Expected Approach Time

[pdiogo]

I have been wondering for a couple days now...

How is the Expected Approach Time calculated?
Is there a formula to calculate this?

[Intruder]

ETD + ETE
Estimated Time of Departure + Estimated Time Enroute

[chevvron]

Intruder : In the UK, EAT's are issued by terminal control when holding is expected to be in excess of a certain time; it's basically if you have comms failure whilst holding so you and ATC both know when you will commence intermediate approach, but of course it also assists the crew in fuel planning for diversions.

[HEATHROW DIRECTOR]

pdiogo.. The EAT cannot be calculated by a simple formula as there are so many variables - weather, landing interval to name but two.

When delays start to build beyond a certain amount, ATC will calculate the landing interval (almost always determined by the wind) and then decide the landing order. At larger airfields this may not necessarily mean "first come, first served" as a higher landing rate is often achieved by "parcelling" together aircraft of similar types. Eg half a dozen A320s followed by half a dozen 747s will produce an overall higher landing rate than 747, followed by A320, followed by 747, etc.

Until a few years ago, EATs were worked out using pen and paper. Now, ATC has computer systems which typically lists all inbound aircraft well in advance of their ETAs. The landing interval is fed in and various adjustments made to the landing order as described above. EATs then becoming instantly available to pass to aircrew. Despite all the modern technology, calculating EATs accurately is still quite difficult. A change in the landing interval - caused, for example, by a sudden change in the wind - can throw everything out..

Intruder..... sorry, I think you're confused. He asked about EATs.

[pdiogo]

Hello,

I understand it now. Thank you very much.

Pedro.

[Intruder]

Intruder : In the UK, EAT's are issued by terminal control when holding is expected to be in excess of a certain time; it's basically if you have comms failure whilst holding so you and ATC both know when you will commence intermediate approach, but of course it also assists the crew in fuel planning for diversions.

Indeed, EATs (or EAC -- Expect Approach Clearance -- in the US) are associated with holding in the approach stack. However, there can be no "formula" for the Pilot to consult in that case.

So, I went back to the "other" -- and much less often used -- case, that of complete lost comms enroute. The formula I gave will yield the time ATC expects the aircraft to start an approach from the IAF serving the most likely active runway when the flight plan was filed.

I know that's a bit ancient, but you never know when someone might need it... :)

[This is a crisis]

EATs are a throwback to procedural approach control.

At my place we have published (to us) elasped times it takes to complete each published approach. Operating procedurally, first aircraft gets 'no delay', second aircraft gets, very simply, an EAT based on the estimate for the beacon of the first aircraft plus the time it should take to make the approach. Third aircraft gets EAT for the second plus the time interval...and so on...

In the old days, pilots used to adjust their speed to arrive at the beacon at their EAT so hopefully they could go straight outbound...now I am showing my age !!