What is the fastest speed a passenger airplane flies at?
How fast does the world's currently fastest passenger plane fly (cruise speed)? Do any passenger planes fly faster than the speed of sound?
Do you mean fastest EVER, fastest in theory, or actual fastest of a currently flying commercial passenger route?
@knut I think you'll find the Tu-144 went faster? - "The Tu-144 supersonic transport was the fastest commercial jet plane at Mach 2.35 (1,555 mph, 2,503 km/h). It went into service in 1975, but soon stopped flying. The Mach 2 Concorde aircraft entered service in 1976 and flew for 27 years." - Wiki
Also you have two separate questions in here, might be worth rephrasing or separating out into two (see [faq])
I mean currently flying. Is there a reason that planes aren't reaching the same speeds as before?
I guess I should split it then. I'll do that after I get an answer to this; that way I can build off it.
Have a look at the Convair 990. It may be long forgotten, having been used in the 60's but it would go close to beating a 747 or A380.
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.
Oh I'm waiting for some plane nut to come along and correct me - there's probably some obscure model that I'm not aware of, which would be amusing. Suffice to say though, you won't be breaking the sound barrier in these.
If you build a running track down the length of an A380 and get Usain Bolt to run towards the front at 44.7 km/h (http://www.bbc.co.uk/news/technology-19506130) while the A380 flies at Mach 0.96 or 1020 km/h, (http://www.a-380.com/about-the-a-380/a-380-specifications/) he will be travelling at Mach 1.002! Anyone wanna sponsor this stunt?
@MarkMayo you're correct as to there only having been 2 SSTs. There's a supersonic (or maybe they scaled it down to transsonic) business jet in prototype stage, but it's had several crashes already and is nowhere near ready for production. As most countries don't allow supersonic overflight except for military aircraft, such aircraft are of extremely limited use and there's little incentive to design and produce them (the cost are very high, sales numbers would be very low, do the math).
It's not in commercial service yet, but SpaceShipTwo does eventually have that goal and Virgin Galactic is already selling tickets on it, IIRC. SpaceShipTwo is a bit faster than Concorde. And by 'a bit faster,' I mean almost twice as fast. Mach number isn't well-defined at that altitude, though. Concorde's service ceiling was about 60,000 ft. SpaceShipTwo's is about 360,000 ft. :)