EAA Homebuilt Aircraft Council Urges: Ensure Proper Fuel Flow
December 6, 2012 - A recent tragic accident in Canada (Transportation Safety Board File # A12O0113-D1-A1) reminds us of the importance of ensuring proper fuel flow before the first flight of any experimental amateur-built aircraft and after any modification or addition to the fuel system.
The aircraft in this accident was an experimental Quad City Challenger II equipped with a Rotax 582 engine. The engine failed after takeoff when insufficient fuel flowed to the carburetor. The cause of the engine failure was a fuel flow sensor with a restrictive orifice that was only 1 millimeter in diameter. A simple fuel flow test performed before the flight would have shown that the system was incapable of delivering the required fuel volume to the engine, and it could have saved the life of the pilot.
The installation of the fuel flow sensor orifice was contrary recommendation of the Rotax 582 installation manual, which calls for a minimum fuel line size of 5 millimeters.
The great benefit of experimental amateur-built aviation is that it allows builders to select from a wide range of products and to install these products on their aircraft as they see fit. However, along with this freedom comes a great responsibility to be sure that those products can work together in a safe manner. The final verification of this process as it related to fuel systems is the fuel flow test as outlined in FAA Advisory Circular 90-89A. This test should be carried out before the first flight of any E-AB aircraft. It should also be performed before flight when any modification or addition has been made to an existing fuel system. This includes modifications to the fuel tank venting system as well.
The NTSB recently recommended to the FAA that it incorporates a requirement for fuel flow testing into its E-AB certification guidelines as published in 8130.2G. If adopted you can be sure the FAA will review the Canadian and British rules on this subject, and the outcome will be a revised regulation that adds significant work, cost, and complexity to the builder. Moreover, it will have a damping impact on the numbers of completed E-AB aircraft and arguably have little, if any, positive effect on the accident rate. It's imperative that E-AB builders ensure adequate fuel flow for all attitudes in which the aircraft will operate, but particularly during high angle of attack at full power.
If EAA members wish to retain control of this process, we must make significant headway in addressing this problem ourselves. To that end, the Homebuilt Aircraft Council is preparing a webinar on fuel system testing that will be available soon.