Landing performance calculation

[sriyadh]

Hi
I'm stuck at few questions.

You are flying at an altitude of 7000 ft and you are 12,5 NM from the runway threshold. TAS: 70 kts, no wind, ISA conditions. How many minutes will it take to descend?

I cant find the formula to calculate this. Can somebody give me this?

[Chilli Monster]

Forget the altitude - just use your calculator to work out how long it will take you to cover 12.5 nm at 70kts ((60 / Speed) x distance = 10 mins 43 secs)

A rate of descent would of course be useful. Altitude loss required / time available for descent. 7000 / 10.71 = 653 fpm

[Pirke]

You could choose to do a quicker descent. The question didn't specify that you should use the exact distance for your descent. Or that your speed should remain constant for that matter, or that the runway is at sea level

What is the context of the question? PPL study?

[ChickenHouse]

Is it only me missing some vital information?

- elevation of the runway? Reason: must be an altiport, because otherwise you would sit in FL070, not Altitude 7000.
- mystical airplane, which does not speed on descent?

[Gertrude the Wombat]

And descend to what? 2,000' for the overhead join?

[Chilli Monster]

What's one of them?

[glendalegoon]

hi

you will eventually learn other things, but thismight help

FIRST OFF in a non pressurized airplane, anything more than a 500 foot per minute descent rate can be uncomfortable to the average person


so, limit yourself at the most to 500 FPM and this would take 14 minutes.

trouble is your are already too close to accomplish this as chilli monster has pointed out that rate of descent and speed/time.


SO...you should have started 14 minutes from the field assuming straight in to the runway.

JOINING THE PATTERN is something different and you might be able to do it at 500 fpm.


in the future you will understand better, but YOU have to decide how to handle your plane and the rate of descent to use.


In a jet we could descend easily at 6000 fpm (though not most efficently)...so there are many factors and as the others have indicated YOU HAVE TO KNOW MORE TO ASK THIS question intelligently

[India Four Two]

sriyadh,

Welcome to PPRuNe.

I agree with glendalegoon. Calculate how long it will take you to descend to circuit altitude at 500 fpm and then calculate the distance required, using your descent TAS (ignore the descent angle - it is small).

For most light aircraft that I fly, I assume two nm per minute. So for a 500 fpm descent, I use four nm per 1000' of height loss.

[Mach Jump]

Chilli Monster's is the only 'correct' answer that can be derived from the information given.


MJ