15 hours Having flown in to Sandown Airport from France the previous day, the pilot was departing for the return trip. After lifting off, the aircraft immediately started to turn left, then pitched up and momentarily reached a steep nose-high attitude, before adjusting to a more normal climb attitude. The pilot, who had not intended to turn left, later reported that he reduced power at a height of about 30ft to keep the aircraft tracking straight ahead. Once the track appeared to straighten, he reapplied power. The flight continued in a nose-up attitude and in a banked skidding turn to the left. It straightened momentarily, lost height, and appeared to enter a stall and incipient spin to the left.
The aircraft, which had been airborne for a total of twenty seconds, crashed
into a grass field 300m to the north of the Rwy 05 threshold and caught fire. The pilot, who was seriously injured, was helped out and given emergency medical assistance before being transferred to a local hospital.
There were a number of eyewitnesses to the accident, and there was also a video recording of the entire flight, together with still photographs taken from alongside the runway. The displacement of the flight control surfaces could be seen in both the photographs and the video footage. At the start of the takeoff roll, the ailerons were in the neutral position and approximately half flap was deployed. The aircraft appeared to accelerate normally along the runway and directional control was maintained. It bounced into the air briefly once or twice, before lifting off after a ground roll of approximately 350m. It immediately started to bank left. Right aileron and right rudder control deflections could be seen, but the left turn continued. The initial climb to a height of about 80ft was steep, and then the climb rate reduced, although a nose-up pitch attitude was maintained throughout. Right rudder and right aileron inputs were apparent throughout the remainder of the flight but the aircraft continued turning left, apparently flying slowly. As it reached almost the reciprocal of the original runway heading there was a marked loss of height, the left wing dropped and it entered an incipient spin.
The AAIB commented: ‘There could be a number of possible reasons why the aircraft made an unintended turn to the left, as it lifted off the ground. However, there was insufficient evidence to identify any particular factor. Once the aircraft had turned away from the runway track, the pilot’s options were limited by the obstacles in his path. The nose-high attitude probably led to a reduction in airspeed, thereby reducing the effectiveness of the flight controls and ultimately leading to a stall… There was insufficient evidence to establish why the aircraft had behaved as it did and why the accident occurred.’
Aircraft Type: Europa XS Date & Time: 10 August 2016 at 1015 Commander’s Flying Experience: PPL, 918 hours, 438 on type Last 90 days: 49 hours Last 28 days: 11 hours When the aircraft arrived overhead the unlicensed grass airfield at Hollym, Yorkshire, the windsock showed surface wind from 310° at less than 10kt, so the pilot decided to land on Rwy 32, which he had last used four years previously. The runway’s first 150m is bounded by a fence on its left side and a cliff, down to the sea, to the right. Thereafter, the left side of the runway opens out onto the main grass airfield and parallels the cliff.
During its landing roll the aircraft slewed to the extreme right side of the runway. Its tailwheel went over the edge of the cliff and, at low speed, it fell tail-first off the cliff into the sea. The accident was not witnessed by anyone, so the emergency services were not initially alerted, but after a few minutes the pilot retrieved and activated his personal location beacon and after some thirty minutes was able to make his way up the cliff to a nearby house. Help then arrived and he was transferred to hospital for treatment to minor injuries
This Europa was a monowheel version, with retractable outrigger wheels mounted on each wing. Following the accident, the right outrigger was found on the runway near the cliff edge. It had failed below its attachment to the wing. The outriggers are described in the aircraft’s owner’s manual as ‘exceedingly
strong and pliable so there is no need to be overly concerned about turning sharply or rough field operation. The outriggers will, if necessary, bend through 90º degrees. However, they are not designed to take significant vertical loads and, on rare occasions, do fail.’
The pilot later commented that the last time he had landed at Hollym, Rwy 32’s mown strip was bounded on both sides by significant fallow ground, providing some margin for error. Reviewing the airfield entry in commercially available flight guides had appeared to confirm to him that this was still the case. At the time of the accident the runway was reported as being fifteen metres wide, with a sketch showing a clear area on each side. However, coastal erosion in the area averages two metres per year, with the cliff on the right of the runway being undermined by the sea and then collapsing in stages. This had resulted in the runway being moved to the left, until it abutted the fence, while the sea continued to erode the ground to the right of the runway.
The CAA’S CAP 793 Safe Operating Practices at Unlicensed Aerodromes recommends that for aircraft with MTOWS of less than 2,370kg, minimum runway width should be 18m. Since this accident the airfield operator has informed the publishers of various flight guides that runway width is now 10m and requested that they include a warning to ‘Beware cliffs on the east side of the airfield’.
Helicopter/ model aircraft conflict
A RAF Chinook helicopter was transiting to Colerne at low level when the handling pilot saw rising ground ahead and started to climb, whereupon a crewmember called that he’d seen a white, fixed-wing model aircraft approximately one metre in length pass just above them. The location was noted and the grid reference passed onto operations staff. No model aircraft flying had been published by NOTAM in the area and no other crew members saw the model aircraft. The Chinook pilot was operating under VFR in VMC and not in receipt of a service but listening out on the UHF low-level common frequency. The model operator could not be traced.
The UK Airprox Board noted: ‘All model operators are required to observe ANO 2016 Article 94(2) which requires that the person in charge of a small unmanned aircraft [a model aircraft] may only fly it if reasonably satisfied that the flight can safely be made, and the ANO 2016 Article 241 requirement not to recklessly or negligently cause or permit an aircraft to endanger any person or property. A CAA website provides information and guidance associated with the operation of Unmanned Aircraft Systems (UASS) and Unmanned Aerial Vehicles (UAVS) and CAP722 UAS Operations in UK Airspace provides comprehensive guidance.
‘In the low level environment some risks are unavoidable if realistic low flying training is to be conducted and a good lookout remains the only mitigation against this sort of Airprox. The model operator was within his rights to be flying his model and it was potentially the low flying and use of terrain masking [by the Chinook] that was a factor in preventing either the model operator or the Chinook’s crew having sufficient time to take any avoiding action. As to what effect a model aircraft with a one-metre wingspan would have if the two had collided remains unknown.
‘The Chinook did not appear on radar recordings… [which was] unsurprising considering the Chinook’s altitude. It was regrettable that the model aircraft operators could not be traced, because without their narrative it was not possible to understand the situation from their perspective… The speed and low altitude of the Chinook was an operational measure designed to prevent detection and this may have worked by denying the model aircraft operator the chance to fly his model away from the Chinook. The model aircraft operator was entitled to use Class G airspace and outside the boundaries of a club or national event [it was] unlikely that a NOTAM would be raised. Ultimately, the aircraft flew into conflict with each other and… with the model passing over the Chinook and neither of its pilots seeing it, collision seemed to have been avoided by providence alone.’ The Board assessed the incident as a Risk A.
Although mitigated through modifications and additional pilot training, Monowheel Europas have suffered a number of loss-of-control landing accidents
The XL is the ultralight version of the CH 601, a popular kitplane (this is not the accident aircraft)
The Slingsby T67 Firefly is one of the few aerobatic trainers available in recent years and is used by many clubs around the country
Model flyers: beware Chinooks flying ‘nap of the earth’ and Chinook crews: beware unsuspecting model flyers!