704 

14 CFR Ch. I (1–1–19 Edition) 

§ 33.28 

or external to the engine. The over-
speed resulting from any other single 
failure must be considered when select-
ing the most limiting overspeed condi-
tions applicable to each rotor. Over-
speeds resulting from combinations of 
failures must also be considered unless 
the applicant can show that the prob-
ability of occurrence is not greater 
than extremely remote (probability 
range of 10

¥

7

to 10

¥

9

per engine flight 

hour). 

(d) In addition, the applicant must 

demonstrate that each fan, compressor, 
turbine, and turbosupercharger rotor 
complies with paragraphs (d)(1) and 
(d)(2) of this section for the maximum 
overspeed achieved when subjected to 
the conditions specified in paragraphs 
(b)(3) and (b)(4) of this section. The ap-
plicant must use the approach in para-
graph (a) of this section which specifies 
the required test conditions. 

(1) Rotor Growth must not cause the 

engine to: 

(i) Catch fire, 
(ii) Release high-energy debris 

through the engine casing or result in 
a hazardous failure of the engine cas-
ing, 

(iii) Generate loads greater than 

those ultimate loads specified in 
§ 33.23(a), or 

(iv) Lose the capability of being shut 

down. 

(2) Following an overspeed event and 

after continued operation, the rotor 
may not exhibit conditions such as 
cracking or distortion which preclude 
continued safe operation. 

(e) The design and functioning of en-

gine control systems, instruments, and 
other methods not covered under § 33.28 
must ensure that the engine operating 
limitations that affect turbine, com-
pressor, fan, and turbosupercharger 
rotor structural integrity will not be 
exceeded in service. 

(f) Failure of a shaft section may be 

excluded from consideration in deter-
mining the highest overspeed that 
would result from a complete loss of 
load on a turbine rotor if the applicant: 

(1) Identifies the shaft as an engine 

life-limited-part and complies with 
§ 33.70. 

(2) Uses material and design features 

that are well understood and that can 

be analyzed by well-established and 
validated stress analysis techniques. 

(3) Determines, based on an assess-

ment of the environment surrounding 
the shaft section, that environmental 
influences are unlikely to cause a shaft 
failure. This assessment must include 
complexity of design, corrosion, wear, 
vibration, fire, contact with adjacent 
components or structure, overheating, 
and secondary effects from other fail-
ures or combination of failures. 

(4) Identifies and declares, in accord-

ance with § 33.5, any assumptions re-
garding the engine installation in mak-
ing the assessment described above in 
paragraph (f)(3) of this section. 

(5) Assesses, and considers as appro-

priate, experience with shaft sections 
of similar design. 

(6) Does not exclude the entire shaft. 
(g) If analysis is used to meet the 

overspeed requirements, then the ana-
lytical tool must be validated to prior 
overspeed test results of a similar 
rotor. The tool must be validated for 
each material. The rotor being cer-
tified must not exceed the boundaries 
of the rotors being used to validate the 
analytical tool in terms of geometric 
shape, operating stress, and tempera-
ture. Validation includes the ability to 
accurately predict rotor dimensional 
growth and the burst speed. The pre-
dictions must also show that the rotor 
being certified does not have lower 
burst and growth margins than rotors 
used to validate the tool. 

[Doc. No. FAA–2010–0398, Amdt. 33–31, 76 FR 
42023, July 18, 2011] 

§ 33.28

Engine control systems. 

(a) 

Applicability. 

These requirements 

are applicable to any system or device 
that is part of engine type design, that 
controls, limits, or monitors engine op-
eration, and is necessary for the con-
tinued airworthiness of the engine. 

(b) 

Validation

—(1) 

Functional aspects. 

The applicant must substantiate by 
tests, analysis, or a combination there-
of, that the engine control system per-
forms the intended functions in a man-
ner which: 

(i) Enables selected values of rel-

evant control parameters to be main-
tained and the engine kept within the 

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