714 

14 CFR Ch. I (1–1–19 Edition) 

§ 33.68 

not be manipulated while the fuel con-
trol device is mounted on the engine 
must be secured by a locking device 
and sealed, or otherwise be inacces-
sible. All other fuel control adjusting 
means must be accessible and marked 
to indicate the function of the adjust-
ment unless the function is obvious. 

(b) There must be a fuel strainer or 

filter between the engine fuel inlet 
opening and the inlet of either the fuel 
metering device or the engine-driven 
positive displacement pump whichever 
is nearer the engine fuel inlet. In addi-
tion, the following provisions apply to 
each strainer or filter required by this 
paragraph (b): 

(1) It must be accessible for draining 

and cleaning and must incorporate a 
screen or element that is easily remov-
able. 

(2) It must have a sediment trap and 

drain except that it need not have a 
drain if the strainer or filter is easily 
removable for drain purposes. 

(3) It must be mounted so that its 

weight is not supported by the con-
necting lines or by the inlet or outlet 
connections of the strainer or filter, 
unless adequate strength margins 
under all loading conditions are pro-
vided in the lines and connections. 

(4) It must have the type and degree 

of fuel filtering specified as necessary 
for protection of the engine fuel system 
against foreign particles in the fuel. 
The applicant must show: 

(i) That foreign particles passing 

through the specified filtering means 
do not impair the engine fuel system 
functioning; and 

(ii) That the fuel system is capable of 

sustained operation throughout its 
flow and pressure range with the fuel 
initially saturated with water at 80 

°

F 

(27 

°

C) and having 0.025 fluid ounces per 

gallon (0.20 milliliters per liter) of free 
water added and cooled to the most 
critical condition for icing likely to be 
encountered in operation. However, 
this requirement may be met by dem-
onstrating the effectiveness of speci-
fied approved fuel anti-icing additives, 
or that the fuel system incorporates a 
fuel heater which maintains the fuel 
temperature at the fuel strainer or fuel 
inlet above 32 

°

F (0 

°

C) under the most 

critical conditions. 

(5) The applicant must demonstrate 

that the filtering means has the capac-
ity (with respect to engine operating 
limitations) to ensure that the engine 
will continue to operate within ap-
proved limits, with fuel contaminated 
to the maximum degree of particle size 
and density likely to be encountered in 
service. Operation under these condi-
tions must be demonstrated for a pe-
riod acceptable to the Administrator, 
beginning when indication of impend-
ing filter blockage is first given by ei-
ther: 

(i) Existing engine instrumentation; 

or 

(ii) Additional means incorporated 

into the engine fuel system. 

(6) Any strainer or filter bypass must 

be designed and constructed so that the 
release of collected contaminants is 
minimized by appropriate location of 
the bypass to ensure that collected 
contaminants are not in the bypass 
flow path. 

(c) If provided as part of the engine, 

the applicant must show for each fluid 
injection (other than fuel) system and 
its controls that the flow of the in-
jected fluid is adequately controlled. 

[Amdt. 33–6, 39 FR 35466, Oct. 1, 1974, as 
amended by Amdt. 33–10, 49 FR 6851, Feb. 23, 
1984; Amdt. 33–18, 61 FR 31328, June 19, 1996; 
Amdt. 33–25, 73 FR 48123, Aug. 18, 2008; Amdt. 
33–26, 73 FR 48285, Aug. 19, 2008] 

§ 33.68

Induction system icing. 

Each engine, with all icing protec-

tion systems operating, must: 

(a) Operate throughout its flight 

power range, including the minimum 
descent idle rotor speeds achievable in 
flight, in the icing conditions defined 
for turbojet, turbofan, and turboprop 
engines in Appendices C and O of part 
25 of this chapter, and Appendix D of 
this part, and for turboshaft engines in 
Appendix C of part 29 of this chapter, 
without the accumulation of ice on the 
engine components that: 

(1) Adversely affects engine operation 

or that causes an unacceptable perma-
nent loss of power or thrust or unac-
ceptable increase in engine operating 
temperature; or 

(2) Results in unacceptable tem-

porary power loss or engine damage; or 

(3) Causes a stall, surge, or flameout 

or loss of engine controllability. The 

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