Most commercial jetliners have a service (or certificated) ceiling of about 42,000 ft (12.8 km; 8.0 mi) and some business jets about 51,000 ft (15.5 km; 9.7 mi). Before its retirement, the Concorde supersonic transport (SST) routinely flew at 60,000 ft (18.3 km; 11.4 mi).