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Most piston engine aircraft in the country require, by regulation, 100LL. Oil companies and the FAA have been working for years to develop a replacement and cam

by dpe82 6y ago

Most piston engine aircraft in the country require, by regulation, 100LL. Oil companies and the FAA have been working for years to develop a replacement and came very close a couple years ago, but since the FAA strongly favors safety and reliability over almost any other consideration it takes a very long time to collect enough data to have confidence a potential replacement is truly equivalent. We have ~80 years of safety data for 100LL. Generally speaking, airports are reluctant to spend money on a second set of tanks, pumps, etc. required during a transition period; though some have - particularly in the midwest where there are a lot of less regulated homebuilt aircraft that can burn alternative fuels. A lot of pilots would love to burn something else. 100LL is relatively nasty and builds up in engines, shortening their life. It's even actively discouraged to burn 100LL in some more modern small aircraft engines like the Rotax 912 and pilots like myself who run that engine look for non-leaded fuel whenever practical because it's healthier for the engine. But well maintained aircraft last just about forever and the legacy fleet is absolutely enormous.

perl4ever 6y ago
"...it takes a very long time to collect enough data to have confidence a potential replacement is truly equivalent. We have ~80 years of safety data for 100LL" It sounds odd to put it this way, because leaded gasoline started being phased out over 40 years ago. In an alternate universe, we would now have 40 years of safety data for unleaded and for leaded.
- labcomputer 6y ago
  > we would now have 40 years of safety data for unleaded and for leaded. When lead was banned in auto gas, it was replaced by MTBE, which itself was banned in most states by 2007. The alternative to MTBE is Ethanol, which is currently used in auto gas. But Ethanol is incompatible with aircraft because it is corrosive to aluminum (and tends to cause more serious vapor-lock problems in fuel lines). In other words, there's no widely-used blend of fuel that could even potentially have 40 years of safety data. Pilots are already used to paying a lot for fuel (more than auto gas), so there's money at stake if someone can come up with an unleaded alternative. It's just that someone has to invent that safe alternative first. On top of that, fuel is a particularly sensitive issue to the FAA because fuel and engine malfunctions are currently the 3rd and 4th leading causes of aircraft accidents (and this is after the FAA has spent decades on safety programs to reduce fuel-related accidents).
  - userbinator 6y ago
    But Ethanol is incompatible with aircraft because it is corrosive to aluminum (and tends to cause more serious vapor-lock problems in fuel lines). Incidentally, this is also an issue with small engines in things like garden equipment --- the ethanol tends to degrade plastics over time too.
  - perl4ever 6y ago
    I was generally aware of MTBE, but I didn't know it was universal since the 70s nor necessary for all grades of fuel. What about iso-octane? Also, I happen to have a car from the 80s and in looking for information about the consequences of using fuel with ethanol, some say it can be a problem while other people say at that point in time it was designed to handle it. So I'm not clear on what diversity there was in the types of fuel available over time.
    - labcomputer 6y ago
      > nor necessary for all grades of fuel. That's moving the goalposts. Piston airplane engines typically (but not universally) have high compression ratios, so they require fuel with a high octane rating. In fact, the only avgas that contains lead today is 100LL (100 octane, low lead). If you want to have a discussion about lead in avgas, you're having a discussion specifically about 100 octane fuel. > What about iso-octane? Definitionally, 100 octane fuel has anti-knock properties similar to 100% iso-octane. You may be able to make an approximately-100% iso-octane blend for lab tests, but it's not really possible to manufacture it in commercial quantities. Keep in mind, "premium" auto gas is usually less than 93 octane, and even that has ethanol.
- tjohns 6y ago
  The problem is there hasn't been a suitable 100-octane unleaded replacement until very recently (see: G100UL or UL102), and lower octane fuels cause detonation. Last I checked, how well the replacements perform is still an open question. Everyone in aviation wants to get off 100LL fuel, we're just waiting for the FAA to certify one of the replacements as safe.
pjc50 6y ago
We have safety data for leaded fuel .. that says it's a neurotoxin.
- raverbashing 6y ago
  Of course But in aviation you're not only worried about the knowns, but also the unknowns. Example: JAL 123, BA 38, TWA 800 and other cases where you believed things to be safe but in reality they were a ticking time bomb and/or would trigger in very weird conditions.
- dpe82 6y ago
  We also know that 100LL is shelf-stable for years and is compatible and safe (from the perspective of those riding in the plane) to use with just about every piston aircraft engine in existence. We don't yet have enough data to know if that's the case for the potential replacements. Automotive gasoline is too low-octane and not stable enough to be used most aircraft, which for some aircraft results in engine failure in flight. There are ongoing efforts to develop an alternative aviation fuel blend, but as I mentioned previously - this takes time. A couple years ago we got close to having an approved alternative - Swift Fuel's UL94. However as an example for why this is hard: one of the objections to that fuel was that it didn't weigh the same as 100LL, meaning its use would alter weight and balance designs of the aircraft that use it. For most airplanes that's not a big deal, for some it is. We have 80 years of aircraft flying around designed more or less around the characteristics of one specific fuel blend and most of those aircraft have decades of life left in them. We all want to get off 100LL, but we also don't want aircraft falling out of the sky as a result.

by dpe82 6y ago

perl4ever 6y ago

"...it takes a very long time to collect enough data to have confidence a potential replacement is truly equivalent. We have ~80 years of safety data for 100LL" It sounds odd to put it this way, because leaded gasoline started being phased out over 40 years ago. In an alternate universe, we would now have 40 years of safety data for unleaded and for leaded.

labcomputer 6y ago
> we would now have 40 years of safety data for unleaded and for leaded. When lead was banned in auto gas, it was replaced by MTBE, which itself was banned in most states by 2007. The alternative to MTBE is Ethanol, which is currently used in auto gas. But Ethanol is incompatible with aircraft because it is corrosive to aluminum (and tends to cause more serious vapor-lock problems in fuel lines). In other words, there's no widely-used blend of fuel that could even potentially have 40 years of safety data. Pilots are already used to paying a lot for fuel (more than auto gas), so there's money at stake if someone can come up with an unleaded alternative. It's just that someone has to invent that safe alternative first. On top of that, fuel is a particularly sensitive issue to the FAA because fuel and engine malfunctions are currently the 3rd and 4th leading causes of aircraft accidents (and this is after the FAA has spent decades on safety programs to reduce fuel-related accidents).
- userbinator 6y ago
  But Ethanol is incompatible with aircraft because it is corrosive to aluminum (and tends to cause more serious vapor-lock problems in fuel lines). Incidentally, this is also an issue with small engines in things like garden equipment --- the ethanol tends to degrade plastics over time too.
- perl4ever 6y ago
  I was generally aware of MTBE, but I didn't know it was universal since the 70s nor necessary for all grades of fuel. What about iso-octane? Also, I happen to have a car from the 80s and in looking for information about the consequences of using fuel with ethanol, some say it can be a problem while other people say at that point in time it was designed to handle it. So I'm not clear on what diversity there was in the types of fuel available over time.
  - labcomputer 6y ago
    > nor necessary for all grades of fuel. That's moving the goalposts. Piston airplane engines typically (but not universally) have high compression ratios, so they require fuel with a high octane rating. In fact, the only avgas that contains lead today is 100LL (100 octane, low lead). If you want to have a discussion about lead in avgas, you're having a discussion specifically about 100 octane fuel. > What about iso-octane? Definitionally, 100 octane fuel has anti-knock properties similar to 100% iso-octane. You may be able to make an approximately-100% iso-octane blend for lab tests, but it's not really possible to manufacture it in commercial quantities. Keep in mind, "premium" auto gas is usually less than 93 octane, and even that has ethanol.
tjohns 6y ago
The problem is there hasn't been a suitable 100-octane unleaded replacement until very recently (see: G100UL or UL102), and lower octane fuels cause detonation. Last I checked, how well the replacements perform is still an open question. Everyone in aviation wants to get off 100LL fuel, we're just waiting for the FAA to certify one of the replacements as safe.

pjc50 6y ago

We have safety data for leaded fuel .. that says it's a neurotoxin.

raverbashing 6y ago
Of course But in aviation you're not only worried about the knowns, but also the unknowns. Example: JAL 123, BA 38, TWA 800 and other cases where you believed things to be safe but in reality they were a ticking time bomb and/or would trigger in very weird conditions.
dpe82 6y ago
We also know that 100LL is shelf-stable for years and is compatible and safe (from the perspective of those riding in the plane) to use with just about every piston aircraft engine in existence. We don't yet have enough data to know if that's the case for the potential replacements. Automotive gasoline is too low-octane and not stable enough to be used most aircraft, which for some aircraft results in engine failure in flight. There are ongoing efforts to develop an alternative aviation fuel blend, but as I mentioned previously - this takes time. A couple years ago we got close to having an approved alternative - Swift Fuel's UL94. However as an example for why this is hard: one of the objections to that fuel was that it didn't weigh the same as 100LL, meaning its use would alter weight and balance designs of the aircraft that use it. For most airplanes that's not a big deal, for some it is. We have 80 years of aircraft flying around designed more or less around the characteristics of one specific fuel blend and most of those aircraft have decades of life left in them. We all want to get off 100LL, but we also don't want aircraft falling out of the sky as a result.