Safety Matters and Safety Briefs are based on the AAIB Bulletin, with additional material from the US National Transportation Safety Board
Pioneer fatality, Merlin malfunction, and more on air displays
Technical fault, weather & high workload
Aircraft Type: Alpi Pioneer 400T Date & Time: 3 January 2015 at 1528 Commander’s Flying Experience: PPL, 201 hours, 5 on type) Last 90 days: 7 hours Last 28 days: 2 hours After an overnight stay on the Isle of Wight, the pilot and his wife and son were returning from Bembridge Airport to the aircraft’s base near Evesham. The weather was overcast and misty so the pilot made arrangements to stay a second night if necessary but later, when he judged that there was sufficient improvement in the weather, he took off from the unmanned airfield at 1500. A retired military pilot saw the aircraft take off. He lost sight of it due to poor visibility when it was about two miles away from him, when he estimated the cloud base at no higher than 1,000ft agl, and when rain began to fall thirty minutes later it reduced to an estimated 300ft/ half-a-mile.
In Popham’s clubhouse several people heard the sound of an aircraft whose height was estimated at 150-400ft agl, just below the cloudbase. One pilot, who was also a qualified technician on Rotax engines, one of which powered the Pioneer, remarked that the engine sounded as if it had a problem. A witnesses who watched the aircraft as it was close to Popham’s western boundary saw it turn left and cross the A303 road which parallels the airfield at an estimated 70-80kt and 200ft agl, apparently on a left base leg for Rwy 03 but ‘too low’. He was surprised when the engine seemed to be throttled back and become quieter while the aircraft descended gently. Other witnesses saw it descending eastwards and pass through the extended centreline of Rwy 03 until it was hidden from view by trees. A passing motorist reported that its wings were ‘wobbling’ and its nose was ‘going down and up’. When he lost sight of it he called the police, as did Popham’s radio operator as he was concerned for the aircraft’s
safety after it disappeared from view. An air ambulance helicopter quickly located the Pioneer’s wreckage in woodland about a quarter of a mile south-east of the airfield. The pilot and his wife had suffered fatal injuries. Their son, who was in the right front seat and seriously injured, was extracted from the inverted fuselage nearly an hour after the accident when the fire service arrived. He later said that he had been told to brace for impact but was unable to recall anything else about the flight.
Detailed examination of the aircraft and its systems by the AAIB revealed chafing damage to the throttle position sensor wire in the wiring loom that was not consistent with impact damage. ‘The damage to the wire from the throttle position sensor to the turbo control unit (TCU) would have created a ground on the wire, causing the TCU to drive the wastegate of the turbo fully closed and trigger an orange flashing TCU warning light on the instrument panel,’ says the AAIB report. ‘It is also likely that engine manifold pressure and rpm would have increased in response to the turbo becoming active, although with the throttle below the takeoff power position, it is unlikely the engine would have exceeded any operating limitations at this point.
‘Given a warning notice contained in the engine’s Operator’s Manual [and the pilot’s] familiarisation training [in the aircraft], it is likely that his response was to isolate the electrical power to the TCU by pulling the circuit breaker. This would have frozen the servo valve and thus the turbo wastegate in the fully closed position. It would also have prevented the overspeed protection logic and the orange and red warning lights from working… [Thus] the pilot may have diverted to Popham to minimise the flight time with a turbo fault, or it may have been because the weather was too poor to continue. Popham was near the planned route, he had passed it on the [previous day’s] flight south, and he was likely to have had it displayed on the navigation app on his tablet computer. The subsequent descent and track, recorded on radar, are consistent with this. The lack of any radio call to Southampton or to Popham, and the fact that the Popham frequency had not been selected, suggest the pilot was fully occupied as he dealt with poor weather, a malfunctioning turbo and diverting to an unfamiliar airfield.
‘With the turbo wastegate fully closed, the pilot would have had to limit the throttle position to keep the engine parameters within limits. With the TCU not powered, the only additional warning of an engine exceedence was the rpm display on the Engine Information System turning yellow and then red. However, this display was very small and the pilot may have overlooked it when he was preparing to land at an unfamiliar airfield in poor weather. If he conducted a go-around from an approach to Rwy 26, he managed to do so without causing a catastrophic engine exceedence. However, during the subsequent circuit, when heading east the engine stopped and the aircraft stalled into trees.
‘It was not possible to determine whether the pilot inadvertently selected too high a throttle position, was unaware of the potential consequences of depowering the TCU, or he had no alternative in order to try to maintain airspeed and altitude. However, with the TCU protection logic disabled, there was no limit on the manifold pressure produced by the turbo until it reached its maximum performance. The engine manufacturer confirmed that excessive manifold air pressure could result in misalignment of the engine crankshaft to an extent that the engine would seize. The evidence from the engine strip and the location and lack of damage to the propeller blades support the conclusion that the engine stopped in flight for this reason. One witness noticed the engine noise reduce before the aircraft was lost from view. ‘Whilst a very specific defect occurred on this aircraft, the engine was still capable of being operated safely with an increased level of pilot monitoring and awareness. It most likely only stopped as a result of the throttle being moved by the pilot to a setting where a damaging level of manifold pressure was reached. Regardless of this, pilots with an SEP Class rating are trained in the need to anticipate engine failures for any reason and to conduct forced landings when necessary.
‘The pilot apparently warned the passengers to brace, indicating that he was conscious immediately before the accident and aware that the aircraft was about to crash. With no engine power available, it is possible that the pilot retracted any flap that had already been extended in an effort to extend the glide and clear the trees. Retracting the flap would have reduced the drag but it would have increased the stall speed, and the evidence from the car driver suggests that the aircraft stalled before it struck the trees.’
In regard to weather conditions during the flight, the AAIB notes: ‘When the pilot reached the mainland coast it was likely that he saw a deterioration in the weather that eroded the safety margins for VFR flight. At this early stage it would have been prudent to divert to a suitable nearby airfield or to have turned back to Bembridge… The poor weather conditions at Popham meant the pilot, who had limited flying experience, especially on this aircraft type, had to fly below the normal circuit height. This would have increased his workload and reduced the time available in which to make critical decisions. When combined with the additional workload created by the engine fault, this may have led to the circumstances surrounding the failure of the engine and would then have limited the options available when confronted with the need to perform a forced landing.’
As a result of this accident the AAIB has made recommendations to the aircraft’s airframe and engine manufacturers regarding the functions of engine and TCU warning lights and appropriate actions to be taken, and the design of Rotax 914 wiring looms. The Light Aviation Association, under whose auspices the aircraft was operated, is conducting reviews of differences training requirements for pilots operating aircraft with turbocharged engines, and also the minimum requirements for instrumentation and wastegate control systems for this type of engine.
Aircraft Type: Spitfire IX Date & Time: 1 August 2015 at 1300 Commander’s Flying Experience: ATPL, 7,710 hours, 294 on type Last 90 days: 145 hours Last 28 days: 52 hours After takeoff from Rwy 29 at Biggin Hill the pilot retracted the undercarriage and reduced power to 2,400rpm and +4 boost but, one or two seconds later, he heard the engine ‘cough’, so he turned the aircraft back towards the airfield, intending to climb overhead to investigate before proceeding. A few seconds later the engine lost power and the pilot could see flames coming from the right-hand exhaust pipes.
He had only about ten to twenty per cent power, just sufficient to reach the airfield, but not to reach a runway, so as the boundary was crossed the pilot levelled the wings and landed straight ahead, fearing that otherwise the aircraft might stall. The Spitfire touched down on its main wheels on waste ground and was heading towards a line of trees. The pilot tried to steer towards a small gap between them but the right wing struck a tree and detached. The aircraft spun round and ran backwards up a bank before coming to rest on its right side. The pilot suffered only minor injuries.
A limited examination of the engine after the accident suggested that a cylinder in the right bank had a broken inlet valve spring with a penetration of the associated induction flame trap. It is unclear whether this alone would have accounted for the substantial power loss.
Airshows need more risk assessment and CAA oversight
The AAIB has published a third Special Bulletin concerning its ongoing investigation into the Hawker Hunter accident during last year’s Shoreham Airshow. Whilst still not its final report, the Bulletin makes fourteen safety recommendations that are broadly in line with new CAA rules arising from the Authority’s own review of air display safety. The AAIB’S recommendations fall into four main categories:
1 Risk management
The AAIB asked the independent Health and Safety Laboratory to review the risk assessment carried by the organisers of the Shoreham Airshow. ( Note that the Shoreham Flying Display Director was a display pilot and Display Authorisation Examiner (DAE) and was formerly the CAA’S head of GA — and the airshow organisers did carry out a risk assessment, despite recent media reports to the contrary — Ed). The five recommendations to the CAA under this heading cover producing improved guidance to enable organisers to manage risks and how they conduct risk assessments; the safety management and other competencies a flying display organiser should demonstrate; what information display aircraft commanders must provide to the organiser regarding their intended sequence of manoeuvres and the area over which they intend to perform them; and, for Permit to Fly aircraft, evidence that the manoeuvres conform with the aircraft’s Permit limitations.
2 Minimum heights
A pilot’s Display Authorisation (DA) gives a minimum height at which the holder may fly during a display with an assumption that ‘normal rules of the air’ apply away from the display line. As this gives rise to a potential lack of clarity, the AAIB recommends that the CAA remove the general exemption to flight at minimum height and specify the boundaries of a flying display within which any permission applies.
3 Separation distances
Air display separation distances between display lines and spectator enclosures have remained unchanged for several years and, in general, the CAA’S mandated distances remain less than those of the US Federal Aviation Administration and other countries’ aviation authorities. The AAIB makes three recommendations: that the CAA require displaying aircraft be separated from the public by a distance sufficient that the risk of injury in case of an accident is minimised; specify the minimum separation distances between display aircraft and ‘secondary crowd’ (i.e. non-paying spectator) areas; and require organisers to designate airspace for aerobatics and safeguard the people and structures below that space.
4 Pilot standards
The AAIB found that display pilots, including the Shoreham Hunter pilot, have been evaluated by DAES who were members of the same team or already known to them. Pilots have also been able to renew their DAS on one type while intending to display several classes or types of aircraft, and there has been no reporting requirement for occurrences where it is felt necessary to stop a pilot’s display on safety grounds. The AAIB recommends that DAES have no conflict of interest with candidates and that a DA is renewed for each class or type or aircraft the holder intends to fly. Additionally, the CAA should publish a list of occurrences and institute a process to suspend the DA of any pilot whose competence is in doubt.
In terms of safety standards, the AAIB noted that CAA experts attend less than ten per cent of displays for which the Authority has given permission, whereas representatives of the FAA attend every authorised display. The AAIB recommends that the CAA should establish and publish target safety indicators for display flying. The full bulletin is at: gov.uk/aaib-reports
Alpi Pioneer 400T: Dave Unwin flight tested the first UK example of this type for the November 2011 edition of Pilot
In its latest Special Bulletin, the AAIB makes fourteen safety recommendations that will impact all display flying and not just fast jets