Easily Overlooked

By Vic Syracuse, EAA Lifetime 180848

This piece originally ran in Vic’s Checkpoints column in the August 2022 issue of EAA Sport Aviation magazine.

I’m thinking that the loose jam nut plague might be under control, as we rarely see one monthly now. Compare that to multiple instances on several aircraft weekly just a few short years ago. I don’t doubt there are still some out there, and I’d still wager I could find a dozen or more in short order just by walking the flightline at EAA AirVenture Oshkosh and snooping around. I think the campaign worked, as we often hear comments such as “I checked the jam nuts” when customers are dropping off their aircraft for maintenance.

We are seeing some other repeat maintenance issues across the fleet, and I’d like to highlight a couple. These would be the top issues that owners/pilots can address. Some may require corrective action, and some may just require a regular check to see if any action is necessary.

The first one has to do with emergency locator transmitters (ELTs). FAR 91.201 covers the requirements for ELTs, and you should familiarize yourself with it, even if you rent an airplane. I am aware of checkrides and air show participation being stopped due to ELT requirements not being met. I will focus on the three key requirements: location, testing, and batteries.

For you builders, the regulation states that the ELT should be affixed to the airplane as far aft as possible. We see many of them installed in the cockpit, so that is the first no-no.

The next requirement is that every 12 months the ELT must be inspected for proper installation, battery corrosion, operation of the controls, and the presence of a sufficient signal radiated from its antenna. We have seen some ELTs whose batteries have corroded to the point that they have leaked outside of the ELT and caused major corrosion to the aircraft structure.

This is what happens when the batteries are allowed to expire. There is the distinct possibility of the battery leaking and causing airframe corrosion, as seen here.

There are two types of ELTs. The older ones broadcast only on 121.5 MHz, which is in the aviation band. The newer 406 MHz ELTs broadcast on a protected international distress frequency monitored by satellites. Most of us older pilots were trained on the analog 121.5 MHz ELTs, and the test was to activate the switch during the first five minutes of any hour and listen on an aviation radio for no longer than three audible beeps.

The digital 406 MHz should only be tested in accordance with the manufacturer’s instructions, as many of them emit various tones to indicate a pass/fail test. The test should be limited to less than 30 seconds. This will preclude the satellites from receiving a signal from the 406 MHz beacon when it is activated. If the selection to the “ON” position is minimized to 30 seconds or less, there is sufficient time protection to prevent crossing the 50-second time threshold for activating the 406 MHz locator signal. No airborne tests of either type of ELT are allowed.

The last item has to do with the battery. Again, FAR 91.207 provides the guidance. Whenever the transmitter has been in use for more than a cumulative hour, or whenever the battery has reached 50 percent of its useful life, it must be replaced. Most ELTs that require a specific battery usually have a replacement date stamped on the battery and come with a decal to be affixed to the outside of the unit. Some ELTs use D cell batteries. For those, look at the expiration date on the battery and use 50 percent of that for the replacement requirement.

Emergency locator transmitter batteries will usually have a stamped replacement date on them unless they use D cell-type batteries. You should use 50 percent of the expiration date on the D cell. In the case of these examples, only one of them was still within date when checked, with the worst one being replaced in 2014 and expiring in 2018. This was discovered in May 2022.

Here’s why we see the lowly ELT causing us so many problems. First, the replacement date of the battery must be marked on the outside of the transmitter and entered into the aircraft records. Less than half of the amateur-built aircraft we look at meet this requirement. The annual testing requirement should also be entered into the logbook. We make sure this is completed during the annual/condition inspection. However, here’s where it starts to go awry, especially for nonbuilder owners.

Rarely do the battery expiration and annual ELT testing coincide. Some batteries are good for 18 months, which puts them on the half cycle, and others are good for five years, which makes them easy to overlook. Some of the ELT batteries are expensive, so it doesn’t make sense to change them out six months early at the condition inspection. The expiration date entry is made in the logbook, and the owner is reminded, but it is often forgotten about. If batteries are due within a couple of months post condition inspection, we will change them, if available. Supply chain problems have been interesting in this area lately.

If the ELT has a control panel installed on the instrument panel, don’t forget that it has a battery in it as well. We have even seen these installed without a battery in them. Usually, that battery has a 10-year life, but it might make sense to change it at the 50 percent useful life as well.

Don’t forget to install and check the battery in the control panel. We have seen quite a few of these installed without a battery in them.

The ELT checks are often overlooked by new builders, as there isn’t any training on the maintenance portion of aircraft ownership. As a designated airworthiness representative, I require that the ELT entry is made in the logbooks prior to issuing the airworthiness certificate. It ensures it is good for the first year and gives me a chance to address the future requirements.

Many A&P mechanics often forget this requirement as well. The most egregious example lately, which prompted me to finally say something, was an RV that came to our shop for a condition inspection. The last ELT entry was in 2014 when the batteries were replaced. No entries since then, and upon disassembly the battery expiration date was 2018. It is now 2022, and the last four condition inspections were signed off by an A&P.

Another maintenance area in which we consistently see problems is with the oil coolers mounted on the aft cylinder baffling. Our little four-cylinder opposed aircraft engines vibrate quite extensively, especially at startup and shutdown. The cylinders also move quite a bit during flight. Hanging an oil cooler off them without the proper supports will lead to an eventual failure of either the baffling, the cooler, or both. Over the last seven years of seeing 200-300 airplanes per year, we have enough experience to state that the failures seem to all occur within the first 300 hours of operation. High-compression/high-horsepower engines seem to be the worst offenders, probably due to the harder pulses created during the ignition sequence. Low-compression engines, and those with composite or wooden props, seem to have fewer problems. Either way, the oil cooler and the baffling should be checked regularly, perhaps at every oil change as a minimum. Most of the time we see cracks beginning around the nut plates or bolts on the baffling, but occasionally, we see something worse. Recently we had an RV-8 that is used regularly for aerobatics, including lots of spins, in the shop for a condition inspection. The oil cooler had completely separated from the baffling and was hanging by the hoses. For some time after it had separated, it had been beating against the engine mount as well. See the pictures for some ways to beef up the mounting. A quick search of many of the type-specific forums will yield some other solutions as well.

If not caught in time, the mount has the potential to completely fail, as seen here. Partial cause here was also due to improper mounting, as the cooler was not attached to the angle portion of the baffling. The oil cooler banging around after detaching from the baffling has the potential to catastrophically fail, causing a loss of engine oil.

Within 300 hours we usually see cracking around the nut plates or baffling for baffling-mounted oil coolers. The mounts should be regularly checked with a bright light, perhaps at every oil change. Initially, the cracks will be small and insidious, but they will propagate and cause fretting as they enlarge.

Oil coolers banging around in the engine compartment can certainly dampen the fun factor. Don’t let that happen to you. Now go check your ELT.

Vic Syracuse, EAA Lifetime 180848, is a commercial pilot, A&P/IA, DAR, and EAA flight advisor and technical counselor. He has built 11 aircraft and has logged more than 10,000 hours in 74 different types. Vic founded Base Leg Aviation, has authored books on maintenance and prebuy inspections, and posts videos weekly on his YouTube channel. He also volunteers as a Young Eagles pilot.

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