Original Message

Section 135.267(c) pertains to certificate holders that schedule flight crews on 'regularly
assigned duty periods' of no more than 14 hours.  There are daily flight time limitations (8 hours in 24-hour shift in single pilot HEMS) and there is duty time limitation (14 hours in 24-hour shift) which is the time on the clock, whether flying or not.

Q: Section 135.267(e) states that "when a flight crewmember has exceeded the daily flight
time limitations in this section ... that flight crewmember must have a rest period before
being assigned or accepting an assignment for flight time ... ". Thus, if the flight time
limitation is exceeded for reasons beyond the control of the certificate holder or the flight
crew, then the increased rest provisions of§ 135.267(e) come into effect..."

FAA: For clarification purposes, we stress that§ 135.267(e) is applicable only if the flight time limitations are exceeded. We remind you that, although § 135.267(c) allows for an extension of flight times within a 14-hour maximum duty period, it does not permit the extension of the (14-hour) duty period. An exceedance of the 14-hour duty period constitutes a violation of § 135.267(c). See Legal Interpretation to Mr. Moody, from Lorelei Peter, Assistant Chief Counsel for Regulations(August 22, 2017).

Q: Would a delay during any segment of the sequence of flights that are operated as helicopter air ambulance allow for an exceedance of the regularly scheduled 14-hour duty day (whether or not a flight time limit may be exceeded)?

FAA: If the operation involves a regularly assigned duty period under § 135.267(c), then
the duty period cannot be extended, and the operation cannot be carried out if the delay will
cause the flight crew to operate beyond the maximum 14-hour duty period threshold.

In other words, each flight segment is reassessed throughout the flight operation. If a pilot knows they will exceed their 14 hour duty period before taking off on say, the final segment, it is a violation of the regs to take off and complete that flight segment. See Legal Interpretation to Mr. Triponey, July 10, 2018