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REMAINING OCTA

MosesK

Topic Author

MosesK created the topic: REMAINING OCTA

Hey,
Just needed some help in understanding and answering this question.

Aircraft is at X
Climbing Ground-Speed 120kts
ROC-800ft/min

The minimum distance from A at which you could commence a continuous climb to A085 and remain outside controlled airspace is
A. 44NM
B.28NM
C.34NM
D.40NM

Although we probably could make a reasonable assumption, it really would help if we knew the initial aircraft level. Did you leave that bit of information out inadvertently ?

Engineering specialist in aircraft performance and weight control.

Again, this just needs a bit of reflection and thought to sort out the answer.

Easiest to work in gradients of ft/nm for comparison, keeping in mind that we will need to "clip" one (or more) steps. Keep in mind that the published height limits are OCTA so we can cruise or clip steps at those heights.

First, your speed is 120 kt or 2 nm/min. At a ROC of 800 ft/min, this is equivalent to a climb gradient of 400 ft/nm.

Looking at the airspace steps -

(a) from your present position to the next step is a 2000 ft climb in 13 nm so the gradient is 2000/13 = 154 ft/nm, well below your climb gradient so you will need to delay the climb so you don't infringe the 4000 ft airspace step.

(b) next step is 4000 ft to 6000 ft in (50-35) = 15 nm for a gradient of 2000/15 = 133 ft/nm, again well below your climb gradient.

(c) once you are past 50 nm, the step is 10000 which is not a concern for an 8500 ft cruise. We now have the overall picture of the climb requirement and you will be planning to just clip 6000 ft at 50 nm.

While we don't expect a problem, just check by working backwards to make sure that no other steps present a concern.

If we start at 6000 ft and 50 nm and work back at 400 ft/nm, then at the 35 nm step, we have just travelled 15 nm for 15 x 400 = 6000 ft. It is pretty obvious that no other steps will present a limitation problem so we just have to work back from the 6000 ft at 50 nm step to figure out where we need to start the climb from 2000 ft. That is to say, how far will it take for us to climb 6000 - 2000 = 4000 ft ? That is easy enough to figure out as 4000 ft / 400 ft/nm = 10 nm (always be on the lookout for easy mental arithmetic - saves lots of time in the exam).

The answer then is that we start the climb 10 nm before the 50 nm step, ie 40 miles from A, so the answer you are after is "D".

Engineering specialist in aircraft performance and weight control.