employed by manufacturer North American, and one (Petersen) was a Navy pilot. Over thirteen flights, eight pilots flew above 264,000 feet or 50 miles, thereby qualifying as astronauts according to the United States definition of the space border. All five Air Force pilots flew above 50 miles and were awarded military astronaut wings contemporaneously with their achievements, including Adams, who received the distinction posthumously following the flight 191 disaster. However the other three were NASA employees, and did not receive a comparable decoration at the time. In 2004, the Federal Aviation Administration conferred its first-ever commercial astronaut wings on Mike Melvill and Brian Binnie, pilots of the commercial SpaceShipOne, another spaceplane with a flight profile comparable to the X-15's. Following this in 2005, NASA retroactively awarded its civilian astronaut wings to Dana (then living), and to McKay and Walker (posthumously). Eleven flights above 50 miles were made in the X-15-3, and two were made in the X-15-1. Every X-15 pilot also flew as a program chase pilot at least once, supporting missions in which they were not flying as lead pilots. Other chase pilots included future astronauts Michael Collins, Fred Haise and Jim McDivitt. The two NB-52 mother ships were most frequently piloted by Fitz Fulton. On one occasion Chuck Yeager, former pilot of the X-15's predecessor X-plane the X-1, the first crewed craft to break the sound barrier, assisted as NB-52 co-pilot for an aborted flight. Flight numbering Two conventions have been used to number the X-15's flights. In one, the numbers 1 through 199 were used to chronologically denote the free flights made by any of the three spaceplanes. For example, flight 1 (8 June 1959) was made by the X-15-1, flight 34 (7 March 1961) was made by the X-15-2, and flight 49 (5 April 1962) was made by the X-15-3. This convention ignores captive and aborted flights. The other convention was an official three-part flight designation number, described in a 1960 letter by NASA flight research director Paul Bikle, and split into three columns below. The first part, a number—1, 2 or 3—would denote the involved X-15 plane. The second part—a number, or "A", or "C"—would denote that individual X-15's chronological free flights; aborted flights were coded as "A", and scheduled captive carry test flights were coded as "C". The third part, a number, would denote the total number of times to-date that the individual X-15