273 

Federal Aviation Administration, DOT 

§ 23.943 

more than idle thrust when the revers-
ing system malfunctions; except that it 
may produce any greater thrust that is 
shown to allow directional control to 
be maintained, with aerodynamic 
means alone, under the most critical 
reversing condition expected in oper-
ation. 

(b) 

For propeller reversing systems. (1) 

Each system must be designed so that 
no single failure, likely combination of 
failures or malfunction of the system 
will result in unwanted reverse thrust 
under any operating condition. Failure 
of structural elements need not be con-
sidered if the probability of this type of 
failure is extremely remote. 

(2) Compliance with paragraph (b)(1) 

of this section must be shown by fail-
ure analysis, or testing, or both, for 
propeller systems that allow the pro-
peller blades to move from the flight 
low-pitch position to a position that is 
substantially less than the normal 
flight, low-pitch position. The analysis 
may include or be supported by the 
analysis made to show compliance with 
§ 35.21 for the type certification of the 
propeller and associated installation 
components. Credit will be given for 
pertinent analysis and testing com-
pleted by the engine and propeller 
manufacturers. 

[Doc. No. 26344, 58 FR 18971, Apr. 9, 1993, as 
amended by Amdt. 23–51, 61 FR 5136, Feb. 9, 
1996] 

§ 23.934

Turbojet and turbofan engine 

thrust reverser systems tests. 

Thrust reverser systems of turbojet 

or turbofan engines must meet the re-
quirements of § 33.97 of this chapter or 
it must be demonstrated by tests that 
engine operation and vibratory levels 
are not affected. 

[Doc. No. 26344, 58 FR 18971, Apr. 9, 1993] 

§ 23.937

Turbopropeller-drag limiting 

systems. 

(a) Turbopropeller-powered airplane 

propeller-drag limiting systems must 
be designed so that no single failure or 
malfunction of any of the systems dur-
ing normal or emergency operation re-
sults in propeller drag in excess of that 
for which the airplane was designed 
under the structural requirements of 
this part. Failure of structural ele-
ments of the drag limiting systems 

need not be considered if the prob-
ability of this kind of failure is ex-
tremely remote. 

(b) As used in this section, drag lim-

iting systems include manual or auto-
matic devices that, when actuated 
after engine power loss, can move the 
propeller blades toward the feather po-
sition to reduce windmilling drag to a 
safe level. 

[Amdt. 23–7, 34 FR 13093, Aug. 13, 1969, as 
amended by Amdt. 23–43, 58 FR 18971, Apr. 9, 
1993] 

§ 23.939

Powerplant operating charac-

teristics. 

(a) Turbine engine powerplant oper-

ating characteristics must be inves-
tigated in flight to determine that no 
adverse characteristics (such as stall, 
surge, or flameout) are present, to a 
hazardous degree, during normal and 
emergency operation within the range 
of operating limitations of the airplane 
and of the engine. 

(b) Turbocharged reciprocating en-

gine operating characteristics must be 
investigated in flight to assure that no 
adverse characteristics, as a result of 
an inadvertent overboost, surge, flood-
ing, or vapor lock, are present during 
normal or emergency operation of the 
engine(s) throughout the range of oper-
ating limitations of both airplane and 
engine. 

(c) For turbine engines, the air inlet 

system must not, as a result of airflow 
distortion during normal operation, 
cause vibration harmful to the engine. 

[Amdt. 23–7, 34 FR 13093 Aug. 13, 1969, as 
amended by Amdt. 23–14, 38 FR 31823, Nov. 19, 
1973; Amdt. 23–18, 42 FR 15041, Mar. 17, 1977; 
Amdt. 23–42, 56 FR 354, Jan. 3, 1991] 

§ 23.943

Negative acceleration. 

No hazardous malfunction of an en-

gine, an auxiliary power unit approved 
for use in flight, or any component or 
system associated with the powerplant 
or auxiliary power unit may occur 
when the airplane is operated at the 
negative accelerations within the 
flight envelopes prescribed in § 23.333. 
This must be shown for the greatest 
value and duration of the acceleration 
expected in service. 

[Amdt. 23–18, 42 FR 15041, Mar. 17, 1977, as 
amended by Amdt. 23–43, 58 FR 18971, Apr. 9, 
1993] 

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