DVI has the specialized expertise to investigate accidents involving experimental amateur-built aircraft. An Experimental Aircraft Expert has to understand the intricacies of aircraft design, aircraft performance, fabrication methods, aircraft maintenance, and flight test methodologies. The challenging aspect to investigating accidents involved experimental aircraft stems from the highly unique nature of each design. Typical homebuilt or amateur built aircraft are customized to the likings of the builder, unlike a standard type certificated aircraft. The builders of a homebuilt aircraft have the latitude and ability to modify designs, specify their own building materials, and make an endless number of modifications. A Homebuilt Aircraft Expert has to be able to evaluate the effects of the choices made by the builder to accurately reconstruct and explain an accident.
History of Experimental Amateur-Built Aircraft
Experimental amateur-built aircraft represent a significant, and growing, proportion of the General Aviation fleet in the United States and around the world. According to the FAA‘s 2010 General Aviation and Part 135 Activity Survey, they account for nearly 10 percent of general aviation aircraft, and 4 percent of the hours flown in general aviation.
The experimental amateur-built category was first adopted in Civil Aeronautics Manual in 1952, and early experimental amateur-built category aircraft were primarily the original designs of their builders or aircraft built from plans shared between builders. The first kits, which consisted of factory-fabricated components and sub-assemblies, were introduced in the 1970s and kit-built experimental amateur-built category aircraft now constitute the largest proportion of experimental aircraft. The FAA publishes, on its website, a listing of kits that have been evaluated and found eligible in meeting the requirement of 14 CFR 21.191(g).
The FAA’s Definition of an Experimental Amateur-Built Category Aircraft
The FAA first identifies an aircraft as amateur-built when it is registered with the FAA Registration Branch. FAA regulations allow for aircraft constructed from an amateur builder‘s original design, purchased plans, or pre-fabricated kit, to be registered as an experimental amateur-built category aircraft provided that the builder (or builders) demonstrate that he or she has fabricated or assembled over one-half of the aircraft. While FAA Advisory Circular (AC) 20-27G provides general guidance to amateur builders regarding the planning and construction of an experimental amateur-built category aircraft and refers builders to technical support available from the Experimental Aircraft Association and others, although its principal focus is to communicate and ensure compliance with the “major proportion” or “51-percent? rule” , namely: The major portion of the aircraft is defined as more than 50 percent of the fabrication and assembly tasks, commonly referred to as the “51-percent rule”. For example, an amateur-built kit found on the FAA List of Amateur-Built Aircraft Kits has 40 percent of the fabrication/assembly completed by the kit manufacturer. In order to be eligible for an experimental amateur-built airworthiness certificate, and per the major portion rule, the fabrication and assembly tasks that may be contracted out (for hire) to another individual (or builder/commercial assistance center) needs to be less than 10 percent.
Airworthiness Certification and Flight Testing of Experimental Amateur-Built Category Aircraft
Experimental amateur-built category aircraft safety is largely managed by the community of experimental amateur-built category aircraft builders, owners, and kit manufacturers rather than by FAA regulatory requirements. A primary focus of FAA regulations governing the experimental amateur-built category aircraft building process seeks to ensure that the major portion of the construction work is done by the builder. Airworthiness certificates are granted to the experimental amateur-built category aircraft builder by the FAA based only on a review of documentation and a one-time inspection of the aircraft after it has been completed. Unlike foreign civil aviation authorities‘standards, there is no requirement for pre-approval of the project or in-process inspections of materials and workmanship.
As part of the airworthiness certification process, experimental amateur-built category aircraft are assigned operating limitations specifying how and where the aircraft can be flown. Experimental amateur-built category aircraft operating limitations specify two phases of operation: Phase I, which is applicable to the flight test period and Phase II, which governs normal operations once testing is complete. Builders of experimental amateur-built category aircraft are required to certify that the flight test has been completed with an entry in the aircraft logbook. Although FAA guidance materials are explicit in advising the builder that the objective of the flight test is to carefully map the performance envelope of the aircraft and develop an aircraft flight manual, neither a flight test plan nor documentation of its accomplishment, in the form of an aircraft flight manual, are required to be submitted to, reviewed, or accepted by an FAA Aviation Safety Inspector (ASI) or FAA Designated Airworthiness Representative (DAR).
Accidents as a Function of Aircraft Age
Previous comparisons of experimental amateur-built category aircraft accident rates to other segments of general aviation have sought explanations for the substantially elevated accident rates, either as a proportion of the active aircraft fleet or of flight hours. One observation is that much higher proportions of experimental amateur-built category aircraft accidents occur early in the operational life of the aircraft, particularly during the Phase I flight test as a condition of airworthiness certification. The figure below compares the cumulative distributions of accident aircraft from 2001 through 2010 at various points in the total airframe lifespan (in hours) for experimental amateur-built category and non- experimental amateur-built category aircraft. Direct comparison of the airframe hours at the time of the accident is difficult because of the likely differences in the operational history of the two groups of aircraft. However, the large difference in the number of experimental amateur-built category aircraft accidents occurring very early in the operational life of the aircraft suggests underlying differences between the two fleets of aircraft. For example, 152 of the 1,622 accident experimental amateur-built category aircraft (9 percent) with airframe data had fewer than 10 airframe hours at the time of the accident, compared with only 18 of the 6,450 non- experimental amateur-built category aircraft (.3 percent) with airframe data. This is despite a total fleet of and number of accidents involving, non- experimental amateur-built category aircraft being several times greater than that of experimental amateur-built category aircraft.