It is difficult to say with certainty what the fastest airplane in the world is, because the answer could be a military secret. There also are many types of flying vessels that might or might not be considered airplanes, depending on whether they are manned or unmanned, their methods of taking off and landing and other factors. What one person might consider to be the fastest airplane might be considered by another person to be a glider or a rocket. A widely accepted answer, however, is that the world's fastest airplane was the Lockheed SR-71, also called the Blackbird, which is said to have reached a speed of 2,193.2 miles (3,529.6 km) per hour.
The Lockheed SR-71 was a jet-powered and piloted airplane that was used to fly reconnaissance missions for the United States Air Force from 1964 until 1998. It is said to have reached an altitude of 16.1 miles (25.9 km). Some people have speculated that the Blackbird's true top speed and other capabilities have never been revealed.
The fastest airplane commercially was the Tupolev Tu-144, nicknamed the Concordski or Konkordski, which is said to have reached 1,550 miles (2,494.4 km) per hour. Technical and safety problems, however, led the Russian company to retire the Tu-144 after a short time. Another one of the fastest commercial airliners was the Concorde, which generally flew at a top speed of 1,330 miles (2,140.4 km) per hour. By comparison, the Boeing 747 operates at a cruising speed of about 550 miles (885.1 km) per hour.
If having a pilot on board is not a criteria, then the X-43 is said to be the fastest airplane in the world. The X-43 is an unmanned scramjet that launches not from the ground but from a B-52 bomber at about 40,000 feet (12.2 km) in the air. On 16 November 2004, the X-43 reached about 7,000 miles (11,265 km) per hour, according to the U.S. National Aeronautics and Space Administration (NASA), although some reports have put the speed even higher.
North American X-15
If the type of engine is not limited to jet-powered engines, then the North American X-15 is the fastest airplane. Powered by a rocket engine, the X-15 is said to have reached a speed of 4,520 miles (7,274 km) per hour. Like the X-43, it is launched mid-air from a B-52. The X-15 has achieved an altitude record of 67 miles (107.8 km) on 22 August 1963, earning some of its pilots the designation of "astronaut" by the U.S. Air Force (USAF). The X-15 is powered by a rocket engine, however, so it is technically half-rocket, arguably eliminating it from being called the fastest airplane in the world.
The U.S. Defense Advanced Research Projects Agency (DARPA) has tested an unmanned hypersonic glider that could be considered the fastest airplane in the world. Launched from Vandenberg Air Force Base in California aboard a Minotaur IV rocket on 11 August 2011, the Falcon HTV-2 reached a speed of about 13,000 miles (20,921.5 km) per hour. First tested in 2010, the Falcon HTV-2's second test flight ended when DARPA lost contact with it about nine minutes into a scheduled 30-minute flight and it automatically crashed itself into the Pacific Ocean. The Falcon HTV-2 was part of a project to develop an aircraft that could reach anywhere in the world in less than an hour.