Research and development are key for developing standards and structural repairs for aircraft.

As aircraft structural repairs range from simple to extremely complex, technicians often wrangle over the type of structure involved.

By learning how to identify different aircraft structures and develop structural repair standards confidently, technicians can be more efficient in repairs and maintenance decision-making.

What's included in the structure of an aircraft?

According to United States aviation safety regulations, an airframe encompasses the following components:

• Fuselage
• Booms
• Nacelles
• Cowlings
• Fairings
• Airfoil surfaces (excluding propellers and rotating airfoils of engines)
• Landing gear (including accessories and controls)

The FAA’s guidance on determining and showing compliance with the structural strength requirements of the airworthiness standards has quadrupled since the days of safe-life and fail-safe design standards to the damage-tolerant requirements demanded today.

A simple search in the agency’s Dynamic Regulatory System returns over 1600 documents on the subject.

The word “structure” appears 159 times in 14 CFR part 25, 14 times in part 23, 85 times in part 27 and 89 times in part 29.

Within these results, the FAA offers guidance for validating repairs and alterations on aircraft structures, such as:

• Research
• Data
• Engineering information
• Analysis

Most of the references in the airworthiness standards deal with material properties and design values required to ensure structural strength is obtained and maintained to accommodate the loads and operating conditions contemplated by the type design.

Why research is key for effective structural repairs

Whether performing a structural repair on an aircraft or developing a new one, the query must begin with research.

For example, a type certificate holder may not have the repair protocol for a specific type of damage in their maintenance manuals or instructions for continued airworthiness.

In all cases, the maintenance provider is responsible for ensuring the work performed will return the aircraft to at least its original or properly altered condition.

The first level of query is to determine the original certification basis for the aircraft and confirm whether there have been any alterations to that basis. Even if using manufacturer’s maintenance manuals or instructions, the instructions may no longer be applicable due to the aircraft’s configuration.

If supplemental type certificates have been installed that impact the structure, the areas must be evaluated under the certification basis of each major alteration.

The development of structural repairs on old aircraft is time-consuming but essential. For instance, to develop effective structural repairs for a fuselage, it’s key to know information like:

• Number of repairs
• Type of repairs
• Status of major or minor repair
• Minor alterations to aircraft
• Major alterations to aircraft

However, maintenance records often don’t provide enough detail to be helpful, and extensive and intensive inspection may be required to identify appropriate parameters for established structural repairs.

In the end, the maintenance provider must have a full understanding of an aircraft’s life, including:

• Certification basis
• Configuration
• Operational environment

By gathering this data, maintenance teams can confidently ensure a structural repair is developed and accomplished correctly.