The risk to air shows

Following the 22 August Shoreham air show crash, in which at least 11 people on a public road have been killed by a display aircraft, the Civil Aviation Authority has promised a complete review of air display safety.

Since comprehensive rules and guidelines already exist and – until now – have protected the public (if not the display pilots) successfully for some sixty years, what can the CAA realistically do except ban air shows over land?

You can find a description of the existing discipline imposed on air display organisers on the Flightglobal website.

After the devastation and loss of life caused on the busy A27 dual carriageway road section next to Shoreham airfield when the Hawker Hunter crashed on it, the media has – understandably – been posing questions about the issue of public roads passing very close to airport runways.

In fact Shoreham aerodrome – the UK’s oldest airport, founded in 1910 – was not constructed next to the existing A27. The part of the A27 road that, today, skirts the airfield at its northern boundary was laid nearly half a century after the airfield was constructed, as part of a bypass for the south coast towns.

Further along the same trunk road to the west, the A27 becomes the M27 as it swings around the Portsmouth/Southampton conurbation. When the M27 was built, it was placed right slap bang at the end of Southampton airport’s runway. The airport had been there for 73 years when that section of the motorway was opened in 1983. When, in May 1993, a Cessna Citation 500 business jet overran the Southampton airport runway onto the M27 it hit two cars, but fortunately no-one was hurt.

Journalists reporting such events, however, quite reasonably ask why runways are built near roads. But their question needs reversing. Planners, in positioning roads close to runway ends, by implication do not consider landings and take-offs to be a risk worth worrying about.

Until something happens. Then all of a sudden, according to reporters who don’t know the history, the airport is the bad guy.

As an immediate measure following Shoreham, the CAA has grounded all Hawker Hunters, and required that vintage jets at displays will not conduct “high energy aerobatics”. That is a reasonable precaution until the investigations report into the recent display crashes of the Hunter and the Folland Gnat that came down killing its pilot about three weeks before.

But in considering further restrictions for the long term the CAA must consider how much pleasure public air displays provide, and that one of the functions they perform is to enthuse the country’s youth with the possibilities of high technology. Air displays are not only the biggest spectator sport in the country apart from football, they generate the future’s pilots, engineers, mechanics and aerodynamicists.

So rather than shutting down events like the Shoreham air show, or dumbing down its displays because of a proximate road, the CAA might consider other possibilities.

Like looking at the statistics that demonstrate what a one-off event this was, and not imposing further restrictions.

Or – if the CAA feels that such a tragic event must generate a visible reaction of some kind – like imposing road traffic diversions while the display is active, or putting traffic lights on the road to keep traffic clear of the perceived risk zone when a particular display is being performed.

The statistics prove that air displays may put pilots at risk, but the risk to the public is infinitesimally low. The CAA’s decisions, hopefully, will reflect that.

 

 

 

 

 

The Shoreham Hunter crash unravelled

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.