When I review accident reports for the Used Aircraft Guide, Im struck by how often pilots mismanage the fuel system. Usually its running one tank dry and not figuring out how to get fuel flowing to the engine from a tank that has fuel. From time to time a pilot pumps fuel overboard because he doesnt understand that on a fuel-injected engine, fuel and fuel vapor is returned from the engine-driven fuel pump to one of the fuel tanks.
Some years ago I was taking an IPC and FR in a Piper Aztec. A few minutes into the climb, I shut off the aux pumps, one at a time. A few seconds later, one engine quit. I turned the pumps back on and the engine restarted. After leveling off and setting low cruise power, I tried turning off the pumps again, and found that the left engine was the problem. It would run fine with the aux pump on; not at all with it off.
When we broke down the 100 most recent P210 accidents, 24 engine/mechanical events topped the list-a rate consistent with other big-bore singles. Of the engine failures, a third were due to improper maintenance, including everything from the wrong bolt torque to use of non-aviation hoses for the turbocharger oil supply and return lines. In that case, the hoses developed numerous leaks, spraying oil throughout the engine room, leading to an inflight fire.
Last winter we reported on the CIES digital fuel sender retrofit for earlier Cirrus models. To recap, the modification is intended to better the accuracy of the original analog float-type fuel quantity senders used in first and second generation SR20 and SR22 aircraft.
The preliminary NTSB report for a parachute-deployed Cirrus SR22 wreck says, in part, “Initial examination of the airplane by an FAA inspector did not reveal any visible fuel in the airplane’s fuel tanks, nor were there any indications of a fuel spill at the accident site. After the airplane was recovered, approximately 26 ounces of fuel was drained from the fuel system.”
While the long-awaited unleaded replacement for 100LL might not quite be ready for the fuel farm, as of early December 2013, it looked to be at least hovering over the horizon. Shell surprised the industry with a late-in-the-year announcement that it has developed an unleaded 100-octane fuel that it intends to submit to the FAA’s fuel approval process.
We’ve been watching and reporting on the progress toward a functional unleaded replacement for 100LL avgas for nearly 30 years. Boiled down, that replacement will have to do three things: 1) meet detonation margins, 2) meet material compatibility requirements—not attack any of the components of existing aircraft fuel systems and the fuel transport and storage, and 3) meet economic realities. That is, sell for a price near that of 100LL. The FAA and private industry have been working the replacement fuel issue for about three decades, spending millions on studies in an attempt to find a fuel that would work. Although the economics are unproven, there are now at least two potential replacement fuels in the U.S. SwiftFuel 100SF has undergone ground testing and has done some flight testing, although not yet on an FAA-approved flight testing program.
Back in 1996, when General Aviation Modifications, Inc., (GAMI) of Ada, Oklahoma, announced that it had developed tuned fuel injectors called GAMIjectors, we were skeptical of claims that these gadgets made the engine smoother and more economical through lean of peak EGT (LOP) operation. After all, we’d seen our share of bolt-on engine devices that promised to enhance engine performance, longevity and cut fuel use than we liked to recall. Few if them worked. But GAMI was persistent and it published detailed engine operational data which helped sell the product to a pilot community accustomed to “trust-us, it-works” marketing. GAMIjectors developed a strong following, with more than 1000 selling in the first year. Loyal acolytes praised them to the skies, insisting that they were burning less fuel and their engines were running cooler. A devoted core of skeptics took the opposite view, arguing that owners were going to burn up their engines, cylinder life would be measured in double digits and the engine manufacturers would deny warranty claims on modified engines.
After months of back-and-forth meetings with industry players, the FAA finally seems to have settled on an unleaded avgas transition plan that foresees an 11-year timeline and a strong central role for the FAA in testing and certifying fuels. The agency is also recommending the formation of another government/industry committee to oversee how an avgas replacement fuel—if one ever emerges—finds its way to the field.
One of the unfortunate side effects of slow aircraft sales has been an erosion in the maintenance base. Many smaller shops have disappeared and some of those that remain are either losing the ability to do some kinds of work or are just declining to accept it.One maintenance procedure on the chopping block has been the resealing or repair of wet wing fuel tanks, especially in Mooneys, but in a few other models as well. At best, repairing weeping wet-wing tanks is a dark art, at worst, it’s something some owners say they have to have done several times to stop the leaks, if even the leaks can be stopped.
The reoccurring head-shaker in the NTSB reports is the pilot who wrecks a perfectly functioning aircraft because of mismanaged fuel burn. But the truth is that eventually even the most conservative gets tempted to push the envelope of fuel endurance. That’s why a fuel computer installation makes sense, and there’s one for every budget. Speaking of budget, fuel computers assist with miserly leaning—a real plus in the world of pricey low lead.
The two leading contenders to replace 100LL with an unleaded equivalent, Swift Enterprises Swift Fuel and General Aviation Modification Inc.s G100UL, both say their fuel will cost more than 100LL. But how much more? We took our own run at it based on what weve been able to glean about these fuels from patent filings and information from the two companies. According to its patent filings and published FAA test data, Swift is a binary blend of mesitylene (also known as trimethylbenzene) and isopentane. Mesitylene is a bit of an exotic, used for specialized solvents and industrial processes. Its a terrific octane enhancer, but so rare in industy that no commodity prices are available. One supplier we contacted sells it for $53 a gallon, a price thats obviously unsustainable for fuel use.
