777 

Federal Aviation Administration, DOT 

§ 29.923 

overspeed expected in service, assum-
ing that speed and torque limiting de-
vices, if any, function properly. 

(i) 

Endurance tests; rotor control posi-

tions.  When the rotor controls are not 
being cycled during the tie-down tests, 
the rotor must be operated, using the 
procedures prescribed in paragraph (c) 
of this section, to produce each of the 
maximum thrust positions for the fol-
lowing percentages of test time (except 
that the control positions need not 
produce loads or blade flapping motion 
exceeding the maximum loads or mo-
tions encountered in flight): 

(1) For full vertical thrust, 20 per-

cent. 

(2) For the forward thrust compo-

nent, 50 percent. 

(3) For the right thrust component, 

10 percent. 

(4) For the left thrust component, 10 

percent. 

(5) For the aft thrust component, 10 

percent. 

(j) 

Endurance tests, clutch and brake 

engagements.  A total of at least 400 
clutch and brake engagements, includ-
ing the engagements of paragraph (b) 
of this section, must be made during 
the takeoff torque runs and, if nec-
essary, at each change of torque and 
speed throughout the test. In each 
clutch engagement, the shaft on the 
driven side of the clutch must be accel-
erated from rest. The clutch engage-
ments must be accomplished at the 
speed and by the method prescribed by 
the applicant. During deceleration 
after each clutch engagement, the en-
gines must be stopped rapidly enough 
to allow the engines to be automati-
cally disengaged from the rotors and 
rotor drives. If a rotor brake is in-
stalled for stopping the rotor, the 
clutch, during brake engagements, 
must be disengaged above 40 percent of 
maximum continuous rotor speed and 
the rotors allowed to decelerate to 40 
percent of maximum continuous rotor 
speed, at which time the rotor brake 
must be applied. If the clutch design 
does not allow stopping the rotors with 
the engine running, or if no clutch is 
provided, the engine must be stopped 
before each application of the rotor 
brake, and then immediately be started 
after the rotors stop. 

(k) 

Endurance tests; OEI power run— 

(1) 

30-minute OEI power run. For rotor-

craft for which the use of 30-minute 
OEI power is requested, a run at 30- 
minute OEI torque and the maximum 
speed for use with 30-minute OEI 
torque must be conducted as follows: 
For each engine, in sequence, that en-
gine must be inoperative and the re-
maining engines must be run for a 30- 
minute period. 

(2) 

Continuous OEI power run. For 

rotorcraft for which the use of contin-
uous OEI power is requested, a run at 
continuous OEI torque and the max-
imum speed for use with continuous 
OEI torque must be conducted as fol-
lows: For each engine, in sequence, 
that engine must be inoperative and 
the remaining engines must be run for 
1 hour. 

(3) The number of periods prescribed 

in paragraph (k)(1) or (k)(2) of this sec-
tion may not be less than the number 
of engines, nor may it be less than two. 

(l) [Reserved] 
(m) Any components that are af-

fected by maneuvering and gust loads 
must be investigated for the same 
flight conditions as are the main ro-
tors, and their service lives must be de-
termined by fatigue tests or by other 
acceptable methods. In addition, a 
level of safety equal to that of the 
main rotors must be provided for— 

(1) Each component in the rotor drive 

system whose failure would cause an 
uncontrolled landing; 

(2) Each component essential to the 

phasing of rotors on multirotor rotor-
craft, or that furnishes a driving link 
for the essential control of rotors in 
autorotation; and 

(3) Each component common to two 

or more engines on multiengine rotor-
craft. 

(n) 

Special tests. Each rotor drive sys-

tem designed to operate at two or more 
gear ratios must be subjected to special 
testing for durations necessary to sub-
stantiate the safety of the rotor drive 
system. 

(o) Each part tested as prescribed in 

this section must be in a serviceable 
condition at the end of the tests. No in-
tervening disassembly which might af-
fect test results may be conducted. 

(p) 

Endurance tests; operating lubri-

cants.  To be approved for use in rotor 

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