Touching down on the numbers...

[Dude~]

I've been reading more Chuck Yeager and was impressed reading about his conistant ability to touch his main gear down inches after the beginning of the runway everytime, to the amazment of his peers.

This made me think about my landings and I realised that I tend to come over the numbers at anything up to 50ft! (Usually because there is no need to be precise unilke Chuck landing at 200kts in his Sabres) So I've been thinking, how many people regularly aim to touch down on the numbers? This then raises the issue of the flare. Surely in order to touch down on the numbers you have to start your flare before the runway begins, which is obviously not possible at some places (tricky on 26 at Elstree). So take for example Stapleford, runway 22, displaced threshold. You are not supposed to touch down befrore the displaced threshold, but is it ok to descend over the under shoot and flare before the numbers?

I'll be interested to hear peoples thoughts on this. I know one advantage of touching down on the numbers is that one day you might be in a situation where you need all the availiable lenght of the runway in order to stop.

[iainpoll]

but is it ok to descend over the under shoot and flare before the numbers?

Only as long as there are no double decker buses trundling down the Abridge Road!

Seriously, that is why the displaced threshold is there:}

I know things will have to improve when I start the CPL, but at the moment an attempt to touch down on the numbers usually results in a 'crunch' it down on the numbers...

My instructor told me the best way to do it is to approach at the short field landing speed, which may put you on the back end of the drag curve in the speed unstable area (so watch it carefully), aiming point just before the numbers. Round out as usual, and once in the flare, when a satisfactory nose high attitude is achieved (and height - dont do it too high!!!), retard the throttle. The theory being that the a/c will touch down as soon as you retard, hopefully on the numbers!!

Anyway, this is just my understanding - my usual advice would be to seek the opinion of an instuctor.

PS The above was for C152/PA28 type thingys.

:ok:

[Genghis the Engineer]

I try to as a point of pride in any type I know well. But, it is physically impossible on 3 out of 4 runways at Popham in anything but a Helicopter.

G

[FlyingForFun]

It's always nice to be accurate, but it doesn't have to be the numbers you touch down on - as long as the runway is long enough, you can choose any point.

When using runway 25 at White Waltham, I usually try to touch down on the intersection with 21. This gives me plenty of space before my intended touch-down point to round out and flare, and more than enough runway to stop on. It's also, IMHO, safer than landing on the numbers in this particular case - the approach brings you in over a housing estate, and if you aim for the numbers in anything other than a glide and the engine quits, you could do some nasty damage.

As for actually being able to land on the numbers, I'd like to claim I could do it regularly, but in reality it's very rare. Much easier with a good short-field approach technique - slower and flatter than normal, with a bit of power to counteract the drag - but this type of approach isn't suitable unless there's a good clear area before the start of the runway. If we use runway 11 at White Waltham I sometimes do this just for the practice, since the approach is almost completely clear, although I hate to think what could happen if the engine dies and leaves me on the railway line at the wrong time so I don't do it regularly.

FFF
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[bar shaker]

I can't see the point, unless you actually need every inch of the strip.

All you are doing is reducing your options and inviting carb ice/unexpected wind gradient/rotor/something else that you weren't expecting to put into the hedge/bus/terrain.

Of course if the numbers are 50m past the threshold...

Keep it safe.

[FlyingForFun]

Bar shaker - the point, surely, is that when you do need every inch of the strip, you have a well-placed confidence in your ability to make use of every inch.

As for reducing options - absolutely right. That's why I only practice my short-field technique on certain runways. And why I aim for the intersection, not the numbers, on certain runways.

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

[SlipSlider]

I try to avoid landing on the numbers on grass runways as there can be a lip or ridge at the edge of the markings, which could put extra stress on the tailwheel if it should just catch awkwardly. That's my excuse anyway!
;)
Slip

[Dude~]

Bar shaker, I'm sure if it only reduced your options then Chuck Yeager would not have done it. I see it more as a shift in options, mainly being that of FlyingforFuns point that some day you might need to be able to do it. I seem to remember a Citation whihc force landed in Greenland. They had no option but to land on a strip too short for their weight, but the pilot put the main gear down something like 13ft (yes they measeured the didtance from edge to tyre marks - the only tyre marks in that region) from the very beggining of the tarmac adn only went off the end at walking pace.

Also, isn't the RAF very stict about touching down promptly? Not sure myself, not a RAF type.

Anyway, I only wanted to arouse thoughts, not really thinking of trying to do this all the time!

[Aerobatic Flyer]

I always try - although there aren't any numbers at most of the places I go.....

A good short field technique shouldn't have you at low speed on the "back of the drag curve" though. That's asking for trouble if there is turbulence, or a downdraft or windshear. It also gives you a lousy view of your touchdown point, and - in my opinion - is altogether a bad thing.

Bear in mind that the aeroplane will touchdown at the same speed every time, regardless of what speed you fly the approach. So make life easier, by flying your approach at the normal speed, with an aiming point an appropriate distance before the chosen touchdown point. This distance should take into account the ground you will cover between starting to flare and touching down. Judging the "appropriate distance" is the difficult part, but you can practice easily if you have a long enough runway.

Make your aiming point the numbers. Fix them in the same spot on the windshield during your final approach, which should be flown at precisely your chosen speed. Without getting into an elevators for speed control vs point and power argument, I personally find it easiest to use the elevators to keep my aiming point in the same place, and use (small) throttle adjustments to keep my speed constant.

When it's time (normally about 3 seconds before you would crash into your aiming point if you didn't move the controls!), start to flare. Where I fly, mostly on sloping runways, I keep a bit of power during the flare and cut the throttle when I want to touch down. When you touch down, note where you are in relation to the numbers. Go around and do it again, and again!

Once you are consistently landing in the same place, you should then be able to land anywhere you choose - be that on the numbers or next to an intersection - just by moving your aiming point. To touchdown on the numbers, you will be aiming somewhere short of the runway.

If for any reason you need to vary your approach speed, you "simply" need to change the distance between your aiming point and your chosen touchdown point.

You will also need to vary the distance between your aiming point and your touchdown point depending on the wind. In a strong headwind, the two points will be close together.

I'm not an instructor, and I realise that the above technique is not what is usually taught for short-field landings (which was the only point in my basic training where I was expected to land on the numbers), but it is safe, and works every time.

[iainpoll]

AF,

Good post. I take your point about the 'back of the drag curve' issue. Not a nice place to be, although I don't find the visibility to be a major problem.

Obviously you fly out of smallish fields, I was just wondering what technique you use when there is no undershoot available, or a steeper approach is required due to trees or terrain - where rounding out before the threshold is not an option?

Cheers

[bar shaker]

Guys I take your point, there's no substitute for a good quiver of skills, but practising precision landing at an intersection is much safer.

Its a bit like turning the fan off to do a PFL. It adds a whole new dimension to the exercise, but isn't something that you would sanely do.

I'm sure that many people fly from fields where you can safely glide onto the numbers, with no risk at all. Most of the fields I fly into have neighbours or obstructions and I wouldn't want to take on the additional risk, just to prove I could do it.

[stiknruda]

I operate out of a 535m strip in a fast tailwheel aircraft....

I always try to put it down on the numbers - in a moderate headwind I can often make the intersection turn-off without going "silly" on the brakes.

Final at 90, last look before the threshold should show 85.

Should the worst ever happen I know that I can get it down and stopped in a relatively short distance.

People who land long may one day run off the end, I've seen it at the above strip twice.

Stik

[Aerobatic Flyer]

iainpoll

If there's no undershoot (which there never is where I fly), the technique is identical.

I fly the approach at a power setting which is approx mid-way between idle and full power (i.e. round about 1700rpm in the aircraft I normally fly). That gives the most options for adjusting the approach path up or down. If I'm getting a bit low, and am heading for where the undershoot area would be if there was one, I've got plenty of power in hand to sort things out. In the same situation with a slow, flat approach I would already have a high power setting so I would risk not making it to the runway.

I don't often fly into flat strips that have trees or obstacles on the approach, and obviously your options are a bit limited. If it's feasible to go around (which it isn't usually, where I fly) I would steepen the approach path with a lower power setting and sideslip if necessary. What I definitely wouldn't do is come in "low and slow" over the trees in a flattish approach.

Bar shaker

Obviously it's stupid to create needless risk. The main thing is precision. If you can always land at the intersection, in different wind conditions, and know how you did it - then landing on the numbers is not going to be an issue if you need to do it.

However, if you always land at the intersection when really you were intending to land on the numbers.... then you won't be able to fly into short strips.

[In Altissimus]

AF: What do you mean by "the aeroplane will touchdown at the same speed every time"? I'm sure I can touch down at anything between 70 and 40kts and stay on the ground - or do you mean for a full-stall landing?

More generally, although I got pretty good at putting it down on the numbers in my previous type - I'm still fairly 'new to type' on my new steed. At the moment if I try to put it down precisely on the numbers, then a certain 'lack of finesse' can be evident at times :hmm: On the other hand, if I set up the approach for, say, a quarter of the way down the runway, and 'go with the flow' - accepting a touchdown where it happens - then a very comfortable landing normally ensues. Is this a common/sensible approach until I'm really at one with the plane?

[Kingy]

I always try to land on the numbers if I can. I do mostly strip flying, often into rather short strips (120M uphill is the shortest) and it is good practice to be as precise as possible even onto bigger runways.

I wish I could get out of the habit in a way as I often end up taxiing much further than I need to!!

Kingy

[Aerobatic Flyer]

In Altissimus

I meant a nice 3-point landing in a taildragger! :)

But the same applies in any light aircraft, really. Forcing it onto the ground with flying speed isn't going to do the undercarriage any good.

As for your 2nd point, I don't want to set myself up as an expert giver of advice, 'cos I'm not an expert! Perhaps someone wiser / more experienced than me can answer?

What worked best for me in landing nosewheel types reasonably consistently was learning to fly taildraggers. I'd recommend it to anyone, even if they have no intention of continuing to fly them afterwards.

Kingy

I thought my 220m uphill was short! Out of interest, where's your 120m strip and what do you fly there in?

[Fly Stimulator]

Kingy,
I wish I could get out of the habit in a way as I often end up taxiing much further than I need to!!

Exactly! I'm the same - I automatically aim for the numbers and have to remind myself when using airports with long runways that it's quicker and more fun to fly half a mile rather than taxi it.

Saves the person coming in next from having to go around too.

I don't suppose this is a problem you have all that often at your 120m strip though.

[White Knight]

Just stumbled across this forum - excellent stuff, I feel very out of touch.
Purely from a professional view the aeroplanes performance is based upon crossing the threshold at 50' and landing ON the numbers at the calculated landind speed - depending on the manufacturer (how is this word spelt ??) that could be Vref, Vls, Vref-7 etc etc so for you guys planning to take the pro's line then very definately aim for touching down on the numbers.
Anything past the numbers is IMHO very gash, whatever type and size of aircraft you fly.

That said - safe flying guys and gals:cool: :cool:

[Genghis the Engineer]

Bear in mind White Knight that many smaller aeroplanes prefer an approach significantly different to 3°, and many smaller aerodromes have considerable approach obstacles above 3° to the numbers.

G

[TheKentishFledgling]

stik,
Didn't see any numbers on your strip to touch down on - have I missed something?

;)

tKF

[Keef]

It's nice to be able to touch down on the numbers, for those times when you need to (like short runways), but I've been more embarrassed when landing on LONG runways when I've touched down too soon, and then been asked to keep my speed up and vacate next...

At Southend, there is an important question on short final - is the central taxiway blocked (in which case, land long). There is a tendency to park jets on the central for engine tests. You can then guarantee that I'll do a greaser and be down to walking pace when I get there. Then I look left and see .... oh bother!

[Kingy]

Aerobatic Flyer

The 120M strip is at Eastbach where I fly from, The field is a hill top site (it's in the AFE guide) and the two main runways are 250M and 350M, but they are one way strips, one take off north, land south the other take off west, land east. Last year we mowed a westerly stripette up the bank for landing into the prevailing wind. Basically, you fly up the valley, then sharp right, slip over the trees and land up the bank between the fence and the tree.

The strip rises about 80ft in it's lenth so its quite steep. I regularly land my Cub up it but have also landed the Taylorcraft, Fred and even the Isaacs Fury there on occasion.

Kingy

[Mike Cross]

Flew in to a Military & Civil Air Safety day at RAF Odiham a couple of years ago in the Luscombe.

Conscious of being watched I got the approach speed nailed perfectly, beautiful landing right on the numbers and stopped with almost no need to backtrack.

"G-BTCH am I OK to backtrack"
"Negative, proceed to the end of the runway and exit left, expedite"

This runway's a mile long! I should have taken off and landed again.:O

Mike

[down&out]

Dude you asked:
Also, isn't the RAF very strict about touching down promptly? Not sure myself, not a RAF type.

No- its the US navy who really need you to land on the mark - miss it and you miss the deck - for the brits, I guess its a different ball game in a harrier;)

Wence I was in the RAF (VR), I flew into Greenham Common, in a bulldog quite a few times. To save 5 min taxing, we would land half way along the runway!

I think landing on the numbers is fine IF you have a short field AND you need max distance ahead of you to safely stop. Otherwise pick a spot with a reasonable saftey balance of distance to stop ahead and distance below you if the engine stops 1st! If you want to practice you precision that’s great - then see how close to your nominated spot you can get.

[Dude~]

White Knight, interesting post. I realise I am unsure of some terminology here. What exactly is the definition of Threshold?

I was aware of some sort of 50ft performance data thing, but I assumed that would be based on touching down in the touchdown zone, something that most GA runways dont have. (again, what is the exact definiton of the landing zone)

I was under the impression that the threshold is the beggining of the tarmac, in which case I'd like to see a 747 cross that at 50ft AND touchdown on the numbers... I'm not argueing, merely trying to work it out!

[Genghis the Engineer]

Field performance calcs are always based upon the assumption of crossing the threshold (the start of the declared LDA) at screen height. For light aircraft screen height is normally at 50ft, but a lot of airliners use 35ft.

The displaced threshold assumes a given distance from screen height to touchdown at the start of the useable runway surface. At 3°/50ft this would be about 190ft, but in practice of-course it can be longer because of the hold-off which is at a much shallower angle than the 3° glideslope.

G

[Aerobatic Flyer]

Genghis

I think a touchdown 190ft after a 50ft screen need a glideslope of around 15°......... or have a missed something?

:confused:

[foghorn]

Keef has a good point, I can think of several aerodromes I've visited where I've been asked to touch down at a certain taxiway, to expedite traffic flow. Of course there was always a huge safety margin even with a very long touchdown.

[Dude~]

Sorry Genghis, I'm being thick, I dont follow you.

You say the threshold is the start of the LDA, so isnt that from the numbers (or piano keys)?

This talk about displaced threshold assumptions is confusing me! Lets take a normal runway with no displaced threshold. The tarmac starts at the piano keys. At what height should a commercial aircraft be when it is directly over the piano keys / numbers?

[B9]

Kingy
Checked my log book to find that I visted Eastbach in Nov 95 in a C172. The landing was fine (on the numbers!) but after a TODA calculation I decided to leave my passenger behind and returned later by car to collect him. I can't recall which strip I used but do remember accelerating along the top of the slope and then turning downhill once I was happy with the speed - a most challenging field. I was also amazed to find Huntair Pathfinder G-MJBZ (that I had once owned) languishing in the corner of the hangar; is it still there?

[Genghis the Engineer]

Sorry, pressed the wrong button - yes about 950ft at 3° from a 50ft screen height. Don't get this with my slide rule!

So far as I'm aware a commercial aircraft should be no higher than the scheduled screen height (50ft or 35 ft usually) over the threshold and no faster than Vref.

Interestingly I've half a dozen books on aircraft performance on the shelf here, and none of them seem to give a definitive definition of threshold (displaced or otherwise). However, taking my Pooleys out I look at page 203 - Dunkeswell, an airfield I've a nodding acquaintance with. That shows a 150m displaced trheshold before Rwy 23 with a stated "pilots must positively identify the displaced threshold to Rwy 23 before committing the aircraft to final approach". The numbers are after that displaced threshold.

G