sentences:  Scheduled airline passenger jet service arrived in Keene during the early 1970s.Delta Air Lines had acquired and merged with Northeast Airlines in 1972, which resulted in Delta introducing McDonnell Douglas DC-9-30 jetliner flights into the airport.According to the March 1, 1973, Delta system timetable, the airline was operating a daily DC-9-30 nonstop to New York LaGuardia Airport (LGA) with this flight, offering direct, no change of plane service to Philadelphia (PHL) and Miami (MIA).