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If your aircraft isn’t airworthy but you need to fly it anyway, here’s how. As every pilot knows, it’s strictly against the rules to fly an unairworthy aircraft: §91.7   Civil aircraft airworthiness. (a) No person may operate a civil aircraft unless it is in an airworthy condition. (b) The pilot in command of a civil aircraft is responsible for determining whether that aircraft is in condition for safe flight. The pilot in command shall discontinue the flight when unairworthy mechanical, electrical, or structural conditions occur. Now that sounds fine in theory, but sometimes it doesn’t work out so well in practice. Recently, for example, one of my clients managed to decapitate a runway light with his propeller at an airport in Florida that didn’t have any maintenance services on the field. We were able to get an A&P to drive to the decapitation site in a pickup truck and hang a loaner prop on the airplane, but we then needed to fly back to the shop to have the engine removed for a proper post-prop-strike teardown inspection. Another client inadvertently let his airplane “go out of annual” while the airplane was tied down at an airport in southern New Jersey. There […]

The term “damage history” is not well-defined. Here are some thoughts on the subject. One of my clients just had a fancy digital engine monitor installed in his airplane. During the installation, the shop hired to do the work drilled a half-inch hole in a non-structural area of the cabin sidewall to accommodate the OAT probe, then realized that the hole was in the wrong place—the OAT probe wouldn’t fit due to interference—and and had to drill another hole in a more suitable location. The shop fessed up to its mistake, and assured my client that the first hole would be patched and painted so that it would be completely undetectable, and that this would be done at no cost to the client. “Oh my god,” the client said to me in obvious panic, “does this mean that my airplane now has ‘damage history’? What will this do to its resale value?” I get this a lot.  In the past two years, for example, there have been a half-dozen prop strikes among my managed maintenance clientele. All occurred either with the gear down-and-locked or down-and-welded, and in all cases but one there was no airframe damage whatsoever. A few of […]

The care and feeding of aircraft batteries. Last month, in Part 1 of this article, we discussed the construction, chemistry, types and characteristics of lead-acid aircraft batteries. This month, we’ll talk about the care and feeding of those batteries, including charging and discharging, conditioning, capacity testing, and deciding when a battery should be retired and replaced. Charging Charging a lead-acid battery involves three phases: (1) a constant-current phase during which charging voltage gradually increases; (2) a constant-voltage phase during which charging current gradually tapers off to very low levels as the battery approaches its fully-charged state; and (3) a float (or trickle) charge phase that maintains the battery in its fully-charged condition and offsets the battery’s natural tendency to self-discharge. Although this is a fairly complicated procedure, we now have very reasonably priced microprocessor-controlled battery charges that can perform this automatically. Keep in mind, however, that your aircraft’s charging system is strictly a constant-voltage charger, which is why it’s a very bad idea to fly with a deeply discharged battery (e.g., after maintenance or a GPU start). The aircraft’s charging system will charge a deeply discharged battery at an excessive rate (because it is a “dumb” charger without current limiting), […]

More about what aircraft owners should know about piston aircraft engine oil. Last month, we began our discussion of piston aircraft engine oil by discussing the types and properties of the various kinds of engine oil available, and I offered some thoughts about which oils I prefer and why. This month, I’ll continue the discussion by addressing oil additives, oil consumption, oil level, oil-change intervals, oil filter inspection and oil analysis. Aftermarket additives For as long as I can remember, there have been pitchmen promoting “miracle in a can” oil additives that claim to eliminate friction and wear, increase fuel economy, improve your landings, raise your IQ, and rescue your marriage. The granddaddy of these is Marvel Mystery Oil. Folks have been pouring this red, sweet-smelling stuff into aircraft engines for more than 80 years. It was developed in 1923 by Burt Pierce, the inventor of the Marvel carburetor, and was intended as a fuel additive to clean carburetor jets. Why folks started using as an oil additive escapes me. The name “mystery oil” came from the fact that Burt Pierce refused to divulge its formula. So far as I can tell, MMO doesn’t do any harm if used in […]