The installation of a 4-point shoulder harness system in aircraft such as the Beechcraft series is a critical safety modification that requires both technical knowledge and adherence to Federal Aviation Administration (FAA) regulations. This article provides a detailed overview of the BAS (Beech Aircraft Safety) 4-point shoulder harness installation process, including the tools required, structural considerations, and regulatory requirements. The information is derived from technical discussions, installation experiences, and manufacturer documentation available in the source materials.
BAS 4-point shoulder harness kits are designed to provide enhanced protection for pilots and passengers in the event of a crash or sudden stop. These systems are particularly relevant for aircraft where shoulder harnesses were not originally equipped. The installation of such a harness is considered a major alteration under FAA guidelines and must be accompanied by a signed FAA Form 337 by a certified A&P (Airframe and Powerplant) or IA (Inspection Authorization) mechanic.
The installation process can vary in complexity depending on whether the aircraft already has the necessary structural reinforcement in place. For aircraft produced prior to 1971, it is unlikely that the original structure supports shoulder harnesses, necessitating additional reinforcement. For later models, the presence of rivet patterns or factory-installed brackets may simplify the installation.
Installation Overview and Planning
A typical installation of a BAS 4-point shoulder harness involves reinforcing the aircraft’s structure to support the harness system, installing the necessary hardware such as inertia reels and mounting brackets, and ensuring proper alignment and functionality of the harness. The process is often completed within a weekend by an experienced team with the right tools and guidance from the manufacturer’s instructions.
The installation can be particularly time-saving if the aircraft already has a rivet pattern in the roof that corresponds to factory-installed brackets. This allows the harness reel to be mounted without requiring significant structural modifications. In such cases, the use of AN470-4 rivets is commonly noted as part of the installation process.
Before beginning, it is important to review the manufacturer’s installation instructions, which may include detailed diagrams and step-by-step guidance. For example, the 2003 BAS installation instructions referenced in the source material were provided to customers in 2005 and serve as a useful reference for planning the project.
Tools and Materials Required
A successful installation requires a range of specialized tools and fasteners. The most critical among these are:
2X Rivet Gun: A high-quality rivet gun with a teasing trigger and rivet set is essential for installing solid rivets. Manufacturers such as U.S. Industrial Tool, Sioux Tools, and Chicago Pneumatic produce reliable models suitable for aircraft work.
Rivet Sets and Spring Retainers: These components ensure that the rivet gun operates correctly and safely during installation.
Cleco Fasteners and Pliers: These are used temporarily to hold parts in place during the installation process.
CherryMax Rivets: These are used when a bucking bar cannot be used on the backside of a solid rivet. They provide a strong, reliable fastening solution and are often used in areas such as the aircraft's stringers.
Inertia Reels and Mounting Brackets: These are part of the harness kit and must be aligned and mounted according to the manufacturer’s specifications.
Headliner Cutting Template: For aircraft with intact headliners, a template can be used to accurately cut a hole for the inertia reel. This is particularly useful for first-time installations.
Structural Reinforcement and Modifications
In many cases, especially for aircraft produced before 1971, structural reinforcement is necessary to support the harness system. This typically involves installing doublers or additional supports to the fuselage. The reinforcement is usually riveted in place and must be strong enough to anchor the inertia reel and shoulder harness.
The reinforcement process may take anywhere from a few hours to a full day, depending on the complexity of the structure. For example, in the case of a Beech Bonanza, structural reinforcement was required to mount the harness system after a forced landing in a corn field. The front seat occupants, who were wearing shoulder harnesses, survived the incident.
When reinforcing the fuselage, it is important to follow the manufacturer’s instructions and to ensure that all rivets are properly seated and torqued. The use of CherryMax rivets, which are designed for aerospace applications, can help ensure a secure and durable connection.
FAA Compliance and Documentation
Since a shoulder harness installation is considered a major alteration, the project must be documented and approved by an FAA-certified A&P/IA mechanic. The mechanic must inspect the installation and sign an FAA Form 337, which is required for any major modification or repair to an aircraft.
In addition to the form, the mechanic must log the installation in the aircraft’s maintenance records. This includes noting the type of modification, the parts used, and any structural changes made during the installation. Proper documentation is essential for maintaining the aircraft’s airworthiness and for future inspections.
For pilots or aircraft owners who plan to perform the installation themselves, it is important to note that only A&P-certified individuals may sign off on the work. This means that while owners can assist with the installation, the final inspection and approval must be conducted by a qualified mechanic.
Comparative Safety Benefits and Use Cases
The importance of 4-point shoulder harnesses is underscored by several real-world incidents and safety reports. For example, a Beech Lister accident in which the pilot and co-pilot died from head injuries during a crash landing highlighted the potential life-saving benefits of such harnesses. In this case, the rear seat passenger, who was not wearing a harness, suffered only a broken arm.
Similarly, a pilot named Dale H. survived a forced landing in a Beechcraft F33A with major chest trauma after not wearing a shoulder harness. His NTSB report detailed the severity of the injury, including a fractured sternum and visible control wheel imprints on his chest. These cases illustrate the critical role that shoulder harnesses can play in reducing injury severity during high-impact events.
From a regulatory and safety standpoint, the National Transportation Safety Board (NTSB) has long advocated for the use of shoulder harnesses in both general aviation and commercial aircraft. While 3-point harnesses are sometimes considered, the source materials indicate that 4-point systems offer superior protection, particularly in high-speed or high-impact scenarios.
Installation Challenges and Considerations
Despite the safety benefits, the installation of a 4-point shoulder harness system is not without its challenges. One of the primary concerns is spinal compression, particularly with certain types of harnesses such as the Hooker-style belts. While these concerns have been raised, the source material does not provide definitive evidence of such risks being realized in practice.
Another challenge is the cost and labor involved in the installation. The labor required can vary depending on the aircraft model and the extent of structural modifications needed. However, the source materials suggest that the installation is generally manageable, with many owners completing the project in under 10 hours.
For those considering a DIY approach, it is important to have a clear understanding of the tools and techniques required. The source materials reference several DIY bracket projects, including a photo album by Jason M. of a factory-installed bracket setup for a retractable overhead "Y" harness. These resources can be invaluable for owners who wish to participate in the installation process.
Alternative Harness Systems and STC Kits
In addition to the BAS 4-point system, several other STC (Supplemental Type Certificate) kits are available for various aircraft models. These include kits offered by Aero Fabricators, Wag-Aero, and Univair, which provide shoulder harness systems for aircraft such as the J-3, PA-11, PA-18, and PA-28 series.
Most STC kits include two main components: the belts and fittings, and the structural reinforcement components. Some systems use inertia reels, while others feature fixed belts. Inertia reel systems tend to be more convenient for pilots, as they allow for easier adjustment and movement within the cockpit.
The cost of the kits can vary, with fixed-belt systems generally being less expensive than inertia reel systems. However, the convenience and added safety of inertia reels often justify the higher cost for many pilots.
Conclusion
The installation of a 4-point shoulder harness system is a critical modification for aircraft where such safety equipment was not originally equipped. The process involves structural reinforcement, rivet installation, and careful alignment of the harness components. While the installation can be completed by an A&P/IA mechanic or with the help of an experienced DIY team, it must be accompanied by the necessary FAA documentation and approvals.
Given the documented safety benefits and the potential for reducing injury severity in the event of a crash or sudden stop, the installation of a 4-point shoulder harness is highly recommended for pilots and aircraft owners. As the source materials indicate, the cost and labor involved are often justified by the added protection and peace of mind.