Create a life-limited-items list
Airplane ownership should start with an evaluation process. Successful buyers start by taking an inventory of their flying history to make sure they buy the airplane that fits their needs. They also must be honest about the expenses of owning an airplane so they don't buy an airplane they can't afford, and so they can properly maintain it after the purchase — and still have enough cash leftover to fly on a regular basis.
Disciplined shoppers leave no stone unturned — they become members of the appropriate type club and spend hours mining tribal knowledge from Web site members-only forums. FAA sites containing pertinent information about the subject airplane are visited. Often e-mails are sent and phone calls are made to other type club members requesting information about details such as parts availability, cost per flying hour, and cruise speeds.
Cash is laid out for a full annual inspection in lieu of a prepurchase survey. Every bit of information is double-checked and evaluated. The savvy airplane buyer knows where the buck stops and is willing to go to almost any length to find the airplane that suits both his needs and pocketbook. After the papers are signed and the airplane has been flown to its new home, it's time to move to the next step in airplane ownership — maintaining airworthiness.
Replacing items
Maintenance technicians are required to complete a document giving detailed instructions for continued airworthiness (an ICA form) when a major repair or alteration form is submitted for a field approval. Maintenance manuals — especially the manuals covering newer airplanes — contain many suggestions for maintaining airworthiness.
Some tasks in maintaining airworthiness are well understood. Everyone knows that all internal combustion engines need regular oil, oil filter, air filter, and spark plug changes. These increase dependability. Most everyone also understands that keeping an airplane clean cuts down on wear and corrosion. But other continuing airworthiness tasks aren't as obvious.
The reason for continued airworthiness is to reduce the likelihood of unscheduled breakdowns and delays. The consequences of ignoring or putting off continuing airworthiness tasks can vary from inconveniences to life-threatening events.
Involved owners collect data from various sources to determine parts replacement times. Some of the sources that help owners establish the component replacement guidelines for their airplane are the experience of other owners of similar airplanes, the experience of maintenance technicians, especially technicians who work where the airplane will be based, and the manufacturer's maintenance manuals, service bulletins, and letters.
Post-purchase inspection and checklist
Preventive maintenance costs less in the long run. This is not immediately apparent because setting up a comprehensive maintenance schedule requires that new owners be willing to spend some money almost as soon as the prop stops after the flight home. This cash will be used to conduct in-depth inspections of a few highly critical components and assemblies, to replace used or worn parts, and to overhaul components. The goal of this step is to establish starting times on the airplane component replacement schedule.
The first dollars should be aimed at critical components. Let's start with the engine. Magnetos should be overhauled or exchanged every 500 hours. This is because of the wear of internal components and the fact that spark power drops as the components wear. Losing a magneto during a hot and heavy takeoff will get your attention.
Paul Quinn of Stratoflex, an aircraft hose manufacturing division of Parker Aerospace, recommends that owners replace every flexible hose on a newly purchased airplane — especially critical firewall forward hoses such as those used to transport the engine fuel and oil — unless maintenance records or date tags attached verify that the hoses have been replaced within the past five years. Landing-gear, brake, and retractable-landing-gear-system hydraulic hoses also need to be checked. I found flexible hoses from 1959 still installed in the brake system of my 1960 Piper Comanche during the first annual after a 2003 purchase.
Maintenance manuals recommend that these hoses be replaced every five years, but unless the hoses are routed very close to high-temperature components, such as turbocharger or exhaust systems, this is pretty conservative. A more common interval is at engine change or 1,000 hours, whichever comes first.
Turbocharger installations require additional maintenance. If proper cool-down procedures are followed and peak turbine inlet temperatures are not exceeded, the components should make it to the 1,000-hour mark without any problem. But the check valves in the oil feed and return hoses should be overhauled or replaced at 1,000-hour intervals.
Wire-type mixture, alternate air, and carburetor heat controls are easy to ignore. These must be disconnected at the engine end and completely removed from their housings by pulling them aft into the cabin to check for excessive wear caused by vibration of the wire within the housing. The most common site for wear is at the exit end of the housing. There's no way to inspect this area without completely removing the wire. A common rule of thumb says to change all engine controls at each engine change or overhaul. It's so much easier to ensure that the controls are routed correctly and free of kinks and twists if the engine is out during installation.
Remote-mounted oil coolers accumulate a surprising amount of carbon. If the maintenance records don't show that the cooler was refurbished at the last engine overhaul, plan on flushing the cooler, or sending it to a cooler repair station to be cleaned.
Propeller governors should also be changed or overhauled at each propeller change or overhaul.
Propellers require regular maintenance and it's cheaper — and a lot safer — to send them in every five years for a tuneup than it is to wait. If these intervals are extended, there's a greater chance of having to pay big bucks to replace major internal parts that are rusted beyond repair.
Today's dry-type pneumatic pumps — vacuum and pressure — are both a blessing and a curse. They're good because their use eliminates paraphernalia such as hoses, oil return lines, and air-oil separators that are required with wet-pump installations. That's countered by the fact that when a dry pump fails there's rarely any warning. And the odds of a failure go up as the hours in use increase. Therefore, dry-pump health should be monitored with a wear port if the pump has one or should be replaced at the manufacturer's suggested intervals, which can vary from 500 to 800 hours. This is doubly important for instrument fliers — who also should have some kind of backup pneumatic system or an autopilot such as those manufactured by S-Tec and Brittain that utilize an electrically powered turn coordinator for attitude reference.
Carburetors and fuel control servos should always be overhauled concurrently with major engine overhauls, or at the equivalent number of hours since last overhaul.
Exhaust system heat exchangers — the part of the system that looks like a muffler — have a finite life. It's smart to send the entire exhaust system to an exhaust repair station during engine overhaul. At the first sign of deformation of the flame tubes or cones — these are located inside the muffler-looking part and can usually be visually checked by looking up the exhaust pipe — remove the part and send it in for repair.
Massive electrode-type spark plugs have an effective life of 300 to 400 hours if they're serviced and rotated on a regular basis. Fine wire-type plugs make more sense over the life of an engine since studies have proven that they're more economical in the long run and resist fouling better than the cheaper massive electrode-style plugs.
Following these steps will significantly reduce the number of maintenance-related delays and will save money in the long run.
Airplane interior
Pneumatically driven gyroscopic instruments — the artificial horizon and directional gyro — work best and last longest when the airplane is flown regularly. With daily usage these instruments last 1,500 to 2,000 hours before an overhaul is needed. Owner-flown gyros usually don't last as long because of bearing lubrication migration that takes place while the gyros are at rest.
An ailing or tired gyro will let the owner know when it's ready for a trip to the overhaul shop by acting sluggish, by precessing faster than 3 degrees in 15 minutes during straight-and-level flight, and by generating a lot of bearing noise and spinning down rapidly after engine shutdown.
One trick mechanics use to identify rough or noisy gyro bearings is to put one end of a screwdriver — or any other noise conductor, such as a wooden dowel — against the gyro instrument and the other end against the hard, bony area of their skull, just forward of their ear. Bearing noise will be easy to hear using this trick. Central gyro system filters and relief valve garter-style filters should be changed every 500 and 100 hours, respectively.
A critical part of the pneumatic system that's often ignored is the firewall-to-gyro instrument hoses. These hoses rarely attract much attention until they start flaking material into the expensive gyros. They're inexpensive to replace — put this task on a 10-year calendar interval.
Betting the safety of your family on seat belts and shoulder harnesses that are more than 10 years old is similar to betting that your retirement income will come from winning the lottery — it's a bad wager. Seat belts and shoulder harness assemblies that are faded, are missing TSO tags, are more than 10 years old (the date of manufacture is printed on the tag), or have broken or missing stitches may not be capable of maintaining rated strength and should be replaced.
Fire extinguishers should be checked for a proper service date, and serviced if necessary.
Aircraft windows are manufactured out of acrylic plastic, which is soft, especially compared to glass. These windows age with exposure to ultraviolet light and will eventually take on a milky appearance. According to the aircraft window experts at L.P. Aero Plastics, well-cared-for airplane windows can last up to 20 years. New windows are clear and distortion free so if there's any hint of milkiness in the windows, set aside some cash for a set of new windows — this is one change that no one is sorry he made.
Around the airframe
Tires are also affected by ultraviolet light. This damage can be detected by a close inspection of the sidewall and tread area for cracks and thin spots. Pilots sometimes mistakenly rationalize that the main landing-gear tires and tubes take all the abuse so it's OK to keep flying with an aged nose tire. When cracks appear it's time to start looking for a new tire.
Buy a new tube when the tire is purchased. Aircraft tubes are natural rubber and are built slightly undersized for ease of installation. During use, tubes stretch to accommodate the tire, which expands slightly when inflated and when spinning rapidly, and if reused will be too big for the new tires. The result will be folds and an increased incidence of accelerated wear and failure.
Fuel bladders — even those manufactured of the latest multi-ply nitrile rubber — also have a finite life. It's not that unusual for a bladder to last 20 years, especially if the airplane has been hangared. Check the maintenance records for the age of these components — if they're more than 10 years old they're moving toward retirement.
Maintaining continued airworthiness is an ongoing job that requires knowledge, diligence, and persistence. The payoff for following through with discipline is the comfort that comes with knowing that your airplane is well maintained, dependable, and safe.
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