181 

Federal Aviation Administration, DOT 

Pt. 23, SFAR No. 23 

Total seating capacity 

Minimum main passenger aisle 

width 

Less than 25 

inches from floor 

25 inches and 

more from floor 

10 through 23 ...........

9 inches .............

15 inches. 

M

ISCELLANEOUS

 

33. 

Lightning strike protection. Parts that 

are electrically insulated from the basic air-
frame must be connected to it through light-
ning arrestors unless a lightning strike on 
the insulated part— 

(a) Is improbable because of shielding by 

other parts; or 

(b) Is not hazardous. 
34. 

Ice protection. If certification with ice 

protection provisions is desired, compliance 
with the following requirements must be 
shown: 

(a) The recommended procedures for the 

use of the ice protection equipment must be 
set forth in the Airplane Flight Manual. 

(b) An analysis must be performed to es-

tablish, on the basis of the airplane’s oper-
ational needs, the adequacy of the ice protec-
tion system for the various components of 
the airplane. In addition, tests of the ice pro-
tection system must be conducted to dem-
onstrate that the airplane is capable of oper-
ating safely in continuous maximum and 
intermittent maximum icing conditions as 
described in FAR 25, appendix C. 

(c) Compliance with all or portions of this 

section may be accomplished by reference, 
where applicable because of similarity of the 
designs, to analysis and tests performed by 
the applicant for a type certificated model. 

35. 

Maintenance information. The applicant 

must make available to the owner at the 
time of delivery of the airplane the informa-
tion he considers essential for the proper 
maintenance of the airplane. That informa-
tion must include the following: 

(a) Description of systems, including elec-

trical, hydraulic, and fuel controls. 

(b) Lubrication instructions setting forth 

the frequency and the lubricants and fluids 
which are to be used in the various systems. 

(c) Pressures and electrical loads applica-

ble to the various systems. 

(d) Tolerances and adjustments necessary 

for proper functioning. 

(e) Methods of leveling, raising, and tow-

ing. 

(f) Methods of balancing control surfaces. 
(g) Identification of primary and secondary 

structures. 

(h) Frequency and extent of inspections 

necessary to the proper operation of the air-
plane. 

(i) Special repair methods applicable to the 

airplane. 

(j) Special inspection techniques, including 

those that require X-ray, ultrasonic, and 
magnetic particle inspection. 

(k) List of special tools. 

P

ROPULSION

 

GENERAL

 

36. 

Vibration characteristics. For turbo-

propeller powered airplanes, the engine in-
stallation must not result in vibration char-
acteristics of the engine exceeding those es-
tablished during the type certification of the 
engine. 

37. 

In-flight restarting of engine. If the en-

gine on turbopropeller powered airplanes 
cannot be restarted at the maximum cruise 
altitude, a determination must be made of 
the altitude below which restarts can be con-
sistently accomplished. Restart information 
must be provided in the Airplane Flight 
Manual. 

38. 

Engines—(a)  For turbopropeller powered 

airplanes. The engine installation must com-
ply with the following requirements: 

(1) 

Engine isolation. The powerplants must 

be arranged and isolated from each other to 
allow operation, in at least one configura-
tion, so that the failure or malfunction of 
any engine, or of any system that can affect 
the engine, will not— 

(i) Prevent the continued safe operation of 

the remaining engines; or 

(ii) Require immediate action by any crew-

member for continued safe operation. 

(2) 

Control of engine rotation. There must be 

a means to individually stop and restart the 
rotation of any engine in flight except that 
engine rotation need not be stopped if con-
tinued rotation could not jeopardize the safe-
ty of the airplane. Each component of the 
stopping and restarting system on the engine 
side of the firewall, and that might be ex-
posed to fire, must be at least fire resistant. 
If hydraulic propeller feathering systems are 
used for this purpose, the feathering lines 
must be at least fire resistant under the op-
erating conditions that may be expected to 
exist during feathering. 

(3) 

Engine speed and gas temperature control 

devices.  The powerplant systems associated 
with engine control devices, systems, and in-
strumentation must provide reasonable as-
surance that those engine operating limita-
tions that adversely affect turbine rotor 
structural integrity will not be exceeded in 
service. 

(b) 

For reciprocating-engine powered air-

planes. To provide engine isolation, the pow-
erplants must be arranged and isolated from 
each other to allow operation, in at least one 
configuration, so that the failure or malfunc-
tion of any engine, or of any system that can 
affect that engine, will not— 

(1) Prevent the continued safe operation of 

the remaining engines; or 

(2) Require immediate action by any crew-

member for continued safe operation. 

39. 

Turbopropeller reversing systems. (a) Tur-

bopropeller reversing systems intended for 

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