14 CFR 33.92 - Rotor locking tests.
If continued rotation is prevented by a means to lock the rotor(s), the engine must be subjected to a test that includes 25 operations of this means under the following conditions:
(a) The engine must be shut down from rated maximum continuous thrust or power; and
(b) The means for stopping and locking the rotor(s) must be operated as specified in the engine operating instructions while being subjected to the maximum torque that could result from continued flight in this condition; and
(c) Following rotor locking, the rotor(s) must be held stationary under these conditions for five minutes for each of the 25 operations.