Hi all,

I answered the below question on Echo Takeoff as 2600kg but the answer was 2700kg, I've been trying to work the question backwards to see where I went wrong but I can't see where the issue is. The only was I can get the answer to work is by using 1% slope instead of 2%, but the ruwnay in the example is 2%.

Could some one help please?

Runway 07/25
Surface long dry grass
Slope 2% down to the southwest
TODA 810m in both directions
wind 070 @ 5kt
Elev 1600ft
QNH 1033 hPa
Temp 25c
Max tailwind component 5kt

It would be a lot easier to answer your question if you were to post a scan of your worked chart. If you have made an error, the scan will show it very quickly.

hi john,

here's how I worked it out.

I'll print a copy out and work it later on - have a meeting to go to now.

Observations from a quick look on the screen - you might

(a) check both runway directions - why have you only looked at the one ?

(b) redo the entry interpolations - Hp and TOD - both are a tad rough

(c) redo the intercarpet lines - they need to be parallel to the scale lines - in particular, DH to TOD carpet is a tad out

Will post again later today.

Now had a chance to play with the chart.

Could I get you to recheck the answer given (2700 kg) in the question bank, please ? (I don't have access to the question so I need to work through you in this case).

Are you sure the answer given is 2700kg? It looks more like 2800kg.

My concern, exactly.

2700kg would require something like getting the altimetry calculations back to front.

My first cut gives a bit over 2600kg or a bit under 2800kg depending on the runway.

Hi all,

Thanks for trying. The question came up in on of the Exercise TOLP.2: Echo Take-off Performance part of the online course, so it was randomly chosen,

Hi Bob, I can cofirm the answer was 2700kg. After I got it wrong the first time, I tried numerous times working back through the answer starting at the 2700kg weight. I tried different combinations of runway and slope. The only way it worked out was with a 1% slope up, but 2% is given in the question.

PH = 1000' (1600'+(1013-1033)x30)

Just to make sure I have the logic right, should we use runway 07 or 25? I chose 07.
Using 07 makes use of the 5kt headwind, and follows CAR 166A 2 (h) but has the 2% up slope, or use 25 which benefits from the 2% down slope but have the 5kt tailwind (which is max tailwind component) which is allowed via CAR 166A 5 (a)

I can confirm the answer was 2700kg.

Answer was wrong, unfortunately .. but the reworking will have given you some useful thinking and practice so all's well there.

A quick looksee suggests that whoever ran the original question may have done the altimetry back to front .. which gives an answer around 2700 kg. I have done both cases in the attachment so that you can see that slack altimetry work can have a serious affect on the final answer.

should we use runway 07 or 25? I chose 07.

Suit yourself, either is fine. In practice, if you are weight critical, you will be running with the weight optimum runway. If not, other considerations will dictate your decision .. eg what is the overrun like on both runways for a potential reject, what is the after takeoff terrain like for a potential engine problem, etc. Wind and slope are considerations but not, necessarily, the critical drivers to a runway selection decision.

Main thing to take away is that you need to be a bit more painstaking and accurate in your chart work. On this occasion, the errors balanced out and your working still came out near the answer .. next time if might not be so fortuitous.

Side notes - ref the attachment, just in case anyone thinks I did it with a paintbrush .. it was done by exporting the CASA page to a drawing package, working it and then making the lines thicker so that you can see them more easily.

On another point, the Echo chart has been drawn pretty dreadfully in the TOD carpet (I have no idea who did the original .. definitely not one of my charts). While one can do a fairly accurate interpolation by a simple regression, that would be outside what the examiner is looking for so the interpolations have been worked linearly.

It's not uncommon for CASA to present you with that type of question in the CPL exam. You will be given a take-off from a strip where the wind is blowing down the slope. If you take off into wind you will have an up-slope and if you take off down wind, you will have a down-slope. Since aeroplanes don't deliver power directly to the wheels, they are notoriously bad at climbing hills, so it is very likely that the down-slope tail wind option will allow the greatest take-off weight. In any case, it's not asking too much to check both possibilities.

However remember that if the wind is more than 5 knots, you would not have the option of taking off down hill since the maximum tailwind component for that aeroplane is 5 knots. You would then be stuck with the up-hill into wind situation.