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• March 1, 2017 Create Date
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Windows and Windshields

1. PURPOSE. This advisory circular (AC) sets forth an acceptable means, but not the only 
means, of demonstrating compliance with the provisions of Title 14, Code of Federal 
Regulations (14 CFR) part 25 pertaining to the certification requirements for windshields, 
windows, and mounting structure. Guidance information is provided for showing compliance 
with 25.775(d), relating to structural design of windshields and windows for airplanes with 
pressurized cabins. Terms used in this AC, such as "shall" or "must," are used only in the sense 
of ensuring applicability of this particular method of compliance when the acceptable method of 
compliance described herein is used. Other methods of compliance with the requirements may 
be acceptable. While these guidelines are not mandatory, they are derived from extensive 
Federal Aviation Administration (FAA) and industry experience in determining compliance with 
14 CFR. This AC does not change, create any additional, authorize changes in, or permit 
deviations from, regulatory requirements. 

2. APPLICABILITY. This advisory circular contains guidance for the latest amendment of the 
regulations and applies to all transport category airplanes approved under the provisions of 
part 25, for which a new, amended, or supplemental type certificate is requested.

a. Annealed glass. Glass that has had the internal stresses reduced to low values by heat 
treatment to a suitable temperature and controlled cooling. 
b. Chemically toughened glass. Annealed glass immersed in a bath of molten salt resulting 
in an ion exchange between the salt and the glass. The composition of the salt is such that this 
ion exchange causes the surface of the glass to be distorted (by expansion), thus putting the 
surface in a state of compression. 
c. Creep. The change in dimension of a material under load over a period of time, not 
including the initial instantaneous elastic deformation. The time dependent part of strain 
resulting from an applied stress. 
d. Cross-linking. The setting up of chemical links between molecular chains. 
e. Modulus of Rupture (MOR). The maximum tensile or compressive longitudinal stress in 
a surface fiber of a beam loaded to failure in bending calculated from elastic theory.