combined failures & factored distance

[gigi116]

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

[Rainboe]

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!

[BizJetJock]

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:eek:
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.:ok:

[roljoe]

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..

[BizJetJock]

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?:ooh:

[roljoe]

Thanks, bizjetrock....the answer is obvious..