Theory Meets Practice – and saves lives

On Feb 15th I spent some time at Lasham where I fly gliders, helping out with the Lasham Cadets. Unfortunately the weather was not good enough for flying so we had some talks. The cadets had to give a talk about various aspects of the theory of flying gliders, whereas the adults gave a mixed set of talks about work they have done.

I want to focus on a particular talk given by one of the parents who is a professional in the aviation industry, previously having been a pilot, now also flying gliders. He was making a point about the importance of being able to link theoretical knowledge to practical application, in this case about the theory of flight and saving lives.

The subject he chose was the accident at Heathrow on 17th Jan 2008 where a Boeing 777 lost power before landing and just managed to touchdown inside the airport but short of the runway. He was particularly highlighting the actions of the captain and the effect it had on the outcome.

As a preamble it is worth noting the layout of the ground on the runway approach in question, 27L. From the airport boundary fence there is about a 1700ft gap before the runway paved surface starts. Here is a detailed map for the flying nerds among us. Just before the airfield fence you have the main A30 road which is a very busy highway. According to the AAIB report S1/2008 the aircraft touched down “some 1000ft short of the paved runway surface”, so there was only 700ft or so between the touchdown point and the road.

However, the key statement is in the interim report on page 4 where is says: “At 240 ft the aircraft commander selected flap 25 in an attempt to reduce the drag”. According to the person giving us the rainy day talk at Lasham, this action is not mentioned in any training, although it will be known by pilots because the effect of flaps is a basic theory of flight item.

Some Theory of Flight
So what are flaps and what do they do? On an airliner they are like big barn doors that, when down, extend from the rear of the wing. They allow the pilot to increase the lift from the wing at slower speeds. Depending upon the aircraft and their setting they also adjust the angle the aircraft flies at so that visibility is usually better for landing. In this case they had 30 degrees of flap which will have given them a slow flying, high visibility approach. Since with physics, you never get something for nothing, the down side will have been the high drag. In this case the autopilot will have been countering this drag with more thrust from the engines because at 30degrees the flaps were giving more drag than lift.

Handling the Emergency
Looking at the approach graph, when the engines gave up, although the glide angle was fairly constant, the airspeed was fluctuating and falling rapidly at some points. This could only go on for so long before the aircraft would have slowed down too far and fallen out of the sky, quite possibly onto the A30 dual carriageway. When the commander selected 25degrees of flap, although the glide angle steepened temporarily, it reduced the drag so that the airspeed stopped falling and the aircraft was able to glide a bit further than it would have done with the 30degrees setting. This would have taken courage because just after reducing the flap there was less lift from the wing so the aircraft lost some height before it stabilised on a better glide angle.

In any pilot’s training the effects of controls like this are covered. It is something that is relevant regardless of the type of aircraft you are flying. It works just as well for a glider as it does for a 200-400 seater airliner. Luckily what happened here was that the pilot had internalised the theory of flight enough to make the right judgement in an emergency, even though the initial response of the aircraft was going to be losing more height, something he would have known.

He managed to make that important link between theory and practice.

The Moral
Although technology can be made to work well a lot of the time, when an emergency occurs you will be vulnerable. A successful outcome will depend upon making the link between theory and practice. It will not be an academic exercise.

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