Except they can't, since there is no approved alternative.
The other problem is that even planes that can run unleaded gas often don't, because it's not available at the airport. Avgas is a tiny market and because of costs most FBOs can't or won't set up another fuel delivery infrastructure to run two fuels over some short transition period.
Because of this, an additional requirement on a replacement is also that it be safely mixable with 100LL in any ratio, because during the transition period this will happen as people fly from airports where it exists to airports where it doesn't.
This problem is being solved (https://www.faa.gov/about/initiatives/avgas/).
There's an increasing number of diesel engines for GA aircraft, and supplemental type certificates to retrofit them into the same. If 100LL got more expensive, you'd see more people opting for the diesels when an engine reaches the end of its life.
e.g. http://www.continentaldiesel.com/typo3/fileadmin/_centurion/...
Yes, it'd be really cool to end up with a lower-lead fuel that's safely combined with 100LL. That's been "imminent" for the last 25 years.
The poster above advocates for a "rip off the band-aid" approach. GA advocates for a gradual, painless transition that, in practice, will never happen. Surely there's some middle ground?
Data seems to imply that the diesel engine lifecycle cost is slightly better now than conventional engines, so electing for a diesel replacement instead of a conventional engine overhaul can make sense... but it's a razor thin difference.
If you made leaded fuels more expensive-- more airfields are going to want to move to UL94, and more people at overhaul time are going to go the diesel path, and the problem will gradually get better.
There's not going to be one single tidy drop-in solution for the entire market. That's why we should tax leaded fuels, and everyone can pick the appropriate solution for them. Some will pick diesel conversions. Some airfields will go 94UL and people will purchase STCs. Presumably some other people will take other paths. And those with the hardest time transitioning can instead pay the tax and burn leaded fuel, still.
3 years is also basically a second at the speeds GA changes at.
Swift charges $100 for a STC, and has coverage of two thirds of the GA fleet.
Really, all that needs to happen is an airport needs to decide that lead free is important to them and they'll pay the premium for Swift's fuel.
But if you taxed the crap out of lead-containing fuels, I suspect more would be interested...
That sounds pretty great actually, for such a simple solution.
If you threw a few billion more at leaded paint remediation, I think you'd make much more of a difference. I think the aviation lead problem should get fixed, but because it's such a small part of the overall problem it makes sense to take a graduated approach instead of giving GA businesses the death penalty. Tax leaded aviation fuels, and use the proceeds to pay for leaded paint remediation.
Graduated approach ignores the decades that have ALREADY been provided as an exception to the lead fuel rules that apply everywhere else - it's already been graduated.
Start at 10% with a commitment to ratchet it up by 4% per year or something. That's enough to start an immediate reduction without destroying the industry.
If you're making choices about engine overhaul now for an overhaul that will last you 7-8 years of light use, fuel costing 40% more at the end of that overhaul will definitely get your attention.
> it's already been graduated.
Doing nothing for decades when it was impossible; and then doing nothing for a decade or two when transition became possible; and then pushing the industry off the cliff is not graduated.
Perhaps that's wrong, but I distinctly remember the statistic and it stuck with me.
A measure like this may be reasonable.
But C/D totals the entire piston aircraft fleet-- $50B+ of capital equip, plus the whole infrastructure and industry around it-- for only a very moderate change in lead exposure. Best estimates I've seen is that this would lower the total population burden from lead by well under 5%.
Much more sane, IMO, to put in a progressively escalating tax on leaded aviation fuels that over time becomes steep. Then airplanes can gradually transition as overhauls become due, etc, as the pressure from operating costs mounts. Presumably those burning the most fuel would transition first, and an industry capable of retrofitting a few percent of the aircraft per year would spring up.