14 CFR §135.271

1. (a)No certificate holder may assign any flight crewmember, and no flight crewmember may accept an assignment for flight time if that crewmember's total flight time in all commercial flight will exceed—
   1. (1)500 hours in any calendar quarter.
   2. (2)800 hours in any two consecutive calendar quarters.
   3. (3)1,400 hours in any calendar year.
2. (b)No certificate holder may assign a helicopter flight crewmember, and no flight crewmember may accept an assignment, for hospital emergency medical evacuation service helicopter operations unless that assignment provides for at least 10 consecutive hours of rest immediately preceding reporting to the hospital for availability for flight time.
3. (c)No flight crewmember may accrue more than 8 hours of flight time during any 24-consecutive hour period of a HEMES assignment, unless an emergency medical evacuation operation is prolonged. Each flight crewmember who exceeds the daily 8 hour flight time limitation in this paragraph must be relieved of the HEMES assignment immediately upon the completion of that emergency medical evacuation operation and must be given a rest period in compliance with paragraph (h) of this section.
4. (d)Each flight crewmember must receive at least 8 consecutive hours of rest during any 24 consecutive hour period of a HEMES assignment. A flight crewmember must be relieved of the HEMES assignment if he or she has not or cannot receive at least 8 consecutive hours of rest during any 24 consecutive hour period of a HEMES assignment.
5. (e)A HEMES assignment may not exceed 72 consecutive hours at the hospital.
6. (f)An adequate place of rest must be provided at, or in close proximity to, the hospital at which the HEMES assignment is being performed.
7. (g)No certificate holder may assign any other duties to a flight crewmember during a HEMES assignment.
8. (h)Each pilot must be given a rest period upon completion of the HEMES assignment and prior to being assigned any further duty with the certificate holder of—
   1. (1)At least 12 consecutive hours for an assignment of less than 48 hours.
   2. (2)At least 16 consecutive hours for an assignment of more than 48 hours.
      1. (i)The certificate holder must provide each flight crewmember at least 13 rest periods of at least 24 consecutive hours each in each calendar quarter.