Under what circumstances are more than two copies of form 337 required?

When a fuel tank is installed in the passenger or baggage compartment, more than two copies of Form 337 are required due to the significant safety and regulatory implications involved. The installation of a fuel tank in these areas poses potential hazards in case of fuel leaks, spills, or fire, making it essential for the FAA to maintain complete documentation and oversight.

This requirement reflects the need for comprehensive documentation to ensure that all modifications meet safety standards and comply with regulations. Additional copies of Form 337 facilitate the needed review by FAA inspectors, enable effective record-keeping, and allow for public transparency in the modification process, ensuring that all stakeholders are informed of potential risks associated with such installations.

In contrast, while modifying avionics, performing a major aircraft overhaul, or reconfiguring the aircraft seating arrangement may involve important technical changes, these actions typically do not invoke the same level of restrictions and documentation requirements as installing a fuel tank in a passenger or baggage compartment, which directly affects safety considerations.