561 

Federal Aviation Administration, DOT 

§ 27.1521 

(1) A limit engine torque must be es-

tablished if the maximum torque that 
the engine can exert is greater than— 

(i) The torque that the rotor drive 

system is designed to transmit; or 

(ii) The torque that the main rotor 

assembly is designed to withstand in 
showing compliance with § 27.547(e). 

(2) The limit engine torque estab-

lished under paragraph (e)(1) of this 
section may not exceed either torque 
specified in paragraph (e)(1)(i) or (ii) of 
this section. 

(f) 

Ambient temperature. 

For turbine 

engines, ambient temperature limita-
tions (including limitations for winter-
ization installations, if applicable) 
must be established as the maximum 
ambient atmospheric temperature at 
which compliance with the cooling pro-
visions of §§ 27.1041 through 27.1045 is 
shown. 

(g) 

Two and one-half-minute OEI power 

operation. 

Unless otherwise authorized, 

the use of 2

1

⁄

2

-minute OEI power must 

be limited to engine failure operation 
of multiengine, turbine-powered rotor-
craft for not longer than 2

1

⁄

2

minutes 

after failure of an engine. The use of 
2

1

⁄

2

-minute OEI power must also be lim-

ited by— 

(1) The maximum rotational speed, 

which may not be greater than— 

(i) The maximum value determined 

by the rotor design; or 

(ii) The maximum demonstrated dur-

ing the type tests; 

(2) The maximum allowable gas tem-

perature; and 

(3) The maximum allowable torque. 
(h) 

Thirty-minute OEI power operation. 

Unless otherwise authorized, the use of 
30-minute OEI power must be limited 
to multiengine, turbine-powered rotor-
craft for not longer than 30 minutes 
after failure of an engine. The use of 30- 
minute OEI power must also be limited 
by— 

(1) The maximum rotational speed, 

which may not be greater than— 

(i) The maximum value determined 

by the rotor design; or 

(ii) The maximum value dem-

onstrated during the type tests; 

(2) The maximum allowable gas tem-

perature; and 

(3) The maximum allowable torque. 
(i) 

Continuous OEI power operation. 

Unless otherwise authorized, the use of 

continuous OEI power must be limited 
to multiengine, turbine-powered rotor-
craft for continued flight after failure 
of an engine. The use of continuous 
OEI power must also be limited by— 

(1) The maximum rotational speed, 

which may not be greater than— 

(i) The maximum value determined 

by the rotor design; or 

(ii) The maximum value dem-

onstrated during the type tests; 

(2) The maximum allowable gas tem-

perature; and 

(3) The maximum allowable torque. 
(j) 

Rated 30-second OEI power oper-

ation. 

Rated 30-second OEI power is 

permitted only on multiengine, tur-
bine-powered rotorcraft, also certifi-
cated for the use of rated 2-minute OEI 
power, and can only be used for contin-
ued operation of the remaining en-
gine(s) after a failure or precautionary 
shutdown of an engine. It must be 
shown that following application of 30- 
second OEI power, any damage will be 
readily detectable by the applicable in-
spections and other related procedures 
furnished in accordance with Section 
A27.4 of appendix A of this part and 
Section A33.4 of appendix A of part 33. 
The use of 30-second OEI power must be 
limited to not more than 30 seconds for 
any period in which that power is used, 
and by— 

(1) The maximum rotational speed, 

which may not be greater than— 

(i) The maximum value determined 

by the rotor design; or 

(ii) The maximum value dem-

onstrated during the type tests; 

(2) The maximum allowable gas tem-

perature; and 

(3) The maximum allowable torque. 
(k) 

Rated 2-minute OEI power oper-

ation. 

Rated 2-minute OEI power is per-

mitted only on multiengine, turbine- 
powered rotorcraft, also certificated 
for the use of rated 30-second OEI 
power, and can only be used for contin-
ued operation of the remaining en-
gine(s) after a failure or precautionary 
shutdown of an engine. It must be 
shown that following application of 2- 
minute OEI power, any damage will be 
readily detectable by the applicable in-
spections and other related procedures 
furnished in accordance with Section 
A27.4 of appendix A of this part and 
Section A33.4 of appendix A of part 33. 

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