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!

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

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

Dude you asked:
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.

Can anyone define Threshold?
 

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!

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

Genghis

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

:confused:

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.

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?

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?

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