The Unbeatable Workhorse: How the McDonnell Douglas DC-9 Outlasted Its Replacement
The McDonnell Douglas DC-9, a venerable workhorse of the skies, remarkably remained in service longer than its intended successor, the MD-87. While the MD-87 was developed as a shorter variant of the MD-80, it proved less economically efficient for the short-haul, high-frequency routes where the DC-9 excelled. Major carriers like Northwest Airlines, and later Delta Air Lines, valued the DC-9's ruggedness, reliability, and suitability for their domestic networks. Consequently, these airlines continued to operate their aging but dependable DC-9 fleets for decades. Delta ultimately retired its last DC-9 in 2014, long after many operators had phased out the supposedly more modern MD-87.
Official Source: https://simpleflying.com/how-mcdonnell-douglas-dc9-outlasted-its-replacement/