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14 CFR Ch. I (1–1–19 Edition) 

§ 33.96 

speed and power specified by the appli-
cant for reverse pitch operation. 

[Doc. No. 3025, 29 FR 7453, June 10, 1964, as 
amended by Amdt. 33–3, 32 FR 3737, Mar. 4, 

§ 33.96

Engine tests in auxiliary power 

unit (APU) mode. 

If the engine is designed with a pro-

peller brake which will allow the pro-
peller to be brought to a stop while the 
gas generator portion of the engine re-
mains in operation, and remain stopped 
during operation of the engine as an 
auxiliary power unit (‘‘APU mode’’), in 
addition to the requirements of § 33.87, 
the applicant must conduct the fol-
lowing tests: 

(a) Ground locking: A total of 45 

hours with the propeller brake engaged 
in a manner which clearly dem-
onstrates its ability to function with-
out adverse effects on the complete en-
gine while the engine is operating in 
the APU mode under the maximum 
conditions of engine speed, torque, 
temperature, air bleed, and power ex-
traction as specified by the applicant. 

(b) Dynamic braking: A total of 400 

application-release cycles of brake en-
gagements must be made in a manner 
which clearly demonstrates its ability 
to function without adverse effects on 
the complete engine under the max-
imum conditions of engine accelera-
tion/deceleration rate, speed, torque, 
and temperature as specified by the ap-
plicant. The propeller must be stopped 
prior to brake release. 

(c) One hundred engine starts and 

stops with the propeller brake engaged. 

(d) The tests required by paragraphs 

(a), (b), and (c) of this section must be 
performed on the same engine, but this 
engine need not be the same engine 
used for the tests required by § 33.87. 

(e) The tests required by paragraphs 

(a), (b), and (c) of this section must be 
followed by engine disassembly to the 
extent necessary to show compliance 
with the requirements of § 33.93(a) and 
§ 33.93(b). 

[Amdt. 33–11, 51 FR 10346, Mar. 25, 1986] 

§ 33.97

Thrust reversers. 

(a) If the engine incorporates a re-

verser, the endurance calibration, oper-
ation, and vibration tests prescribed in 

this subpart must be run with the re-
verser installed. In complying with this 
section, the power control lever must 
be moved from one extreme position to 
the other in not more than one second 
except, if regimes of control operations 
are incorporated necessitating sched-
uling of the power-control lever motion 
in going from one extreme position to 
the other, a longer period of time is ac-
ceptable but not more than three sec-
onds. In addition, the test prescribed in 
paragraph (b) of this section must be 
made. This test may be scheduled as 
part of the endurance run. 

(b) 175 reversals must be made from 

flight-idle forward thrust to maximum 
reverse thrust and 25 reversals must be 
made from rated takeoff thrust to max-
imum reverse thrust. After each rever-
sal the reverser must be operated at 
full reverse thrust for a period of one 
minute, except that, in the case of a re-
verser intended for use only as a brak-
ing means on the ground, the reverser 
need only be operated at full reverse 
thrust for 30 seconds. 

[Doc. No. 3025, 29 FR 7453, June 10, 1964, as 
amended by Amdt. 33–3, 32 FR 3737, Mar. 4, 

§ 33.99

General conduct of block tests. 

(a) Each applicant may, in making a 

block test, use separate engines of 
identical design and construction in 
the vibration, calibration, endurance, 
and operation tests, except that, if a 
separate engine is used for the endur-
ance test it must be subjected to a cali-
bration check before starting the en-
durance test. 

(b) Each applicant may service and 

make minor repairs to the engine dur-
ing the block tests in accordance with 
the service and maintenance instruc-
tions submitted in compliance with 
§ 33.4. If the frequency of the service is 
excessive, or the number of stops due 
to engine malfunction is excessive, or a 
major repair, or replacement of a part 
is found necessary during the block 
tests or as the result of findings from 
the teardown inspection, the engine or 
its parts must be subjected to any addi-
tional tests the Administrator finds 

(c) Each applicant must furnish all 

testing facilities, including equipment 

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