system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: this wonky jet stream giving planes the extra speed from a tailwind. What happens if a 777 breaks the sound barrier?

How bad can this extra fast jet stream really be for commercial travel? Is it dangerous? Do planes have ways to slow down if they get caught in it?


Edit: wow. Lots of information. Thanks people.
gpt
We can measure the speed of an aircraft in two ways - ground speed, and airspeed.

Ground speed is how an observer, stationary, on the ground would perceive the aircraft. Airspeed is how fast it's going relative to the air that it's in. If you have an aircraft that's doing an airspeed of 500mph in a 200mph tailwind, it'll give it a ground speed of 700mph.

It's rather like if you're on a 100mph train and start to jog down the carriage at 4mph - to an observer by the side of a track, you're doing 104mph, but the effect on your body is no different to you doing 4mph.

It's the airspeed that's important when it comes to deciding if an aircraft is going to hit problems. It may be really fast to a ground based observer, but it's quite normal for the aircraft.