| 1 | YX | Midwest Express Airlines, Inc. | ICAO: MEP, Callsign: Midex, IATA Prefix: 453, Name changed to Midwest Airlines, Inc. w.e.f. 28 February 2003. | USA | AVCODES |
| 2 | YX | Midwest Airlines, Inc. | ICAO: MEP, Callsign: Midex, IATA Prefix: 453, Name changed to Republic Airlines, Inc d/b/a Midwest Airlines, Inc. Name changed from Midwest Express Airlines, Inc. w.e.f. 28 February 2003. | USA | AVCODES |
| 3 | YX | Republic Airlines, Inc d/b/a Midwest Airlines, Inc. | ICAO: MEP, Callsign: Midex, IATA Prefix: 453, Merged into Frontier Airlines w.e.f. 03 November 2010. Name changed from Midwest Airlines, Inc. w.e.f. 23 June 2009. | USA | AVCODES |
| 4 | YX | Republic Airline, Inc. | ICAO: RPA, Callsign: Brickyard, IATA Prefix: 453, Designator RW* recalled by IATA | USA | AVCODES |
| 5 | YXA | National Airports Authority Of India | | IND | AVCODES |
| 6 | YXEU | YIWU TIMEX INDUSTRIAL INVESTMENT CO.,LTD | | PRC | BIC |
| 7 | YXOP | YERXAS OIL & POWER | | | SCAC4 |
