ATPL Performance question - downslope factorization

[flyer696]

Hi!

I'm studying for ATPL Performance exam. I'm confused which factor shall I use for calculation of TORA with downslope. The question from databank is:

An aircraft is scheduled for takeoff and TODR is 800m under normal conditions, ISA, sea level. Your airfield is: Pressure Alt. 2000ft, temp. +21 celsjus, 5kts tailwind, 2% downslope. Adjust TODR using following factors:

pressure alt. +/- 20m/1000ft
Runway slope +/- 15m/1% slope
tailwind +10m/1kt
Temperature +/- 5m 1 celsjus ISA deviation.

Do I need to decrease TODR because of downslope or not? One database says yes and other one says no so which one is correct? Can you explain it to me and give a document where I can find definitive answer? Or maybe you know what JAA thinks is correct?

[jackcarls0n]

Not sure about the JAA or any authority...but in practical application always TODR decreases with downslope. We take off from runway that is about 300-400 m in total lenght but has a slope of 6.5% to 12% without which the take off would not be possible if it didn't had the downslope.

The reason for this is the downslope allows for the increase in airspeed which happens due to gravity.

Can show them the physics books or this http://www.nordian.net/pdf/jaa_performance_demo.pdf

[flyer696]

I know the basic theory but I need the JAA way to correctly answer that particular kind of questions at the exam.

[FlyingStone]

If I remember correctly, JAA approved answer is that only upslope is taken into consideration when calculating takeoff distance. Conversely, when calculating landing distance (or accelerate-stop distance) only downslope has to be taken into account.

[flyer696]

Are you 100% sure about that?

[FlyingStone]

It should be correct, but do check it with your ATPL books...

[keith williams]

The definitive reference for this is EU OPS. I do not have a link for it, but if you go to the EASA website and do a search you will probably find it.

Or if this fails, go to the UK caa website caa.co.uk and do a search for CAP698. This is a book that is provided for candidates taking the Performance exam in the UK.

At the beginning of the MEP1 section you will find the factors to apply for take-off. This section includes the following.



d) Take-off distance should be increased by 5% for each 1% upslope. No factorisation is permitted for downslope.


If you have never seen the CAP books it would be worth looking at them. They contain lots of useful information for the exams and they can all be downloaded free of charge.

The books to search for are.

CAP696 JAR FCL Examiantions Loading Manual.
CAP697 JAR FCL Examiantions Flight Planning Manual.
CAP 698 JAR FCL Aeroplane Performance Manual.

[flyer696]

I know CAPs but I thought that they apply to performance charts. My question is not related to performance charts. But maybe I'm wrong...

[keith williams]

Although the CAP698 contains a lot of performance charts it also contains a lot of other material. The MEP 1 and SEP 1 sections for example, include the rules for factorisation and some practical exercises.

If you plan to take the exams in Poland you may or may not be permitted to take the CAPs into the exams( I don't know) . But they are still a valuable source of study material. As an example they contain the answer to your question regarding the use of downward slope when calculating TODR.

As another example, Section 4 Pages 7 and 8 contain the criteria used to calculate TOR, ASD and TODR from test flight distances. This material is used in a number of performance exam questions.

But as I said in my earlier post, if you want the definitive document you need to go to the EU OPS Manual.