Aircraft windshields are regularly inspected for problems that could reduce visibility or compromise the windshield. Some issues are acceptable or require repair, depending on their permissible limits. You may have questions about these limitations, how to avoid potential problems, and what to do if the windshield fails inspection.
We are frequently asked these questions, so we have addressed them in this article to help you make more informed decisions about mitigating windshield damage and choosing repair or replacement options.
What is an Aircraft Windshield Made Of?
Aircraft windshields (also known as windscreens and transparencies) must withstand extreme temperatures and pressure in order to protect pilots while still allowing them to see outside.
As a result, windshields are made up of laminated layers of glass, acrylic, polycarbonate plastics, or a combination of these materials that are bonded together with polymeric material. Many aircraft windshields include an interlayer heating system for deicing and anti-fogging. The exact combination and thickness of the layers will differ depending on the type of aircraft windshield and the manufacturer.
Aircraft Windshield Manufacturer’s Allowable Limits
Each aircraft windshield manufacturer specifies allowable limits in the aircraft maintenance manual (AMM). These limits define what issues are acceptable, require repair, or will fail inspection. Not all issues will cause the windshield to fail. Failures are determined by how many issues are present and their location (e.g., in the pilot’s line of vision).
Always consult the AMM when assessing your aircraft’s windshield because the limits vary by windshield type and manufacturer.
Types of Aircraft Windshield Issues and Damage
Below is a list of common aircraft windshield issues.
- Chips and nicks
- Delamination
- Haze
- Bubbles
- Scratches
- Crazing
- Fogging
- Warping or deformation
- Cracks
- Broken fasteners
- Cracked mounting components
- Malfunctions in the windshield heating system
While not all these issues will result in the windshield failing inspection, others will. These issues include broken fasteners, cracked mounting components, and malfunctions with the windshield’s heating system. Refer to the AMM to determine whether these issues require repair or replacement.
What Causes Aircraft Windshield Damage – And How to Mitigate Damage?
Aircraft windshield damage is caused by various factors – from negligence to environmental hazards. While some damage is beyond human control, other damage can be mitigated by following manufacturer guidelines. If issues materialize, review the AMM to determine the next steps, such as repairing small chips or scratches to prevent potential windshield failures.
Improper Cleaning Products
Using unapproved cleaning products, such as paper towels or shop rags, can scratch the surface of the windshield. Always refer to the manufacturer’s guidelines for properly cleaning and maintaining your aircraft’s windshield.
Interlayer Heat Systems
Aircraft windshields feature a heating system to prevent icing on the glass during flight. Heating systems should be on during the whole flight. Turning the heating system on while in flight to combat icing can cause thermal shock. The drastic temperature change may result in the windshield cracking or delaminating.
If the heating system short circuits, it may cause uneven temperature distribution and result in cracking the windshield’s outer layer.
You may be able to repair or replace the system rather than replace the windshield if the interlayer heating system fails. If the windshield is damaged, then it may need to be replaced.
Moisture Between Layers
Moisture may enter between laminated layers if there are gaps along the window edges. Trapped moisture could turn to ice while flying in colder temperatures. If the moisture turns to ice, it will expand, causing the windshield to delaminate or crack.
Inspect windshield edges and “hump seals” for cracks or gaps to avoid moisture from getting between the layers.
Environmental Elements
Environmental factors may cause damage. For instance, hail can crack the windshield, or volcanic ash, lingering in the upper atmosphere, can cause abrasions to the windshield’s surface. Refer to the AMM for guidance on environmental damage.
Bubbles Between Layers
Bubbles may be present between the laminated windshield layers, which can happen during manufacturing. The amount and placement of the bubbles may be within allowable limits. If the bubbles exceed the limits, the windshield must be replaced.
Bird Strikes
Bird strikes may also damage aircraft windshields. The extent of the damage depends on the size of the bird. Generally, bird strikes happen during take-offs, landings, or while the aircraft is at a low altitude.
Source – cla.aero
