Hunter

Shoreham and the future of air shows

David Learmount , , , , , , , , , , ,

No person or organisation associated with the 2015 Shoreham flying display accident escaped criticism – implied or actual – in the Air Accident Investigation Branch’s final report.

When the aircraft that later crashed, the Hawker Hunter T7, took off from its North Weald, Essex base heading for Shoreham to fly the display, it had several time-expired or unserviceable components in it. In retrospect the AAIB report says it was not in compliance with its permit to fly, yet none of these faulty components caused the accident.

The Flying Display Director hired to manage show safety was fully qualified in terms of knowledge, experience and expertise to oversee all aspects of the flying display, but the report implies there were some things – like the exact display routine the Hunter was to fly – he should have risk-assessed manoeuvre by manoeuvre. Yet even if he had, the crash might still have happened.

The Hunter’s pilot was fully qualified in terms of experience, training, flying recency and medical fitness to carry out the display he had planned, but on the day he got one of the aerobatic manoeuvres badly wrong, making mistakes that are difficult to understand in somebody so experienced.

The mistakes meant that he himself was seriously injured when thrown clear of the aircraft on impact with the A27 highway next to the airfield, but 11 people on the road were killed.

By flying a similar Hunter through the same manoeuvres, the AAIB has determined that the pilot could not have pulled the aircraft out of his “bent loop” without hitting the ground once he had passed the apex too low and failed, at that point, to carry out an “escape manoeuvre” by rolling the aircraft upright.

If he had used his ejection seat during the high speed descent from the loop it would not have saved him, and the pilotless aircraft would have continued to impact with the ground, possibly in much the same place. The only way the pilot could have prevented killing the people on the A27, says the report, was to crash the aircraft into nearby fields, but during the last second or so he probably still hoped he could avoid harm to road-users by pulling up in time.

Why was he too low at the loop’s apex?

He should have entered the loop from a 500ft base, but he started at about 185ft. The height of the top of a loop compared with the entry height is a product of speed and engine power at entry. The aircraft should have entered at a minimum 350kt with full power selected, but the Hunter entered at 310kt with less than full power until well into the pull-up. The pilot should have aimed for a 4,000ft apex with 150kt indicated airspeed over the top, but in fact it got to less than 3,000ft with 105kt.

Unless the pilot recognised the lack of energy at that point and carried out the rolling escape manoeuvre, he and the aircraft were doomed.

Why a pilot with so much experience of teaching, let alone flying, aerobatic manoeuvres failed to heed these indicators that the loop was going wrong may never be known, because trauma has obliterated the details of the fatal flight from the pilot’s memory, according to the report.

Air shows involve risk. A study by the AAIB has recently quantified that risk, and my blog a year ago describes the findings in detail.

The final Shoreham report confirms the impressions given by the earlier AAIB bulletins on the subject. Because no-one in an on-site air display audience in UK has been killed since the early 1950s, such success appears to have led to complacency.

Not rampant complacency, but a relaxed belief that all the people involved are experts who know what they are doing, so they don’t need to be given the third degree before a show.

The sign that not all was well was the number of serious air display accidents, mostly fatal, that occurred just outside the area controlled by the display organisers – just like the Shoreham Hunter crash.

The AAIB found that 65% of all air show accidents came into that category, but almost always the only person harmed was the pilot. So nobody, including the CAA, raised the alarm, until now.

Meanwhile aerodromes used for decades as air show venues have suffered encroachment at their boundaries by expanding residential and industrial development. This affects the profiles aircraft are allowed to fly during a display, and flight display directors are bound to take this into account.

No longer are display lines, and entry and exit profiles dependent purely on where the display audience “crowd line” is, they have to take into account what each aircraft would have to do in the event of a technical or operational mishap during the display to avoid crashing into a nearby populated zone.

These are considerations that will affect air shows in the future. If a flying display stops being exciting, it might as well give up. Or go somewhere else more rural.

Coastal air displays will survive, because the escape route for aircraft in trouble is obvious.

The best example of the conundrum air show organisers face is what has happened to the traditional Red Arrows display at the biennial Farnborough International Air Show. When the Reds reviewed their Farnborough routine in detail following the tightened guidelines published in the early Shoreham bulletins, they found they had to curtail their display considerably.

In a statement following the release of the Shoreham final report, the CAA says: “We are fully committed to ensuring that all air shows take place safely, for the six million people who attend them each year in the UK and for the communities in which they take place.”

Let’s hope the CAA means what it says.

Shoreham air display accident – interim report

David Learmount , , , , ,

According to the UK Air Accident Investigation Branch’s interim factual report on the Shoreham air show crash, nothing detectable was wrong with the Hawker Hunter at any point in the display.

It has been confirmed that the aircraft entered the fatal vertical manoeuvre at a height of 200ft when 500ft would have been the normal minimum – and certainly wiser – thus leaving very little room for misjudgement in a trajectory that is frighteningly easy to get wrong, even for a skillful and experienced pilot.

The intent in a normal vertical manoeuvre like this loop-with-roll would be to complete it at the entry height, but certainly not less when the aircraft began the manoeuvre close to the ground. In fact the aircraft began to pull up from 200ft above ground level and finished by impacting the surface.

There may yet be more to this story than the AAIB has just revealed, but there were cameras and a microphone in the cockpit which should confirm most of what it is possible to know.

Air displays contain risk, like Formula 1 and other sports do. If they didn’t, nobody would go to watch them. But they are not intended to extend the risk to non-participants. That is the part that needs examination.

The Shoreham Hunter crash unravelled

David Learmount , , , , , , , , ,

A lot of misleading comment about the 22 August Shoreham air show crash has already been written. Here’s an attempt to put the event into context.

First, these are some topical issues surrounding the short aerobatic flight by the Hawker Hunter T7.

It’s clear that when this Hunter was on its run-in towards Shoreham aerodrome from the north, following the Adur river valley in line with the airfield’s runway 20, it was very low. My estimate is 300ft or even less as it approached its pull-up point close to the airfield boundary, and other experienced aerobatic pilots say it was lower still.

Most pilots would choose – or be ordered to adopt – a minimum of 500ft above airfield level as a base for their pull-up into a looping manoeuvre, because they need that height to give them room for error in judging the exit height at the base of the manoeuvre.

Five hundred feet (150m) is not high – it does not give spectators a crick in their necks to watch the aircraft pass at that height. It only allows a small margin for height error when exiting from vertical manoeuvres. But 300ft or lower at entry provides even less.

A pilot intending to carry out a vertical manoeuvre like aerobatic looping – or simultaneous looping-and-rolling as in a barrel roll – normally aims to complete it at the same height he enters it. As well as being common sense, that makes it look precise and disciplined to spectators.

Coming out of a vertical manoeuvre lower than the entry height – unintentionally – has probably killed more display pilots than any other single category of air display accident. Loops, barrel rolls, stall-turns, wing-overs and chandelles are not difficult to perform safely at a high level where there’s lots of room to correct errors. But to carry them out with precision at low level requires tight discipline, and constant monitoring of the aircraft’s pitch and roll rates in conjunction with the rapidly changing airspeed in the climb and descent phases. It is incredibly easy to let the pitch rate – or the pitch-and-roll rate – decay slightly during the descent phase, and that can be terminal. It was for the T7 at Shoreham, whatever the reason.

Meanwhile there have been actual criticisms from pilots of several other aspects of the conduct of this flight.

The Hunter had drop-tanks beneath its wings. These are fuel tanks that are used when the aircraft needs to extend its range or airborne endurance, and are ideally removed for aerobatic displays because the aircraft is then lighter and has less aerodynamic drag. But the existence of these drop tanks, empty of fuel, would not have been the cause of this accident.

The aircraft also could be seen to have flaps deployed during all – or most – of its short sortie. This low flap-setting is used at take-off, and can be used when airborne to tighten the aircraft’s turning radius in combat, but at the cost of increasing drag considerably and thus reducing speed. A former RAF Hunter pilot I know well told me he would not have used any flap for the manoeuvres we watched, but he agreed that flap deployment would not, alone, have been a cause for this accident. But other Hunter pilots have posted on the Professional Pilots’ Rumour Network that flap was commonly used in aerobatic manoeuvres, including by the Black Arrows, the predecessors to the Red Arrows.

An observation that has come out of a video released today suggests the pilot had trouble getting this aircraft off the runway at take-off. The video shows the ill-fated aircraft carrying out a very long take-off run, lifting off right at the far end of the runway at its North Weald base and then staying low before climbing away. It has been suggested that the aircraft’s engine was under-performing.

If there had been something wrong with the engine, especially in a single-engine aircraft like this, no pilot would continue the flight, especially into an aerobatic sequence.

It’s a common tactic for display pilots to hold the aircraft on the runway for a little longer than necessary during take-off, and then hold it low above the runway for a while after unstick, so the aircraft accelerates more rapidly and can then be manoeuvred more dramatically for crowd-pleasing purposes.

It’s also worth remembering that the Hunter may have been a fast and agile aircraft for its time, but is not a patch on modern jets like the Typhoon and Tornado. It’s a 1950s aeroplane with a single, un-reheated Rolls-Royce Avon jet engine. It does NOT have the afterburner engines that can power a jet vertically into the sky.

Aeroplanes like the Hunter need empathetic pilots to get the best performance out of them, because the brute force of a modern jet engine is not there to get them out of trouble when they need it.

More than any other factor in this accident, the puzzle for me is why the aircraft crash-landed on the busy main road when the pilot – if he was conscious – seemed to have had a choice of veering left from that fatal descent toward the A27 and landing on the west side of the airfield, if not the runway itself (the spectators were on the runway’s east side).

On its final approach toward the road the aircraft was descending steeply out of a looping manoeuvre, so it should have had sufficient speed to bank safely to the left and head for the open grass of the airfield. It would only have required a turn left through about 45deg to have lined up parallel to the runway.

That presupposes the pilot was fully conscious and there was nothing else wrong with the aircraft. In 2011 one of the Red Arrow pilots suffered G-induced loss of consciousness during a high speed, high-G turn close to the ground, and crashed fatally.

Was something wrong with the aircraft? In the video footage, nothing is seen falling off it, no puffs of smoke from the engine, and in some footage of the aircraft’s last moments there is visible heat haze behind the engine jetpipe, and engine noise could clearly be heard, suggesting the engine was at least running even if not generating full power.

But in a video released later there appear to be a couple of visible flashes near the aircraft just before the apex of the looping manoeuvre, when the aircraft was completely inverted. But there were no associated bangs, the engine noise was unchanged, and the flashes did not show on any other videos of the same sector.

The pilot, if he suspected engine trouble, would have had the option of rolling upright and abandoning the display. The fact he didn’t suggests he saw no trouble at that point.

It will take all the forensic magic of the Air Accident Investigation Branch to find the answers, because there are no black boxes on an aircraft like this.