How fast does the world's currently fastest passenger plane fly (cruise speed)? Do any passenger planes fly faster than the speed of sound?
Sadly, neither is available any longer with access to fly on them.
So then we look to the two major manufacturers with almost supersonic capabilities.
Long considered the fastest passenger plane, the Boeing 747 has several variants, each with slightly different speeds. The fastest of them are the 747-400, 747-400ER and 747-8L, all of which can cruise at Mach 0.855ish, and have top speeds of Mach 0.92. So close!
Then we look at Airbus. Their fastest, we're looking at the A380. Its cruising speed is said to be Mach 0.85, while its top speed was shown in a demonstration in 2005 to be Mach 0.96. Even closer!
So with conventional passenger jets, no, we can't go faster than the speed of sound, and Mach 0.96 is the theoretical maximum you'll reach, although it's unlikely you'll be on a flight doing that (they did it with a shallow dive and without passengers/cargo).
Part of the reason for this is design - the entire design of the plane needs to change if one is to break the sound barrier - the pressure and forces exerted on the aircraft would likely see them break apart. Another is the noise pollution - there's a very large sonic boom when the Concorde used to break the barrier.
HOWEVER, you can 'cheat'. If you're in say, a 777 going fast with a massive tail-wind, your effective groundspeed could be faster than it, even though the plane isn't reaching the same pressures. There's a detailed discussion of when this has happened online.
No, there is none and there will be none (until a new supersonic jet comes out). The reason is once supersonic speed is reached the drag resistance of the airplane increases enormously because shock waves are created and maintained. So you need much more fuel for a neglible increase of speed.
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Jet fighters with supercruise still have an increase of drag, but first they are modeled to minimize the impact and second they are moving with Mach >1.2 to leave the so-called transsonic regime of Mach 0.8-1.2.
"Transsonic" means that the air around the plane moves in some regions with subsonic speed (slowest under the wings) and in some regions with supersonic speed (highest above the wings). In fact a normal jet has a small shock wave above the wings during the flight.
If every air molecule of the plane moves with supersonic speed, the drag decreases again because the interaction of the sub- and supersonic areas increase the drag.
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