14 CFR §35.39

Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗

Endurance tests on the propeller system must be made on a representative engine in accordance with paragraph (a) or (b) of this section, as applicable, without evidence of failure or malfunction.

(a)Fixed-pitch and ground adjustable-pitch propellers must be subjected to one of the following tests:
1. (1)A 50-hour flight test in level flight or in climb. The propeller must be operated at takeoff power and rated rotational speed during at least five hours of this flight test, and at not less than 90 percent of the rated rotational speed for the remainder of the 50 hours.
2. (2)A 50-hour ground test at takeoff power and rated rotational speed.
(b)Variable-pitch propellers must be subjected to one of the following tests:
1. (1)A 110-hour endurance test that must include the following conditions:
  1. (i)Five hours at takeoff power and rotational speed and thirty 10-minute cycles composed of:
    1. (A)Acceleration from idle,
    2. (B)Five minutes at takeoff power and rotational speed,
    3. (C)Deceleration, and
    4. (D)Five minutes at idle.
  2. (ii)Fifty hours at maximum continuous power and rotational speed,
  3. (iii)Fifty hours, consisting of ten 5-hour cycles composed of:
    1. (A)Five accelerations and decelerations between idle and takeoff power and rotational speed,
    2. (B)Four and one half hours at approximately even incremental conditions from idle up to, but not including, maximum continuous power and rotational speed, and
    3. (C)Thirty minutes at idle.
2. (2)The operation of the propeller throughout the engine endurance tests prescribed in part 33 of this chapter.
(c)An analysis based on tests of propellers of similar design may be used in place of the tests of paragraphs (a) and (b) of this section.