779 

Federal Aviation Administration, DOT 

§ 29.951 

minutes duration each at 60 to 80 per-
cent of maximum continuous speed. 

(2) Acceleration and deceleration 

must be accomplished in a period not 
longer than 10 seconds (except where 
maximum engine acceleration rate will 
require more than 10 seconds), and the 
time for changing speeds may not be 
deducted from the specified time for 
the overspeed runs. 

(3) Overspeed runs must be made with 

the rotors in the flattest pitch for 
smooth operation. 

(e) The tests prescribed in paragraphs 

(b) and (d) of this section must be con-
ducted on the rotorcraft and the torque 
must be absorbed by the rotors to be 
installed, except that other ground or 
flight test facilities with other appro-
priate methods of torque absorption 
may be used if the conditions of sup-
port and vibration closely simulate the 
conditions that would exist during a 
test on the rotorcraft. 

(f) Each test prescribed by this sec-

tion must be conducted without inter-
vening disassembly and, except for the 
lubrication system failure test re-
quired by paragraph (c) of this section, 
each part tested must be in a service-
able condition at the conclusion of the 
test. 

(Secs. 313(a), 601, 603, 604, Federal Aviation 
Act of 1958 (49 U.S.C. 1354(a), 1421, 1423 1424), 
sec. 6(c), Dept. of Transportation Act (49 
U.S.C. 1655(c))) 

[Amdt. 29–3, 33 FR 969, Jan. 26, 1968, as 
amended by Amdt. 29–17, 43 FR 50601, Oct. 30, 
1978; Amdt. 29–26, 53 FR 34216, Sept. 2, 1988] 

§ 29.931

Shafting critical speed. 

(a) The critical speeds of any shafting 

must be determined by demonstration 
except that analytical methods may be 
used if reliable methods of analysis are 
available for the particular design. 

(b) If any critical speed lies within, 

or close to, the operating ranges for 
idling, power-on, and autorotative con-
ditions, the stresses occurring at that 
speed must be within safe limits. This 
must be shown by tests. 

(c) If analytical methods are used and 

show that no critical speed lies within 
the permissible operating ranges, the 
margins between the calculated crit-
ical speeds and the limits of the allow-
able operating ranges must be adequate 

to allow for possible variations be-
tween the computed and actual values. 

[Amdt. 29–12, 41 FR 55472, Dec. 20, 1976] 

§ 29.935

Shafting joints. 

Each universal joint, slip joint, and 

other shafting joints whose lubrication 
is necessary for operation must have 
provision for lubrication. 

§ 29.939

Turbine engine operating 

characteristics. 

(a) Turbine engine operating charac-

teristics must be investigated in flight 
to determine that no adverse charac-
teristics (such as stall, surge, of flame-
out) are present, to a hazardous degree, 
during normal and emergency oper-
ation within the range of operating 
limitations of the rotorcraft and of the 
engine. 

(b) The turbine engine air inlet sys-

tem may not, as a result of airflow dis-
tortion during normal operation, cause 
vibration harmful to the engine. 

(c) For governor-controlled engines, 

it must be shown that there exists no 
hazardous torsional instability of the 
drive system associated with critical 
combinations of power, rotational 
speed, and control displacement. 

[Amdt. 29–2, 32 FR 6914, May 5, 1967, as 
amended by Amdt. 29–12, 41 FR 55473, Dec. 20, 
1976] 

F

UEL

S

YSTEM

 

§ 29.951

General. 

(a) Each fuel system must be con-

structed and arranged to ensure a flow 
of fuel at a rate and pressure estab-
lished for proper engine and auxiliary 
power unit functioning under any like-
ly operating conditions, including the 
maneuvers for which certification is 
requested and during which the engine 
or auxiliary power unit is permitted to 
be in operation. 

(b) Each fuel system must be ar-

ranged so that— 

(1) No engine or fuel pump can draw 

fuel from more than one tank at a 
time; or 

(2) There are means to prevent intro-

ducing air into the system. 

(c) Each fuel system for a turbine en-

gine must be capable of sustained oper-
ation throughout its flow and pressure 
range with fuel initially saturated with 

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