(a) Each certificate holder shall provide at least the following flight attendants on each passenger-carrying airplane used:

1. (1) For airplanes having more than 19 but less than 51 passengers—one flight attendant.
2. (2) For airplanes having more than 50 but less than 101 passengers—two flight attendants.
3. (3) For airplanes having more than 100 passengers—two flight attendants plus one additional flight attendant for each unit (or part of a unit) of 50 passengers above 100 passengers.