14 CFR § 135.338

For the purposes of this part:

A flight instructor (aircraft) is a person who is qualified to instruct in an aircraft for a particular type, class, or category aircraft.

A flight instructor (FSTD) is a person who is qualified to instruct only in an FSTD for a particular type, class, or category aircraft.

Flight instructors are those instructors who perform the functions described in §§ 135.321(a) and 135.323(a)(4) and (c).

No certificate holder may use a person, nor may any person serve as a flight instructor in a training program established under this subpart unless, with respect to the type, class, or category aircraft involved, that person—

Holds the pilot certificates and ratings required to serve as a pilot in command in operations under this part;

Has satisfactorily completed the appropriate training phases for the aircraft, including recurrent training, that are required to serve as a pilot in command in operations under this part;

Has satisfactorily completed the proficiency or competency checks that are required to serve as a pilot in command in operations under this part;

Has satisfactorily completed the applicable training requirements of § 135.340.

Completion of the requirements in paragraphs (b)(2), (3), and (4) of this section shall be entered in the individual's training record maintained by the certificate holder.

A flight instructor (FSTD) must accomplish the following—

Fly at least two flight segments as a required crewmember for the type, class, or category aircraft involved within the 12-month period preceding the performance of any flight instructor duty in an FSTD; or

Satisfactorily complete an approved line-observation program within the period prescribed by that program preceding the performance of any flight instructor duty in an FSTD.

The flight segments or line-observation program required in paragraph (d) of this section are considered completed in the month required if completed in the calendar month before, or in the calendar month after, the month in which they are due.

A person who serves as a required flightcrew member while performing flight instructor duties must also meet the requirements of this chapter for the duty position in which they are serving.