When amateur builders complete their homebuilt projects, if their work passes muster the FAA awards them an airworthiness certificate and an operational leash, a Phase I test period of usually 25 to 40 flight hours. The certification of the powerplant and prop combination plays a role in the Phase I duration.
Ideally, homebuilders have already read Advisory Circular 90-89, Amateur-Built Aircraft and Ultralight Flight Testing Handbook, and developed a series of flight tests cards that will, once flown, lead to all the necessary performance data and numbers that will allow builders to safely and efficiently operate their flying machines.
In talking to homebuilders and writing about the construction of their airplanes, I can count on one hand those who actually created—and completed—a flight-test plan. The majority of the others bored aimless holes in the sky for the prescribed Phase I test time.
When it comes to operational data, they often get by with the performance numbers provided by the kit manufacturer. Their airplanes are often heavier than the kit prototype, and they often include modifications and different engine and prop combinations. When asked if they adjusted the prototype’s numbers for these differences, they often say, “They are close enough.”
Close may work for hand grenades and nuclear weapons, and too often “close enough” aircraft performance numbers can be just as lethal. To motivate homebuilders to actually create and fly flight-test programs that reveal aircraft-specific performance data, in the draft update of AC 98-89B, the FAA temps them with a “operationally centric or task-based experimental aircraft flight-test plan.”
Instead of boring holes in the sky for a prescribed number of hours, the Phase I test period is completed when builders finish flying a flight-test plan as discussed in the AC, crunched the numbers, and compiled them in the airplane’s flight manual. The flight test plans do not need FAA approval, but they must include the flight test points discussed in the AC.
If builders do not want to create their own flight-test plan, they can use one provided by the kit manufacturer or other qualified sources. For those seeking the path of greater economy and efficiency, there is the EAA Flight Test Manual & Test Cards ($22.95). Introduced in 2018, it is part of EAA’s How-To Series, it steps through the required tasks, explains how to fly them, and how to crunch the resulting data.
The FAA is accepting comments on the draft AC 90-89B Change 1 through April 29. Maybe by AirVenture 2022 I’ll meet some homebuilders who snagged this Phase I carrot and are willing to share their opinions of its nourishment of aviation safety and efficient use of time.
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