902 

14 CFR Ch. I (1–1–14 Edition) 

§ 35.21 

the development of any unsafe condi-
tion of the propeller between overhaul 
periods. 

§ 35.21

Variable and reversible pitch 

propellers. 

(a) No single failure or malfunction 

in the propeller system will result in 
unintended travel of the propeller 
blades to a position below the in-flight 
low-pitch position. The extent of any 
intended travel below the in-flight low- 
pitch position must be documented by 
the applicant in the appropriate manu-
als. Failure of structural elements need 
not be considered if the occurrence of 
such a failure is shown to be extremely 
remote under § 35.15. 

(b) For propellers incorporating a 

method to select blade pitch below the 
in-flight low pitch position, provisions 
must be made to sense and indicate to 
the flight crew that the propeller 
blades are below that position by an 
amount defined in the installation 
manual. The method for sensing and 
indicating the propeller blade pitch po-
sition must be such that its failure 
does not affect the control of the pro-
peller. 

[Amdt. 35–8, 73 FR 63347, Oct. 24, 2008] 

§ 35.22

Feathering propellers. 

(a) Feathering propellers are in-

tended to feather from all flight condi-
tions, taking into account expected 
wear and leakage. Any feathering and 
unfeathering limitations must be docu-
mented in the appropriate manuals. 

(b) Propeller pitch control systems 

that use engine oil to feather must in-
corporate a method to allow the pro-
peller to feather if the engine oil sys-
tem fails. 

(c) Feathering propellers must be de-

signed to be capable of unfeathering 
after the propeller system has sta-
bilized to the minimum declared out-
side air temperature. 

[Amdt. 35–8, 73 FR 63347, Oct. 24, 2008] 

§ 35.23

Propeller control system. 

The requirements of this section 

apply to any system or component that 
controls, limits or monitors propeller 
functions. 

(a) The propeller control system 

must be designed, constructed and vali-
dated to show that: 

(1) The propeller control system, op-

erating in normal and alternative oper-
ating modes and in transition between 
operating modes, performs the func-
tions defined by the applicant through-
out the declared operating conditions 
and flight envelope. 

(2) The propeller control system 

functionality is not adversely affected 
by the declared environmental condi-
tions, including temperature, electro-
magnetic interference (EMI), high in-
tensity radiated fields (HIRF) and 
lightning. The environmental limits to 
which the system has been satisfac-
torily validated must be documented in 
the appropriate propeller manuals. 

(3) A method is provided to indicate 

that an operating mode change has oc-
curred if flight crew action is required. 
In such an event, operating instruc-
tions must be provided in the appro-
priate manuals. 

(b) The propeller control system 

must be designed and constructed so 
that, in addition to compliance with 
§ 35.15: 

(1) No single failure or malfunction of 

electrical or electronic components in 
the control system results in a haz-
ardous propeller effect. 

(2) Failures or malfunctions directly 

affecting the propeller control system 
in a typical airplane, such as struc-
tural failures of attachments to the 
control, fire, or overheat, do not lead 
to a hazardous propeller effect. 

(3) The loss of normal propeller pitch 

control does not cause a hazardous pro-
peller effect under the intended oper-
ating conditions. 

(4) The failure or corruption of data 

or signals shared across propellers does 
not cause a hazardous propeller effect. 

(c) Electronic propeller control sys-

tem imbedded software must be de-
signed and implemented by a method 
approved by the Administrator that is 
consistent with the criticality of the 
performed functions and that mini-
mizes the existence of software errors. 

(d) The propeller control system 

must be designed and constructed so 
that the failure or corruption of air-
plane-supplied data does not result in 
hazardous propeller effects. 

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