Professional Pilot Training (includes ground studies) A forum for those on the steep path to that coveted professional licence. Whether studying for the written exams, training for the flight tests or building experience here's where you can hang out.

Flight Planning P.E.T.....HELP!!!

Old 1st Mar 2009, 11:30
  #1 (permalink)  
Thread Starter
 
Join Date: May 2008
Location: Tatooine
Posts: 27
Flight Planning P.E.T.....HELP!!!

Hi, I'm doing the ATPL distance learning course and am having a bit of trouble with Point of Equal Time. Any help would be greatly appreciated. So here's the problem:

Formula:
Time to destination = D-X/O
Time to return = X/H
X/H = (D-X)/O
X = DH/(O + H)

Question:
A – B 1240 nm
TAS 340 KNOTS
Wind Component +20 knots outbound

D = 1240
H = 320
O = 360

X = 1240x320/(360+320)
X = 396800/680 = 583.5

So far I'm correct according to the answer in the book, however when I try to find the time it goes a bit awry.

So from the formula given above:
Time to return = X/H
583.5/320=1.82 = 1hr 42min

And to double check it's the same time to continue on to B
D-X = 1240-583.5 = 656.5

Again from the formula given above:
Time to destination = D-X/O
656.5/360 = 1.82 = 1hr 42min

Now, the answer given in the book is 1hr 37min. Which would be correct for the Time to return if we changed the formula to read X/O

In that case the time to continue to B cannot be 1hr 37min because 656.5 divided by either 360 or 320 does not give 1hr 37min. So in this case it is not a PET.

It all looks a bit confusing, I know, but I've done 7 of these questions all with similar results. It's probably something so obvious I'll kick myself. But that's the problem with distance learning, sometimes you've got to figure things out for yourself. Anyway, thanks for reading and again any help would be greatly appreciated.
MetalGear is offline  
Old 1st Mar 2009, 13:10
  #2 (permalink)  
 
Join Date: Sep 2004
Location: Where you left me.
Posts: 162
Unless I've missed something, they've used the O groundspeed in the initial formula by mistake. Unless they mean start at B and continue to B by turning round!?

The error would give 1240x360/680 = 656.5, leaving 583.5 to run outbound at 360kts, which is 1h37m.

By the way, 1.82 in your calcs is not 1h42, it's 1h49.
r44flyer is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.