Landing on undulating runways

[FlyingForFun]

I'd be interested to hear from anyone who regularly flies into a field with an undulating runway. I suppose I'm talking about anything from an Elstree-style runway (the initial dip on 26 followed by the upward hill) through to private strips on ground which is not flat. I'm not talking about a constant up-slope or down-slope, nor about bumpy runways, both of which I can handle - I'm specifically interested in fields with several rises and falls over the course of the runway.

The reason I ask is because I visited Elstree for the first time last weekend, and found it extremely tricky. I made two landings there, both pretty much identical. Because it was a bumpy day, I was keeping my speed up a little bit. I started off by being high over the trees on final to 26. This made it difficult to get the speed back. I rounded out over the numbers, but then floated a short way down the runway due to my excessive speed. And that's where it went wrong. What happened, I think, is that I maintained a constant height relative to the far end of the runway (where my attention was focused). As I drifted down the runway, I reached the start of the up-slope part of the runway, and the ground rose to meet the aircraft. This resulted in a main-wheel first landing, something which every tail-dragger pilot knows is a bad thing (unless a wheel-landing was intended of course).

So any advice from pilots who handle this kind of thing regularly would be appreciated. Where exactly do you focus your attention in order to ensure that you remain at the correct height above the bit of runway you're currently overhead through the flare? Any Elstree pilots care to comment? And I'm sure there are many fields which are far more tricky in this respect!

Thanks!

FFF
-------------

[Tall_guy_in_a_152]

I had a similar experience on my one and only Elstree landing. I had attributed my high approach to 26 to the unusual aspect ratio of the runway (relatively wide) which (now that you mention it) is compounded visually by the up-slope at the western end.

As FFF says, I'm sure there are many more extreme examples of both these runway 'features', but in my limited experience Elstree is the worst.

TG

[BlueRobin]

Crest and dips are a problem that befalls the commercial guys too. E.g. original runway at Manchester has a big rise about 1/2 way along.

Hmmm...for a Europa to have a problem, the frequency of peaks must be high given the a/c's short landing distance?

My theory - armchair advice this Mr D... Your problem started with the protracted float, so keep the speed down to minimise it. Land on a uphill part with this short-field landing config. Make sure you don't have too much float/lift under wings as this will mean the subsequent crest acts as a ski-jump.

[M14P]

I absolutely buried my work-plane at Helsinki the other day - Rwy 15 has a Manchester-style bump in it. Everyone knows about it - the best I could come up with (having made a few excuses in the breifing for the ensuing thumper) was to say "Here it comes...!" about three-quarters of a second before impact.

Humfff!

[pulse1]

FFF,

I am so glad that you asked this question because I suspect that many of us have this problem. I certainly do and it is compounded by the combination of turbulence (high approach speed) and obstacles requiring a steeper than usual approach.

In my case, this causes a more sudden transition between looking at the flare point and then at the end of the runway.

In my gliding days, at Dunstable, we were taught to follow the ground but you cannot do this by looking at the end of the runway. It's a lot easier in a glider too. We used to laugh at the many aborted attempts of GA pilots trying to cope with the severe changes of slope.

I hope that we can get some good advice here.

[QNH 1013]

Undulating Runways: For practice try:

Eggesford in Devon

Nayland in Essex? (very different)

Fishburn in County Durham


They are all grass, and Nayland feels like landing on the side of a house roof.

[drauk]

FFF, something to think about is the discussion that has gone on here before about where to look to judge the round-out/flare.

You no doubt remember the postings of Chuck Ellsworth on this subject. Actually, in a more recent thread I recall you summarising the early postings he had made, where you discussed the fact that the different parts of the approach had different names and that was the cause of some of the confusion (I can't find that thread right now unfortunately). However, I think you actually misquoted him in that you said once you agreed that you were talking about having reached the flare point you transition your viewpoint to the end of the runway. (As this is from memory I apologise if I've misrepresented the posting you made) He actually said that was absolutely the wrong thing to do. And with Elstree's upsloping runway the problem is even more marked. Instead he recommends about 500' in front of you, if you're landing at around 50-70knts.

All my flying has been at Elstree and I'm not sure precisely where I focus when I'm landing, but on neither runway is it the far end. Solving your problem isn't made any easier by the fact that you can't fly circuits at Elstree, unless you do so with a resident instructor (and then only one from Cabair or Firecrest).

[QDMQDMQDM]

I don't think there's a magic formula -- just do it a lot, get the speed right and touch down where you planned to touch down. If you don't touch down at the right place on an undulating runway you can get into trouble -- too much float, downsloping etc. -- so it's more important to fly accurately than on 7000 feet of tarmac.

It's down to practice, like everything else.

QDM

[Wycombe]

Have only landed there once, but found that the westerly runway at Kemble has a bit of a strange perspective. The undershoot is in a dip and I found that the threshold came up to meet me, resulting in an arrival a few seconds earlier than anticipated!

Anyone else found this?

[Bluebeard2]

I used to fly quite a lot from Elstree, so I was used to the humpy runway. Can't say 26 ever presented too much of a problem, although I did used to always aim for the start of the pan for a round out just prior to the threshold - in a C152/C150 this would normally get you on at the numbers and would give you a fighting chance of a turnoff at alpha (the first taxiway on the left after the numbers) without excessive braking or a huge backtrack.

Funnily enough, it was the rarely used 08 which used to give me the willies. Apart from the 2deg downslope (plus trees at the end), the undershoot and threshold were flat, which did make judging the angle of descent very tricky. Just to add to one's woes, there would be a downdraft off the trees if there was a southerly wind, which would handily take 50ft off you. Nice.

[FlyingForFun]

Wow - seems like this is causing lots of people problems. Strange that I've never seen it discussed before!

Drauk, you're memory of what Chuck and I said is pretty much correct. I seem to recall that one of us (I think it was me) suggested that the common advice to "look at the end of the runway" was given because it is usually a good approximation to the correct place to look, but Chuck did give a formula or a guideline which was dependant on your speed. But I'm not sure that helps in this case... even if you concentrate on a point which is the correct distance in front of you, if the runway is moving up and down beneath you you won't have the visual references to be able to compensate for it.

Predictably, the Elstree fliers such as Drauk don't say that they have problems. So I'm sure there is a solution, which all the Elstree pilots instinctively know without even realising they know it.

Is there anyone who trained or who has done lots of flying at somewhere with a flatter runway, then moved to somewhere like Elstree? How did you find it when you first moved there? Have you learnt to deal with it since you've been there? Do you know what you did to learn to deal with it?

QNH, thanks for the suggestions of other places to go. Do you know if any of them offer free landing fees off of circuits?

FFF
--------------

[QDMQDMQDM]

No landing fees at all at Eggesford -- circuit to your heart's content on a VERY undulating runway.

QDM

[Dude~]

I used to fly from Popham and have recently started flying from Elstree. I think the key thing is to be consistant. Make sure your approach is stable, on speed, none of this 'extra 5kts for saftey' and a reasonable height, rate of descent and power/flap setting.

Airline pilots 'fly the numbers' and it works for them. If you arrive over the threshold at the right speed it gives a much better chance to land well, than if you arrive over the threshold off centre/ too high / too fast.

Of course, a stable, precise approach will not directly help on an undulating runway. Here you need to be prepared for whats going to hapopen. You need to think about the slope of the landing zone, and prepare mentally. It doesnt matter if you level off then let the runway rise to meet you rather than you sinking to meet the runway. Just so long as the speed is correct. At Popham, I tended to 'round out' (not flare yet) in a shallow bank to align with the runway, then power completely off and a gentle flare since the runway continues its downslope for a while. Here, a normal flare (ie maintaining height at the expense of airpseed) would leave you gaining height over the runway. THe opposite happens at Elstree on 26 where you need to flare and almost enter a very slight climb to prevent impacting the runway with too high a rate of descent. This is exasperated by aircraft with high Vat speeds. What this means is that your airspeed is going to decay very quickly so a little power may be helpfull, but then of course, at Elstree there is not much room to play with.

I once spent a whole summer at a grass strip with no obstacles and 900m practising presicion landings, and high rate of descent / high drag / power off flares. You have to be precise, otherwise you end up stalling at 4 or 5 feet.

Anyway, I have dribbled on enough. Think about the anatomy of your landings and go over it again and again then it will flow better when you come to fly. A relaxed mind will perform much better than a mind struggling to keep ahead of the aircraft!

[Tinstaafl]

I have to operate into these sorts of runways so on reflection I think this is how I do it...

There seems to be a some competing requirements in the situation:

1. Some reference for pitch attitude control ie the end of the runway or some point along it far enough away to remove the perception of rate of longitudinal closure

2. Some reference to determine rate of vertical closure ie sink (or the opposite.... )

3. Some reference that might allow you to anticipate #2.

I think that with a flat (note: not necessarily level) runway then looking some distance down the runway can accommodate all those tasks. As soon as the runway becomes undulating, crested or dipped then that single reference point becomes inadequate.

1. Pitch reference: I use some length down the runway OR the end of the runway if it's short OR the visible horizon if it's crested.

This gives me an attitude reference point that is relatively constant. If crested then as I lose the crest I transfer to using further along the runway.

2. Sink rate: I tend to look much closer. Not very far in front of the cowling (10m? 20m? 50m? Not sure, but it's quite close). I also pay more attention to my peripheral vision.

Using the perceived sink rate I modify my 'normal' flare & hold off, pitching a bit faster if I'm sinking fast, less so if I'm not sinking enough. The goal is to approx. fly parallel to the surface regardless of its slope then achieve a controlled sink.

This is a very short term 'reaction' type input.


3. Anticipation: If I can see the runway is falling away/going to fall away then I plan not to hold off as much, allowing the a/c to descend. Similarly, if I can see the runway rising ahead of me then I pitch more with the aim of flying parallel to the surface (not the horizontal).

This is a slightly longer term modifier to #2 above.

The end result is that I scan ahead & back throughout the process.


Additionally I modify my power usage. If a downslope is the first 'problem' then I'll reduce power earlier &/or faster. If an upslope I'll reduce power later &/or more slowly. If quite a steep up slope initially I'll sometimes fly a quite shallow approach gradient (obstacles permitting of course) to reduce the amount of flight path change needed.

Another 1 or 2 kts above 1.3 Vs can be useful to give a **little** extra energy for the extra pitch up for the upslope. I don't mean 10 kts or whatever, but just the aiming for the fast side of the required speed instead of the slow side.

[redsnail]

FFF,
Good question. I've operated on some fairly entertaining strips in my time. Consistancy and practice are the key.
As you know, a good landing follows from a good approach.
So, a nice stabilised approach is the key. Get the numbers right will help the landing enormously.
Go to the aircraft manual and see what they say for the approach speed. For fun, calculate out the 1.3Vs speed too. This will hopefully convince you that you don't need to add extra speed for your approach. (ie you are well above the stall already). As you've found out, the extra speed becomes a liability when landing. ie the float etc.
I rarely add anything more to the Vref speed other than what our ops manual says we can. Reason? No performance data on "extra" additives.
So, we've hopefully got the mechanics of flying the approach sorted. Now, what about the strange and sometimes confusing visual cues? (The beauty of PAPI and VASI). It does come easier with practice but pick a point on the runway and fly to it. Shift the eyes away from the point when you can't see it. Try not to be rough or jerky at this point. The aeroplane will do what you ask.
The objective is to land where you want it to. Not where it thinks it should.
Nailing a good landing (and approach) into a tricky aerodrome feels great.
Don't fall into the trap of being "spooked" by the conditions. Stay on top of the aeroplane and use the published speeds and techniques.

[gasax]

I routinely fly onto a strip which has steep slopes and intermediate bumps. A lot of what is posted above is not very helpful.

Too many baby airline pilots - PAPIS on a runway that really undulates????? Get real the diference in level here is certainly visible but it is not big enough to be an excuse for a poor landing - all of the variation will be within the ground effect zone, so if the aircraft is pitched up enough to keep the nosewheel clear you will see/feel very little difference.

Some of the other posters have the guist of it - looking at the end of my strip is not possible - it is out of sight! What is very important is looking at the touchdown point and making sure that the aircraft is pitched up sufficiently to ensure landing mainwheels first. The second action is to land using power. Most of the time I arrive with a fair level of sink, that added pitch increases the effect, the only way to land now is to apply power to control your height above the landing point.

This usually means increasing to power to 25% of so in the roundout to check the sink and then landing at idle. It does need a bit of practice but it is straightforward.

Landing without power requires extra speed, because of the added drag during the flare, and it makes the whole process less forgiving.

But as far as undulations are concerned, on the down part simply hold the attitude and do not let the sink rate build. If you attempt to alter the attitude of the aircraft to match the downslope disaster lurks there. The throttle is the answer.

[Dude~]

Gasax,

I don't like your comment about too many baby airline pilots. You cannot diss flying the numbers. High speed approaches are the cause of numerous nose gear collapses amongst inexoerienced pilots.

You also say, 'What is very important is looking at the touchdown point', well only up to a point, but then this has beaten beaten to death before so we shant go into that here.

As for power, I think thats absolute bull. There is no need for power in the round out in light singles, maybe in a heavy single or light twin when rate of descent is high. Power will simply increase the landing run. It is perfectly possible to round out and flare without power, it simply has to be acurate because the aircraft will decelarate more quickly than with some power. Power will do nothing to help Flying For Fun's landings.

Just my oppinion and experience of course!

[QDMQDMQDM]

Power will simply increase the landing run.

No. Low speed, full flap, fistful of power, back of the drag curve, chop the power, plonk down exactly where you want and stop.

QDM

[FlyingForFun]

Tinstaafl - thanks, that was exactly the answer I was looking for! I think I will try to practice looking closer to the aircraft for sink rate clues before going somewhere like Eggesford to practice.

Everyone else, keep the advice coming, it all helps. Might be worth re-emphasising that I'm flying a tail-dragger, so keeping the attitude high enough to land main-wheels first isn't enough, I have one very specific attitude in which I must land. Nose-low and I bounce, nose-high and it'll stay on the ground but may not stay in one piece if I do that too often.

There is a theme, which Reddo has emphasised, about not adding an extra few knots. This sounds like a very valid point. On the day in question it was pretty gusty. I have a Vs0 of 42kts, and I usually use Va of 55kts. Flapless landings are not an option since the gear and flaps are on the same lever. Because of the gusts, I was approaching at 60kts - the gusts were reducing the IAS to below 50kts at times. Maybe I would be better sticking to airfields I know, or staying on the ground, in these conditions in future - at least until I'm more capable of handling these undulations.

FFF
------------

[Dude~]

I agree entirely QDM, but Gasax didnt mention the low speed, full flap back of drag curve thing.