121: US Airline Regulations (14CRF121)
123.45: Common use VHF Frequency (aka "Fingers")
135: US Charter/Non-scheduled Regulations (14CFR135)
141: US Pilot School Regulations (14CRF141)
61: US Pilot and Instructor Regulations (14CFR61) (also ad hoc flight training or flight school operation under 14CFR61)
91: US General Aviation Regulations (14CRF91)
9E: Endeavor Airlines