JulianUK
Topic Author
Posts: 105
Joined: Sat Apr 29, 2006 6:00 am

### Equi Time Point (ETP) Settings On FMS Question

Trying to understand the Equi Time Point feature on FMS systems, and got totally confused, so need some help! Can someone explain it in non technical terms please! Thanks, J

[Edited 2006-05-21 13:28:21]

gordonsmall
Posts: 2106
Joined: Sun Jul 01, 2001 1:52 am

### RE: Equi Time Point (ETP) Settings On FMS Question

An ETP (equal time point) is basically the point at which it'll take a shorter time to continue to the next suitable diversion airfield than to turn back to the last one.

There are many ways of calculating the ETP besides using the FMC, some complex and accurate, others simpler but not quite so accurate.

When I was studying the relevant module of my ATPL exams, I would always forget to take into account the time taken to reverse course when calculating them!

EDIT: Spelling.

[Edited 2006-05-21 13:51:03]
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CosmicCruiser
Posts: 2056
Joined: Tue Feb 22, 2005 3:01 am

### RE: Equi Time Point (ETP) Settings On FMS Question

 Quoting Gordonsmall (Reply 1):An ETP (equal time point) is basically the point at which it'll take a shorter time to continue to the next suitable diversion airfield than to turn back to the last one.

Unless I'm a lot more tired than I think EQUAL Time Point means EQUAL time. Therefore, AT the ETP it's EQUAL time to either alternate. That's the point, before the ETP you turn back, after you continue, generally speaking.

gordonsmall
Posts: 2106
Joined: Sun Jul 01, 2001 1:52 am

### RE: Equi Time Point (ETP) Settings On FMS Question

 Quoting CosmicCruiser (Reply 2): Unless I'm a lot more tired than I think EQUAL Time Point means EQUAL time. Therefore, AT the ETP it's EQUAL time to either alternate. That's the point, before the ETP you turn back, after you continue, generally speaking.

Common sense would suggest that you are correct, and I have queried this very issue on more than one occasion with more than one instructor, however the UK CAA are absoloutely insistent that the the decision to turn back should be made BEFORE you reach the ETP and that AT the ETP you continue by default, at least that's what I've been told they expect me to say in my written exams.

I've already had enough run-ins and cross-words with the CAA in my short aviation career, so I'll leave any further arguing to those with more faith in the Campaign Against Aviation .... I'm quite willing to tell them the earth is flat if it'll help in my quest for an ATPL!

[Edited 2006-05-22 11:43:02]
Statistically, people who have had the most birthdays tend to live the longest.

CosmicCruiser
Posts: 2056
Joined: Tue Feb 22, 2005 3:01 am

### RE: Equi Time Point (ETP) Settings On FMS Question

I was afraid that you would be looking at it from that point, meaning that yes, to be technically correct, if you turn back EXACTLY at the ETP you would have further to go just by the shear nature that you must do a 180 ( ok 135, 155, etc) and would travel past the ETP. I was just pointing out that the ETP means exactly that...CC

gordonsmall
Posts: 2106
Joined: Sun Jul 01, 2001 1:52 am

### RE: Equi Time Point (ETP) Settings On FMS Question

 Quoting CosmicCruiser (Reply 4):I was just pointing out that the ETP means exactly that...

Indeed! I agree completely that in it's literal sense it is an EQUAL time, and if it was up to me common sense would prevail!

Unfortunately the UK CAA are not known for their appreciation of common sense or simplicity, and it's them I have to convince that I know what I'm talking about - even if it is wrong!
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