Fastest Plane In The World

The fastest plane in the world can potentially have a few answers.  This all depends on your qualifications of a "plane," as we will see in the following points.  The fastest plane, including the fastest unmanned plane, fastest manned rocket-powered aircraft, and fastest plan without the previous distinctions.

X-43.  The X-43 is the fastest plane in the world if you remove common criteria that may remove it from the equation.  It is classified as a scramjet, where it launches from a B-52 at 40,000 feet.  NASA has stated that it has reached Mach 9.6, though you will commonly see it's fastest speed at Mach 9.8.  It is the fastest unmaned plane in the world.

X-15.  The X-15 is the fastest plane in the world if it is required to be manned.  However, it is also launched from a B-52. and is powered by a rocket engine (why a third category is needed here).  It has reached top speed at Mach 6.72.

SR-71 Blackbird (YF-12).  If the fastest plane in the world cannot be unmanned, launched from a B-52, and contain a rocket-powered  engine, the SR-71 is the fastest plane in the world.  It is jet-powered and a piloted airplane, where it has reached Mach 3.2, though some dispute that its full capabilities were not revealed.  Introduced in 1964, it went out of service from the U.S. Air Force in 1998.

Many believe that the fastest plane in the world is unknown, due to possible secrecy from governments.  However, one of these three aircrafts serves as the fastest plane in the world, depending on the criteria needed for a "plane."