combined failures & factored distance
Thread Starter
Joined: Mar 2005
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From: I would like to know
combined failures & factored distance
EXAMPLE :
We have a combined failure with "antiskid inop" (AFM correction of 40 % on landing distance) and "flap failure" (correction of 30 %).
Should I increase landing distance by 70 % (40+30) or calculate the first correction anche THEN multiply by 30 ?
Results are-of course-different and AFM do not give me any information on that.
Thanksssssss
We have a combined failure with "antiskid inop" (AFM correction of 40 % on landing distance) and "flap failure" (correction of 30 %).
Should I increase landing distance by 70 % (40+30) or calculate the first correction anche THEN multiply by 30 ?
Results are-of course-different and AFM do not give me any information on that.
Thanksssssss
Last edited by gigi116; 25th June 2008 at 10:58.
Warning Toxic!
Disgusted of Tunbridge
Disgusted of Tunbridge
Joined: Jan 2005
Posts: 4,011
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From: Hampshire, UK
The increased allowance for anti-skid is because of degraded braking. By factoring it onto the flap failure, you are increasing the penalty for anti-skid above what was in the makers mind. Therefore in my opinion, you add them separately and not factor one on top of the other. That is what I would do. There are tables for defects in the QRH, and if the maker wanted increased penalties to apply, then there would be a combined failure mode given.
I would say I think it unfair to be hammered with that in the simulator!
I would say I think it unfair to be hammered with that in the simulator!
Joined: Oct 2003
Posts: 662
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From: If this is Tuesday, it must be?
Our QRH specifically states that speed increments are additive but distance factors are cumulative, i.e. you multiply by 1.3 for the extra speed/less drag of failed flaps then by 1.4 for the lack of anti-skid
However, since the starting figure is the actual landing distance, not the field length required for normal landing (ALD x 1.67) it's not as bad as it first looks. Your example gives a total factor of 1.82, so not dramatically longer than your normal runway.
However, since the starting figure is the actual landing distance, not the field length required for normal landing (ALD x 1.67) it's not as bad as it first looks. Your example gives a total factor of 1.82, so not dramatically longer than your normal runway.
Joined: Feb 2008
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From: Standby...call you back..
Verry interesting question...
and considering the fact that when everything's ok, you have to factorize the landing distance, for commercial ops...
When in trouble ...this should be ignored ???..this is a question ..not a statement..This safety margin could be considered as well !!!
So with the same exemple.. (ald x 1.82) x 1.67
thanks for your feelings..
and considering the fact that when everything's ok, you have to factorize the landing distance, for commercial ops...
When in trouble ...this should be ignored ???..this is a question ..not a statement..This safety margin could be considered as well !!!
So with the same exemple.. (ald x 1.82) x 1.67
thanks for your feelings..
Joined: Oct 2003
Posts: 662
Likes: 5
From: If this is Tuesday, it must be?
The lawyer's answer is that no further factoring is required. The normal ops landing distance factor is purely a planning consideration, once you are airborne you use actual distances for calculations.
However, it's a bit of a no-brainer that if you have a choice of places to land flapless/no anti-skid or whatever, one has 1 metre more than the figure you've calculated and the other has a lot more - which do you choose?
However, it's a bit of a no-brainer that if you have a choice of places to land flapless/no anti-skid or whatever, one has 1 metre more than the figure you've calculated and the other has a lot more - which do you choose?
