fly727
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Joined: Tue Jul 29, 2003 8:27 am

Embraer, Landing Distance With Multiple Failures

Fri Nov 08, 2013 6:12 pm

Dear all:

Certain abnormal and emergency procedures contained in the Quick Reference Handbook and Aircraft Operations Manuals (on Embraer aircraft) require multiplying a normal landing distance published in the manuals by a specific factor in order to account for the reduced ability of the aircraft to stop or a greater approach speed that the failure calls for.

For example, in case of a dual hydraulic failure, due to the fact that the airplane won't have spoilers and only emergency braking will be available, the actual distance in which the airplane will stop is 2.86 times that of the required if no abnormality is presented at the same weight. The QRH instruct us pilots to multiply the UNFACTORED landing distance (that is the REAL, the ACTUAL, the one which the manufactured DEMONSTRATED during certification) by 2.86, resulting in a FACTORED one that we will have to use.

In case of a multiple failure, each of which adds a certain factor to the landing performance, would it be necessary to add the factors, multiply one factor by the other or taking the most restrictive of all would be deemed reasonable?

Again an example. Failure A calls for a greater landing distance of 1.2 times the normal required landing distance. If presented alone, no problem, only a 20% additional runway is required based upon the actual distances published by the manufacturer. In the same way, failure B calls for a landing distance of 1.3 times the normal. if both independent failures are presented, should I multiply the normal distance by 2.5?

Information provided by Embraer is very scarce; here at Tech/Ops your inputs are always valuable.

Thanks for your opinions.

RM.
There are no stupid questions... just stupid people!
 
Maverick623
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RE: Embraer, Landing Distance With Multiple Failures

Fri Nov 08, 2013 8:12 pm

Quoting fly727 (Thread starter):

In case of a multiple failure, each of which adds a certain factor to the landing performance, would it be necessary to add the factors, multiply one factor by the other or taking the most restrictive of all would be deemed reasonable?

I'm not sure of any scenario where two separate, independent faults that would adversely affect landing performance would not be in the QRH. Do you maybe have an example?
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Web500sjc
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Joined: Tue Sep 15, 2009 4:23 am

RE: Embraer, Landing Distance With Multiple Failures

Fri Nov 08, 2013 9:21 pm

Quoting Maverick623 (Reply 1):
I'm not sure of any scenario where two separate, independent faults that would adversely affect landing performance would not be in the QRH. Do you maybe have an example?

Airplane simulators are very fun...

engine failure - land flaps 3, increase landing distance by 1.25

brake failure - increase landing distance by 1.6



we factored in one correction and then factored in the next correction

so 1000 unfactored normal

1250, factored for engine failure

2000, factored engine failure and brake failure
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pilotpip
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RE: Embraer, Landing Distance With Multiple Failures

Tue Nov 12, 2013 2:54 am

The 170/190 QRH from the factory has a number of charts for non-normal situations in the performance section as you mentioned. I don't know which aircraft you are in, or what procedures you use (company, or Embraer SOPM) but here is what Embraer says in their factory QRH:

"In the event of multiple failues (excluding cascade failures) with different landing configurations and/or landing distance correction factors, the crew should use good judgement to determine the safest course of action."

You're right, not much guidance. I would strongly suggest you take this to your program manager/ chief pilot as well as discussing it with someone at Embraer.

Also remember, there is another great little tidbit in the QRH that I think many people forget. To paraphrase it says something to the effect of "This guide can not address every situation and does not take the place of experience and knowledge of the aircraft systems."
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mrocktor
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RE: Embraer, Landing Distance With Multiple Failures

Wed Nov 27, 2013 9:51 pm

As noted in the "disclaimers" in the manuals mentioned here, published guidance does not cover every possible scenario. It is not required to cover any scenario considered extremely remote (less than one in 10.000.000 hours), and most independent dual failure scenarios are extremely remote. Any single failure with multiple effects (like hydraulics taking out half your brakes, some spoilers and a reverser) will be covered in the manual.

That said, you can apply some engineering knowledge to make your "good judgment" as good as it can be:

For conditions where the multiple factors are related to the same deceleration mechanism, you probably want to multiply the factors. Example: I have one pair of brakes failed and 2 of 8 spoilers inoperative. Lets say the factors are respectively 1.6 and 1.2 for those conditions. Since the spoilers are used to dump lift, the spoiler failure is making the remaining brakes less effective (i.e. the two failures interact). So in this you could use 1.6 * 1.2 = 1.92 as a factor (unless the manual contains other guidance for this condition).

Same would apply to brakes+contaminated runway, since both are related to your ability to decelerate via friction.

For conditions where the factors are unrelated, you can probably just add the factors (excluding the base landing distance - more on that in a minute). Example: I have one pair of brakes failed and the left thrust reverser failed (bear with me here, I know T/R generally does not go into performance, so you would not need a factor). Lets say for the purpose of this example you have factors of 1.6 and 1.1 respectively for these conditions. In this case you could use 1+(1.6-1)+(1.1-1) = 1.7, where the whole +1 -1 nonsense is to account for the fact that a factor of 1.6 is 60% additional runway, and a factor of 1.1 is 10% additional runway and we are trying to add the required additional runway length, since we don't expect the reverser failure and the brake failure to have any significant effect.

Next, anything affecting your energy state (say, increased approach speed because your flaps are stuck) should be handled multiplicatively (like the first example) with any other factor. The higher energy interacts with any and all of your deceleration features - so if any of those are failed the effects will be cumulative.

Last but not least, always keep in mind that energy has a quadratic relationship with speed (i.e. is proportional to the square of your speed), while most deceleration features (everything except aerodynamic drag) are linear in nature (i.e. they reduce your energy at a constant rate). So a 10% reduction in deceleration does NOT mean a 10% increase in landing distance. It is more. A 20% increase in approach speed does NOT mean a 20% increase in landing distance. It is more.

And finally, all of this is mostly moot. If you are dealing with multiple independent failures affecting your deceleration capability you should land at the longest available runway within reach regardless (unless that means a long diversion and you have reason to land ASAP, like a fire on board).

PS: This information is provided for educational purposes only. Don't sue me if you have an overrun!

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