How should aircraft owners prepare for the switchover from 100LL to its replacement? In a previous post, I stated that if — or when — 100LL goes away, the only fuel that will be universally available for general aviation will be one that is chemically very similar to 100LL, but without the lead, and an octane rating of around 94.
If you have a low compression ratio engine qualified on 80/87 or mid-90 octane fuels, you really do not need to change anything. The only concern is that when the engine is overhauled and broken in on straight unleaded fuel, there maybe a problem with exhaust valve recession. If I owned one of these aircraft, I would wait until 100LL is about to go away and then buy a barrel. Then after I had my engine overhauled, I would add a gallon or so of 100LL to each fill-up during the break-in process. The only problem here is that it may not be legal to store a drum of fuel in your garage, so you will need to look into the legal and insurance aspects of storage or find a place where it can be stored.
If you have a high compression ratio engine, you have a more difficult decision to make. This is like trying to solve an algebra problem with three equations and four or more unknowns. The good news is that if you have a common Lycoming or TCM engine, you can be confident they will develop a system to qualify most of their engines on the new fuel. This will probably also be true of common engines like the P&W R-2000, R-2800 engines and several others. The bad news is that the new systems may be expensive and may require some de-rating of the engine.
Another factor to consider is that we do not know when — or if — 100LL will go away (remember there is an election this year and another big one in 2012). So what is the best plan? A lot depends on how many hours are on your engine, what kind of condition it is in, and how much you fly. If you have a low time engine, just keep flying and see what happens. The longer you can delay the decision, the more information you will have when you finally need to do something.
If you have a mid or high time engine, I would baby it as long as possible. If you do need an overhaul, check with the manufacturer or your rebuilder to see if there is a system or modification that can be fitted to allow operation on a 94 octane fuel.
If you have a rare aircraft with a high compression ratio engine or an engine where the manufacturer is no longer in business, you have the same concerns as the previous owners, but with another variable to consider. For low and mid time engines, just keep flying. For high time engines, I would start doing some homework and looking for STCs to replace your engine with a more common model or brand that will probably be able to be modified to run on a new fuel. However, there will be a few models or cases for which there is no good option. For example if you own a DC-3 with an 1820 CW engine, you may need to consider replacing the aircraft.
The best advice is to procrastinate. Wait as long as possible. During the wait, spend time learning about your options and the cost and advantages and disadvantages of each option. The more you know, the better your chances of making a good decision when the time comes.
But remember, when 100LL is finally done away with, there is going to be a mad scramble for new engines and systems, so timing is going to be critical.
Ben Visser is an aviation fuels and lubricants expert who spent 33 years with Shell Oil. He has been a private pilot since 1985. You can contact him at Visser@GeneralAviationNews.com.