JAA ATPL Training Questions - CAP698 from UK CAA

[jimmy2times]

Hello
I am studying towards an exam (Performance and Flight Planning) which refers to CAP698 from UK's CAA.

I am have some uncertainty as to how to the Regulatory Factor for calculating the Take Off Distance REQUIRED.

In CAP698 they apply in the example a Regulatory Factor of 1.15 to the take off distance required for the MEP1 Aircraft (see Page 2 Section 3) because it is an Unbalanced field.

In the case of SEP1 Aircraft (see Page 2 Section 2) in the example they do not mention that it is an unbalanced field and do not apply that Regulatory factor of 1.15. So if it is balanced, I think they should then multiply the result by 1.25 (no stopway of clearway)...? I am confused

There is no place where this nuance is explicitly explained. So can someone clarify to my when to use the 1.15 (TODA) factor, when to use the 1.3 (ASDA) and the 1.25 (TORA) when it comes to applying factors to the TOD from the graph?

Here is CAP698 online: http://www.caa.co.uk/docs/33/CAP698.pdf

Thank you in advance!

[keith williams]

You need to understand the difference between

a. The Take-off Distance (TOD)
b. The Take-off Distance Required (TODR)

To calculate the TOD we start with the graphical distance and apply the slope and surface condition factors. This is what has been done for the SEP in Section 2 page 2.

To calculate the TODR we start with the TOD and apply the regulatory factor.
The process is to start with the graphical distance and apply the slope, surface condition and regulatory factors. This is what has been done for the MEP in Section 3 page 2.

When doing the performance exam it is essential that you look very carefully at what they are asking for. That "R" at the end of the TORR, TODR and LDR make all the difference in deciding which option is correct.

[jimmy2times]

Many thanks Keith. I think I am starting to understand that nuance.

So just to clarify, if I am asked to calculate the TOD then it's the graphical distance and surface and condition factors.

If I am asked to calculate the TODR then it's the graphical distance with surface/condition factors AND the REGULATORY factor.

And if this is a question of TODR, then the regulatory factor is 1.15 for unbalanced field, and 1.25 for balanced (no stopway/ clearway)
If it is a question of ASDR, then the regulatory factor is 1.3

Am I getting it right?

Thanks

[keith williams]

You are correct up to the point where you included the term "balanced field".

The CAP says the following


a) When no stopway or clearway is available the take-off distance when multiplied by 1.25 must not exceed TORA.

b) When a stopway and/or clearway is available the take-off distance must:
i) not exceed TORA
ii) when multiplied by 1.3, not exceed ASDA
iii) when multiplied by 1.15, not exceed TODA

A balanced field is simply one in which the TODA is equal to the ASDA.
A field with identical stopway and clearway is a balanced field. A field with no stopway and no clearway is also a balanced field.

The 1.25 factor applies where there is no stopway and no clearway.
The 1.15 factor applies when there is a stopway and/or a clearway.

If it is a question of ASDR, then the regulatory factor is 1.3

Not quite. In all of the cases above we are comparing the TODR with the TORA, ASDA and TODA.

So for example if we have a stopway and/or a clearway we must ensure that

i) The TOD is not longer than the TORA
ii) 1.3 x the TOD is not longer than the ASDA
iii) 1.15 x the TOD is not longer than the TODA

If have no stopway and no clearway we simply need to ensure that 1.25 x TOD is not longer than the TORA.


Curiously although you will find the terms TORR, TODR and LDR, you will not find the term ASDR anywhere in the EASA regulations. Although you may find that it comes up frequently in perf related conversation.

Later in the course you will come across the terms "balanced take-off" and "balanced V1 take-off) These relate to the distance required and not to the distances available.

[jimmy2times]

So it means that if I have no stopway and no clrearway, then in order to find the TODR the graphical TOD must be multiplied by 1.25 (and condition/surface factors).

If I have for example only a stopway but no clearway, then the TODR is the graphical distance multiplied by 1.15 (and condition/surface factors).

If I have only a clearway, then the graphical distance will be multiplied by 1.3 (and condition/surface factors).

If I have a balanced field with stopway and clearway (TODA = ASDA, i.e. clearway and stopway are of same length) then graphical distance must be multiplied by 1.3 (and condition/surface factors).

Quite confusing all this I must admit :) Thanks for the clarifications!!

[keith williams]

It all looks a bit complicated at first, but CAP698 Section 2 page 4 and Section 3 Page 6 contain worked examples. If you work through them it should become clearer.