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Within 60% of landing distance

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Within 60% of landing distance

Old 31st Mar 2020, 12:24
  #1 (permalink)  
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Within 60% of landing distance

Firstly I have searched extensively through old posts and have failed to find the answer. Some post came close to the answer I am looking for but for some reason Iím still not quiet getting it.

My question:
According to CAT.POL.A.230 Landing-dry runways it states:

(a) The landing mass of the aeroplane determined in accordance with point CAT.POL.A.105(a) for the estimated time of landing at the destination aerodrome and at any alternate aerodrome shall allow a full-stop landing from 50 ft above the threshold:
(1) for turbojet-powered aeroplanes, within 60 % of the landing distance available (LDA);

So for example:
LDR= 1200m
1200 x 1.67 = 2004m
Runway= 3000m so no problem I can land.

Now if I read the above statement word for word. ĎWithin 60% of the landing distance available (LDA)í
60% of my 3000m runway = 1800m.

Can someone explain what Iím missing here?
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Old 31st Mar 2020, 12:31
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LDR (1200m) is less than 0.6 x LDA (1800m), so all is good.
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Old 31st Mar 2020, 12:48
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Join Date: Sep 2004
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Yep, just as FlyingStone put it, your 1200m is 'within' the 60% of 3000, i.e. 1800m. You don't need to have 1.67 times the LDR (i.e. 2004m) to be within 60% of the 3000m.
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Old 31st Mar 2020, 13:43
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Okay I think I may be starting to see where Iím misunderstanding this. When I read the Ďwithin 60% of the landing distance availableí I immediately get 60% of my runway in my example 1800m (60% of 3000m). Since my LDR required is 1200m Iím then applying the 60% correction to that figure and getting the 2004m. 2004m is what Iíve calculated I will land with but I need to land with 1800m, so it appears Iíve corrected both figures by 60% instead of calculating one. What do you think?
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Old 31st Mar 2020, 14:42
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Yeah, you're unnecessarily doubling the penalty.

The regulation requires correction to the Landing Distance Available (LDA), not the Landing Distance Required (LDR). LDA is the length of the runway, LDR is the distance it will take the aircraft to stop.

Think of it like this - you have to prove you can stop on the runway if the runway was shortened to 60% of its total length.

So:

Corrected LDA = 3,000m * 0.6 = 1,800m.
LDR = 1,200m

You're good to go as you have a spare 600m over what is required to stop the aircraft.
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Old 31st Mar 2020, 15:22
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Originally Posted by A350 View Post
Okay I think I may be starting to see where Iím misunderstanding this. When I read the Ďwithin 60% of the landing distance availableí I immediately get 60% of my runway in my example 1800m (60% of 3000m). Since my LDR required is 1200m Iím then applying the 60% correction to that figure and getting the 2004m. 2004m is what Iíve calculated I will land with but I need to land with 1800m, so it appears Iíve corrected both figures by 60% instead of calculating one. What do you think?
To keep it easy :
At Dispatch stage take your aircraft published ALD (actual landing distance) and multiply by 1.67 for a DRY Runway. You should be at or below your runway LDA (Landing Distance Available).
Same for a wet runway, but multiply by 1.92.
Once you are done with dispatch then you start considering In Flight Landing Distances, i.e. you must fit in the runway. Your operator might consider an additional safety factor (factored landing distance) to be added to your ALD (15% extra).
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