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727 

Federal Aviation Administration, DOT 

§ 33.83 

(2) Continuation of the rain ingestion 

during subsequent rapid deceleration 
to minimum idle, then 

(3) Continuation of the rain ingestion 

during three minutes at minimum idle 
power to be certified for flight oper-
ation, then 

(4) Continuation of the rain ingestion 

during subsequent rapid acceleration 
to takeoff power. 

(c) 

Engines for supersonic airplanes. In 

addition to complying with paragraphs 
(a)(1) and (a)(2) of this section, a sepa-
rate test for supersonic airplane en-
gines only, shall be conducted with 
three hailstones ingested at supersonic 
cruise velocity. These hailstones shall 
be aimed at the engine’s critical face 
area, and their ingestion must not 
cause unacceptable mechanical damage 
or unacceptable power or thrust loss 
after the ingestion or require the en-
gine to be shut down. The size of these 
hailstones shall be determined from 
the linear variation in diameter from 1- 
inch (25 millimeters) at 35,000 feet 
(10,500 meters) to 

1

4

-inch (6 millime-

ters) at 60,000 feet (18,000 meters) using 
the diameter corresponding to the low-
est expected supersonic cruise altitude. 
Alternatively, three larger hailstones 
may be ingested at subsonic velocities 
such that the kinetic energy of these 
larger hailstones is equivalent to the 
applicable supersonic ingestion condi-
tions. 

(d) For an engine that incorporates 

or requires the use of a protection de-
vice, demonstration of the rain and 
hail ingestion capabilities of the en-
gine, as required in paragraphs (a), (b), 
and (c) of this section, may be waived 
wholly or in part by the Administrator 
if the applicant shows that: 

(1) The subject rain and hail con-

stituents are of a size that will not 
pass through the protection device; 

(2) The protection device will with-

stand the impact of the subject rain 
and hail constituents; and 

(3) The subject of rain and hail con-

stituents, stopped by the protection de-
vice, will not obstruct the flow of in-
duction air into the engine, resulting 
in damage, power or thrust loss, or 
other adverse engine anomalies in ex-
cess of what would be accepted in para-
graphs (a), (b), and (c) of this section. 

[Doc. No. 28652, 63 FR 14799, Mar. 26, 1998] 

§ 33.79

Fuel burning thrust augmentor. 

Each fuel burning thrust augmentor, 

including the nozzle, must— 

(a) Provide cutoff of the fuel burning 

thrust augmentor; 

(b) Permit on-off cycling; 
(c) Be controllable within the in-

tended range of operation; 

(d) Upon a failure or malfunction of 

augmentor combustion, not cause the 
engine to lose thrust other than that 
provided by the augmentor; and 

(e) Have controls that function com-

patibly with the other engine controls 
and automatically shut off augmentor 
fuel flow if the engine rotor speed drops 
below the minimum rotational speed at 
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. 

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728 

14 CFR Ch. I (1–1–24 Edition) 

§ 33.84 

(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 
compliance can be shown shall be sub-
stantiated and defined in the installa-
tion instructions required by § 33.5. 

[Doc. No. 28107, 61 FR 28433, June 4, 1996, as 
amended by Amdt. 33–33, 77 FR 39624, July 5, 
2012; 77 FR 58301, Sept. 20, 2012] 

§ 33.84

Engine overtorque test. 

(a) If approval of a maximum engine 

overtorque is sought for an engine in-
corporating a free power turbine, com-
pliance with this section must be dem-
onstrated by testing. 

(1) The test may be run as part of the 

endurance test requirement of § 33.87. 
Alternatively, tests may be performed 
on a complete engine or equivalent 
testing on individual groups of compo-
nents. 

(2) Upon conclusion of tests con-

ducted to show compliance with this 
section, each engine part or individual 
groups of components must meet the 
requirements of § 33.93(a)(1) and (a)(2). 

(b) The test conditions must be as 

follows: 

(1) A total of 15 minutes run at the 

maximum engine overtorque to be ap-
proved. This may be done in separate 
runs, each being of at least 2

1

2

minutes 

duration. 

(2) A power turbine rotational speed 

equal to the highest speed at which the 
maximum overtorque can occur in 
service. The test speed may not be 
more than the limit speed of take-off 
or OEI ratings longer than 2 minutes. 

(3) For engines incorporating a reduc-

tion gearbox, a gearbox oil tempera-
ture equal to the maximum tempera-
ture when the maximum engine over-
torque could occur in service; and for 

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