| 1 | URR | Aurora Airlines | Callsign: Air Aurora, Founded in 2005. Ceased operations in 2009. | SLO | AVCODES |
| 2 | URR | Aurora Airlines | | | ICAO1 |
| 3 | URR | Union R.R. Co. (Pittsburgh, PA) | 1/1975-7/2005 | | NAKINA |
| 4 | URR | Union R.R. Co. (Pittsburgh, PA) | 1/75-7/2000 | | NRHS |
| 5 | URR | UNION RAILROAD CO. (PITTSBURGH, PA) | | | PWRC |
| 6 | URR | Union Railroad Pittsburgh | | | RSRV |
| 7 | URR | UNION RAILROAD COMPANY | | | SCAC4 |
| 8 | URR | Union R.R. Co. (Pittsburgh, PA) | | USA | TRAFFIC |
