Approach & Landing

After a couple of wild early attempts, by around ten or so flights into training I was starting to get stuck into the approach and landing phase.

The approach is ideally a short straight flight from the final turn of the circuit that you fly to get down safely to the landing area or runway. A fundamental of approach control is to use the airbrakes to control your rate of descent. At the same time you need to use the stick (controlling the nose attitude) to control your speed - which is more critical near the ground to avoid a stall or spin. See circuit planning for information on choosing an approach speed - which should be set by the turn onto the diagonal leg. Photo: Puchacz on final approach at Aboyne (click for a larger image)

This all takes a bit of getting used to. It is tempting at first to lower or raise the nose in order to 'aim' at the runway. But if that is left unchecked the speed can rise or fall alarmingly leading to serious trouble. Early in training, the instructor normally operates the airbrakes during the approach and landing to let you get the hang of speed control. Then he operates the stick and lets you practice using the airbrakes to control the rate of descent. Only then do you have a go at them both together. It's normally too hard at first for the student to confidently coordinate the stick & rudder as the ground rushes up alarmingly.

The descent in a glider is much steeper than for a powered aircraft, in order to leave a larger safety margin. The idea is to keep height and speed "up your sleeve" in case turbulence or an area of sink is encountered, e.g. due to a sudden reduction in the wind speed. If a glider approached for a landing on a normal glide angle, it would be very close to the ground for much of the approach. Any loss of lift would easily lead to a dangerous undershoot - i.e. landing short of the runway. So the approach angle for a glider is deliberately made steeper - around ten degrees compared to the powered approach of around three degrees. Another advantage of using the airbrakes is that a steeper descent angle makes it easier to judge where the touchdown will be. By descending more steeply than usual with the airbrakes about a half to two-thirds extended, you try to maintain a constant rate of descent while holding the nose at the correct attitude to maintain a safe speed. If an undershoot situation develops, the airbrakes are quickly reduced or closed completely to extend the glide. This use of the airbrakes provides a similar effect to increasing the throttle in a powered aircraft - but only for a short while. At the same time you must not instinctively raise the nose to 'gain height' or you will lose speed and risk a stall or spin. Photo: Landing in Australia (surely should be upside down?)

On some older aircraft, or if you end up far too high on the approach, another technique can be used to quickly lose height without diving. This was demonstrated to me one day: Because we were rather close to the airfield on a final turn we were too high even for full airbrake, so it looked like we would overshoot (pass the far end of the runway). So the instructor showed me sideslipping. By holding a left bank while applying opposite right rudder, the glider descended rapidly. In no time we were back on a sensible angle of approach and he flew us normally to a gentle touchdown.

In circuit planning the circuit is constructed around a landing reference point - normally about a third of the way along the runway or into the airfield. On the approach you look at this point and keep it in the same relative angle by using the airbrakes (rate of descent) and stick (course) down to the reference point.

As the approach nears the runway, by around 20 feet high it is helpful to stop looking at the reference point and instead look well ahead as the ground rapidly nears. This is like driving a car at a similar speed (around 70 mph). Otherwise you may fly straight into the ground or balloon due to yanking the stick in an instinctive avoiding action. At this height you gently level out the glider - called the round-out - so that the glider flies about five feet above and parallel to the runway. Then you slowly keep the stick coming back so that the extra speed slowly bleeds-off by converting to height. It's a losing battle and you will slowly sink. By the time the stick is fully back, you should be settling onto the runway on the main whell and tail wheel together just above the stalling speed. This is called a fully held-off landing.

On the ground you do the same as during the start of the takeoff : steer with the rudder and keep the wings level with the stick (ailerons). As for the takeoff, this sudden change from coordinated stick and rudder to uncoordinated stick and rudder takes a bit of mental adjustment, and at about 70 mph on a runway fifteen feet (at Aboyne) wide you have to be quick. Make those mental cogs turn quickly !

Even when my circuit planning was good enough to get us into a decent position for the final turn onto the approach, I still found it hard at first to get the final turn correct. It seemed to be either too late or too early, so that plenty adjustment was required to line us up straight with the runway. My first hands-on landing reveals the frantic pace of events:

On base leg, as we approached the imaginary extended runway centreline, I turned us through 90 degrees so we were roughly lined-up for the landing. But we weren't quite on the correct path, so I made a couple of hurried adjustments. Stick and rudder. Stick and rudder. By now the runway was starting to approach very fast, as if we would fly right on past it. Something still to do ? 'What about some airbrake ?' the instructor cheerfully suggested. I hastily opened and held the airbrake handle at about the halfway extended position, and now we were sinking nicely towards the runway.

As we rapidly descended towards the ground, the instructor was strangely quiet. It still looked like we were going to reach the runway threshold, our speed was good at around 55 knots, and I was only meandering gently around the extended centreline. We whizzed over the boundary wall at about 50 feet and I spotted the little white faces of several pilots looking up at us from a huddle of gliders beside the main hanger. Now the ground was rushing up at us very fast. Better do something ! I tugged back on the stick and just as we began to level out there was a big bump and we were careering along the runway at about 65 miles per hour. I had forgotten to round out until almost too late.

With the glider seat only inches above the tarmac the groundspeed seemed much faster than in a car. 'Steer with the rudder' came the cry from the back. We were indeed veering left so I kicked right and we swung back towards the centre of the runway. Then off to the right again. A kick to the left and we were suddenly brushing the grass on the left side of the runway. Right kick. Left kick. Overcorrecting. We were weaving like a drunk - but still on the narrow runway. 'Keep the wings level' came another distant yell. Now I started rather frantic stick waggling to stop us from a wing dragging, risking a ground loop. Hard left. Hard right. Meanwhile the end of the runway was rapidly approaching, with the hidden steep drop beyond the end. 'Wheel brake!' came the helpful cry. I leaned forwards and pulled the blue brake knob, and now our speed was dropping fast. And then we stopped and one wing settled gently onto the grass. Time to breathe again.

I was sweating and felt exhausted. What a huge amount of concentration it had taken to stay on the controls from takeoff right through to landing without the instructor taking over at any point. But it was a good feeling. A bit of a training milestone to go through the whole thing from start to finish. Suddenly I realised I could maybe have 'saved the day' in true Hollywood fashion if the instructor had fainted or otherwise departed while we were aloft. (Well, maybe.)

The need for prompting throughout the ground roll is apparently common problem for beginners - most students relax too much as soon as the wheels hit the deck: it is important to keep 'flying' the glider until it is at a standstill. This is underlined by the legal definition of a flight: from the time the wheels start rolling for the takeoff, to the time the wheels stop rolling after the landing.

On other (poor) landing occasions, sometimes I was still trying to line us up with the runway below 50 feet. So the instructor had to take over, once as low as 10 feet when I accidentally pulled us into a climb while frantically trying to turn us hard to the right. Not good as you then risk ballooning. If you are out of position on the final approach it is important to sort it out as soon as possible so that you leave more time to concentrate on the other tasks at the critical last stage of the flight. Most bad landings are a result of a bad circuit. Get it right higher up and it's a lot easier lower down (in theory at least).

On several occasions during my training the flying conditions were poor for good landing practice. On many days there was a strong crosswind. That means you have to 'crab' the glider your track over the ground and your heading are rather different. That takes a bit of practice - as does remembering to kick the rudder at the last minute so your wheels line up with the runway in the landing. If you detect much of a crosswind in the circuit, it is a good idea to adjust the final turn onto the approach so that you allow for the subsequent drift: For example in a standard crosswind landing there is a headwind just before turning onto the approach - so you should turn a little later. Then the crosswind will drift you back in line with the runway - rather than further out of line. On more than one occasion I was not allowed to complete the landing as the crosswind was too severe.

Ballooning

One day I was landing in a strong crosswind and was rather distracted by (lack of?) directional control. As the ground rushed up, swaying a little from side to side - rushing rather too fast I sensed - I glanced at the airspeed indicator and to my horror we were accelerating above 65 knots - whoops ! I started the round-out early to reduce some of the speed and made a final airbrake adjustment to correct the gliding angle. Inevitably all the excess flying energy resulted in a balloon as I had raised the nose too fast. Rather than flying parallel to the ground at about 10 feet, we were starting to climb again. I correctly held the nose where it was to let the glider start descending again. I remembered that if you push the stick forwards while ballooning you might simply nose-dive onto the runway, unless the balloon is really severe. Despite using up rather more runway than planned, we were now settling back into a reasonable float. I kept the stick coming back slowly to keep raising the nose and losing speed and to sink us gently onto the runway. I was a little slow in doing this so we landed early with more of a bump than I expected. Then I struggled a little more to keep us on the runway as we thundered along at 55 knots, keeping the wings level and pulling the wheel-brake knob to get us stopped. I was prompted to fully open the airbrake to help us slow down and to prevent a gust from lifting us into the air again.

Undershooting & Overshooting

On a later flight, as we turned onto the base leg the instructor said that he would fly the approach and landing, as he wanted to show me the visible clues of an undershoot and an overshoot. (In any case there was probably too much crosswind for a student landing attempt.)

He announced he was setting a precise speed of 53 knots and I watched as the dial magically locked onto that speed. Then he turned us onto final and as usual opened about half airbrake and lined us up towards the reference point. He said he was using a reference point of the yellow line across the runway that marks the start of the usable tarmac. Normally the reference point is a couple of hundred feet further along the runway, but using the line made this demonstration clearer. A key technique on the approach is to keep the reference point stationary in the view over the nose. If your speed and rate of descent are constant and so is the reference point then you are heading straight for it.

The instructor then opened full airbrake and as we descended more steeply the reference point slowly slid up in the view ahead. This was a sure sign that we were now on an undershoot trajectory that would result in a landing short of the runway. Undershooting - almost landing short of the airfield.

Then the instructor closed the airbrakes to reduce our rate of decent, and the yellow line sank down again - and kept moving down indicating that we were on an overshoot trajectory that would make us fly past the runway. Then with the airbrake set at roughly half again, the reference point settled back into a stationary position in the canopy above the nose. All the time the speed had been almost exactly 53 knots. Impressive.

This was a very nice demonstration of how the airbrake is used to control the rate of decent - while maintaining a constant approach speed with little stick adjustments. It is essential that the airspeed is kept constant as any change in the speed is due to a change in the glide angle which also affects the position of the reference point. If you are using the reference point technique to make an accurate landing, you don't want to make the airbrakes and stick fight against each other as they independently alter the position of the reference point. You set the speed with the stick and trim to keep it constant, so you have are a good safety safe margin above the stall speed. Then you use the airbrakes to control the rate of descent and monitor it via reference point. A refinement is that you need to put the nose a little down when you extend the airbrakes as the lift-destroying drag otherwise causes a slight loss of speed. And you need raise the nose a little when you close the 'brakes to stop any slight gain in speed. Keep the speed constant.

One undesirable habit a student can develop is opening the airbrakes at the start of every approach - as if the airbrake lever is a 'prepare to land' lever. This can soon lead to serious trouble: you mustn't open the airbrakes until they are necessary or you may undershoot. Another close call due to undershooting

This is especially risky on a windy day when the glider has more trouble on the approach in penetrating the wind towards the runway - if the airbrakes are opened early or too much there is an even greater risk of an undershoot.

Around flight number thirty, because an earlier instructor had commented on my need for more accurate coordination of airbrake (to control rate of descent) and elevator (to control airspeed), I was taken through an exercise. From a steady glide at height I opened the airbrakes fully and as we started to descend quickly I got a feel for how much the airspeed decayed due to the extra drag, adjusting the stick forwards slightly to regain the lost speed. Then I closed the airbrakes fully and we accelerated again as the drag reduced, so I pulled the stick back a little to lose the excess and regain normal flying speed. And then we did it again. So as you extend the airbrakes, you normally need to lower the nose slightly to maintain airspeed. Likewise, when you retract the airbrakes you normally need to raise the nose slightly to maintain airspeed. Although in an approach situation, closing the airbrakes is normally because you are undershooting, and reducing speed can be a problem. This was a very useful exercise, because until now I had been trying to do this coordination on the action-packed final approach with other things to worry about like lining up with the runway; and I'd also only been using part-airbrake, so I couldn't really feel the range of speed change involved - and get a feel for how to compensate. Ideally I'd have experienced this sooner.

I was discussing airbrakes with an experienced pilot one day and he suggested that you should think of the airbrakes as a device to reduce penetration - i.e. to reduce the distance travelled forwards for a given loss of height. Another effect of the airbrakes is to increase the stall speed, which you need to be aware of if flying slowly. And in particular, airbrakes make a glider more stable, less prone to the effects of turbulence, which is another advantage during the approach and landing.

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