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If a commercial plane encounters strong tailwinds, would the pilots set the autopilot for a fixed arrival time (if that is possible), or would it be ok to arrive way ahead of schedule?

I imagine this could disturb airport operations, and that there are fuel economy considerations: if I was the airline, I would try to minimize fuel consumption.

But if I were ATC, random arrival times could cause chaos. Passengers in turn would probably be happy to arrive as fast as possible. It seems like there are conflicting interests.

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  • $\begingroup$ As a side comment, all eastbound flights over the Atlantic have strong tailwinds (jet streams). $\endgroup$ – mins Jan 4 '19 at 16:19
  • $\begingroup$ Above the continental US too, no? I was recently on a Dulles - SFO flight which got 200 mph headwinds on the first half the flight - then 50 mph tailwinds over Utah, Nevada and the Sierras to California. $\endgroup$ – Frank Jan 4 '19 at 16:25
  • $\begingroup$ For the Atlantic, it is quite noticeable indeed, as eastbound flights reach Europe in about 9 hours whereas westbound flights from Europe take 11 hours to reach the US (roughly). $\endgroup$ – Frank Jan 4 '19 at 16:29
  • $\begingroup$ Yes over US, either the polar jet stream or the subtropical one. See this news for example. You may want to ask a new question about the practical effect of the jet streams over lands. $\endgroup$ – mins Jan 4 '19 at 16:44
  • $\begingroup$ @mins A jetstream is a unique phenomenon that resides at the tropopause at frontal boundaries, into the upper corner of the warm air mass, where there is a kind of watermelon seed through your fingers effect that makes a fairly narrow little river of air flow at high speed. Flights may be able to get into a jet or may not, but what you're really describing is pressure pattern flow and prevailing winds which generally favour west to east. When the eastbound North Atlantic Tracks are set up each morning, the track system is shifted north to south to take best advantage of the pressure patterns. $\endgroup$ – John K Jan 4 '19 at 19:05
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It will depend on constraints at the arrival airport. If there are no constraints, they will choose a speed that minimizes fuel burn, and arrive early if that's how it works out.

It's possible that the arrival airport may have constraints on arrival volume. As you pointed out, for busier areas, if aircraft arrive earlier than expected, it could cause things to get backed up. In that case ATC may have an aircraft adjust their speed or enter a hold in order to delay their arrival until capacity allows. Slowing down early is more efficient than arriving too soon and having to fly a holding pattern.

In areas without radar coverage, such as oceanic crossings, aircraft may be required to hold a certain airspeed in order to maintain separation from aircraft ahead and behind. In this case a pilot may not have much choice until they exit the oceanic airspace, and any adjustments would have to be made after that point.

ATC will do their best to ensure the safe and expeditious flow of traffic, but safety has to come first. While a pilot can choose to not follow ATC instructions in the case of an emergency, and in the interest of safety pilots have some amount of discretion in declaring emergencies as they see necessary, doing so just to reduce cost or for convenience would not be acceptable and may attract some scrutiny.

It's also possible that there would be constraints on the ground at the arrival airport. If the aircraft is scheduled to arrive at a certain gate at a certain time, and it arrives early, there may be another aircraft still occupying the gate, or support staff may not be ready to receive the aircraft. This would require the pilots to coordinate with the airline. If alternate arrangements can't be made, the airline might actually prefer the aircraft to be not arrive early. They would probably prefer to sit on the ground, with the engines off if possible, as that burns much less fuel than doing the waiting in the air.

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Given a strong tailwind and freedom by ATC, most pilots will aim for the most fuel efficient power setting, to reduce costs; they are part of a business after all.

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  • $\begingroup$ Is it ok to arrive with fuel tanks half full? Is the fuel kept in the tanks in that case? Years ago, I heard planes had to dump fuel before landing for safety reasons. $\endgroup$ – Frank Jan 4 '19 at 16:27
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    $\begingroup$ While a plane can be overweight, and need to dump fuel, this is more typically a problem when a plane prepped for a long flight has to make an emergency landing much sooner than planned. It would be truly exceptional for a tailwind to be soooo strong that the plane would be overweight after a scheduled, planned route. (Remember, the pilots know the wind forecast before they take off, so they know if they'll have a tailwind and approximately how strong it will be.) $\endgroup$ – abelenky Jan 4 '19 at 16:30
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    $\begingroup$ Airplanes have a max landing weight, but usually a couple hours of flying is enough to get below it. Lots of airliners don't have fuel dumping systems so if the airplane is above MLW they have to stooge around to burn it off, or if it's an emergency they'll land overweight, which requires the airline to do a special landing gear inspection. $\endgroup$ – John K Jan 4 '19 at 19:09
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It depends... If I was a miles per gallon tightwad and was flight planning for a certain mach # in order to get there in a certain time, and found myself in a high altitude jet stream with a crazy tailwind, I might decide to slow down closer to the "min drag" speed of my plane to improve the air miles per gallon, knowing I can still arrive at the planned time. Otherwise, I would just take the early arrival as a bonus.

However, if I'm heading for a saturated-traffic airport like Chicago, and an unexpected tailwind is going to make me arrive 20 minutes before the arrival time expected by ATC from the flight plan filed (and where I may have a reservation time slot assigned), and that arrival is going to add too much to the incoming crowd, ATC will probably put me in a hold to delay my arrival, which I won't have any choice about unless I request a fuel-state priority or declare an emergency.

One thing you can be certain of is that the airline itself will not on its own accord do anything to increase its fuel burn just to avoid arriving early; only if ATC forces it to. Better to be on the ground sitting on the ramp, with one engine shut down and one idling, as you sit for 15 minutes waiting for the gate you arrived early at to become free.

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