One of the most difficult decisions an aircraft owner must make is when to replace, overhaul, or rebuild their engine. Everything that moves eventually wears out, and an aircraft engine is no exception. Parts wear out; parts deteriorate; and parts break. This is true in aviation more than any industry.
Aircraft need constant repair, inspection, and upkeep whether they are flown constantly and especially when they are hardly flown at all. Engine manufacturers recognize frequency of flight as a big contributor to engine health. A majority of engines that don’t reach TBO can be attributed to owners not flying enough. In fact, Lycoming adds 200 hours to the recommended TBO for many engines if they consistently run more than 40 hours per month.
The primary goal and responsibility of the aviation industry is safety. When discussing the mechanical aspect of aviation, we are talking about reliability. Unlike automobile engines, the goal of an aircraft engine manufacturer is not to maximize power and performance but to maximize reliability.
In the world of aircraft engines, environmental conditions play a major role in causing wear-and-tear. Whether it is an environment where temperature change is dramatic, or corrosive salt water air, or even a dry, dusty environment, excessive internal corrosion can be the result.
In addition to external environment, piston engines experience a large deal of expansion and contraction when the engine is warmed up and cooled down in the normal routine of operation. The more metal expands and contracts, the more prone it is to wear and deterioration.
On a daily basis, piston engine components take a beating. This is why regular overhauls are so important; not just to maximize engine life, but to ensure enough power for the safe and reliable operation of the aircraft in all flying conditions.
The manufacturer establishes an engine’s TBO to ensure reliability and to provide reusable major components at overhaul time. TBO is the number of hours the engine manufacturer expects you can operate the engine before it needs to be taken apart and have parts replaced or repaired. Two thousand hours between overhauls is common, assuming the engine has been properly maintained. In most general aviation applications, this interval is a recommendation only and is not mandatory by regulation.
Engine manufacturers have their own specific requirements for what needs to be done to an engine to qualify as an engine overhaul. An overhaul consists of removing an engine, completely disassembling and assessing its overall condition, and assessing components of the engine to see if they meet new tolerance standards, serviceable tolerance standards, or are not serviceable.
It Goes A Long Way (Maintenance)
Now more than ever, pilots and aircraft owners are trying to keep their piston engines flying as long as possible. It is more cost-effective to repair an engine rather than replace it. While many operators prefer to stick with manufacturers’ recommendations, there are many things you can do as an owner or operator to prevent problems with your piston engine and improve your chances of delaying the expense of an overhaul. So, what does it take to keep a piston engine reaching its TBO, time after time?
It is recommended that you change your oil every 25 hours in engines with an oil screen and every 50 hours for those with a spin-on oil filter. Lycoming recommends that the oil be changed every four months if the hour limit isn’t reached.
Changing your oil and filters regularly is going to maximize your aircraft engine life. Acid accumulation in the oil and moisture content will build up and eat away at the engine and cause corrosion. You should also carefully consider which oil you use. Continental and Lycoming both have a list of Ashless dispersant oils that are acceptable choices.
There are also additives to consider including in your regular maintenance. Adding CamGuard after each oil change can help with corrosion protection. Make sure to check with your engine manufacturer before using any additives. Continental does not recommend the use of additives or concentrates in any of its aircraft engines, and they warn that doing so may void the engine warranty.
Keeping track on how long a quart of oil typically lasts can also help you detect issues. A rise in oil consumption can indicate a problem with the engine.
A Flight a Day Keeps TBO Away
A healthy engine requires frequent use. Hitting that magic number of 40 hours a month flying time is vital to maintaining your engine life. The very best thing you can do for your engine is to fly it once a week, long enough to get the temperature up to the normal range. In certain climates where humidity is high, the consequences of not flying your aircraft are more severe. If you are unable to fly once a week, the general consensus is to fly at least once a month.
It is insufficient to pull the airplane out of the hangar, start it up, and run it for a few minutes. This can actually be harmful to your engine because it doesn’t normally get to temperature on the ground, and all the moisture that is created during a ground run simply stays in the engine. Ground running can also be damaging to the engine because airflow over the engine is not adequate to properly cool the cylinders.
Replace, Overhaul, or Rebuild?
One of the more difficult decisions an owner has to make is when to replace, overhaul, or rebuild an engine that is running properly and passing all required inspections at its TBO time. There are several things to think about.
The manufacturer establishes an engine’s TBO to ensure reliability and to provide reusable components at overhaul time. Operating the engine beyond TBO may save you money initially, but the engine components you wear beyond the recommended overhaul time may cost you more than what you saved by not overhauling the engine at TBO.
Second, operating the engine beyond TBO will diminish its reliability. Metal fatigue, small (but growing) cracks, and other types of internal engine wear and damage (which do not show up on routine inspection procedures) may make themselves known in a disastrous way. Finally, there may be serious and expensive legal considerations beyond the FARs in civil court for not following the engine manufacturer’s maintenance recommendations.
Good maintenance can and will go a long way toward ensuring that your engine reaches TBO. Regular oil and filter changes, timing checks, spark plugs, air filters, and using the proper grade of fuel are extremely important to engine life and reliability.
The most important step in safeguarding your engine is to simply pay attention. If you notice anything unusual, have your aircraft looked at as soon as possible. With proper care and maintenance, your engine can last for a long time and provide you with a safe and reliable aircraft.