702 

14 CFR Ch. I (1–1–24 Edition) 

§ 33.17 

(b) Conform to approved specifica-

tions (such as industry or military 
specifications) that ensure their having 
the strength and other properties as-
sumed in the design data. 

(Secs. 313(a), 601, and 603, 72 Stat. 759, 775, 49 
U.S.C. 1354(a), 1421, and 1423; sec. 6(c), 49 
U.S.C. 1655(c)) 

[Amdt. 33–8, 42 FR 15047, Mar. 17, 1977, as 
amended by Amdt. 33–10, 49 FR 6850, Feb. 23, 
1984] 

§ 33.17

Fire protection. 

(a) The design and construction of 

the engine and the materials used must 
minimize the probability of the occur-
rence and spread of fire during normal 
operation and failure conditions, and 
must minimize the effect of such a fire. 
In addition, the design and construc-
tion of turbine engines must minimize 
the probability of the occurrence of an 
internal fire that could result in struc-
tural failure or other hazardous effects. 

(b) Except as provided in paragraph 

(c) of this section, each external line, 
fitting, and other component, which 
contains or conveys flammable fluid 
during normal engine operation, must 
be fire resistant or fireproof, as deter-
mined by the Administrator. Compo-
nents must be shielded or located to 
safeguard against the ignition of leak-
ing flammable fluid. 

(c) A tank, which contains flammable 

fluids and any associated shut-off 
means and supports, which are part of 
and attached to the engine, must be 
fireproof either by construction or by 
protection unless damage by fire will 
not cause leakage or spillage of a haz-
ardous quantity of flammable fluid. 
For a reciprocating engine having an 
integral oil sump of less than 23.7 liters 
capacity, the oil sump need not be fire-
proof or enclosed by a fireproof shield. 

(d) An engine component designed, 

constructed, and installed to act as a 
firewall must be: 

(1) Fireproof; 
(2) Constructed so that no hazardous 

quantity of air, fluid or flame can pass 
around or through the firewall; and, 

(3) Protected against corrosion; 
(e) In addition to the requirements of 

paragraphs (a) and (b) of this section, 
engine control system components that 
are located in a designated fire zone 

must be fire resistant or fireproof, as 
determined by the Administrator. 

(f) Unintentional accumulation of 

hazardous quantities of flammable 
fluid within the engine must be pre-
vented by draining and venting. 

(g) Any components, modules, or 

equipment, which are susceptible to or 
are potential sources of static dis-
charges or electrical fault currents 
must be designed and constructed to be 
properly grounded to the engine ref-
erence, to minimize the risk of ignition 
in external areas where flammable 
fluids or vapors could be present. 

[Doc. No. FAA–2007–28503, 74 FR 37930, July 
30, 2009] 

§ 33.19

Durability. 

(a) Engine design and construction 

must minimize the development of an 
unsafe condition of the engine between 
overhaul periods. The design of the 
compressor and turbine rotor cases 
must provide for the containment of 
damage from rotor blade failure. En-
ergy levels and trajectories of frag-
ments resulting from rotor blade fail-
ure that lie outside the compressor and 
turbine rotor cases must be defined. 

(b) Each component of the propeller 

blade pitch control system which is a 
part of the engine type design must 
meet the requirements of §§ 35.21, 35.23, 
35.42 and 35.43 of this chapter. 

[Doc. No. 3025, 29 FR 7453, June 10, 1964, as 
amended by Amdt. 33–9, 45 FR 60181, Sept. 11, 
1980; Amdt. 33–10, 49 FR 6851, Feb. 23, 1984; 
Amdt. 33–28, 73 FR 63346, Oct. 24, 2008] 

§ 33.21

Engine cooling. 

Engine design and construction must 

provide the necessary cooling under 
conditions in which the airplane is ex-
pected to operate. 

§ 33.23

Engine mounting attachments 

and structure. 

(a) The maximum allowable limit 

and ultimate loads for engine mount-
ing attachments and related engine 
structure must be specified. 

(b) The engine mounting attach-

ments and related engine structure 
must be able to withstand— 

(1) The specified limit loads without 

permanent deformation; and 

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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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