757 

Federal Aviation Administration, DOT 

§ 35.15 

flight hour). Since the estimated prob-
ability for individual failures may be 
insufficiently precise to enable the ap-
plicant to assess the total rate for haz-
ardous propeller effects, compliance 
may be shown by demonstrating that 
the probability of a hazardous propeller 
effect arising from an individual fail-
ure can be predicted to be not greater 
than 10

¥

8

per propeller flight hour. In 

dealing with probabilities of this low 
order of magnitude, absolute proof is 
not possible and reliance must be 
placed on engineering judgment and 
previous experience combined with 
sound design and test philosophies. 

(b) If significant doubt exists as to 

the effects of failures or likely com-
bination of failures, the Administrator 
may require assumptions used in the 
analysis to be verified by test. 

(c) The primary failures of certain 

single propeller elements (for example, 
blades) cannot be sensibly estimated in 
numerical terms. If the failure of such 
elements is likely to result in haz-
ardous propeller effects, those ele-
ments must be identified as propeller 
critical parts. For propeller critical 
parts, applicants must meet the pre-
scribed integrity specifications of 
§ 35.16. These instances must be stated 
in the safety analysis. 

(d) If reliance is placed on a safety 

system to prevent a failure progressing 
to hazardous propeller effects, the pos-
sibility of a safety system failure in 
combination with a basic propeller fail-
ure must be included in the analysis. 
Such a safety system may include safe-
ty devices, instrumentation, early 
warning devices, maintenance checks, 
and other similar equipment or proce-
dures. If items of the safety system are 
outside the control of the propeller 
manufacturer, the assumptions of the 
safety analysis with respect to the reli-
ability of these parts must be clearly 
stated in the analysis and identified in 
the propeller installation and oper-
ation instructions required under § 35.3. 

(e) If the safety analysis depends on 

one or more of the following items, 
those items must be identified in the 
analysis and appropriately substan-
tiated. 

(1) Maintenance actions being carried 

out at stated intervals. This includes 
verifying that items that could fail in 

a latent manner are functioning prop-
erly. When necessary to prevent haz-
ardous propeller effects, these mainte-
nance actions and intervals must be 
published in the instructions for con-
tinued airworthiness required under 
§ 35.4. Additionally, if errors in mainte-
nance of the propeller system could 
lead to hazardous propeller effects, the 
appropriate maintenance procedures 
must be included in the relevant pro-
peller manuals. 

(2) Verification of the satisfactory 

functioning of safety or other devices 
at pre-flight or other stated periods. 
The details of this satisfactory func-
tioning must be published in the appro-
priate manual. 

(3) The provision of specific instru-

mentation not otherwise required. 
Such instrumentation must be pub-
lished in the appropriate documenta-
tion. 

(4) A fatigue assessment. 
(f) If applicable, the safety analysis 

must include, but not be limited to, as-
sessment of indicating equipment, 
manual and automatic controls, gov-
ernors and propeller control systems, 
synchrophasers, synchronizers, and 
propeller thrust reversal systems. 

(g) Unless otherwise approved by the 

Administrator and stated in the safety 
analysis, the following failure defini-
tions apply to compliance with this 
part. 

(1) The following are regarded as haz-

ardous propeller effects: 

(i) The development of excessive 

drag. 

(ii) A significant thrust in the oppo-

site direction to that commanded by 
the pilot. 

(iii) The release of the propeller or 

any major portion of the propeller. 

(iv) A failure that results in excessive 

unbalance. 

(2) The following are regarded as 

major propeller effects for variable 
pitch propellers: 

(i) An inability to feather the pro-

peller for feathering propellers. 

(ii) An inability to change propeller 

pitch when commanded. 

(iii) A significant uncommanded 

change in pitch. 

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