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2 planes, not plains
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On some plainsplanes (airplus, sorry no reference) there is a “sprint mode” that uses more fuel but goes faster. Airlines may therefore decide to time their flights not using the “sprint mode”, so as to save fuel costs, but be willing to use it if they are running late.

Flights are also timed so that can keep to timings even if the wind is in the “wrong” direction, therefore often a flight can go faster than the planners assumed.

On some plains (airplus, sorry no reference) there is a “sprint mode” that uses more fuel but goes faster. Airlines may therefore decide to time their flights not using the “sprint mode”, so as to save fuel costs, but be willing to use it if they are running late.

Flights are also timed so that can keep to timings even if the wind is in the “wrong” direction, therefore often a flight can go faster than the planners assumed.

On some planes (airplus, sorry no reference) there is a “sprint mode” that uses more fuel but goes faster. Airlines may therefore decide to time their flights not using the “sprint mode”, so as to save fuel costs, but be willing to use it if they are running late.

Flights are also timed so that can keep to timings even if the wind is in the “wrong” direction, therefore often a flight can go faster than the planners assumed.

1
source | link

On some plains (airplus, sorry no reference) there is a “sprint mode” that uses more fuel but goes faster. Airlines may therefore decide to time their flights not using the “sprint mode”, so as to save fuel costs, but be willing to use it if they are running late.

Flights are also timed so that can keep to timings even if the wind is in the “wrong” direction, therefore often a flight can go faster than the planners assumed.