× Welcome to the CPL Performance question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.

## Performance Exam Query's

• Posts: 7

### MaxCavill created the topic: Performance Exam Query's

Hi all,

I have my CPL Performance exam in a little less than a week and had some questions.

1. When you are given a question for landing distance required or maximum landing weight, which runway do I choose for the chart when given multiple runways? (1 runway's longer than the other, 1 has a higher slope, 1 has a headwind etc.) Which runway do I choose?

2. When given a PNR/ETP question with a significant crosswind, how do I calculate what my effective TAS is? Since TAS reduces as crosswind strengthens, where do I derive the new TAS along track?

3. When using a landing chart for the echo, should I use density height or, pressure height and temperature for the initial point of the chart.

• John.Heddles
• Offline
• ATPL/consulting aero engineer
• Posts: 383

### John.Heddles replied the topic: Performance Exam Query's

Subject to any curious things the examiner might like, in which case Bob/Stuart will correct me, the following is the standard approach to things.

1.... which runway do I choose for the chart when given multiple runways?

At the planning stage, you use the lesser weight of the best runway using the forecast and the best runway using nil wind (if the longest runway is level and has no other considerations, that would be the nil wind case to consider). I would also consider the situation where the wind might do something silly and factor that into the runway MLW analyses. The latter consideration is a depending on the aerodrome sort of thing and is not amenable to rules of thumb.

Approaching the destination, use the best runway unless the most into wind runway is acceptable.

2. .... how do I calculate what my effective TAS is? Since TAS reduces as crosswind strengthens, where do I derive the new TAS along track?

Subject to seeing the full question, just a trigonometric calculation. If you use a Jeppesen style whizz thing, the wind grid lets you do the calculation. If you use a Dalton, you can use the wind triangle. But, wouldn't you rather use the G/S ?

Note that your TAS doesn't reduce with the crosswind, the effective TAS does. You might benefit from a review of how the Jepp gadget runs the wind triangle calculation.

3. ..... should I use density height or, pressure height and temperature for the initial point of the chart.

The two should end up in the same line coming out of the carpet. If not, that is a deficiency in the original drawing of the carpet.

Engineering specialist in aircraft performance and weight control.