A question that arose while watching FR24 this morning.

If two aircraft request the same altitude on a long haul flight (e. g. for the NAT tracks or other crowded airspace), who decides which of the two actually has their wish come true? Do airlines try to game this process? Or can it happen that certain airlines get preferential treatment?

After all, being stuck at a lower, suboptimal altitude for several hours can have a significant impact on fuel burn.

Also, if a long haul flight passes over an area with many short haul flights (e. g. a flight from Asia to western Europe that passes over eastern Europe), is it common to preemptively request an altitude above typical narrowbody altitudes? Most narrowbodies can't go above FL390 - FL410 and often stay lower, while widebodies at the end of their flight can often go higher (FL430, some even FL450). Or does this create issues where you're "stuck" above the low-flying traffic when you want to descend towards your destination?

Not a commercial pilot nor involved in ATC or operations, so I'm really curious.

The airline, using their dispatchers, will file for a certain altitude and the relevant ATC will either accept it or change it based on operational needs. The flight crew will also add in their input based on any changing circumstances along the way. Incidentally, higher altitudes aren't always better - that will vary based on winds, weight and other factors. On a long haul flight, it isn't rare to see an aircraft have two or three cruising altitudes.

N1120A wrote:

On a long haul flight, it isn't rare to see an aircraft have two or three cruising altitudes.

True, but if two airlines operate the same or similar routes with similar aircraft, it seems likely that both aircraft would like to be at the same optimal cruise altitude and on the same route. There are some really crowded airways, e. g. between the middle East and Europe, or east coast US and Europe, or within China.

For example, you could have a UA 787 flying EWR-LHR and an AA 787 flying PHL-LHR that both want the same NAT, with the same or similar altitude steps.

But obviously ATC can only allow one of them to get their way. The other will have to make do with some suboptimal routing. Lower, higher, or offset horizontally.

How does ATC make this decision, then?

mxaxai wrote:

A question that arose while watching FR24 this morning.

If two aircraft request the same altitude on a long haul flight (e. g. for the NAT tracks or other crowded airspace), who decides which of the two actually has their wish come true? Do airlines try to game this process? Or can it happen that certain airlines get preferential treatment?

After all, being stuck at a lower, suboptimal altitude for several hours can have a significant impact on fuel burn.

Also, if a long haul flight passes over an area with many short haul flights (e. g. a flight from Asia to western Europe that passes over eastern Europe), is it common to preemptively request an altitude above typical narrowbody altitudes? Most narrowbodies can't go above FL390 - FL410 and often stay lower, while widebodies at the end of their flight can often go higher (FL430, some even FL450). Or does this create issues where you're "stuck" above the low-flying traffic when you want to descend towards your destination?

Not a commercial pilot nor involved in ATC or operations, so I'm really curious.

You do indeed sometimes get "stuck" lower. Sometimes you'll tactically ask for higher before it is really optimal in order to avoid the situation, figuring that you'll burn less in total. And sometimes that tactic works.

mxaxai wrote:

N1120A wrote:

On a long haul flight, it isn't rare to see an aircraft have two or three cruising altitudes.

True, but if two airlines operate the same or similar routes with similar aircraft, it seems likely that both aircraft would like to be at the same optimal cruise altitude and on the same route. There are some really crowded airways, e. g. between the middle East and Europe, or east coast US and Europe, or within China.

For example, you could have a UA 787 flying EWR-LHR and an AA 787 flying PHL-LHR that both want the same NAT, with the same or similar altitude steps.

But obviously ATC can only allow one of them to get their way. The other will have to make do with some suboptimal routing. Lower, higher, or offset horizontally.

How does ATC make this decision, then?

Not necessarily lower, higher or offset. It can also be before or after. Which is why NAT segments are typically constant Mach number.

If memory serves, the NAT entry time is assigned and must be met with high accuracy by the aircraft in question.

Starlionblue wrote:

If memory serves, the NAT entry time is assigned and must be met with high accuracy by the aircraft in question.

Okay, but if two aircraft ask for the same NAT entry time, how does ATC prioritize? First come first serve?

mxaxai wrote:

Okay, but if two aircraft ask for the same NAT entry time, how does ATC prioritize? First come first serve?

ATC in the U.S. is all about "first come first served" though there are situations where one cannot do that simply especially in the terminal environment where I worked. Preferential treatment is a phrase the FAA does not like though it may appear at certain times the largest carrier at a HUB airport is given that type of treatment, but having worked at a HUB TRACON you don't have the time to deal with that kind of nonsense as it will put you in the toilet faster than you can say it.

So yes, there is some game time decisions that take place in all aspects of altitude assignments with many factors taking place, and no specific answer for it all.

IAHFLYR wrote:

ATC in the U.S. is all about "first come first served" though there are situations where one cannot do that simply especially in the terminal environment where I worked. Preferential treatment is a phrase the FAA does not like

I see, thanks. So there's some element of timing and luck involved whether you get your requested altitude or flight path. I wonder if this is the same in other jurisdictions?

Starlionblue wrote:

mxaxai wrote:

A question that arose while watching FR24 this morning.

If two aircraft request the same altitude on a long haul flight (e. g. for the NAT tracks or other crowded airspace), who decides which of the two actually has their wish come true? Do airlines try to game this process? Or can it happen that certain airlines get preferential treatment?

After all, being stuck at a lower, suboptimal altitude for several hours can have a significant impact on fuel burn.

Also, if a long haul flight passes over an area with many short haul flights (e. g. a flight from Asia to western Europe that passes over eastern Europe), is it common to preemptively request an altitude above typical narrowbody altitudes? Most narrowbodies can't go above FL390 - FL410 and often stay lower, while widebodies at the end of their flight can often go higher (FL430, some even FL450). Or does this create issues where you're "stuck" above the low-flying traffic when you want to descend towards your destination?

Not a commercial pilot nor involved in ATC or operations, so I'm really curious.

You do indeed sometimes get "stuck" lower. Sometimes you'll tactically ask for higher before it is really optimal in order to avoid the situation, figuring that you'll burn less in total. And sometimes that tactic works.

mxaxai wrote:

N1120A wrote:

On a long haul flight, it isn't rare to see an aircraft have two or three cruising altitudes.

True, but if two airlines operate the same or similar routes with similar aircraft, it seems likely that both aircraft would like to be at the same optimal cruise altitude and on the same route. There are some really crowded airways, e. g. between the middle East and Europe, or east coast US and Europe, or within China.

For example, you could have a UA 787 flying EWR-LHR and an AA 787 flying PHL-LHR that both want the same NAT, with the same or similar altitude steps.

But obviously ATC can only allow one of them to get their way. The other will have to make do with some suboptimal routing. Lower, higher, or offset horizontally.

How does ATC make this decision, then?

Not necessarily lower, higher or offset. It can also be before or after. Which is why NAT segments are typically constant Mach number.

If memory serves, the NAT entry time is assigned and must be met with high accuracy by the aircraft in question.

Then why on most flights I have been on. Which is many. We either pass a or get passed by a plane at a relatively short distance.

IAHFLYR wrote:

mxaxai wrote:

Okay, but if two aircraft ask for the same NAT entry time, how does ATC prioritize? First come first serve?

ATC in the U.S. is all about "first come first served" though there are situations where one cannot do that simply especially in the terminal environment where I worked. Preferential treatment is a phrase the FAA does not like though it may appear at certain times the largest carrier at a HUB airport is given that type of treatment, but having worked at a HUB TRACON you don't have the time to deal with that kind of nonsense as it will put you in the toilet faster than you can say it.

So yes, there is some game time decisions that take place in all aspects of altitude assignments with many factors taking place, and no specific answer for it all.

This is true here in the U.S. and many other nations, but not in all. I can remember many occasions where a certain Asian nation would check with their nation's airlines for altitudes requests (only) after we called for clearance. So we learned to call about 20 minutes prior to departure in order to give ATC enough time to query the other (their nation's) carriers for their preferred altitude on the same airway - we got whatever was left over and this was usually something relatively low, like FL290 or 270. So in turn, we needed more fuel and we learned to add to the flight plan quantity.

rlwynn wrote:

Starlionblue wrote:

mxaxai wrote:

A question that arose while watching FR24 this morning.

If two aircraft request the same altitude on a long haul flight (e. g. for the NAT tracks or other crowded airspace), who decides which of the two actually has their wish come true? Do airlines try to game this process? Or can it happen that certain airlines get preferential treatment?

After all, being stuck at a lower, suboptimal altitude for several hours can have a significant impact on fuel burn.

Also, if a long haul flight passes over an area with many short haul flights (e. g. a flight from Asia to western Europe that passes over eastern Europe), is it common to preemptively request an altitude above typical narrowbody altitudes? Most narrowbodies can't go above FL390 - FL410 and often stay lower, while widebodies at the end of their flight can often go higher (FL430, some even FL450). Or does this create issues where you're "stuck" above the low-flying traffic when you want to descend towards your destination?

Not a commercial pilot nor involved in ATC or operations, so I'm really curious.

You do indeed sometimes get "stuck" lower. Sometimes you'll tactically ask for higher before it is really optimal in order to avoid the situation, figuring that you'll burn less in total. And sometimes that tactic works.

mxaxai wrote:

True, but if two airlines operate the same or similar routes with similar aircraft, it seems likely that both aircraft would like to be at the same optimal cruise altitude and on the same route. There are some really crowded airways, e. g. between the middle East and Europe, or east coast US and Europe, or within China.

For example, you could have a UA 787 flying EWR-LHR and an AA 787 flying PHL-LHR that both want the same NAT, with the same or similar altitude steps.

But obviously ATC can only allow one of them to get their way. The other will have to make do with some suboptimal routing. Lower, higher, or offset horizontally.

How does ATC make this decision, then?

Not necessarily lower, higher or offset. It can also be before or after. Which is why NAT segments are typically constant Mach number.

If memory serves, the NAT entry time is assigned and must be met with high accuracy by the aircraft in question.

Then why on most flights I have been on. Which is many. We either pass a or get passed by a plane at a relatively short distance.

Those aircraft passing are on another track and/or another altitude. If they were on the same track+altitude passing would violate separation.

Constant Mach segments and ATC assigned Mach numbers ensure that aircraft which are on the same track+altitude don't violate separation in case they are relatively close.

mxaxai, sometimes air traffic control has the flexibility to offer the pilot options in order to climb to a higher altitude. For example, a brief vector off course; or an airspeed adjustment if the airway is not under speed control criteria; then the pilot has the option of deciding if the option offered provides more optimum fuel management or if remaining at the assigned altitude is a better alternative until a higher altitude is available.

reference your question, " . . . does this create issues where you're "stuck" above the low-flying traffic when you want to descend towards your destination?"

No, not necessarily. In most cases, when aircraft are approaching the terminal area and are flying a published arrival procedure, such as a Standard Terminal Arrival Route or a profile descent procedure, arrivals and departures are separated laterally--departure and arrival corridors--such that there are few, if any, restrictions to an aircraft descending into the arrival airport, other than those restrictions published on the procedure.

e38

[/quote]This is true here in the U.S. and many other nations, but not in all. I can remember many occasions where a certain Asian nation would check with their nation's airlines for altitudes requests (only) after we called for clearance. So we learned to call about 20 minutes prior to departure in order to give ATC enough time to query the other (their nation's) carriers for their preferred altitude on the same airway - we got whatever was left over and this was usually something relatively low, like FL290 or 270. So in turn, we needed more fuel and we learned to add to the flight plan quantity.[/quote]

You just leave us hanging like that. At least give us a hint. I was thinking the PRC.