703 

Federal Aviation Administration, DOT 

§ 33.27 

(2) The specified ultimate loads with-

out failure, but may exhibit permanent 
deformation. 

[Amdt. 33–10, 49 FR 6851, Feb. 23, 1984] 

§ 33.25

Accessory attachments. 

The engine must operate properly 

with the accessory drive and mounting 
attachments loaded. Each engine ac-
cessory drive and mounting attach-
ment must include provisions for seal-
ing to prevent contamination of, or un-
acceptable leakage from, the engine in-
terior. A drive and mounting attach-
ment requiring lubrication for external 
drive splines, or coupling by engine oil, 
must include provisions for sealing to 
prevent unacceptable loss of oil and to 
prevent contamination from sources 
outside the chamber enclosing the 
drive connection. The design of the en-
gine must allow for the examination, 
adjustment, or removal of each acces-
sory required for engine operation. 

[Amdt. 33–10, 49 FR 6851, Feb. 23, 1984] 

§ 33.27

Turbine, compressor, fan, and 

turbosupercharger rotor overspeed. 

(a) For each fan, compressor, turbine, 

and turbosupercharger rotor, the appli-
cant must establish by test, analysis, 
or a combination of both, that each 
rotor will not burst when operated in 
the engine for 5 minutes at whichever 
of the conditions defined in paragraph 
(b) of this section is the most critical 
with respect to the integrity of such a 
rotor. 

(1) Test rotors used to demonstrate 

compliance with this section that do 
not have the most adverse combination 
of material properties and dimensional 
tolerances must be tested at conditions 
which have been adjusted to ensure the 
minimum specification rotor possesses 
the required overspeed capability. This 
can be accomplished by increasing test 
speed, temperature, and/or loads. 

(2) When an engine test is being used 

to demonstrate compliance with the 
overspeed conditions listed in para-
graph (b)(3) or (b)(4) of this section and 
the failure of a component or system is 
sudden and transient, it may not be 
possible to operate the engine for 5 
minutes after the failure. Under these 
circumstances, the actual overspeed 

duration is acceptable if the required 
maximum overspeed is achieved. 

(b) When determining the maximum 

overspeed condition applicable to each 
rotor in order to comply with para-
graphs (a) and (c) of this section, the 
applicant must evaluate the following 
rotor speeds taking into consideration 
the part’s operating temperatures and 
temperature gradients throughout the 
engine’s operating envelope: 

(1) 120 percent of the maximum per-

missible rotor speed associated with 
any of the engine ratings except one- 
engine-inoperative (OEI) ratings of less 
than 2

1

⁄

2

minutes. 

(2) 115 percent of the maximum per-

missible rotor speed associated with 
any OEI ratings of less than 2

1

⁄

2

min-

utes. 

(3) 105 percent of the highest rotor 

speed that would result from either: 

(i) The failure of the component or 

system which, in a representative in-
stallation of the engine, is the most 
critical with respect to overspeed when 
operating at any rating condition ex-
cept OEI ratings of less than 2

1

⁄

2

min-

utes, or 

(ii) The failure of any component or 

system in a representative installation 
of the engine, in combination with any 
other failure of a component or system 
that would not normally be detected 
during a routine pre-flight check or 
during normal flight operation, that is 
the most critical with respect to over-
speed, except as provided by paragraph 
(c) of this section, when operating at 
any rating condition except OEI rat-
ings of less than 2

1

⁄

2

minutes. 

(4) 100 percent of the highest rotor 

speed that would result from the fail-
ure of the component or system which, 
in a representative installation of the 
engine, is the most critical with re-
spect to overspeed when operating at 
any OEI rating of less than 2

1

⁄

2

min-

utes. 

(c) The highest overspeed that results 

from a complete loss of load on a tur-
bine rotor, except as provided by para-
graph (f) of this section, must be in-
cluded in the overspeed conditions con-
sidered by paragraphs (b)(3)(i), 
(b)(3)(ii), and (b)(4) of this section, re-
gardless of whether that overspeed re-
sults from a failure within the engine 

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