The first MD-80, DC-9 line number 909, made its first flight on October 18, 1979.
Although two aircraft were substantially damaged in accidents, test flying was completed on August 25, 1980, when the first variant of MD-80, the JT8D-209-powered MD-81 (or DC-9-81), was certified under an amendment to the FAA type certificate for the DC-9.
The flight-testing leading up to certification had involved three aircraft accumulating a total of 1,085 flying hours on 795 flights.
The first delivery, to launch customer Swissair took place on September 13, 1980.

As the MD-80 was not in effect a new aircraft, it continues to be operated under an amendment to the original DC-9 FAA aircraft type certificate (a similar case to the later MD-90 and Boeing 717 aircraft).
The type certificate issued to the aircraft manufacturer carries the aircraft model designations exactly as it appears on the manufacturer's application, including use of hyphens or decimal points, and should match what is stamped on the aircraft's data or nameplate.
What the manufacturer chooses to call an aircraft for marketing or promotional purposes is irrelevant to the airworthiness authorities.
The first amendment to the DC-9 type certificate for the new MD-80 aircraft was applied as DC-9-81, which approved on August 26, 1980.
All MD-80 models have since been approved under additional amendments to the DC-9 type certificate.
In 1983, McDonnell Douglas decided that the DC-9-80 (Super 80) would be designated the MD-80.
Instead of merely using the MD- prefix as a marketing symbol, an application was made to again amend the type certificate to include the MD-81, MD-82, and MD-83.
This change was dated March 10, 1986, and the type certificate declared that although the MD designator could be used in parentheses, it must be accompanied by the official designation, for example: DC-9-81 (MD-81).
All Long Beach aircraft in the MD-80 series thereafter had MD-81, MD-82, or MD-83 stamped on the aircraft nameplate.

Although not certified until October 21, 1987, McDonnell Douglas had already applied for models DC-9-87 and DC-9-87F on February 14, 1985.
The third derivative was similarly officially designated DC-9-87 (MD-87), although no nameplates were stamped DC-9-87.
For the MD-88, an application for a type certificate model amendment was made after the earlier changes, so there was not a DC-9-88, which was certified on December 8, 1987.
 The FAA's online aircraft registry database shows the DC-9-88 and DC-9-80 designations in existence but unused.
The first MD-80, DC-9 line number 909, made its first flight on October 18, 1979. Although two aircraft were substantially damaged in accidents, test flying was completed on August 25, 1980, when the first variant of MD-80, the JT8D-209-powered MD-81 (or DC-9-81), was certified under an amendment to the FAA type certificate for the DC-9. The flight-testing leading up to certification had involved three aircraft accumulating a total of 1,085 flying hours on 795 flights. The first delivery, to launch customer Swissair took place on September 13, 1980.
As the MD-80 was not in effect a new aircraft, it continues to be operated under an amendment to the original DC-9 FAA aircraft type certificate (a similar case to the later MD-90 and Boeing 717 aircraft). The type certificate issued to the aircraft manufacturer carries the aircraft model designations exactly as it appears on the manufacturer's application, including use of hyphens or decimal points, and should match what is stamped on the aircraft's data or nameplate. What the manufacturer chooses to call an aircraft for marketing or promotional purposes is irrelevant to the airworthiness authorities. The first amendment to the DC-9 type certificate for the new MD-80 aircraft was applied as DC-9-81, which approved on August 26, 1980. All MD-80 models have since been approved under additional amendments to the DC-9 type certificate. In 1983, McDonnell Douglas decided that the DC-9-80 (Super 80) would be designated the MD-80. Instead of merely using the MD- prefix as a marketing symbol, an application was made to again amend the type certificate to include the MD-81, MD-82, and MD-83. This change was dated March 10, 1986, and the type certificate declared that although the MD designator could be used in parentheses, it must be accompanied by the official designation, for example: DC-9-81 (MD-81). All Long Beach aircraft in the MD-80 series thereafter had MD-81, MD-82, or MD-83 stamped on the aircraft nameplate.
Although not certified until October 21, 1987, McDonnell Douglas had already applied for models DC-9-87 and DC-9-87F on February 14, 1985. The third derivative was similarly officially designated DC-9-87 (MD-87), although no nameplates were stamped DC-9-87. For the MD-88, an application for a type certificate model amendment was made after the earlier changes, so there was not a DC-9-88, which was certified on December 8, 1987.  The FAA's online aircraft registry database shows the DC-9-88 and DC-9-80 designations in existence but unused.
McDonnell Douglas MD-80