275 

Federal Aviation Administration, DOT 

§ 23.957 

jet pump drive flow, and for all other 
purposes for which fuel is used. 

(b) 

Gravity systems. The fuel flow rate 

for gravity systems (main and reserve 
supply) must be 150 percent of the 
takeoff fuel consumption of the engine. 

(c) 

Pump systems. The fuel flow rate 

for each pump system (main and re-
serve supply) for each reciprocating en-
gine must be 125 percent of the fuel 
flow required by the engine at the max-
imum takeoff power approved under 
this part. 

(1) This flow rate is required for each 

main pump and each emergency pump, 
and must be available when the pump 
is operating as it would during takeoff; 

(2) For each hand-operated pump, 

this rate must occur at not more than 
60 complete cycles (120 single strokes) 
per minute. 

(3) The fuel pressure, with main and 

emergency pumps operating simulta-
neously, must not exceed the fuel inlet 
pressure limits of the engine unless it 
can be shown that no adverse effect oc-
curs. 

(d) 

Auxiliary fuel systems and fuel 

transfer systems. Paragraphs (b), (c), and 
(f) of this section apply to each auxil-
iary and transfer system, except that— 

(1) The required fuel flow rate must 

be established upon the basis of max-
imum continuous power and engine ro-
tational speed, instead of takeoff power 
and fuel consumption; and 

(2) If there is a placard providing op-

erating instructions, a lesser flow rate 
may be used for transferring fuel from 
any auxiliary tank into a larger main 
tank. This lesser flow rate must be ade-
quate to maintain engine maximum 
continuous power but the flow rate 
must not overfill the main tank at 
lower engine powers. 

(e) 

Multiple fuel tanks. For recipro-

cating engines that are supplied with 
fuel from more than one tank, if engine 
power loss becomes apparent due to 
fuel depletion from the tank selected, 
it must be possible after switching to 
any full tank, in level flight, to obtain 
75 percent maximum continuous power 
on that engine in not more than— 

(1) 10 seconds for naturally aspirated 

single-engine airplanes; 

(2) 20 seconds for turbocharged sin-

gle-engine airplanes, provided that 75 
percent maximum continuous natu-

rally aspirated power is regained with-
in 10 seconds; or 

(3) 20 seconds for multiengine air-

planes. 

(f) 

Turbine engine fuel systems. Each 

turbine engine fuel system must pro-
vide at least 100 percent of the fuel flow 
required by the engine under each in-
tended operation condition and maneu-
ver. The conditions may be simulated 
in a suitable mockup. This flow must— 

(1) Be shown with the airplane in the 

most adverse fuel feed condition (with 
respect to altitudes, attitudes, and 
other conditions) that is expected in 
operation; and 

(2) For multiengine airplanes, not-

withstanding the lower flow rate al-
lowed by paragraph (d) of this section, 
be automatically uninterrupted with 
respect to any engine until all the fuel 
scheduled for use by that engine has 
been consumed. In addition— 

(i) For the purposes of this section, 

‘‘fuel scheduled for use by that engine’’ 
means all fuel in any tank intended for 
use by a specific engine. 

(ii) The fuel system design must 

clearly indicate the engine for which 
fuel in any tank is scheduled. 

(iii) Compliance with this paragraph 

must require no pilot action after com-
pletion of the engine starting phase of 
operations. 

(3) For single-engine airplanes, re-

quire no pilot action after completion 
of the engine starting phase of oper-
ations unless means are provided that 
unmistakenly alert the pilot to take 
any needed action at least five minutes 
prior to the needed action; such pilot 
action must not cause any change in 
engine operation; and such pilot action 
must not distract pilot attention from 
essential flight duties during any phase 
of operations for which the airplane is 
approved. 

[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as 
amended by Amdt. 23–7, 34 FR 13093, Aug. 13, 
1969; Amdt. 23–43, 58 FR 18971, Apr. 9, 1993; 
Amdt. 23–51, 61 FR 5136, Feb. 9, 1996] 

§ 23.957

Flow between interconnected 

tanks. 

(a) It must be impossible, in a grav-

ity feed system with interconnected 
tank outlets, for enough fuel to flow 
between the tanks to cause an overflow 
of fuel from any tank vent under the 

VerDate Mar<15>2010 

10:12 Mar 18, 2014

Jkt 232046

PO 00000

Frm 00285

Fmt 8010

Sfmt 8010

Y:\SGML\232046.XXX

232046

pmangrum on DSK3VPTVN1PROD with CFR