213 

Federal Aviation Administration, DOT 

§ 25.109 

Where— 

Tire Pressure = maximum airplane operating 

tire pressure (psi); 

µ

t/gMAX

= maximum tire-to-ground braking 

coefficient; 

V = airplane true ground speed (knots); and 
Linear interpolation may be used for tire 

pressures other than those listed. 

(2) The maximum tire-to-ground wet 

runway braking coefficient of friction 
must be adjusted to take into account 
the efficiency of the anti-skid system 
on a wet runway. Anti-skid system op-
eration must be demonstrated by flight 
testing on a smooth wet runway, and 
its efficiency must be determined. Un-
less a specific anti-skid system effi-
ciency is determined from a quan-
titative analysis of the flight testing 
on a smooth wet runway, the max-
imum tire-to-ground wet runway brak-
ing coefficient of friction determined 
in paragraph (c)(1) of this section must 
be multiplied by the efficiency value 
associated with the type of anti-skid 
system installed on the airplane: 

Type of anti-skid system 

Effi-

ciency 

value 

On-Off ........................................................................

0.30 

Quasi-Modulating .......................................................

0.50 

Fully Modulating ........................................................

0.80 

(d) At the option of the applicant, a 

higher wet runway braking coefficient 
of friction may be used for runway sur-
faces that have been grooved or treated 
with a porous friction course material. 
For grooved and porous friction course 
runways, the wet runway braking 
coefficent of friction is defined as ei-
ther: 

(1) 70 percent of the dry runway brak-

ing coefficient of friction used to deter-
mine the dry runway accelerate-stop 
distance; or 

(2) The wet runway braking coeffi-

cient defined in paragraph (c) of this 
section, except that a specific anti-skid 
system efficiency, if determined, is ap-
propriate for a grooved or porous fric-
tion course wet runway, and the max-
imum tire-to-ground wet runway brak-
ing coefficient of friction is defined as: 

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