Scheduled evening atlantic services

[CJ1234]

As a short hauler, I'm not too familiar with long haul ops. I was under the impression that between certain times, the NATs work westbound, and then at night time, NATs work eastbound. Yet, there are BA flights (e.g.LHR-BOS) which are leaving the UK at 7pm. How does this work? Surely NATs are working eastbound by then? similarly, there are flights going from BOS to LHR at 8am local time.

I have trawled various resources (mainly internet) and found no answer. Anyone who can quench my curiosity, please do so! Would be appreciated.

1234

[HEATHROW DIRECTOR]

Flights over the Atlantic operate H24 in either direction although there will obviously be peak times for each. To understand the flow, compare times in US cities with those in Europe and then the flight times. Eg London to Los Angeles takes 11-12 hours. So, a flight leaving the UK during our afternoon will get to LA in early evening. A flight leaving the UK at 9am would arrive in New York around mid-morning. Coming back can present problems with noise curfews at some EU airports. Eg a flight from Chicago to London would have to leave quite early in their morning to arrive here by late evening.

HTH

[The SSK]

Because of the time difference, daylight eastbounds have to start very early and arrive very late so there aren’t many city pairs that can support them (either commercially or operationally … avoiding airport curfews etc).

BOS-LON is one of the shortest transatlantic routes (just over 6h eastbound and only 5h time difference) so is a good candidate. It does require the aircraft to overnight in BOS so it makes sense to operate the westbound as late as possible to minimise aircraft downtime but also to access the demand for people who want (or need) to do a full days’ work before flying off.

[Doors to Automatic]

Transatlantic flights use standardized aircraft routes called North Atlantic Tracks (NATs). These change daily in position (although altitudes are standardised) to compensate for weather—particularly the jet stream tailwinds and headwinds, which may be substantial at cruising altitudes and have a strong influence on trip duration and fuel economy.

Although during the peak westbound hours most tracks will be reserved for westbound traffic there will be at least one or two tracks open in the opposite direction. The same holds true when the peak switches to Eastbound.

[Polarhero]

There is always the option to fly a random route.

[WetFeet]

The NAT tracks are westbound by day and eastbound by night because that ties in with the majority of traffic. There is nothing to stop anyone going at different times but priority is given to the majority flow.

If you want to fly westbond at night, no problem, but you will be kept clear of the eastbound traffic.

Bear in mind as well that there is no radar on the North Atlantic so clearance issued before entry has to be conflict free for the entire crossing. The timing of the tracks, Datum levelsand availability of levels are all calculated to take account of that.

[kenparry]

Bear in mind as well that there is no radar on the North Atlantic so clearance issued before entry has to be conflict free for the entire crossing.

Not necessarily. The separation is of course procedural, based on the position reports given by all aircraft. On the NAT tracks you should be free of conflicts, because of speed control and time separation at the NAT track entry point, but when on random tracks further South (e.g. Europe to the Caribbean) it's not that unusual to have a level change, or even a route change, imposed in mid-ocean by ATC for separation reasons. It's happened to me several times.

[WetFeet]

kenparry

All flights, whether on the tracks or random, are conflict free to landfall when the clearance is issued.

Clearances can be changed when in Oceanic airspace, as you say, because other traffic, unknown when first clearance is issued, has to be fitted into the traffic pattern. This particularly happens with traffic to/from the Caribbean as that traffic is not known to Gander or Shanwick when they issue their clearances. But that doesn't get away from the fact that when Gander and Shanwick issue clearances, that clearance is conflict free to landfall as far as known traffic is concerned at the time.

[galaxy flyer]

CJ1234

Remember the track system is based on minimum time routes; that is, take best advantage or least disadvantage due to winds. So, when the night eastbound system (best tailwind) is in use, a westbound flight would be trying to minimize the prevailing headwind. This tends to naturally separate laterally the opposite direction tracks. At times, though, an opposite direction flight will just have to "suck it up" and fly the crossing a lower than optimum level. OTOH, bizjets tend to cross on random routes above FL 410 and hence are not a traffic conflict for very many. Typically, on a crossing in a GLEX at FL430 or FL 450, the random route crosses many of the tracks, above them.

GF

[Mr Angry from Purley]

CJ1234
There are quiet a few Westbound flights in the dark hours, DHL Air for example have a EMA-CVG at 2040z and 0230z and a LEJ-JFK at 0105z. I believe they use the opposite tracks but i bow to LHR Directors superior knowledge and i only supply the crew. Likewise they come back eastwards around 0900-1200z against the normal "flow"

[kenparry]

Wetfeet:

All flights, whether on the tracks or random, are conflict free to landfall when the clearance is issued.

With respect, that can't be wholly correct. Before landfall you leave oceanic and enter domestic airspace on all the routes I've flown - and by the time you get to that, there may well be aircraft there that had not even filed a flight plan when you (or I) entered oceanic airspace hours earlier.

Can you back up with inside knowledge of the ATC procedures your assertion of conflict free clearances?

[WetFeet]

Maybe I should have been a bit more specific. When Gander or Shanwick issue a clearance it will be free of conflict against any traffic KNOWN TO THEM.

If a flight subsequently enters Santa Maria, New York or Reykjavik areas etc then there may be conflicting traffic there, which will be resolved by coordination, but at the time the original clearance is issued by Gander or Shanwick it was conflict free against traffic KNOWN TO THEM.

I can't back this up with excerpt from documentation as I have retired now. I can only base my comments on having been an Oceanic controller for 25 years.

[kenparry]

WetFeet

OK, thanks for the amplification. That makes sense.

kp

[rab-k]

WetFeet is quite correct, we'll only issue clearances on the basis of known traffic. (Hope you're enjoying retirement BTW :ok:)

As for traffic against the majority flow; the 'slack' times between the OTS being active are called 'Transition Periods', where everything is classed as a 'Random' flight. Prior to the OTS activation times, priority over level allocation on the basis of direction of flight will come into effect in stages, leading up to the time at 30W when the tracks will become active, and any aircraft infringing the incoming OTS in the opposite direction should be clear of them.

During OTS periods any flight going against the majority flow will either avoid the active OTS or fly below or, if it has the ability, above it; hence you still have random flights going against the majority flow at all times of day/night, albeit with restrictions in terms of flight levels allocated for them.

[A321COBI]

I also only fly europe but I would assume nats would be working eastbound by that time