In recent months many light aviation enthusiasts have been asking about progress on FAA’s proposed rewrite of the Light-Sport Aircraft regulations. Following a lengthy teleconference in 2019, the Light Aircraft Manufacturers Association is pleased to provide a further update for the agency’s work on MOSAIC, or Modernization of Special Airworthiness Certification. Here is our earlier article on this subject.
This update is one of a continuing series. As time passes and FAA progresses toward its goal — of issuing a NPRM, Notice of Proposed Rule Making — LAMA requests a teleconference or in-person visit to learn the rule writers’ latest concepts and language decisions.
This progress reports identifies new discoveries and clarifies previous statements that may now be better understood.
Some Key Messages
FAA is moving forward on the rulemaking project yet everything remains in progress while the agency gathers internal assessments. What follows is as accurate as possible at this time but changes will occur.
Nor can FAA personnel guarantee that current proposals, as discussed in this progress report, will appear the NPRM.
LAMA will continue asking FAA for greater clarification until the agency enters “ex parte,” a quiet period when they can no longer discuss the project. That period remains in the future at this time.
Common Question — When?
Almost everyone wants to know when this is coming, especially after an early (incorrect) statement that the change was coming by a date now well in the past. MOSAIC is not coming soon. Even though rule writers are progressing, this will take many more months.
FAA generally agreed with our back-calendar estimate that the NPRM may be forthcoming in late 2021 or early 2022. This was based on the perceived amount of work remaining.
The NPRM must be released about that time to allow FAA to have a finished regulation by the end of 2023. The 2023 date is a deadline set by the U.S. Congress as part of approving FAA’s budget — called the FAA Reauthorization Act of 2018.
While changes in wording are inevitable, it is the big changes on which we will focus here. Please remember, MOSAIC encompasses more than LSA, but LAMA’s focus remains entirely on matters of interest to the LSA producer community, to other businesses that serve that market, and to the recreational pilot community.
FAA functions under the Department of Transportation. DOT approved this project for rulemaking under its Fall 2019 Unified Rulemaking Agenda. FAA advised that interested parties can go to this link and enter the following code in the field labeled “RIN” — 2120-AL50
This action by the Department of Transportation does not mean an NPRM will follow soon.
FAA Proposals Under Consideration
What LAMA Originally Requested:
• SLSA (fully built, not kit) Gyroplanes
• Aerial Work / Commercial Use
• Electric Propulsion
• Single Lever Control (in-flight adjustable prop)
More Changes Under Consideration (to present-day LSA):
• Increased weight (see below)
• Four seats
• Retractable gear
• Maximum stall speed
• Capped horsepower
• Increased airspeed
• Hybrid propulsion
Questions raised since LAMA’s last progress report:
• Will Sport Pilot-certificate holders be allowed to fly four seaters?
• Can Sport Pilots do aerial work or commercial use flying?
• What changes will be made to LSA mechanics, specifically LSR-M?
• What about turbine powerplants?
FAA’s Goals Remain the Same:
• “LSA of the future should remain “safe, simple, and easy to fly.”
• “We want to be less prescriptive …to leave more for industry to decide.”
• “LSA has been a successful development” (LSA experience was key in the rewrite of Part 23).
• FAA sees “opportunities to safely expand this sector of aviation while decreasing burden on the industry” and seeks to “make this a positive for industry.”
More on Weight Increase
— Power Index —
Perhaps the greatest amount of interest focuses on proposed weight changes.
Repeating, FAA will not specify a particular aircraft weight (as it does not do so for Part 23 certified aircraft of today). Instead, FAA may employ something called the Power Index (basically a formula) to determine the size of an aircraft. Nonetheless, aircraft weight will increase, perhaps rather dramatically. Indeed, weight may rise to 3,000 pounds (1,360 kilograms).
If FAA will not set a specific weight, how do we know weight will increase and what can provide wise limits?
FAA may use “Power Index.” (Words like “may” are frequently used because this regulation is only a proposal at this time, however, FAA personnel have seen what we are reporting here and offered clarifying suggestions to our language.) For those more technically oriented, at the bottom of this post is an engineering analysis by Powered Sport Flying publisher — and engineer, plus LAMA board of directors member — Roy Beisswenger.
A number of pilots and aircraft developers, surprised by the large potential increase in weight, have wondered what will keep these aircraft from becoming very large. If FAA will not specify a weight, what will prevent LSA 2023 from becoming heavier aircraft beyond the scope of LSA and the Sport Pilot certificate?
In addition to the Power Index concept, here are methods to describe and constrain unlimited weight as learned in LAMA’s last conference with FAA:
- 200 horsepower hard point — As with other parts, this is not fully determined yet but 200 horsepower may be a cap
- 50 knot stall — presumably with lift devices; such as flaps or leading edge devices deployed
- 1.2 Power Index (still being devised; please do not assume this is a final value FAA will accept for rule making) — See “TECH TALK” at the end of this article
- Thus, aircraft that fit the criteria will likely weigh less than 3,000 pounds (≈1365 kilograms)
More Questions Answered
Airspeeds — Referring to maximum horizontal and never-to-exceed speeds (Vh and Vne), FAA said, “These may be higher than in the current rule, but will still be limited.”
At present, FAA has given no specifics on speed, but reading between the lines, LAMA expects maximum flight speeds could be 140-150 knots.
Pilot & Mechanic Certificates — Related to FAA’s ultimate decisions about what a Sport Pilot is allowed to fly and for what flight missions, what about mechanics? Specifically, what changes are coming?
FAA is examining what type of mechanics (LSR-M or A&P) can do what kind of work on specific systems of aircraft.
As an example, will a LSR-M be allowed to work on an in-flight adjustable prop, retractable landing gear, or electric/hybrid propulsion systems?
These questions are still being evaluated, but FAA acknowledges that the issue may work itself out through the industry consensus standards process as it has for similar maintenance issues.
FAA General Comments on
Sport Pilot and Mechanic Questions
Most of LAMA’s work has been with the Aircraft Certification division of the rule writing staff. That focus is of keenest interest to those designing and manufacturing aircraft.
However, matters regarding operation of LSA falls under Flight Standards, the people who manage Part 61 (airmen certification) and Part 65 (mechanics).
Because MOSAIC is such a wide-ranging rule, various other FAA departments will address areas of their expertise. Note that this is a central reason why the regulation will take all of the next two years to fully develop.
FAA is evaluating what type of mechanics (LSR-M or A&P) can do what kind of work on specific systems of aircraft but maintain their focus on the consensus standards process to sort out maintenance issues.
This report is current and was reviewed in March 2020. It is as accurate as we can make it at this time, but it bears repeating one more time: this is a regulation still in process. Many changes may occur. Despite that caveat, the report shows where FAA is generally headed with MOSAIC. Keep your seat belts fastened!
T E C H T A L K
“Power Index Explored More Deeply”
by Roy Beisswenger
The FAA is loath to have prescriptive weight limits in MOSAIC. Instead, they are working with other kinds of formulae to describe limits without specifically calling out the actual weight of the aircraft.
One idea floated within the FAA was to use a calculation called a Power Index or Ip. It is described by the formula:
Ip = {(W/S)/(W/P)}1/3, where:
W = maximum takeoff weight (MTOW) in pounds,
S = wing area in square feet,
P = maximum rated power in horsepower at sea level and standard temperature.
If the Ip value worked out to be less than 1.2, it was proposed at one point that the aircraft would fit within the definition of a Light Sport Aircraft. This formula would only work for airplanes, not applying to rotorcraft, powered parachutes and weight shift control trikes.
Earlier, an Excel spreadsheet escaped from the FAA that allowed a user to plug in different values for maximum gross weight, wing area, and maximum horsepower and it would instantly calculate the Power Index value.
Industry people played around with the spreadsheet, putting in different values. Soon they found that no matter what value they put in for the weight of an aircraft, it never changed the Ip. This became a topic of vigorous discussion.
However, there is a very simple explanation for the lack of sensitivity of the formula to weight. And in fact, the explanation comes from algebraically simplifying the equation itself. When you do that, you find that even though weight appears in the original equation, it quickly drops out since it is in both the numerator and the denominator.
So let’s start with the original equation:
Ip = {(W/S)/(W/P)}1/3
If you divide by a fraction, that means that you are multiplying by the inverse of that fraction. (The inverse meaning that you switch the numerator and denominator.) Doing that, you get this:
Ip = {(W/S) * (P/W)}1/3
That means that the weight is being divided by the weight, which works out to 1. The equation then solves to:
Ip = {P/S}1/3
That means that weight has no influence on the Power Index. Instead, the power index is essentially a ratio between the power of the engine in horsepower and the size of the wing.
Now that the equation is simplified, we can do something else interesting. Let’s solve for Max Power:
Ip = {P/S}1/3
Ip³ = P/S
Ip³ * S = P
In other words, the larger the wing, the more power you can use. That certainly makes sense from a safety point of view.
Solving for Max Wing Size:
S = P/Ip³
That says the same thing. The more power you have, the larger your wings need to be. Let’s see what that looks like with some real world numbers. If you have a 100-hp motor (for example, the very common 100-hp Rotax 912ULS) then for an Ip of 1.2, your smallest possible wing size is:
S = 100/1.4³ = 57.87 square feet
As an example, the wing area of a Flight Design CTSW is 107.0 square feet indicating that it is considerably larger than the minimum 57.87 square feet defined by an Ip of 1.2.
This probably means that an Ip of 1.2 is unlikely to be the only way that a light sport airplane will be defined with MOSAIC. Perhaps a smaller number will be used or perhaps it is only going to be one way of defining a light sport airplane (see above constraints). Perhaps a minimum stall speed (above) may also be included. That way a maximum gross weight won’t be cooked directly into the regulations, but will still end up being a consideration for airplane designers.
