14 CFR Part 25.607 – Fasteners
In this post, we will explore the next regulation, 14 CFR Subpart C Section 25.607 – Fasteners.
Before you read on, I suggest you read through this advisory circular: AC20-71
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§ 25.607 Fasteners
In the previous posts, we looked at:
- 14 CFR Subpart C Section 25-301: Loads
- 14 CFR Subpart C Section 25-303: Factor of Safety
- 14 CFR Subpart C Section 25-305: Strength and Deformation
- 14 CFR Subpart C Section 25-307: Proof of Structure
- 14 CFR Subpart C Section 25-365: Pressurized Compartment Loads
- 14 CFR Subpart C Section 25-561: General Emergency Landing Ultimate Loads
- 14 CFR Subpart C Section 25-562: Emergency Landing Dynamic Loads
- 14 CFR Subpart C Section 25-601: Hazardous Unreliable Design Features
- 14 CFR Subpart C Section 25-603: Materials
- 14 CFR Subpart C Section 25-605: Fabrication Methods
In the last post we studied the importance of fabrication methods and process specifications. In this post we will dig into a very important design feature that must be used for critical fasteners to comply with this regulation.
(a) Fasteners: Dual Locking Devices
As is clear from part (a) of this regulation (see the regulation text above), removable fasteners that are primarily intended to transfer shear load (single or double) between critical joint members must incorporate two separate locking devices or features. This is applicable to bolts that also serve as axis of rotation for the joint members.
It is common practice to include one locking device, such as self-locking nut with a detent in the threads. But for critical applications such as control surfaces rotating using clevis and bolt fulcrum parts, dual locking devices are mandatory as the loss of this bolt (slipping or sliding out due to failure of the single locking device) would impact safe flight and landing.
(b) Fasteners: Environmental Impacts
This could be high temperatures, corrosion, cracks etc. Therefore, only approved materials with proper heat treatments must be used for critical applications. Common fastener specifications include NAS, MS or Hi-Lok type fasteners that are commonly used for most applications.
(c) Fasteners: Rotating Bolts
If the bolt or fastener is designed to rotate in the applications, or is allowed to rotate, then a self-locking nut or any self-locking device is not allowed. In such cases, other non friction type devices must be used such as cotter pins that pass through the shank and the head of the bolt.
Read this article for more details: Non Self-Locking Nuts
Alright, I think that pretty much sums it up. Cheers! Oh and don't forget to comment and share this post, use the sharing methods below.