The FAA rules that govern certification of “small” airplanes are a mess. Finally, the FAA has begun the lengthy process of trying to change FAR Part 23 so that both the makers of basic piston singles, as well as those designing advanced turbine powered airplanes, can know what to expect when seeking certification.
Not long after the end of World War II, the fundamental airplane certification standards were established by the CAB, the forerunner of the FAA. Rules in CAR 3 set certification standards for airplanes with a maximum takeoff weight of 12,500 pounds or less, while CAR 4 rules governed the certification of heavier airplanes. CAR 3 was for “small” airplanes while CAR 4 covered “large” or “transport” airplanes.
Why the certification standards were divided at 12,500 pounds takeoff weight is unclear. As far as I know, there was no landmark airplane at that weight that would have provided a historic reason to pick 12,500. I’ve often heard that the DC-3, which was certified before CAR 3 and 4 were established, had something to do with the weight break, but the DC-3 can weigh double the 12,500 pounds so that makes no sense.
Whatever the reason for picking 12,500 pounds as the point where small airplanes become large, that weight limit stuck as the rules were rewritten into FAR Part 23 and FAR Part 25 in the 1970s. In general, an airplane in the Part 25 category must have enough redundancy of thrust and systems that it can continue on to a safe landing at an airport after critical failures. Airplanes in Part 23 do not have the same restrictions.
The certification standards were working reasonably well until it became feasible to build light business jets. The earliest civil jets all weighed more than 12,500 pounds maximum, so they naturally went into the CAR 4 or Part 25 transport category. But then Bill Lear created the Learjet 23 and purposefully set the max weight right at 12,500 pounds to remain in the light airplane category.
Lear hoped for a simplified certification standard, but more importantly wanted approval for single-pilot operation of his little jet. It was an automatic that airplanes weighing more than 12,500 pounds needed a crew of at least two pilots. The Learjet 23 did receive certification under the small airplane rules but at the last minute the FAA imposed a special condition requiring two pilots. The follow on Model 24 Learjet, which looks nearly identical to the 23, was recertified in the transport category.
Cessna’s original Citation 500 weighed much less than 12,500 pounds but, because it was a jet, was lumped into Part 25 and also required two pilots. A few years later Cessna build the Citation I-SP that was certified for single-pilot flight because it was a Part 23 “small” airplane, even though the only changes were a transponder ident button on the yoke and requirement for the pilot to use a headset with a boom mic.
So now jets were in Part 23 if they weighed less than 12,500 pounds. But what if a regional turboprop airliner needed to grow to more than 12,500 but couldn’t meet all of the rules of Part 25? The FAA solution was the Commuter category of Part 23 that allowed the Beech 1900, Merlin Metro, and several other airplanes to weigh more than 12,500 pounds.
At first the Commuter category was reserved only for airplanes already certified and in production, not new development projects. New business jets such as the Beech Premier and Citation CJ2 were capped at 12,500 pounds to remain in Part 23. But the weight limit didn’t hold and now several new business jets weighing more than the 12,500-pound standard are certified under Part 23 in the Commuter category.
To certify high-performance jets such as the Citation CJ4 or the Embraer Phenom 300 under Part 23 the FAA creates a huge number of special conditions the airplanes must meet. For example, the jets must meet the same engine failure minimum climb takeoff profile of the large jets, but that is imposed as a special condition on those airplanes and not extended to all airplanes in Part 23.
But the special conditions and the rule tweaking necessary to fit high-performance jets into a certification standard originally designed for piston singles and twins have a way of creeping down into all Part 23 certification projects. It’s really tough for the same people to take the same Part 23 rule and apply it logically to a basic piston single and to a jet designed to cruise at 45,000 feet and 450 knots. What has been happening is that the complexity of the certification process that is necessary for jets has found its way down into the certification of piston airplanes.
I’m not predicting this is the path the FAA’s review of FAR 23 will follow, but I would like to see a third set of rules developed. I think FAR 23 should be overhauled and aimed at piston airplanes and light turboprops, which would satisfy the rule’s original mission. Then there should be a new category created to certify most business jets weighing up to 50,000 pounds or so. And then Part 25 can be the rule for true transport airplanes that are many times larger and more complex than the typical business jet.
The issue is that a 20,000-pound business jet is a very different type of airplane flying a very different mission than an 800,000-pound true transport jet, but they are lumped under the same Part 25 rules. If there were three certification rule categories then they could be appropriate for pistons, business jets, and true transport airplanes.
Who knows what will come from the FAA’s rewrite of Part 23, but if they don’t kick the business jets out of the top end of the rule, there is no hope for simplifying the certification standards for basic pistons at the bottom end of the rule.