8 ms·

I’m surprised they didn’t slow down to conserve fuel and arrive on-time. In the USA, if your flight is more than 20 minutes early, you are usually stuck on the

I’m surprised they didn’t slow down to conserve fuel and arrive on-time. In the USA, if your flight is more than 20 minutes early, you are usually stuck on the tarmac waiting for a gate. 80 minutes of fuel for that plane must be very expensive. Is it possibly to fly that plane, at say 200 knots ground speed, and save on fuel? Or are they stuck at their speed they filed in the flight plan, to keep traffic separation?

t0mas88 7y ago
It doesn't always work to go slower. The speed of least drag is an airspeed, not a ground speed. And commercial jet engines are most efficient around 90% thrust, not at lower settings. So going slower can make you less efficient.
- t-writescode 7y ago
  Does less efficient result in more total fuel loss, in this specific case, since the engine will be running for a different amount of time?
  - t0mas88 7y ago
    Can't really tell without knowing their weight and available cruising levels. But in general you should not run a commercial jet engine at lower thrust settings. The optimum altitude as calculated by the flight management system is essentially the altitude at which 90% thrust gets you the best cruise speed. That's also why flying low is really bad for fuel consumption, you're going to have to decrease thrust and you'll be aerodynamically less efficient at the same time.
    - WalterBright 7y ago
      At lower altitude the jet has to push aside a lot more air.
      - NikolaeVarius 7y ago
        Yes, but to the previous posters point, turbofans operate much less efficiently at lower altitudes. They are optimized to run the majority of cruise at a very specific set of altitude and power output settings. This is compounded by the fact that fuel load also assumes a set of assumptions of the flight plan
    - dnhz 7y ago
      This sounds wrong to me because I've read that the plane uses 90% thrust or something around that to take off, and at cruise, less thrust is needed.
      - VBprogrammer 7y ago
        I'm not sure where the 90% comes from. What is it refering to? Rotor stage RPM, static thrust, fuel flow? In general turbine engines are limited mostly by the temperature at the first stage of turbine blades after the combustion stage. It's hard to get reliable instrumentation in this zone so a proxy temperature is often taken from a later stage. In older airliners there was a table of max ITT values varying with altitude and outside air temperature. In modern FADEC engines the computer does the same calculations. It's not unusual for smaller jets to be set at their max continuous thrust setting shortly after takeoff and be left there until the beginning of the descent. Modern airliners will be flying a cost optimised Mach number. That Mach number is entered on their flight plan and is used as a basis for ensuring they are separated from other flights on the north Atlantic tracks so they wouldn't be able to change it readily. The interesting part of all of this is that they would have been assigned an altitude for the crossing, at high altitudes maximum speeds drop (because flutter margins are proportional to velocity rather than effective pressure) but stall speeds increase so the range of viable flying speeds is actually quite limited at cruise altitudes. They probably couldn't have slowed down if they wanted too.
        dnhz 7y ago
        I was referring to the N1 and N2 values. But I realized I was wrong and that jet engines do operate at say 90% N1 during cruise.
  - colechristensen 7y ago
    Aircraft performance metrics of all sorts are generally U shaped. There will be an optimum altitude and airspeed for a chosen regime and deviating from it in either direction will result in lower performance. So if you are shooting for miles per pound of fuel, there is a best. You will lose total trip fuel if you throttle up and go faster and you will lose total trip fuel if you throttle down and go slower.
- ses1984 7y ago
  Air resistance goes up by the square of the velocity, so it takes more and more thrust to go faster. The most efficient thrust per unit of speed is therefore somewhat less than the most efficient thrust per unit of fuel. I've only had some college physics and no aeronautical engineering so I could be way off. Of course there are other factors like the amount of lift per unit of velocity and so on...
  - CPLX 7y ago
    > Air resistance goes up by the square of the velocity But you measure speed in this context relative to the air, not the ground. The fact that the plane is now moving across land much much quicker due to winds aloft is completely irrelevant from an aerodynamics perspective. The plane doesn’t even “know” that it’s getting there sooner.
    - ses1984 7y ago
      I'm strictly arguing with the point about engines being efficient at 90% thrust which is independent of wind.
  - danaliv 7y ago
    > Air resistance goes up by the square of the velocity This is true of form drag. Airplanes are also subject to a somewhat counterintuitive induced drag that is inversely proportional to airspeed. The minimum total drag is therefore somewhere between a slow speed and a fast speed. There are three optimal speeds depending on what you're trying to optimize. Maximum range (distance per unit of fuel) is best glide speed, which would be a painfully slow way to get somewhere. Maximum endurance (time per unit of fuel) is roughly max endurance divided by 1.316—even slower. "Optimum cruise," or Carson's speed (max speed per unit of fuel) is roughly max endurance times 1.316.
    - ses1984 7y ago
      What's the relationship of these values to the efficiency curve of the engines? I'm pretty sure best glide speed times 1.3 can be achieved with less than 90% thrust from the engines of a typical commercial airliner.
mstade 7y ago
Same in Europe, it's happened to me multiple times. It really riles people up for some reason, with people just flat out ignoring crew orders to remain seated etc.
jontro 7y ago
I would think it was to reach London before they closed off airports due to the storm
ReptileMan 7y ago
I asked similar question about angle of attack (both 737 max and AF447) - can't they just look at a glass of water to see they are at wrong angle. But with planes it doesn't work that way - everything is relative to the air outside, not the ground. With good tailwind you still have to go with your cruising speed relative to the tailwind. Your ground speed will be insane. The opposite is with headwind.
- rvnx 7y ago
  Maybe a gyroscope + glass of water ?
  - XMPPwocky 7y ago
    No. Angle of attack behaves in some very non-obvious ways- For example, if you maintain the same attitude, but decrease thrust so that your forward airspeed drops, and you begin descending... your angle of attack increases, despite the aircraft not actually rotating. Why? When you start descending, the air below now seems to be "coming up at you"- you go from ---> (=== to 7 (=== / / if that ASCII art helps at all (equals signs being the wing) Now consider how roll, yaw, and crosswinds affect this- as the AoA becomes variable across the wing...
  - t0mas88 7y ago
    Doesn't work. The stall is about the angle at which the airflow meets the wing. The gyroscope (with or without glass of water) will tell you the attitude of the plane, but nothing about the direction from which the air meets the wing. You can stall in a nose down attitude if you're descending fast, the air comes from "below" and you try to pull out ift the dive thereby increasing the angle at which the air meets the wing. All the while your nose is still pointing below the horizon.
- aaronmdjones 7y ago
  As other comments have mentioned, a glass of water tells you nothing about the conditions outside the plane, which are the ones that matter. But also, it is sometimes useless at telling you about the conditions inside the plane too. If you're rolling and yawing at the same time (known as a coordinated turn), the water in the glass will stay level (relative to the bottom of the glass), and the glass will not slide along its surface, even in a 20 degree bank.
alibarber 7y ago
Agree that it’s a pain when it happens (the gate delay) but Heathrow closes at night so these are some of the first flights to land so it might not be much of a problem. All the morning (evening departures) transatlantic flights I’ve been on west -> East have arrived suspiciously early too so I suspect there’s some schedule padding going on...
- chipsa 7y ago
  They schedule the flights months out. The know how fast the jet stream is going maybe a couple days out. So yes, schedule padding to make sure a weak jet stream doesn't cause people to miss connections.
elwesties 7y ago
There is also the question of relative airspeed. Planes need to create enough lift to stay in the air. With a large tailwind they need to go faster to keep enough air flowing over the wings thus higher ground speed to keep the same relative air speed.
- histriosum 7y ago
  This is a common misconception, but very much incorrect. I am a private pilot. When an airplane is in a body of air which is moving across the ground, the airplane moves within that body of air with no knowledge that it is in a strong wind. Airspeed is unaffected, except for gusts or shear events. The airplane maintains it's normal airspeed within that body of air, even though that body of air is moving very quickly in relation to the ground. This is evident in all phases of flight. For example, landing into a strong headwind does not change the approach speed required or the thrust required to obtain that approach speed. The only allowance is for gusty conditions, during which a gust will momentarily affect airspeed due to the inertia of the airplane. The heavier the airplane, the more time it takes a gust or shift to defeat the airplanes inertia.
  - Filligree 7y ago
    I'm confused. Are you saying that it'll maintain its normal ground speed despite flying through fast-moving air? Or that it maintains the same air-speed? The former doesn't make any sense, but the latter is what the GP was saying.
    - histriosum 7y ago
      The ground speed will vary, but the airspeed will not be affected by wind (except momentarily for gusts or shears). The poster I replied to was implying that due to the strong tailwind, they had to maintain an increased airspeed. That is incorrect. The airplane has no idea it is in a tailwind, and airspeed will be unchanged.
      - JshWright 7y ago
goatforce5 7y ago
I once took a Boston -> London flight that arrived significantly early thanks to the arctic jet stream. But that meant we arrived before the landing curfew ended at 6am so the aircraft was put in a holding pattern above central London for 30 mins or so, and I flew more or less over my home in East London a few times (I could see it out the window as we flew overhead). We landed a few minutes after 6am, and by the time I got through immigration and customs and rode home during the morning rush hour on the tube it would have been 8 or 8:30am. Super frustrating that the last mile took 3 hours to complete!
- teh_klev 7y ago
  Back in 2002 a flight I took from Boston to London arrived into LHR airspace about 45-50 mins earlier than it should have due to a decent tailwind from the jetstream. Sadly we stacked for an hour and a half and ended up arriving later than the scheduled arrival time....because fricken Heathrow bottlenecks, and we almost missed our connecting flight back to Scotland. Grrr.
supernova87a 7y ago
Not only that, but Heathrow I understand has heavy curfew / noise fines for arriving before 6am. Maybe to the tune of several tens of thousands of GBP. I figure you would wait to takeoff just to avoid those -- but maybe equally on the departure end they're paying for occupying a gate... https://www.heathrow.com/content/dam/heathrow/web/common/documents/company/doing-business-with-heathrow/flights-condition-of-use/consultation-documents/Conditions-of-Use-Consultation-Draft-2017.pdf https://www.heathrow.com/content/dam/heathrow/web/common/doc... "Schedule 5"
- selectodude 7y ago
  You get a few freebies every year and they’re far more accommodating for arrivals than departures since they’re much quieter.
pale-hands 7y ago
Good question. Maybe (just speculating here) because it would be dangerous to land with too much fuel on board? Planes dump fuel for that reason when aborting shortly after takeoff, but that may only be a problem with tanks close to full.
- xvf22 7y ago
  After a transatlantic flight it's highly unlikely you'll land over your maximum landing weight. That situation usually happens only when they have to land within an hour of takeoff.
Reason077 7y ago
> "In the USA, if your flight is more than 20 minutes early, you are usually stuck on the tarmac waiting for a gate." I've experienced this in the US and Canada too, but it doesn't seem to be a problem at Heathrow in my experience. LHR is slot constrained, but not gate constrained. Worst case, you end up on a remote stand with a bus ride in to the terminal.
- LeoPanthera 7y ago
  Heathrow has a very specific restriction - no landings before 6am, due to the noise for local residents.
  - Reason077 7y ago
    Correct. Noise curfews are common at European airports.
  - iso947 7y ago
    This flight landed 0443 Landings before 6am are allowed, but are limited in numbers.
    - jfk13 7y ago
      For more detail: https://www.heathrow.com/company/local-community/noise/operations/night-flights https://www.heathrow.com/company/local-community/noise/opera...
newnewpdro 7y ago
AIUI you can only save fuel by not loading it, they can't land with substantial fuel remaining onboard without damaging the airframe. They'll just circle the destination to use up the excess fuel.
briandear 7y ago
200kts ground with a 250 kts tailwind is impossible. The plane would have an indicated airspeed of -50kts.
danaliv 7y ago
> Or are they stuck at their speed they filed in the flight plan, to keep traffic separation? When you cross the Atlantic you're usually in sequence on a track. Slowing down one flight slows down all the flights behind it. (Just checked and the flight in question was indeed on a track.)
dghughes 7y ago
And Heathrow has some sort of "AI" system for scheduling landings and take offs. Even telling pilots of aircraft exactly when they can start their engines and when to start to taxi. It was a great documentary I think a math program it wasn't all about the Heathrow system. This isn't the show but it seems to explain the system: https://www.nats.aero/news/nats-trialling-use-artificial-intelligence-heathrow-airport-cut-delays/ https://www.nats.aero/news/nats-trialling-use-artificial-int...
- dx034 7y ago
  That's something pretty much all airports do, just that normally the air traffic controller schedules that. With an airport the size of Heathrow and at capacity, they just use more automation to optimize for throughput and reduce fuel consumption.
  - cjrp 7y ago
    In Europe, a lot of this is done by EUROCONTROL's Central Flow Management unit. They'll issue a "Calculated Take Off Time" and the ground/tower controller at the airport will get the plane to the runway at the correct time to meet the slot.
- iso947 7y ago
  Specifically telling pilots at other airports when to start taxiing. You can have a ground delay in Cyprus because you haven’t got a slot at Heathrow.
philjohn 7y ago
It helps that Heathrow has an entire terminal (T5) dedicated for use by British Airways, so gates aren't as big an issue. On a personal note, you get so little sleep on a redeye flight as it is, I'd have been a bit miffed wake up so soon!
iav 7y ago
There were extreme wind conditions on that day and the wind was expected to get worse through the day. The pilots wanted to arrive as early as possible to beat the storm. Source: I was on a Norwegian flight at exactly the same time and the pilot explained this logic to us and also mentioned that we were on pace to break this record. Unfortunately, the pilot couldn't land in the wind conditions and we had to divert. Good thing we had that extra fuel too as the diversion was to Copenhagen which is quite far.
jsjohnst 7y ago
They probably couldn’t slow down at that altitude without stalling. The window of possible air speeds at that altitude is rather small. Further, fuel efficiency would drop off dramatically too, but I feel the major contributing part is likely the stall speed.
joncrane 7y ago
They actually want to be as light as possible (within reason) when they land. They would have to fuel the flight light, which I doubt would ever happen because what if the atmospheric conditions changed on the way?

t0mas88 7y ago

It doesn't always work to go slower. The speed of least drag is an airspeed, not a ground speed. And commercial jet engines are most efficient around 90% thrust, not at lower settings. So going slower can make you less efficient.

t-writescode 7y ago
Does less efficient result in more total fuel loss, in this specific case, since the engine will be running for a different amount of time?
- t0mas88 7y ago
  Can't really tell without knowing their weight and available cruising levels. But in general you should not run a commercial jet engine at lower thrust settings. The optimum altitude as calculated by the flight management system is essentially the altitude at which 90% thrust gets you the best cruise speed. That's also why flying low is really bad for fuel consumption, you're going to have to decrease thrust and you'll be aerodynamically less efficient at the same time.
  - WalterBright 7y ago
    At lower altitude the jet has to push aside a lot more air.
    - NikolaeVarius 7y ago
      Yes, but to the previous posters point, turbofans operate much less efficiently at lower altitudes. They are optimized to run the majority of cruise at a very specific set of altitude and power output settings. This is compounded by the fact that fuel load also assumes a set of assumptions of the flight plan
  - dnhz 7y ago
    This sounds wrong to me because I've read that the plane uses 90% thrust or something around that to take off, and at cruise, less thrust is needed.
    - VBprogrammer 7y ago
      I'm not sure where the 90% comes from. What is it refering to? Rotor stage RPM, static thrust, fuel flow? In general turbine engines are limited mostly by the temperature at the first stage of turbine blades after the combustion stage. It's hard to get reliable instrumentation in this zone so a proxy temperature is often taken from a later stage. In older airliners there was a table of max ITT values varying with altitude and outside air temperature. In modern FADEC engines the computer does the same calculations. It's not unusual for smaller jets to be set at their max continuous thrust setting shortly after takeoff and be left there until the beginning of the descent. Modern airliners will be flying a cost optimised Mach number. That Mach number is entered on their flight plan and is used as a basis for ensuring they are separated from other flights on the north Atlantic tracks so they wouldn't be able to change it readily. The interesting part of all of this is that they would have been assigned an altitude for the crossing, at high altitudes maximum speeds drop (because flutter margins are proportional to velocity rather than effective pressure) but stall speeds increase so the range of viable flying speeds is actually quite limited at cruise altitudes. They probably couldn't have slowed down if they wanted too.
      - dnhz 7y ago
        I was referring to the N1 and N2 values. But I realized I was wrong and that jet engines do operate at say 90% N1 during cruise.
- colechristensen 7y ago
  Aircraft performance metrics of all sorts are generally U shaped. There will be an optimum altitude and airspeed for a chosen regime and deviating from it in either direction will result in lower performance. So if you are shooting for miles per pound of fuel, there is a best. You will lose total trip fuel if you throttle up and go faster and you will lose total trip fuel if you throttle down and go slower.
ses1984 7y ago
Air resistance goes up by the square of the velocity, so it takes more and more thrust to go faster. The most efficient thrust per unit of speed is therefore somewhat less than the most efficient thrust per unit of fuel. I've only had some college physics and no aeronautical engineering so I could be way off. Of course there are other factors like the amount of lift per unit of velocity and so on...
- CPLX 7y ago
  > Air resistance goes up by the square of the velocity But you measure speed in this context relative to the air, not the ground. The fact that the plane is now moving across land much much quicker due to winds aloft is completely irrelevant from an aerodynamics perspective. The plane doesn’t even “know” that it’s getting there sooner.
  - ses1984 7y ago
    I'm strictly arguing with the point about engines being efficient at 90% thrust which is independent of wind.
- danaliv 7y ago
  > Air resistance goes up by the square of the velocity This is true of form drag. Airplanes are also subject to a somewhat counterintuitive induced drag that is inversely proportional to airspeed. The minimum total drag is therefore somewhere between a slow speed and a fast speed. There are three optimal speeds depending on what you're trying to optimize. Maximum range (distance per unit of fuel) is best glide speed, which would be a painfully slow way to get somewhere. Maximum endurance (time per unit of fuel) is roughly max endurance divided by 1.316—even slower. "Optimum cruise," or Carson's speed (max speed per unit of fuel) is roughly max endurance times 1.316.
  - ses1984 7y ago
    What's the relationship of these values to the efficiency curve of the engines? I'm pretty sure best glide speed times 1.3 can be achieved with less than 90% thrust from the engines of a typical commercial airliner.

mstade 7y ago

Same in Europe, it's happened to me multiple times. It really riles people up for some reason, with people just flat out ignoring crew orders to remain seated etc.

jontro 7y ago

I would think it was to reach London before they closed off airports due to the storm

ReptileMan 7y ago

I asked similar question about angle of attack (both 737 max and AF447) - can't they just look at a glass of water to see they are at wrong angle. But with planes it doesn't work that way - everything is relative to the air outside, not the ground. With good tailwind you still have to go with your cruising speed relative to the tailwind. Your ground speed will be insane. The opposite is with headwind.

rvnx 7y ago
Maybe a gyroscope + glass of water ?
- XMPPwocky 7y ago
  No. Angle of attack behaves in some very non-obvious ways- For example, if you maintain the same attitude, but decrease thrust so that your forward airspeed drops, and you begin descending... your angle of attack increases, despite the aircraft not actually rotating. Why? When you start descending, the air below now seems to be "coming up at you"- you go from ---> (=== to 7 (=== / / if that ASCII art helps at all (equals signs being the wing) Now consider how roll, yaw, and crosswinds affect this- as the AoA becomes variable across the wing...
- t0mas88 7y ago
  Doesn't work. The stall is about the angle at which the airflow meets the wing. The gyroscope (with or without glass of water) will tell you the attitude of the plane, but nothing about the direction from which the air meets the wing. You can stall in a nose down attitude if you're descending fast, the air comes from "below" and you try to pull out ift the dive thereby increasing the angle at which the air meets the wing. All the while your nose is still pointing below the horizon.
aaronmdjones 7y ago
As other comments have mentioned, a glass of water tells you nothing about the conditions outside the plane, which are the ones that matter. But also, it is sometimes useless at telling you about the conditions inside the plane too. If you're rolling and yawing at the same time (known as a coordinated turn), the water in the glass will stay level (relative to the bottom of the glass), and the glass will not slide along its surface, even in a 20 degree bank.

alibarber 7y ago

Agree that it’s a pain when it happens (the gate delay) but Heathrow closes at night so these are some of the first flights to land so it might not be much of a problem. All the morning (evening departures) transatlantic flights I’ve been on west -> East have arrived suspiciously early too so I suspect there’s some schedule padding going on...

chipsa 7y ago
They schedule the flights months out. The know how fast the jet stream is going maybe a couple days out. So yes, schedule padding to make sure a weak jet stream doesn't cause people to miss connections.

elwesties 7y ago

There is also the question of relative airspeed. Planes need to create enough lift to stay in the air. With a large tailwind they need to go faster to keep enough air flowing over the wings thus higher ground speed to keep the same relative air speed.

histriosum 7y ago
This is a common misconception, but very much incorrect. I am a private pilot. When an airplane is in a body of air which is moving across the ground, the airplane moves within that body of air with no knowledge that it is in a strong wind. Airspeed is unaffected, except for gusts or shear events. The airplane maintains it's normal airspeed within that body of air, even though that body of air is moving very quickly in relation to the ground. This is evident in all phases of flight. For example, landing into a strong headwind does not change the approach speed required or the thrust required to obtain that approach speed. The only allowance is for gusty conditions, during which a gust will momentarily affect airspeed due to the inertia of the airplane. The heavier the airplane, the more time it takes a gust or shift to defeat the airplanes inertia.
- Filligree 7y ago
  I'm confused. Are you saying that it'll maintain its normal ground speed despite flying through fast-moving air? Or that it maintains the same air-speed? The former doesn't make any sense, but the latter is what the GP was saying.
  - histriosum 7y ago
    The ground speed will vary, but the airspeed will not be affected by wind (except momentarily for gusts or shears). The poster I replied to was implying that due to the strong tailwind, they had to maintain an increased airspeed. That is incorrect. The airplane has no idea it is in a tailwind, and airspeed will be unchanged.
    - JshWright 7y ago

goatforce5 7y ago

I once took a Boston -> London flight that arrived significantly early thanks to the arctic jet stream. But that meant we arrived before the landing curfew ended at 6am so the aircraft was put in a holding pattern above central London for 30 mins or so, and I flew more or less over my home in East London a few times (I could see it out the window as we flew overhead). We landed a few minutes after 6am, and by the time I got through immigration and customs and rode home during the morning rush hour on the tube it would have been 8 or 8:30am. Super frustrating that the last mile took 3 hours to complete!

teh_klev 7y ago
Back in 2002 a flight I took from Boston to London arrived into LHR airspace about 45-50 mins earlier than it should have due to a decent tailwind from the jetstream. Sadly we stacked for an hour and a half and ended up arriving later than the scheduled arrival time....because fricken Heathrow bottlenecks, and we almost missed our connecting flight back to Scotland. Grrr.

supernova87a 7y ago

Not only that, but Heathrow I understand has heavy curfew / noise fines for arriving before 6am. Maybe to the tune of several tens of thousands of GBP. I figure you would wait to takeoff just to avoid those -- but maybe equally on the departure end they're paying for occupying a gate... https://www.heathrow.com/content/dam/heathrow/web/common/documents/company/doing-business-with-heathrow/flights-condition-of-use/consultation-documents/Conditions-of-Use-Consultation-Draft-2017.pdf https://www.heathrow.com/content/dam/heathrow/web/common/doc... "Schedule 5"

selectodude 7y ago
You get a few freebies every year and they’re far more accommodating for arrivals than departures since they’re much quieter.

pale-hands 7y ago

Good question. Maybe (just speculating here) because it would be dangerous to land with too much fuel on board? Planes dump fuel for that reason when aborting shortly after takeoff, but that may only be a problem with tanks close to full.

xvf22 7y ago
After a transatlantic flight it's highly unlikely you'll land over your maximum landing weight. That situation usually happens only when they have to land within an hour of takeoff.

Reason077 7y ago

> "In the USA, if your flight is more than 20 minutes early, you are usually stuck on the tarmac waiting for a gate." I've experienced this in the US and Canada too, but it doesn't seem to be a problem at Heathrow in my experience. LHR is slot constrained, but not gate constrained. Worst case, you end up on a remote stand with a bus ride in to the terminal.

LeoPanthera 7y ago
Heathrow has a very specific restriction - no landings before 6am, due to the noise for local residents.
- Reason077 7y ago
  Correct. Noise curfews are common at European airports.
- iso947 7y ago
  This flight landed 0443 Landings before 6am are allowed, but are limited in numbers.
  - jfk13 7y ago
    For more detail: https://www.heathrow.com/company/local-community/noise/operations/night-flights https://www.heathrow.com/company/local-community/noise/opera...

newnewpdro 7y ago

AIUI you can only save fuel by not loading it, they can't land with substantial fuel remaining onboard without damaging the airframe. They'll just circle the destination to use up the excess fuel.

briandear 7y ago

200kts ground with a 250 kts tailwind is impossible. The plane would have an indicated airspeed of -50kts.

danaliv 7y ago

> Or are they stuck at their speed they filed in the flight plan, to keep traffic separation? When you cross the Atlantic you're usually in sequence on a track. Slowing down one flight slows down all the flights behind it. (Just checked and the flight in question was indeed on a track.)

dghughes 7y ago

And Heathrow has some sort of "AI" system for scheduling landings and take offs. Even telling pilots of aircraft exactly when they can start their engines and when to start to taxi. It was a great documentary I think a math program it wasn't all about the Heathrow system. This isn't the show but it seems to explain the system: https://www.nats.aero/news/nats-trialling-use-artificial-intelligence-heathrow-airport-cut-delays/ https://www.nats.aero/news/nats-trialling-use-artificial-int...

dx034 7y ago
That's something pretty much all airports do, just that normally the air traffic controller schedules that. With an airport the size of Heathrow and at capacity, they just use more automation to optimize for throughput and reduce fuel consumption.
- cjrp 7y ago
  In Europe, a lot of this is done by EUROCONTROL's Central Flow Management unit. They'll issue a "Calculated Take Off Time" and the ground/tower controller at the airport will get the plane to the runway at the correct time to meet the slot.
iso947 7y ago
Specifically telling pilots at other airports when to start taxiing. You can have a ground delay in Cyprus because you haven’t got a slot at Heathrow.

philjohn 7y ago

It helps that Heathrow has an entire terminal (T5) dedicated for use by British Airways, so gates aren't as big an issue. On a personal note, you get so little sleep on a redeye flight as it is, I'd have been a bit miffed wake up so soon!

iav 7y ago

There were extreme wind conditions on that day and the wind was expected to get worse through the day. The pilots wanted to arrive as early as possible to beat the storm. Source: I was on a Norwegian flight at exactly the same time and the pilot explained this logic to us and also mentioned that we were on pace to break this record. Unfortunately, the pilot couldn't land in the wind conditions and we had to divert. Good thing we had that extra fuel too as the diversion was to Copenhagen which is quite far.

jsjohnst 7y ago

They probably couldn’t slow down at that altitude without stalling. The window of possible air speeds at that altitude is rather small. Further, fuel efficiency would drop off dramatically too, but I feel the major contributing part is likely the stall speed.

joncrane 7y ago

They actually want to be as light as possible (within reason) when they land. They would have to fuel the flight light, which I doubt would ever happen because what if the atmospheric conditions changed on the way?