I recently took a BA 777 flight from Dulles to LHR... The Pilot announced that it would be a shorter journey time wise due to the prevailing wind.
1 hour into the flight and I heard some one say "a 777 can't go this fast".
I know a little about the 777, but in no way professionally. But I looked at the GPS info and the ground speed was hitting 760 mph...
Shortly after, we reduced speed to around 650 mph, and then later it came down again, but considerably.
We were over London in 5.5hrs...
While impressed, I was left wondering what the hell is the maximum structural limit on both the aircraft and the wings.
Your question is similar to many others that I have received before, typically like ‘Does a strong tail wind cause the plane to fly supersonic?’
Flying in an easterly direction to London, one would usually expect to encounter strong tail winds due to the prevailing jet streams. Hence you would normally take a shorter time to get to London than to get back to Dulles.
Hence the common question from travelers when encountering a strong tail wind in a jet stream is whether the plane has actually broken the sound barrier?
Well the answer is no. The Boeing 777 that you flew on is a subsonic plane only. It means she is designed to fly below the speed of sound. Even if there is a strong tail wind pushing the plane forward and the ground speed may have exceeded the theoretical speed of sound, in reality, the plane has not gone supersonic.
The confusion arises between the understanding of ground speed and the plane’s speed. The ground speed is the speed at which an object travels relative to a fixed point on the Earth's surface. The difference between ground speed and airspeed is caused by the influence of winds on the overall speed of the aircraft.
This is analogous to you walking at 2 mph along a walkalater (travelator) that is moving at 2 mph. Your actual movement towards your plane at the gate is pretty fast at 4 mph (2 + 2) but as far as you are concerned, you are still walking at 2 mph!
So even if you were seeing a ground speed of 760 mph on the GPS, the Boeing 777 has never exceeded it structural limits of the plane or its wings it was designed for!
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