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Faro
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Displaced Threshold: Ducking On Landing?

Sat Dec 22, 2007 1:56 pm

When landing on displaced threshold runways, isn't there an urge to duck below the nominal approach slope in order to aim for a landing screen height at the very end of the runway instead of at the displacement point, thereby landing a little shorter than normal? Also, are there safeguards or controls to ensure pilots don't do this?

Faro
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CosmicCruiser
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RE: Displaced Threshold: Ducking On Landing?

Sat Dec 22, 2007 2:54 pm



Quoting Faro (Thread starter):
When landing on displaced threshold runways, isn't there an urge to duck below the nominal approach slope in order to aim for a landing screen height at the very end of the runway instead of at the displacement point

No

Quoting Faro (Thread starter):
Also, are there safeguards or controls to ensure pilots don't do this?

No, you just stay on the G/S, VASI, PAPI etc
 
citationjet
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RE: Displaced Threshold: Ducking On Landing?

Sat Dec 22, 2007 10:21 pm

Maybe not.

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RE: Displaced Threshold: Ducking On Landing?

Sat Dec 22, 2007 11:26 pm

no, no

Displacement of a threshold reduces the length of runway available for landings. The portion of runway behind a displaced threshold is available for takeoffs in either direction and landings from the opposite direction. A ten feet wide white threshold bar is located across the width of the runway at the displaced threshold.
 
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RE: Displaced Threshold: Ducking On Landing?

Sat Dec 22, 2007 11:42 pm

I don't know why a pilot would want to land short just because there is a displaced threshold. If the pilot is worried about the length of the runway, then a short approach will be followed as normal. However a short approach can be done on any runway regardless of whether it has a displaced threshold.

Now I'm sure there are some pilots that will land a bit shorter on a runway in order to cut taxi times down, but overall that is far less common than landing long.
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pilotpip
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RE: Displaced Threshold: Ducking On Landing?

Sun Dec 23, 2007 2:31 am

Nope. I don't pay attention to them. You can only roll out on them as is, why bother landing on them?

I won't even land "short" as it is to make a shorter taxi. That's what brakes and reversers are for. It's not safe, it's not legal. There's a reason we have a touch down zone.
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RE: Displaced Threshold: Ducking On Landing?

Sun Dec 23, 2007 2:52 am



Quoting CosmicCruiser (Reply 3):
Displacement of a threshold reduces the length of runway available for landings.

What more can you say
 
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Faro
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RE: Displaced Threshold: Ducking On Landing?

Sun Dec 23, 2007 11:40 am

Thanx everyone, I was under the wrong impression about these displaced threshold landings. I guess people do give them the importance they deserve.

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RE: Displaced Threshold: Ducking On Landing?

Sun Dec 23, 2007 2:14 pm



Quoting CosmicCruiser (Reply 3):
The portion of runway behind a displaced threshold is available for takeoffs in either direction and landings from the opposite direction.

Well, is that always true?

The yellow pointers in the particular photo that CitationJet so kindly posted are stopways for rejected take-off only, not for extended take-off run or addition to landing distance.

The white arrows before a displaced threshold are stopways for RTO, or for extended take-off runs. Correct?

I might have misunderstood you post though  Smile
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CosmicCruiser
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RE: Displaced Threshold: Ducking On Landing?

Sun Dec 23, 2007 3:00 pm



Quoting BoeingOnFinal (Reply 8):
I might have misunderstood you post though

I just posted an excerpt from the AIM where it states that its use is for RTO, landing from opposite direction, and sometimes T/O but never for same direction landing.
 
BoeingOnFinal
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RE: Displaced Threshold: Ducking On Landing?

Sun Dec 23, 2007 3:21 pm



Quoting CosmicCruiser (Reply 9):
I just posted an excerpt from the AIM where it states that its use is for RTO, landing from opposite direction, and sometimes T/O but never for same direction landing.

Understood  Smile

Since we are on the subject, in what cases are the individual areas certified for TORA and LDA?

I always assumed that TORA was from the T/O end threshold or a prospective extended T/O area, to the opposite threshold. And that if a clearway was present it would be used to calculate TODA. Can you ever extend the TORA past the opposite threshold?

I also assumed that the LDA was from screen height above landing threshold and to the opposite threshold. Can you extend this particular distance past the opposite threshold?

Thanks in advance from an eager to learn student  Smile
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mandala499
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RE: Displaced Threshold: Ducking On Landing?

Sun Dec 23, 2007 6:01 pm

If this topic is made due to the 346@Quito... AFAIK, there's a difference between a displaced threshold and that runway when you're doing an ILS approach...

Whatever the runway... it's wise not to use the area before the threshold... so why duck down in Quito? Coz, there the issue isn't a displaced threshold, but more like a displaced glideslope... If you see the runway and you duck down, as long as you're landing after the threshold, you're legal... BUT, if you become unstable due to the ducking manouver... that's a different problem.

Quoting BoeingOnFinal (Reply 10):
Can you ever extend the TORA past the opposite threshold?

If I remember correctly, yes, as long as TORA is not > TODA.... but better check the books. Although I don't see the point in doing so, you can have a displaced threshold for reasons other than obstacles (t/o or ldg)...
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Faro
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RE: Displaced Threshold: Ducking On Landing?

Fri Dec 28, 2007 4:28 pm



Quoting Mandala499 (Reply 11):
If this topic is made due to the 346@Quito... AFAIK, there's a difference between a displaced threshold and that runway when you're doing an ILS approach...

It's this kind of thing I was considering in fact:


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I had thought that pilots would have a natural tendency to duck beneath the nominal approach slope when landing on runways with displaced thresholds. This is apparently not the case in general, but I wonder whether with short runways and difficult approaches as pictured above, people do still duck. In this snapshot and from the skid marks' location at the beginning of the runway, it would seem that most landings were made from a screen height at the displaced threshold that is somewhat less that the nominal 35 feet.

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AJ
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RE: Displaced Threshold: Ducking On Landing?

Fri Dec 28, 2007 10:19 pm



Quoting Faro (Thread starter):
When landing on displaced threshold runways, isn't there an urge to duck below the nominal approach slope

Yes, there is often an urge to do so. The urge is particularly strong when breaking out of cloud at minima and seeing that you are already approaching overhead the threshold. This urge is suppressed and hopefully stopped through training just like any other urge experienced in flying, particularly instrument flying.
 
Buzz
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RE: Displaced Threshold: Ducking On Landing?

Sat Dec 29, 2007 12:08 pm

Hi again Faro, Buzz here. I don't fly for a living, I fly for fun. There's a couple places around PDX with displaced thresholds. KVUO (Pearson airfield) runway 26 comes to mind. If you were to land on the end of the runway, you'd drag yourself through some trees. I recall one guy did that with an Ercoupe...

So the displaced threshold is for obstacle clearance, assuming a 3 degree glideslope.

Do you have that often in your area... is LSGG short for Geneva?

g'day
 
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Faro
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RE: Displaced Threshold: Ducking On Landing?

Sat Dec 29, 2007 1:39 pm



Quoting Buzz (Reply 14):
So the displaced threshold is for obstacle clearance, assuming a 3 degree glideslope.

Do you have that often in your area... is LSGG short for Geneva?

Heya Buzz, LSGG is indeed Geneva but I learned to fly in Annemasse (LFLI) which is just over the border in France; much cheaper there. As for the displaced threshold I agree that it's for obstacle clearance; simply I would think that there is an instinctive urge to duck that must be consciously countered and disciplined. Perhaps in certain circumstances and certain airfields (cf my last post above), this is more difficult than others.

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CosmicCruiser
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RE: Displaced Threshold: Ducking On Landing?

Sat Dec 29, 2007 2:38 pm

[

Quoting Faro (Reply 12):
I wonder whether with short runways and difficult approaches as pictured above, people do still duck. In this snapshot and from the skid marks' location at the beginning of the runway,

No not really. That doesn't mean some pilots don't as seen in your photo but the available runway must be at or longer than your landing dist or you shouldn't be landing there. As you mentioned a "difficult app" would be the place you certainly wouldn't want to be deviating from the correct profile

Quoting Faro (Reply 15):
Perhaps in certain circumstances and certain airfields (cf my last post above), this is more difficult than others

If I may add once more the emphasis that you should not have bad habit patterns that you will do this SOMETIMES at certain airports but not at others. Bad habit indeed
 
mandala499
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RE: Displaced Threshold: Ducking On Landing?

Sat Dec 29, 2007 6:17 pm



Quoting Faro (Reply 12):
It's this kind of thing I was considering in fact:
This is apparently not the case in general, but I wonder whether with short runways and difficult approaches as pictured above, people do still duck. In this snapshot and from the skid marks' location at the beginning of the runway, it would seem that most landings were made from a screen height at the displaced threshold that is somewhat less that the nominal 35 feet.

Ahaa...

Well, a few things to note in this runway... No VASI/PAPI, no 500ft markets and no aiming bars either. So technically there's no "ducking" to do... *grin* But anyways, seriously, no visual slope guidance, no aiming bars or whatever you can aim at after the threshold within an acceptable touchdown distance from threshold. In this case I'm not that surprised a few landings are made before the displaced threshold... Perhaps a few decided to "just aim slightly ahead of the threshold"... And if those people just thought "get over the hill, the fence and then plant it"... I wouldn't be surprised (though I don't recommend anyone to think that way)... But then again...

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Even when they had the aiming bar, some still touched before the threshold...

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