Safety Matters and Safety Briefs are based on the AAIB Bulletin and UK Airprox Board reports, with additional material from the US National Transportation Safety Board
Flap misadventure, undercarriage mishaps and latest Airprox reports
Fatal full-flap takeoff
Aircraft Type: Cessna F150M Date & Time: 17 October 2016 at 1021 Commander’s Flying Experience: PPL(A), 363 hours, 9 on type Last 90 days: 7 hours Last 28 days: 2 hours The pilot had started flying from Bourn Airfield six months before the accident. At that time he had not been familiar with the Cessnas which were available at the local flying club, so he was checked out by an instructor in both a Cessna 150 and C152 and completed four hours of dual training, a proficiency check, twenty minutes of solo flight, and several subsequent flights accompanied by the same instructor. On the day of the accident he planned to take his father-in-law for a flight to Enstone and booked the C150, whose fuel tanks he was seen to top off to just below their filler caps. After pre-flighting he taxied to the threshold of Rwy 18, followed by a C152 with an instructor and student aboard, then radioed that that he was ‘rolling’. The C152’s occupants saw the aircraft get airborne but not apparently climbing, and realised that its flaps were fully deployed. The instructor tried to radio a warning to the pilot, but it was too late to be effective and there was no response. The C150 continued towards a line of trees beyond the end of the runway, its nose pitched up, its left wing dropped and it entered an incipient spin, descending quickly to the ground. People from the flying club and a nearby industrial site ran to the scene and helped the badly injured passenger from the aircraft. The unconscious pilot was released but rescuers were not able to sustain his breathing. Emergency services arrived and a paramedic continued to attempt to resuscitate him, but without success.
The aircraft had come to rest in a steep nose-down attitude against trees. Marks close to their bases indicated that it had struck the ground in a near vertical attitude The impact was consistent with it having been in a spin to the left, with the velocity vector primarily in the downwards, as opposed to horizontal, direction. The flaps were at their maximum 40° deflection, and absence of abrasion marks on them or adjacent fuselage structure indicated that they had been in this position prior to impact.
Until the accident flight the pilot had not flown a C150 without an instructor. Notes the AAIB: ‘Although [the C150] has many similarities with the C152, there are some significant differences. Flap selection and indication are different and the C152 has a greater available payload.’ ( Weight-and-balance calculations made by the AAIB suggested that, with full fuel, two occupants and 48 lb of baggage aboard, the C150 had been about 88 lb
above its maximum authorised weight — Ed.) ‘The C150’s flap switch does not give a visual indication of the selected position [though] final production models (this was an earlier aircraft) were fitted with a redesigned flap selector with detents for the flap position and a position indicator beside the switch. The C152 flap selection and indicator is similar, but the maximum flap travel was reduced from 40° to 30°.’
The aircraft’s Flight Manual included the following note: ‘Flap deflections greater than 10° are not recommended at any time for takeoff.’ The instructor who had previously flown with the pilot stated that he thought it was likely that 10° flap would have been selected for takeoff on the grass runway surface as this was the club policy and had been practised during the pilot’s training and familiarisation flights. The checklist in the aircraft’s Flight Manual does not include deploying the flaps prior to a walkround inspection, but the pilot’s commercially available checklist, like many others commonly in use, did include this action.
His instructor commented that the pilot’s use of the checklist was methodical and during training they had had discussions about the layout of this checklist, specifically that selection of the master switch ON as part of the ‘Internal’ checks before carrying out a long sequence of actions including retracting the flaps, might drain the aircraft’s battery. The instructor said that the pilot had made some marks on his checklist to highlight this problem. The checklist, recovered from the aircraft after the accident, was open at the ‘Vital Actions’ page which included selecting Flaps 10° for takeoff in accordance with club policy.
The AAIB report concludes: ‘The takeoff was attempted with 40° flap, probably unintentionally, which led to an inability to climb because of the additional drag. This was exacerbated by the aircraft being above its maximum allowable weight. A gentle turn to the left towards open ground or an early decision to abort the takeoff and land ahead could have prevented the accident. It is likely that the pilot did not realise why the aircraft was not climbing. A late attempt to retract the flaps would not have been an effective mitigation, as it takes approximately six seconds to fully retract the flaps and flap retraction would have caused a temporary loss of climb performance.
‘The flaps were seen to be fully deployed during the pilot’s pre-flight inspection and it was not determined whether they were ever retracted subsequently. The flap switch on this aircraft did not give any visual cue of the flap position, unlike the otherwise similar C152. Thus, the flaps may have remained deployed until takeoff, or may have been re-deployed prior to takeoff. In the latter case the pilot would not have intended to deploy full flap, so its selection would have been accidental. To deploy the flaps to 40° requires a sustained action on the switch for about nine seconds, so it is unlikely that this would be achieved by an accidental input, although it remains a possibility.
‘If the pilot had completed the actions as detailed on his amended checklist, that is, the master switch remaining OFF until immediately before engine start, then with no electrical power the flaps would not have retracted at ‘Item 8 Flaps — Up and check symmetrical operation.’ In this circumstance it is possible that the position of the flaps and their failure to move when selected UP escaped his notice.
‘The next opportunity to check the flaps through use of the checklist was as part of the ‘Vital Actions’, where the flaps are set at 10° for takeoff. However, there are eleven items in this section of the checklist and a further five items for the ‘Take Off’ checklist. It would be easy to overlook one action, and there is the potential for additional distraction with a passenger on board. It is also of note that the majority of the pilot’s previous flying had been in touring motor glider aircraft which were not equipped with flaps.
‘Significant differences exist in the design and operation of flaps between C150 and C152 aircraft. The C150 has the facility to deploy 40° flap, but inappropriate use of this flap causes performance penalties and handling problems which can lead to accidents for unwary pilots. The spring-loaded switch, as fitted to (the accident aircraft) and most C150s, does not give the pilot a visual cue of the selected flap position, unlike the C152’s. It is therefore important that this difference is emphasised during pilot training.’ However, the AAIB report notes that: ‘A mechanical flap position indicator was provided in the left forward door post/ windscreen pillar; in addition the flap extension could be seen from within the cockpit. The indicator consisted of a spring-loaded pointer running in a slot in the pillar, with calibration marks from 0°-40° degrees on the surrounding trim.’
The report continues: ‘There have been two recent accidents in the UK whereby the inadvertent use of 40° flap on the Cessna 150 has been a causal factor. It is considered that a greater focus during training/type familiarisation on flap selection and indication, and the effect of full flap configuration on aircraft performance and handling characteristics,
could prevent further accidents. The following Safety Recommendation is therefore made: That the Civil Aviation Authority promulgates to flying instructors the need for specific training to highlight the differences between the C150 and C152 flap switch designs. Training should also include the effect on aircraft performance and handling of Flap 40°.’ A General Aviation Safety Committee study of UK stall/spin accidents noted that there have been eleven such accidents on Cessna 150s but only one on a C152, with sixty per cent more hours flown by the latter type. It recommended that ‘The Cessna 150 and Cessna 152 should not be treated as the same type, and in particular pilots transferring from the Cessna 152 to the Cessna 150 should undertake formal Familiarisation Training.’
Left-hand, right-hand confusion
Aircraft Type: Maule Star Rocket Date & Time: 28 April 2017 at 1110 Commander’s Flying Experience: PPL, 183 hours, 20 on type Last 90 days: 7 hours Last 28 days: 7 hours The aircraft had flown from Goodwood to Eaglescott, whose airfield manager had taken a telephone call from the pilot when he requested PPR and advised him to arrive in the overhead at 2,000ft QFE for a standard overhead join for a left-hand circuit for Rwy 07. The pilot made the required radio call, and as he approached the overhead reported that he was letting down on the dead-side for a right-hand circuit on 07. The airfield manager said that as the radio calls were confident, and there was no other traffic, he did not correct the pilot, who then reported ‘Downwind Rwy 07’ at a position that the manager considered to be closer to the airfield than normal.
He continued to watch the Maule and noticed that after it had made a slight descent on the base leg it then flew a right orbit, so he made a radio call suggesting that the pilot go-around and complete a standard left-hand circuit. The pilot did not respond and continued orbiting. The manager then made a second call when the aircraft was pointing towards the airfield stating “Go-around, go-around, climb straight ahead, and perform a standard left-hand circuit.” The aircraft then seemed to make a 45˚ join onto final from base leg and when on final approach appeared to start a go-around. During this manoeuvre the aircraft descended but the pilot did not adequately monitor airspeed and it stalled. With insufficient height to fully recover, it crashed in a field short of the runway. Pilot and passenger were uninjured, but the aircraft was extensively damaged.
The AAIB comments: ‘The pilot had correctly written in his flight plan that he should fly a left-hand circuit. He used a tablet device to navigate and, en route, checked the airfield information recorded on the device, which stated that pilots should fly a right-hand circuit. On re-checking the airfield information on the device after the accident, the pilot realised that this referred to gliders and that fixed-wing powered aircraft should fly a left-hand circuit. With a passenger sitting in the front right seat, it would have been difficult for the pilot in the left seat to remain in sight of the runway when flying a right-hand circuit close to the airfield.’
Airmanship a key issue The UK Airprox Board reviewed seventeen aircraft-to-aircraft and fourteen aircraft-to-drone incidents at its July meeting. Five of the aircraft-toaircraft incidents were assessed as having a definite risk of collision (Category B), as were seven of the drone incidents.
‘The main theme this month was airmanship,’ says the Board. ‘[There were] five cases of sub-optimal integration with other aircraft either in the visual circuit or radar pattern; three incidents resulting from pilots not acting on traffic information or assuming that the other pilot had seen them; and three events involving pilots flying in airspace that they were not entitled to operate within or not fully understanding the implications of the airspace they were using.
‘As ever, the integration incidents were largely avoidable if pilots had thought ahead and allowed for the fact that the other airspace users might have been there, and two of these incidents happened when the pilots knew about the other aircraft, had it visual, but still got themselves into a situation where they ran out of ideas and options because they did not make early enough decisions.’
The Board’s Airprox of the Month involved a Piper PA-28 and Cessna 152 in the Biggin Hill circuit. The Piper’s pilot joined the circuit downwind and was aware that he was catching up on the C152 ahead. ‘He tried to slow down, assessed that he probably wouldn’t get his approach in, but thought he would continue, watch the C152 land, and go-around over the top of it,’ says the Board. ‘He turned base and final, but then found himself directly in conflict with the C152 and became uncertain of what he should do to resolve the situation. Running out of ideas, he ended up flying very close to the C152 before eventually going around. Shaken by the incident, the PA-28 pilot realised he should have done something about the situation much earlier, such as orbiting downwind, going around early, or even leaving the circuit entirely. However, having got himself into a situation where he was now so close to the other aircraft, he didn’t know what to do for the best.
‘Although it’s easy to be wise after the event, the lesson is that an early decision is the key to resolving any situation where your plan doesn’t seem to be working out. Although it’s sometimes difficult to swallow your pride, as the old adage goes “If there’s any doubt, then there’s no doubt” — make a new plan that removes the uncertainty. Full details of this and other incidents can be found at: airproxboard.org.uk in the ‘Airprox Reports and Analysis’ section.
The C150’s spring-loaded flap selector switch does not give the pilot a visual clue of the selected flap position
The the position of the C152’s flap selector switch indicates what degree of flap has been selected
Maule Star Rocket (not the accident aircraft) — see ‘Left-hand, right-hand confusion’