Because they needed to be completely sure that they had a replacement fuel that wouldn't start making planes fall out of the sky.

That's the excuse. Basically the real reason is that they only care about safety of the planes, not of the people handling the fuel (e.g. pilots, ground staff), or breathing the toxic fumes (everybody on or near an airport). So, they only care about safety when it is a very narrowly scoped notion of that concept.

Bureaucracies are weird like that. This is fundamentally not about people's safety but about covering their own safety (i.e. ass coverage). The problem is not something bad might happen but that they'd be held accountable for it.

Never mind that something bad has been known to happen for the last half century or so that they are not being held accountable for. People actually get sick and die because of leaded fuel but it's not their problem. And never mind that the bad thing that might happen is basically some ancient engines not running that well with unleaded fuel. That's why certification processes exist for engines. You can test this and decide to not certify certain engines for unleaded fuel. Ensuring people fly around with certified engines definitely is their problem. Any modern engine is basically certified for unleaded fuel already.

I mean, planes falling out of the sky is a fairly significant safety issue. "Safety of the plane" is misleading if there's people inside the planes lol.

Some piston engines are really high compression and it's hard to prevent knocking without leaded fuel.

And to be clear, "knocking" means engine detonation, which very quickly leads to catastrophic engine failure. Which is something that you don't want while in flight.

Until now, the only alternative was to fly a turbine-powered aircraft that can run on Jet-A. The problem with those is that turbines are far too expensive, and terribly inefficient at low altitude - both of which have kept them out of reach for most of general aviation.

Admittedly Turboprops can be somewhat more efficent at lower altitudes than turbojet and turbofan engines. But still not terribly efficient at say sightseeing or cropdusting altitudes, and they are still a lot more expensive than avgas engines (and that is not even accounting for the fact that the aircraft designed to use them are bigger and more expensive than many avgas based prop planes).

Oh please. Single engine planes are far more than toys for rich people. General aviation is training new airline pilots, medical flights, aerial surveying, charter flights otherwise inaccessible areas, and a method to fly supplies to areas during emergencies. This level of ignorance is extremely frustrating.

Yeah, but what is the proportion of these flights relative to rich-people hobby flights? That matters.

Quick napkin math here...

The estimate is that about 65% of general aviation traffic is related to "business and public services". [1][2] The other 35% is personal in nature. From that, about 22% is flight instruction for new pilots - most of whom are trying to get into the airlines. [3]

So that would mean about 13% of general aviation is recreational.

(Also, for what it's worth, many general aviation pilots I know aren't rich by any stretch.)

[1]: https://download.aopa.org/hr/Report_on_General_Aviation_Tren...

[2]: https://www.govinfo.gov/content/pkg/GAOREPORTS-GAO-01-916/ht...

[3]: http://www.dviaviation.com/files/45181042.pdf

Maybe in more rural areas. But are you really going to tell me that 65% of general aviation traffic in LA, SF, NYC,..etc is related to 'business and public services'. Do private jets for executives count as for 'business services'.

The numbers I gave were national averages for the US. Of course those numbers will vary by location.

That said... you'd be surprised how many flights out of the small GA airports in big cities aren't personal flights. Air ambulance, news crews, law enforcement, firefighting (usually more on the periphery of the city), utility companies doing inspections, and aerial photography all tend to operate from these locations.

On the other hand, I'd certainly expect the number of flight school operations to be higher in areas with a large population.

Rural areas are more likely to be recreational plus agricultural, due to proximity of sophisticated clients in big cities.

If someone's traveling to/from a work purpose, why wouldn't a corporate jet flight be categorized as a business service?

Taking that same jet to ski in Tahoe? Personal/recreational. Taking it to a business meeting with a customer/prospect? Business.

A lot of what people think as "Silicon Valley" is actually centered around general aviation industry - for example San Mateo County at least in 2015 had majority share if its economy based on aviation, with majority of it being GA

Going to need a source for that claim - generally the largest industry in a given area is government, then hospitals or schools, then some specific niche. I don't think there's any airplane manufacture in NorCal anyway - this would be a bit more believable about Wichita.

Because you're looking for "airplane manufacturer" and possibly large one. Though for example just a stolen throw from Google Mountain View campus you have Northrop and Lockheed-Martin.

I can't find the original webpage after 7 years, but the source was San Mateo County page related to county-owned airports, and it included all sorts of aviation industry (both flying and ground side)

Every single airline pilot has had to train in a small piston aircraft that runs on leaded fuel. There simply has been no alternative if we want to have a supply of trained pilots.

Not to mention medivac flights, overnight delivery of many laboratory medical specimens from doctors' offices, law enforcement, high-quality aerial imagery in maps apps, farming, access to rural communities in areas like Alaska...

Cessna's are used to access small regions in many countries can't even be accessed if it wasn't for a Cessna due to lack of funds, places that take up to 3 days by motorcycle. The fuel mix is basically copied worldover.

I believe the typical American who sees the upper middle class, the same way the rest of the world sees america as.

All the piston engine aviation in my general vicinity is commercial paid transporting. I live in an area with a lot of islands.

I'm sure that they train wide-body aircraft pilots on the multi-million dollar planes rather than something cheaper

Usually they start on a plane like Cessna 152 that is older hab their parents. Even military pilots start like that, just tend to switch for newer turboprops sooner.

For reference - considerable portion (possibly even majority, especially if you don't count USA due to different licensing) of airline pilots will have their first jet/turboprop experience when they will be training on airliner after getting their "frozen ATPL". In one airline it was common for chief of training to give every new trainee a copy of MSFS 2004 with professional addon for the first plane you'd graduate for, and the better trainees used that to become familiar with plane - cause usually the largest previous plane they flew would be a small twin piston plane like Piper Seneca.

Airline pilots in the US need 1500 hours of flight time to earn their ATP (airline transport pilot) certificate.

For non-military pilots, most of those hours come from general aviation aircraft.