Actual Vs Planned Landing Distance

[mutt]

It appears that our new training provider is advising crews that the "correct" landing distance for part 91 operations is the actual landing distance, and that planned landing distances using the 60/40 rule only apply to part 135.

In theory this is correct, certainly part 91 doesn't stipulate any requirements.

I would presume that the JAA regulations are similar.

So what is your personal limit for landing runway length requirements under normal operations? Are you happy to use Actual Runway Length or do you apply any additional requirements?

Mutt

[Yogibaboo]

Usually I use exact numbers from AFM. On really short runways I overfly threshold not higher that 10 ft, instead of 50 ft. Never need more than 70% of calculated distance to be fully stopped. That gives me safety margin.

Yogi

[I.R.PIRATE]

Depends...do you feel lucky punk? Well do,ya?

Am I wiling to go into a strip that has available the same amount of runway that I require? I doubt it, unless it was an emergency. I like somewhat of a fudge factor, maybe 20-30 % added to the required length. If it is the difference between actually getting a client into his destination, I will consider the alternatives in the area, and if the terrain allows an approach to land on the numbers, but I don't look at less than 15%.

This would obviously be Adapted for the prevailing conditions. If its rainy and wet, I like to look at the factored numbers as a sensible guide to what is expected. I just feel that I don't want to have to answer questions like : why did you slide off the end of a wet runway that was shorter than your factored wet distance required - even on a 91 mission, I think you will have some 'splainin to do.

[galaxy flyer]

Mutt

The mob I'm with uses the 'factored' distance foBr all planning and operational purposes. Ops, based on ALD, are possible but require management review unless an emergency. Any LDA less than 4000' requires management approval regardless of factored distance. We've turned down ops for ALD, widths narrower than 75' and questionable PCN.

Yes, FAR 91 ops.

YOGI. How's the braking action in the grass?

GF

[His dudeness]

We use 80%, so the factor is 1.25...works well for us...for wet runway we use 1.44.

[Yogibaboo]

do you feel lucky punk? Well do,ya?

My pleasure, if that really makes you happy.

[Joe le Taxi]

My pet hate is airfields that declare the runway wet when it nothing of the sort - It can often make the difference between being able to get in/out and not.

Farnborough was giving wet the other day, when not only was it not wet, it wasn't even damp - the tarmac was completely dry. Wet means the surface is so wet, it is reflective - any less than that, and it is damp (ie changed colour due water).

[mutt]

So glad I gave up the day job..... sorry



Yogibaboo, you have stated in another post that the shortest runway you have landed a CJ1 on was 2953 feet, obviously this was acceptable as per the AFM, but to me it sounds as if you are using the availability of the thrust reversers to provide your fudge factor. But what happens if your air/ground sensor fail and you cant use the thrust reversers?

Mutt

[Joe le Taxi]

Yes - its in a CAA CRD definition document (I cant copy and paste the PDF tho)

Are you sure about your definitions, mutt? Unless I am going senile, more than 3mm (or equiv) is contaminated, not wet, and slippery refers to braking action - a different matter (although it may well go together with a contaminated runway).

[His dudeness]

Yogibaboo, you have stated in another post that the shortest runway you have landed a CJ1 on was 2953 feet, obviously this was acceptable as per the AFM, but to me it sounds as if you are using the availability of the thrust reversers to provide your fudge factor. But what happens if your air/ground sensor fail and you cant use the thrust reversers?

Mutt, I guess you agree that:

a) the CJ1 has no thrust reversers, just attenuators They have a marginal effect on aborted takeoff (5%)

b) Jet landing performance charts are always excluding T/Rs or in case of the CJ1 the attenuators (there might be additional charts with T/Rs, but for certification they are not required nor used in planning)

[mutt]

a) the CJ1 has no thrust reversers, just attenuators They have a marginal effect on aborted takeoff (5%)

5% isn't a great deal, but my point was basically about Yogibaboo being happy to use the ACTUAL runway length as shown in the AFM, while others are applying fudge factors.

always excluding T/Rs

True.... the AFM states how the landing distance was derived.... in our case..

1. Immediately after touchdown, the nose was lowered and full brakes were applied. Auto ground spoiler deployment was initiated at main gear touchdown by wheel speed spin-up. If the auto ground spoiler system was not armed, the speed brakes were manually deployed after brake application, and appropriate time delays have been included in the landing distances for this procedure. Credit was not taken for reverse thrust.

We use the 60/40 rule, although the shortest runway that we use is Luton, so that's about 2x Actual Landing Distance, and we consider that "Short"

Mutt

[I.R.PIRATE]

Yogi, my post was actually being constructed when you posted yours, so I had not seen your posting when I pressed send. My post was in response to Mutt's first post, but it seems that your consequent post, which appeared ahead of mine, sort of made the point I was getting at.

I don't mind if you want to use actual distance, I am not here to judge, I just wanted to imply that I don't feel lucky enough to use the absolute minimum numbers. Guess I am not such a good driver yet, but maybe one day. I like to give myself a fighting chance, when things don't go one hundred percent my way.

I have used maximum braking in my aircraft before, and I know for a fact that we could stop it way shorter than actual numbers by unceremoniously dumping it onto the numbers after a four red approach, and then throwing out TRs and standing on the brakes. But do I want to do that with pax onboard?

Rather not.

[His dudeness]

but my point was basically about Yogibaboo being happy to use the ACTUAL runway length as shown in the AFM, while others are applying fudge factors.

Now you made go in the cellar, getting the ole stuff out...

LDR at MLM/SL.
at 50° is 2880 ft
at 30° it is 2690ft
at 15° it is 2590ft
and at 0° we look at 2510 ft

Assuming he hits the deck with 2 pax/2 crew and a bit of luggage, a reasonal reserve of, say 800lbs,the A/C would weight aroung 9300lbs.
Then the numbers are:
2710 ft
2590 ft
2490 ft
2410 ft

Without pax/luggage and maybe 600lbs remaining we might look at a LDW of 8500lbs:
2560 ft
2450 ft
2360 ft
2280 ft

Getting out of there is poss at SL at (FAR/JAR 25 perfomance):

30° at 9500lbs
20° at 10100lbs
15° at 10200lbs
0° at 10500lbs

MTOM is 10700lbs

So, there is always a little margin. (not too much, granted, but...)

Given the fact that the airplane has one tire at each gear leg and one electrically operated tiny little brake pump (like al 5XX series Citations IIRC), there is always some tradeoff in safety or greater risk in these airplanes than in bigger ones (FAR25)

Having said that, I feel this difference in risk is not a big one and would personally operate into 2953ft of runway in CJ1 without thinking of myself of being a cowboy...I would explain the higher risk to the owner / pax before, so he/she could make her mind up and decide whether its worth it or not. IŽd also let them know that if there is too much of a crosswind or damp/wet runway I wouldnŽt go there.

[Yogibaboo]

Thank you His Dudeness

Thank you His Dudeness. Great job!!! I do exactly the way you described.

Wet runway? Strong crosswind?

Boss, today you will drive back home from the airport 2 hours instead of 2 minutes as usually. And he has never said NO.

And yes, we do not operate from this runway during winter/snowing season.

Yogi

P.S. I operate Citation XLS+ from that runway as well. Never used thrust reversers. No need for that. Usually stop at 60-70% of the runway.