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
Sad outcomes, avoidable errors and the latest Airprox summary
Fatal power loss on takeoff?
Aircraft Type: Europa Date & Time: 28 May 2017 at 1200 Commander’s Flying Experience: LAPL, 1,146 hours, 880 on type Last 90 days: 7 hours Last 28 days: 1 hour The pilot was making his third flight in the aircraft that day. Witnesses saw it lift off from Coal Aston’s Rwy 29, but it did not appear to be climbing well, and as it passed them they heard the engine noise reduce and ‘splutter’. The Europa then started a left turn at the end of the runway before descending out of sight in a steep nose-down attitude, followed moments later by a ‘thud’. Witnesses south of the airfield who saw the aircraft flying very low in a banked attitude heard the sound of a crash, immediately alerted emergency services and ran to the accident site. The pilot had not survived the impact.
Although the aircraft was severely disrupted, wing and tail surfaces remained attached to the fuselage, which had crumpled in the engine/cockpit area, and the rear fuselage had detached. Flying controls were intact and there was no evidence to suggest that they would not have operated normally. The instrument panel was heavily fragmented so it was not possible to determine pre-impact switch positions. The rpm gauge was stuck at 4,100 rpm and the fuel pressure gauge at 0.14bar, which is below the 0.15 - 0.40bar minimum fuel pressure specified by engine manufacturer Rotax.
The engine’s fuel filter assembly was removed and its element was inspected. It was found contaminated with general dirt and debris which included insect remains. Flow tests carried out using the filter element fitted at the time of the accident and a new filter both recorded fuel flows well in excess of that required by the engine at full power.
A sample of the aircraft’s fuel was found to be consistent with forecourt unleaded fuel to EN228 specification and it contained 4.5% ethanol (E5 Mogas). Historically, suitable Light Aviation Association Permit aircraft such as this had been able to operate on unleaded Mogas to EN228 standard (forecourt unleaded fuel), but around 2010 fuel companies started to introduce ethanol [in response to an EU directive] to preserve fossil fuels. The usual choice is ethanol, currently not exceeding 5% by volume, and the resultant fuel is designated E5 Mogas.
Until late 2014 the CAA prohibited the use of Mogas containing ethanol in single-engine piston aeroplanes, but then transferred responsibility for choice of fuel and provision for appropriate guidance to the aircraft’s type design organisation, in this case the LAA, whose technical guidance notes: ‘A vapour return line must be fitted to circulate a small amount of surplus fuel, and any vapour back to the fuel tank’, while the manufacturer’s manual for the Rotax 912/912S engine, as fitted to this Europa, states: ‘The [vapour] return line prevents malfunctions caused by the formation of vapour lock.’
This accident aircraft/engine combination can be approved to use E5 Mogas and although it was fitted with the required placards, no logbook entry or checklist could be found to show the required procedure to use E5 Mogas had been completed or verified by an LAA inspector. Analysis of the aircraft and engine logbooks show that between June 2006 and June 2011 there were a number of reports of the engine ‘rough running’, but after rectification work and replacement of fuel and ignition system parts no subsequent reports were recorded, although the pilot’s personal flying logbook entry for a flight made ten months before the accident contained the annotation ‘Vapour lock – not nice’.
The AAIB report concludes: ‘The aircraft was seen to take off on the accident flight but it did not achieve a ‘normal’ rate of climb. The engine power was reduced although it was still producing power at impact. Evidence from the wreckage and witnesses suggests it may have been operating at approximately 4,000 rpm. This would represent about 40% of takeoff power, probably sufficient to maintain level flight or a small climb gradient, but any turn would diminish this performance…
‘The aircraft was at an estimated height of 100-150ft when the left turn began; starting to turn at such a low height suggests the pilot was aware of a problem… The partial loss of power could have led the pilot to consider a turnback, believing he could maintain height, but in the takeoff phase as soon as any turn is started the associated reduction in climb performance is likely to require a descent to maintain airspeed… The ground cues during the low level turn downwind could have given the pilot an impression of an increasing and higher than actual airspeed, and thereby led to a stall. Any pre-stall indications of buffet would have been very brief; a recovery from such a low height would not have been possible…
‘There was one significant anomaly relating to the fuel system that may have been relevant to the accident. The fuel vapour return line was connected to the inlet of the fuel selector valve, rather than to the fuel tank. This would have the effect of routing any fuel vapour that formed in the fuel system back to the engine instead of returning to the fuel tank to dissipate… The aircraft was using E5 Mogas, and although it was eligible to use this fuel, no evidence of the relevant procedures to approve its use could be found. The checklist that is completed as part of this procedure includes an inspection to ensure a fuel vapour return line is installed to route any vapours back to the fuel tank… [On this aircraft] it would have been returned to the engine, where it is likely it would disrupt its fuel supply, reducing the power it was able to produce.’
Height misjudgement on landing
Aircraft Type: Van’s RV-7A Date & Time: 12 August 2017 at 1325 Commander’s Flying Experience: LAPL, 88 hours, 43 on type Last 90 days: 23 hours Last 28 days: 8 hours This was the pilot’s third landing on grass, and his second on Sywell’s Rwy 23 that day. Surface wind was 280º/14kt. The aircraft was positioned over the runway centreline, but the pilot had difficulty judging his height above it and landed heavily on the aircraft’s nosewheel, which collapsed.
The propeller struck the ground and the aircraft slid to a halt in a tail-high attitude, resting on its lower engine cowling.
The pilot commented that just before touchdown he was not aware of any useful ground features in his field of vision to help him to judge his height accurately. The 30m wide runway’s edge markings are 3m x 1m chalked slabs, spaced 80m apart and slightly recessed into the ground, which he said were almost invisible just before touchdown and that the grass landing surface was too featureless to help him judge the aircraft’s height.
Sywell’s operator said that the markings on Rwy 23 accord with the CAA’S ‘Licensing of Aerodromes’ publication and had been re-chalked less than four months before the accident. The AAIB says that it has reported on several previous accidents in which the nose landing gear legs of Van’s Rv-series aircraft have bent back or collapsed, many of them occurring on grass runways. Its report also mentions an ‘Anti Splat kit’ for RVS which is intended to reduce nose gear resonance and prevent the nose landing gear leg from tucking under. The aircraft involved in this accident was so fitted.
Latest Airprox reports
At its October meeting the Airprox Board reviewed eighteen aircraft-toaircraft and sixteen aircraft-to-drone incidents. Seven of the aircraft-toaircraft incidents were assessed as Risk B: ‘safety much reduced either due to serendipity, misjudgement, inaction, or where emergency avoiding action was taken at the last minute’. Four of the incidents involving drones were Risk A, seven Risk B, most involving conflicts between drones and commercial airliners, but one concerned a Cessna 152 inbound to Biggin Hill. The pilot did not see it, but his non-pilot passenger, who had been alerted to look out for other traffic, reported that it was “about the size of a football and passed vertically level and about three light aircraft lengths horizontally” from the Cessna.
‘Because we work about four months in arrears, it’s usual at this time of the year when assessing the summer’s crop of incidents that late- and non-sightings account for many Airprox as folk got airborne in large numbers over the summer with sometimes rusty lookout,’ says the Board’s latest report. ‘Seven of this month’s incidents were attributed to this cause. That is not to criticise individuals, the limitations of the human eye in the aviation environment are well documented, as is the need to ensure a robust lookout and scan technique as a
result. It is simply that when other priorities, pressures or tasks start to distract us, discipline is required to overcome any lack of currency and maintain lookout as a key part of the “Aviate-navigate-communicate” and “Lookout-attitude-instruments” mantras. Something to think about when we all dust off our flying gloves again next year.’
Noteworthy in the report is an Airprox near RAF Linton-on-ouse involving two RAF Shorts Tucano turboprop trainers and an autogyro. ‘This incident primarily demonstrated how misunderstanding between pilots and ATC can suddenly snowball into a real issue,’ says the Board, ‘but the added uncertainty as to the intentions of the autogyro pilot as he flew near to the approach path of RAF Linton at 1,000ft certainly exacerbated the problem for them.
‘ATC were trying to be helpful by passing information to the Tucanos about a primary-only radar track (i.e. they had no height information) as they made a radar-to-visual recovery to Linton. Unfortunately, the Tucano leader misinterpreted their call and ended up unintentionally turning towards the autogyro he was trying to avoid. If the autogyro pilot had called up Linton ATC, then that would have removed all doubt as to his track, height and intentions, and therefore enabled ATC to provide the Tucanos, and perhaps him, with a better service.
‘There’s no requirement to make such a call of course, but if you can do so as you pass close to an airfield’s MATZ/ATZ then why not? Sometimes pilots worry that ATC will then try to control them, but they won’t: they might ask if you can help by altering course or height slightly, but simply offering them information is not an invitation for them to take over!’
To view the Board’s monthly reports in detail visit airproxboard.org.uk