Who's Online

We have 1243 guests online

Live Traffic Feed

Life in the Skies

'A Local Bestseller!'

What Tony says
(See here)
and Book Launch video here
What others say

Les Posen

Yvonne Lee

Louisa Lim & Allan Koay

Aireen Omar, Asran & Bo Lingam

38 Readers' Comments
(See here)

Get an autographed copy here

AMAZON.COM  -  To Order, please Click here 

(eBook) Kindle edition - please Click here

Latest Comment

ETOPS and CRM querie
Hi, If the two engines Boeing 777 is just as good

SIA Plane on Fire
To be clear, the aircraft was evacuated, though it

Is it true that comp
The problem is a computer on any aircraft is only

A successful SIA Cad
Is there any deadline for application? If it is op

Should I proceed wit
I am reading some people's post, and to be honest,

A cadet pilot sharin
Before the test, the examiner said that they made

Thunderstorms and th
Hi Captain Lim, I would like to know if there ha

What happens if I ge
I have seen a comment from a Flight attendant that

What are the eyesigh
Captain, I am in class 11 in India and want to bec

What are the eyesigh
PLEASE stop asking about your eyes!!! Read the art

Paperback Version

 For Local Availability - Check Here
Home > ETOPS > Could you explain what "wet footprint" is all about?
Could you explain what "wet footprint" is all about?
Flying - ETOPS
Written by Capt Lim   
Tuesday, 14 October 2008 04:11

Hi Capt Lim,

I am an ex-Air Force pilot where I flew transport planes from small turboprops to the Airbus A310. Now I am flying as a corporate pilot, and while surfing on aeronautic matters in the web, I found that term ‘wet footprint'. It seems to be "when flying over water, the maximum distance one could glide, should engine[s] fail, and still end up landing in the water" - so confusing isn't it?.

Could you please give me some more information about it - how to compute it, etc?


Manuel Alcaide

Hi Manuel,

Remember my answer on ETOPS (‘Engine Turns or Passengers Swims') here? Well ‘wet footprint' is another term to mean that some commercial aircraft are not allowed to operate along this portion of the route unless it has the ETOPS coverage.

If you have some knowledge on ETOPS (read more here), you are most unlikely to be confused by this explanation ‘when flying over water, the maximum distance one could glide, should engine[s] fail, and still end up landing in the water'. Anyway, the explanation is only partially correct - ‘not maximum distance one could glide' but rather ‘maximum distance flown on one engine'.

Yes, you would end up landing in the water because you were not supposed to fly past the PNR or ‘point of no return' from a suitable diversion airport. PNR is sometimes known as the ETP or ‘equal time point'.

Let's say if you are flying across the water from London to Keflavik in Iceland, you are required to calculate the ETP. This calculation serves as a planning strategy so that if you have an emergency before the ETP you can turn back to your chosen alternate airport at, for instance, Glasgow in Scotland. If the emergency occurs past the ETP, then you must continue on to Keflavik. If you insist on turning back now, you may get ‘wet', meaning, you end up in the water!

Most trans-oceanic flights today would require an ETOPS of at least 120 minutes for any 2-engines commercial aircraft. (Boeing 777 has ETOPS of more than 180 minutes) This means that at any point in the flight, a suitable airport able to handle the particular aircraft must be available on one engine within 2 hours.

How do one calculate the ETP? 

The answer is basically as follows:-

ETP = (DxGSret)/(GSret + GSfwd)


D =  Total distance for the flight
GSret =Ground speed from the ETP back to the origin (GS return)
GSfwd = Ground speed from the ETP to the destination (GS moving forward at the ETP before you turn around to return)

Today, most computer generated flight plans (CFP) would calculate all these details for you. On the Airbus A320 and above, the Flight Management Computer works that out for you in the air as well.


TrackBack URI for this entry

Comments (3)

Subscribe to this comment's feed
would you please explain about When & Why we should have life raft on board?

A , 20 Mar, 2010
as far as i know ETOPS means extended twin engine operation system...correct me if i am wrong...thank you captain
mark , 01 Dec, 2012
PNR and ETP are actually two different things. PNR is the point where with the available fuel the aircraft could return or continue and must be further then the ETP. ETP is the point where it will take the same amount of time to reach either destination or departure aerodrome taking into account the different ground speeds in each direction.
PlainDriver , 06 Oct, 2016

Write comment

smaller | bigger


Paperback Version

 For Local Availability - Check Here

Recommended By..


'A Local Bestseller!'

Recommended by

Patrick Smith
Boston USA

Capt Meryl Getline
ex-United Airlines USA

Capt Doug Morris
Canadian Airlines

Capt  Robert J Boser
ex-United Airlines USA

38 Readers' Comments
(See here)

Get an autographed copy here

AMAZON.COM  -  To Order, please Click here 

(eBook) Kindle edition - please Click here

View Book Launch video here

Follow me


Like What You Read?

If you like what you read, more stories are found in my book LIFE IN THE SKIES (Preview here) and you can purchase a copy here. To check for any latest updates or postings, you can follow my Twitter at @CaptKHLim or Facebook here

MH 370 Interviews

Click here to View

10 Most Popular Posts

Disclaimer | Privacy
2004 - 2011 © AskCaptainLim.com | Site Concept by eQuilec.com