Is being "available" (on call) for a flight under FAR Part 135 at an hour's notice considered being "on duty"?
No. But it's not rest, either.
Since when has a principle operations inspector (POI) been assigned the authority to interpret regulation?
Since never. (it was a rhetorical, trick question). Not the option of the POI.
Duty time is time assigned by the employer as duty. Time not on duty is not necessarily rest.
Rest must be determined looking forward, not back. That is, one cannot simply state that one hasn't flown for 10 hours (or as applicable under given circumstances), and therefore have adequate rest. Rest time must be free from all company related duty. Rest time may include duty to another company, however.
Rest time must be free from all responsibility for work or duty. This does not preclude one from carrying a pager on one's own volition, however. For example, an employee who must have 10 hours of rest prior to duty has had no work assignments in the previous 24 hours. He elects to carry a pager in hope of picking up an assignment. The company does not require him or her to do so, but will call him and at least try the pager, if they can't get another crew. The pager rings, the pilot flies. He has not been required to carry the pager, and doing so has not interrupted his rest period.
If a pilot carries a cell phone or pager because he is on call, then it's not rest. If the pilot carries the cell phone or pager on his own and happens to accept a flight, but has no obligation to do so, then it can still be considered rest.
In a legal interpretation dated 10-05-87, the FAA Chief Legal Counsel noted "The Agency has interpreted "duty" as including actual work for a certificate holder or present responsibility for work if the occasion should arise."
If the company has no expectation that the employee must be available to fly, but the employee volunteers or agrees to do so without that responsibility, it does not interfere with a rest period. Carrying the pager at company request = no rest. Carrying the pager at pilot's volition with no company assignment or responsibility = no problem.
In the same legal interpretation cited above, the FAA Chief Legal Counsel also noted "The Agency has interpreted privosions substantively identical to 135.263(b) to the effect that a flight crewmember's receipt of one telephone call from his air carrier employer during a required rest period does not violate a regulation such as 135.263(b)."
In a different interpretation dated 12-9-99, the applicant submitted the following question: "During the crew's rest period, may the certificate holder initiate contact with the crew to assign a trip, which is scheduled to begin "after" the crew's rest period?"
The FAA Chief Legal Counsel responded: "A period of time during which a pilot has a present responsibility for work should the occasion arise, does not qualify as a rest period. The question you ask, however, concerns the situations where the pilot does not have a present responsibility to do anything for the air carrier, not even to answer the telephone or a pager. This pilot, when contacted, is merely being notified of a flight assignment to take place at the conclusion of his or her rest period. The pilot, during the rest period, was not obligated to be available to answer the telephone or a pager. Accordingly, a certificate holder may attempt to initiate contact with a flight crewmember to assign a trip scheduled to begin after the required rest period without violating 135.263(b)."