Header1200x385

facebook_page_plugin
× Welcome to the CPL Navigation 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.

Time Intervals Between points

  • Bill17
  • Topic Author

Bill17 created the topic: Time Intervals Between points

29. Given: ATD 2200 DEP TO DEST is a straight-line track
Planned GS 117kt
TI- DEP to first feature/ proportional marker 23 min
TI- first to second feature/ proportional marker 20min
TI- second feature/ proportional marker to DEST 18min
A pinpoint is obtained at 2223 at the first marker and another pinpoint is obtained at 2243, 4 miles short of the second marker. The ETA at DEST

a) Is within ± 2min and need not be revised
b) Is revised to 2303
c) Cannot be revised without knowing the distances between pinpoints
d) Is revised to 2305


Had a bit of trouble with this question>
#1

Please Log in or Create an account to join the conversation.

  • John.Heddles
  • Offline
  • ATPL/consulting aero engineer
  • Posts: 843
  • Thank you received: 101

John.Heddles replied the topic: Time Intervals Between points

OK, you can do this with your calculator/prayer wheel, whatever, or you can just do some rough, back of a fag packet mental calculations. Always be on the lookout for nice easy peasy round number problems which just cry out for a quick and dirty mental calculation solution.

(a) we are looking at a single leg. First assumption is to see if we can run the calculations with a constant wind.

(b) G/S = 117 kts. That's just too close to 120 kts to be coincidence (2 nm/min).

(c) planned interval to the first fix is made good. G/S matches plan.

(d) time expected at the next fix comes up 4 nm short of the fix so the wind has changed and G/S has reduced. Therefore, the time to get to the second fix will be a bit more than 2 min, ie we will be at least 2 min late at the second fix.

(e) distance to the destination is a bit less that from the first to second fix so, presuming that the wind change holds for the last calculation, we should be about 2+ mins (for the lost time from the first to the second fix) + 2+ mins (for the second fix to the destination) which is going to be, say, around 5 minutes late at the destination (give or take a bit).

The answer is going to be (d).

Engineering specialist in aircraft performance and weight control.
#2

Please Log in or Create an account to join the conversation.

Time to create page: 0.076 seconds