FAA Form 337

Regulatory Guidance – Aircraft Maintenance & Repair

Appendix A to Part 43, Title 14 – Major Alterations, Major Repairs, and Preventive Maintenance

• Major Alterations: Significant modifications to aircraft structures or systems that may affect the aircraft's performance or airworthiness.

• Major Repairs: Extensive repairs to critical components that are essential for maintaining the aircraft's structural integrity and safety​

• Preventive Maintenance: Routine tasks that aircraft owners or operators can perform to ensure continued airworthiness without requiring specialized certification.

FAA Guidance & Advisory Circulars (ACs)

MRADA R6.0 – A Job Aid It provides maintenance personnel with guidelines on compliance for 337’s.

FAA Order 8110.113 – This order provides policy guidance for the approval of major repairs and alterations on aircraft. It outlines procedures for field approvals and defines the responsibilities of mechanics, inspectors, and FAA personnel to ensure regulatory compliance.

FAA Order 8300.13A CHG 1 – This order establishes guidelines for continued airworthiness of aircraft and components. It includes inspection requirements, repair procedures, and best practices to maintain safe and reliable aircraft operations.

AC 120-73 – This advisory circular provides guidance on conducting damage tolerance assessments for aircraft repairs. It helps operators and repair stations evaluate structural repairs and ensure compliance with FAA safety standards.

AC 120-93 – Focused on fuel tank system safety, this circular explains inspection and maintenance procedures to prevent ignition hazards. It helps operators comply with FAA fuel tank safety regulations.

AC 20-157 – Provides certification and compliance guidelines for aircraft flight control systems. It addresses issues related to system reliability, redundancy, and operational safety.

AC 20-162B – This circular outlines airworthiness requirements for electrical wiring interconnection systems (EWIS). It helps mechanics and manufacturers ensure that wiring systems meet safety and durability standards.

AC 20-168 – Covers aircraft flammability design considerations and provides guidance on reducing fire risks. It includes recommendations for materials, fire-resistant coatings, and compliance with FAA fire safety regulations.

AC 21-47 – Explains the process of obtaining production approvals for aircraft parts and components. It outlines quality control measures to ensure compliance with FAA manufacturing standards.

AC 23-21 – Provides guidance on small aircraft certification, including design, performance, and operational requirements. It assists manufacturers and operators in meeting FAA safety standards.

AC 23-23 – Addresses load analysis for small aircraft, helping engineers and mechanics ensure structural integrity. The circular explains methodologies for calculating and verifying load factors.

AC 23-24 – Focuses on structural substantiation for small airplanes, providing engineers with best practices for strength and durability testing. It also includes compliance strategies for FAA certification.

AC 33-9 – Covers certification standards for aircraft engines, including safety, efficiency, and durability requirements. It provides manufacturers with guidelines for compliance with FAA regulations.

AC 43.13-1B CHG 1 – A widely used advisory circular that provides acceptable methods for aircraft inspection and repair. It serves as a key resource for mechanics and repair stations to ensure compliance with FAA maintenance regulations.

AC 43.13-2B – Provides approved techniques for aircraft alterations and repairs. It includes guidance on acceptable modifications and necessary documentation for FAA approval.

AC 43.9-1G – Details the proper methods for recording maintenance activities in aircraft logbooks. This circular ensures that maintenance records meet FAA regulatory requirements.

AC 43-210A CHG 1 – Provides procedures for aircraft inspections, alterations, and approval processes. It helps mechanics and repair stations understand FAA documentation requirements.

AC 91.21-1D – Offers guidance on the use of personal electronic devices on aircraft. It helps operators assess the potential for interference with aircraft systems.

AC 20-188 – Establishes fire protection standards for aircraft, including materials and testing procedures. It provides recommendations for compliance with FAA fire safety regulations.

Legal Interpretations & Other FAA Documents

Bowers 2016 Legal Interpretation – Clarifies FAA regulations on maintenance responsibilities and repair station authority. It addresses common industry concerns about maintenance approvals.

Collins 2011 Legal Interpretation – Provides FAA guidance on aircraft maintenance responsibility and operator obligations. It helps clarify regulatory interpretations for mechanics and repair stations.

Rude 2015 Legal Interpretation – Discusses compliance issues for aircraft mechanics, including regulatory obligations and enforcement considerations. It helps ensure adherence to FAA maintenance rules.

AC 120-77B – Covers flight deck security measures, including access control and threat mitigation strategies. It provides best practices for maintaining a secure cockpit environment.

STC Guidance

AC 20-166A – Provides guidance on continued operational safety monitoring for aircraft and aircraft products. It explains reporting requirements, defect investigations, and best practices for maintaining compliance with FAA safety standards.

AC 21-40A – Outlines application procedures for obtaining an Export Airworthiness Approval. It helps manufacturers and exporters understand the requirements for certifying aircraft and parts for international markets.

AC 21-51 – Provides guidance on type certification procedures for aircraft and aviation products. It explains the FAA's regulatory framework for certifying new aircraft designs and modifications.

AC 20-180 – Covers FAA-approved fuel system modifications, particularly for alternative fuels and fuel additives. It details design, testing, and certification processes to ensure airworthiness.

AC 23-17C – Discusses certification requirements for small aircraft in the normal, utility, acrobatic, and commuter categories. It focuses on changes in aircraft safety and performance standards.

AC 23-22 – Provides airworthiness compliance guidance for small airplanes. It helps aircraft designers and mechanics understand how to meet FAR Part 23 certification requirements.

AC 23-24 – Focuses on structural substantiation for small airplanes, detailing methodologies for strength calculations, material selection, and load factor assessments. It ensures compliance with FAA regulations for safe aircraft structures.