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Federal Register / Vol. 86, No. 52 / Friday, March 19, 2021 / Rules and Regulations In addition to the applicable airworthiness regulations and special conditions, the Boeing Model 7878
airplane must comply with the fuel vent and exhaust emission requirements of 14 CFR part 34 and the noise certification requirements of 14 CFR
part 36.
The FAA issues special conditions, as defined in 14 CFR 11.19, in accordance with 11.38, and they become part of the type certification basis under 21.101.
Novel or Unusual Design Features The Boeing Model 7878 airplane will incorporate the following novel or unusual design features:
Lufthansa Technik is proposing to install large non-structural glass items in Model 7878 airplanes. Possible installations of large non-structural glass items include, but are not limited to, the following items:
Glass partitions.
Glass floor installations.
Glass attached to the ceiling.
Glass parts integrated in the stairway.
Wall or Door mounted mirrors and glass panels.
Mirrors as part of a door blow out panel.
Glass plate installed in a doorframe.
Washstand with glass-panel.
The installation of these glass items in the passenger compartment, which can be occupied during taxi, take-off and landing TT&L, is a novel or unusual design feature with respect to the installed material. The applicable airworthiness regulations do not contain adequate or appropriate safety standards for this design features.

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Discussion The use of glass results in trade-offs between the one unique characteristic of glassits capability for undistorted or controlled light transmittance, or transparencyand the negative aspects of the material. Glass, in its basic form as annealed, untreated sheet, plate, or float glass, when compared to metals, is extremely notch-sensitive, has a low fracture resistance, has a low modulus of elasticity, and can be highly variable in its properties. While reasonably strong, it is nonetheless not a desirable material for traditional airplane applications because it is heavy about the same density as aluminum, and when it fails, it breaks into extremely sharp fragments that have the potential for injury, and which have been known to be lethal. Thus, the use of glass traditionally was limited to windshields, and instrument or display transparencies. The regulations in
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25.775 only address, and likewise only recognize, the unique use of glass in windshield or window applications where no other material will serve. This regulation does address the adverse properties of glass, but pilots occasionally are injured from shattered glass windshields.
The FAA divides other uses of glass in the passenger cabin into four groups.
These groups were created to address the practical and functional uses of glass. The four groups are as follows:
The first group is glass items installed in rooms or areas in the cabin that are not occupied during TT&L, and a person does not have to enter or pass through the room or area to get to any emergency exit.
The second group is glass integrated into a functional device the operation of which is dependent upon the characteristics of glass, such as instrument or indicator protective transparencies, or monitor screens such as liquid crystal displays or plasma displays. This group may be installed in any area in the cabin regardless of occupancy during TT&L. Acceptable means of compliance for these items may depend on the size and specific location of the device containing the glass.
The third group is small glass items installed in occupied rooms or areas during TT&L, or rooms or areas that a person does not have to enter or pass through to get to any emergency exit.
The FAA defines a small glass item as less than 8.8 lbs 4 kg in mass.
The fourth group is large glass items, the subject of these special conditions, installed in occupied rooms or areas during TT&L, or rooms or areas that a person must enter or pass through to get to any emergency exit. A large glass item is defined as 8.8 lbs 4 kg or greater in mass. Groups of glass items that collectively weigh 4 kg or more would also be included. The mass is based on the amount of glass that becomes hazardous in high inertial loads.
The glass items in groups one, two, and three are restricted to applications where the potential for injury is either highly localized, such as flightinstrument faces, or the location is such that injury due to failure of the glass is unlikely, for example mirrors in lavatories, because these installations necessitate the use of glass. These glass items typically are addressed in a method-of-compliance issue paper for each project based on existing part 25
regulations, or in established policy.
These issue papers identify specific tests that could include abuse loading and ball-impact testing. In addition,
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these items are subject to the inertia loads contained in 25.561, and maximum positive-differential pressure for items like video monitors to meet 25.789.
The items in group four are much larger and heavier than previously approved, and raise additional safety concerns. These large, heavy glass panels, primarily installed as architectural features, were not envisioned in the regulations. The unique aspects of glass, with the potential to become highly injurious or lethal objects during emergency landing, minor crash conditions, or in flight, warrant a unique approach to certification that addresses the characteristics of glass that prevented its use in the past. These special conditions were developed to ensure that airplanes with large glass features in passenger cabins provide the same level of safety as airplanes using traditional, lightweight materials. The FAA
reiterates this intention in the text of the special conditions by qualifying their use for group four glass items.
These special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to that established by the existing airworthiness standards.
Applicability As discussed above, these special conditions are applicable to the Boeing Model 7878 airplane. Should Lufthansa Technik apply at a later date for a supplemental type certificate to modify any other model included on Type Certificate No. T00021SE to incorporate the same novel or unusual design feature, these special conditions would apply to that model as well.
Conclusion This action affects only a certain novel or unusual design feature on one model of airplane. It is not a rule of general applicability and affects only the applicant who applied to the FAA
for approval of these features on the airplane.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping requirements.
Authority Citation The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 106f, 106g, 40113, 44701, 44702, 44704.

The Special Conditions Accordingly, pursuant to the authority delegated to me by the
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