726 

14 CFR Ch. I (1–1–19 Edition) 

§ 33.81 

which the augmentor is intended to 
function. 

[Amdt. 33–6, 39 FR 35468, Oct. 1, 1974] 

Subpart F—Block Tests; Turbine 

Aircraft Engines 

§ 33.81

Applicability. 

This subpart prescribes the block 

tests and inspections for turbine en-
gines. 

[Doc. No. 3025, 29 FR 7453, June 10, 1964, as 
amended by Amdt. 33–6, 39 FR 35468, Oct. 1, 
1974] 

§ 33.82

General. 

Before each endurance test required 

by this subpart, the adjustment setting 
and functioning characteristic of each 
component having an adjustment set-
ting and a functioning characteristic 
that can be established independent of 
installation on the engine must be es-
tablished and recorded. 

[Amdt. 36–6, 39 FR 35468, Oct. 1, 1974] 

§ 33.83

Vibration test. 

(a) Each engine must undergo vibra-

tion surveys to establish that the vi-
bration characteristics of those compo-
nents that may be subject to mechani-
cally or aerodynamically induced vi-
bratory excitations are acceptable 
throughout the declared flight enve-
lope. The engine surveys shall be based 
upon an appropriate combination of ex-
perience, analysis, and component test 
and shall address, as a minimum, 
blades, vanes, rotor discs, spacers, and 
rotor shafts. 

(b) The surveys shall cover the 

ranges of power or thrust, and both the 
physical and corrected rotational 
speeds for each rotor system, cor-
responding to operations throughout 
the range of ambient conditions in the 
declared flight envelope, from the min-
imum rotational speed up to 103 per-
cent of the maximum physical and cor-
rected rotational speed permitted for 
rating periods of two minutes or 
longer, and up to 100 percent of all 
other permitted physical and corrected 
rotational speeds, including those that 
are overspeeds. If there is any indica-
tion of a stress peak arising at the 
highest of those required physical or 

corrected rotational speeds, the sur-
veys shall be extended sufficiently to 
reveal the maximum stress values 
present, except that the extension need 
not cover more than a further 2 per-
centage points increase beyond those 
speeds. 

(c) Evaluations shall be made of the 

following: 

(1) The effects on vibration charac-

teristics of operating with scheduled 
changes (including tolerances) to vari-
able vane angles, compressor bleeds, 
accessory loading, the most adverse 
inlet air flow distortion pattern de-
clared by the manufacturer, and the 
most adverse conditions in the exhaust 
duct(s); and 

(2) The aerodynamic and 

aeromechanical factors which might 
induce or influence flutter in those sys-
tems susceptible to that form of vibra-
tion. 

(d) Except as provided by paragraph 

(e) of this section, the vibration 
stresses associated with the vibration 
characteristics determined under this 
section, when combined with the ap-
propriate steady stresses, must be less 
than the endurance limits of the mate-
rials concerned, after making due al-
lowances for operating conditions for 
the permitted variations in properties 
of the materials. The suitability of 
these stress margins must be justified 
for each part evaluated. If it is deter-
mined that certain operating condi-
tions, or ranges, need to be limited, op-
erating and installation limitations 
shall be established. 

(e) The effects on vibration charac-

teristics of excitation forces caused by 
fault conditions (such as, but not lim-
ited to, out-of balance, local blockage 
or enlargement of stator vane passages, 
fuel nozzle blockage, incorrectly sched-
ule compressor variables, etc.) shall be 
evaluated by test or analysis, or by ref-
erence to previous experience and shall 
be shown not to create a hazardous 
condition. 

(f) Compliance with this section shall 

be substantiated for each specific in-
stallation configuration that can affect 
the vibration characteristics of the en-
gine. If these vibration effects cannot 
be fully investigated during engine cer-
tification, the methods by which they 
can be evaluated and methods by which 

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