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Jetstreams are streams of high-moving west-to-east winds (200mph to 300mph, source) which most pilots are trained to use to cut down on their fuel costs (source). In the same linked article, it mentions private jets almost always fly at maximum speed anyway, even when on a jetstream.

Assuming a pilot maintains the same airspeed before and after entering a jetstream, how much would be the expected change in groundspeed in practice? Is it just the airspeed plus the tailwind?

I imagine it depends on the type of the aircraft, so consider only a typical commercial airplane (Boeing, Airbus? I'm not sure which one is more typical).

I'm just curious in knowing how the plane's speed is affected and why it changes that way.

markovchain
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    Welcome to aviation.SE! We already have a lot of questions on airspeed, ground speed and wind, this question or this one could be a good starting point. – Pondlife Apr 28 '17 at 13:29
  • @Pondlife Thanks! Feel free to mark this one as a duplicate to either one. And thanks for the links to both :) – markovchain Apr 28 '17 at 13:36
  • It works like you have assumed: Just add velocity vectors (velocity of aircraft relative to air and wind velocity relative to ground). There is no maximum ground speed, only maximum airspeed. As jet streams don't change aircraft airspeed, a pilot takes full advantage of them, whatever its current groundspeed. It's also the same than a person walking in a moving train, there is not effect of the train speed on the person (in non-relativist physics), but the ground speed is the sum of velocity vectors. – mins Apr 28 '17 at 14:16
  • The difference between private jets and commercial, is privates want to get there are soon as they can, whereas commercials are on a schedule. It benefits the airline more to throttle back in a tail wind to maintain the arrival time, and save fuel, than it does to get there early. – Trevor_G Apr 28 '17 at 16:38
  • Just to clarify the OP's referenced speeds... The jetstream in the thermosphere that moves at 200-300MPH is not the same jetstream that aircraft fly in. The lower Jetstream (at about 30,000ft) that aircraft use only flows along at about 100MPH avg. The official definition of the jetstream starts at 50kts, and 50-150 is what is normally observed. – Jimmy Apr 28 '17 at 16:48

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