What You Should Know Before Buying a Used Aircraft

Knowledge is power when it comes to navigating the used aircraft market. A good pre-buy inspection will ensure a surprise-free future for you and your aircraft.

Things to Keep in Mind When Searching for an Airplane.

Airframe:

This is the only component that can’t really be replaced (unlike the engine or prop) so during the pre-buy, a majority of the time is spent looking for corrosion and non reported non documented damage. Some damage is technically acceptable as long it has been properly repaired and documented. Non-reported damage is normally safe but can lead to discounts in the price of the aircraft.

Engine: 

The second most expensive thing on the airplane and MOST important.
A little bit about engines: There are a couple terms to understand when reading ads and listings for used planes.

– New; this term is recognized by the FAA as an engine that have never been started/run. All parts are new and it’s built by the engine manufacturer.

– Rebuilt; this term is also recognized by the FAA and represents an engine that has been reassembled using parts that are new or within wear limits of a new part. In the process, the old engine is dismantled, parts are measured, and if they measure to the tolerance of a new part, they are reused. *Important * only a engine manufacturer such as Continental or Lycoming can ‘rebuild’ a engine. The total time of this engine after rebuild will be ‘0’ and will come with a new logbook and the engine manufacture will keep any old logbooks associated with the engine.

– Overhaul; this is the last of the 3 terms recognized by the FAA. This term means an engine that has been dismantled and all parts measured for a wear limit range. As long as the part fits inside this range, the part is considered airworthy and can be reused. An A&P mechanic can perform this ‘overhaul’ and return the engine to service as well as an FAA Certified Repair Facility. The logbooks and total time on the engine will continue after a standard overhaul. So, to be clear, unlike a new or rebuilt engine, the total time does not reset to ‘0’.

It is important to note that there are other terms such as “TOP Overhaul engine” which is claimed to be ‘rebuilt’ by an A&P or an engine shop. These are not proper terms and probably fall into the category of a standard ‘overhaul’.
An engine can be overhauled multiple times and have a high total engine time ( TTE). This is not particularly desirable as when the engine manufacturer rebuilds the engine it comes with all the new engine components (new lifters, rockers, etc). Plus it’s been overhauled by regular mechanics and not a factory that specializes and overhauls only its own engines .

Some Terminology to Note

  1. TT – This means the ‘total time’ on the engine since new or rebuilt.
  2. TTE– Total time engine or engine total time (ETT).
  3. TSMOH – Time or hours on the engine since last major overhaul.
  4. TSTOH – Time since top overhaul (again, this is not really recognized and means normally the cylinders were all replaced.- engine total time still continues).
  5. TSN- Time since new (or rebuilt).
  6. AFTT – This means Airframe Total Time (normally when you see the TSMOH or TTE it means the engine is the original from the date of manufacture of the aircraft).
  7. TBO– Time between overhaul (or before overhaul) – The time the manufacture says the engine can run until it should be overhauled.
A close up of the valve covers on a lycoming TIO-540-A2C in Piper Navajo in with us for regularly scheduled maintenance.

Considerations for Finding a Good Engine

Disclaimer – Engines will all fail at some point. They turn over a finite amount of revolutions and will fail at a weak point. Most general aviation aircraft are air cooled engines with huge temperature ranges that require small adjustments slowly. A car engine by comparison is water cooled and can be made to stay within 4 degrees of a temperature at all times, even while developing higher horsepower outputs. Aircraft engines can fail at anytime so we look for parameters to minimize this risk. The best option is to buy a run out engine and install a new one taking care of it from day one, however, this is not feasible for most. We can only do so much to identify problems that lead to failures. Here are some of the things to be cautious about.

1. Any engine that has not been overhauled in the last 15 years.
After 10 years since the last overhaul the relative price starts coming down. 15 years since overhaul would be my limit. Most major engine manufactures recommend 8 years time between overhauls.

2. Any gap more than 1 year of not running the engine ( unless properly pickled)
Engines need oil. Not running the engine for a year will dry out the internals and lead to premature wear. The cylinder walls and piston rings will suffer first. Lower compression and excessive oil consumption will show the cylinders needing piston rings, cylinders honed, and valve guides and valves. The worst thing is when the buyer says he pulls the plane out every month or year and runs it up for a while. This leads to oil making acid which will eat all the bearings. (water boils off the engine at 180F and the oil wont get this hot unless its flown. It will actually cause MORE water to mix into the oil reacting with the carbon deposits from combustion creating acid).

3. Any engine that doesn’t fly at least 50 hours per year. (unless its been properly pickled) Take the engine TSMOH and divide by the years since overhaul.

4. Any engine at ‘mid time’ (say 800 to 1200hrs SMOH) will most likely need the cylinders repaired. Not a big deal just a consideration. Normally the valves, valve guides, rings and cylinder should be serviced.
($4-8K depending on the engine)

5. Low cylinder compression. Every 100 hours or annually compression on the cylinders are measured for indications of wear on the valve seats and piston rings. Lower compression mean more wear. Looking back a couple years and comparing compression usually reveal trends.
A good compression is usually between 70-80 psi. 50-60psi is lower but can be acceptable under certain circumstances and anything below 50 needs work. (usually I complain if its below 60)

6. Prop strike engines. You can tell these when the airframe have new body parts and a brand new propeller but no engine inspection. Stay away from these.

7. Engine accessories:
Mags – Need overhauled or inspected in last 500 hours or 5 years.
Propeller – Last 10 years needs overhaul or corrosion will ruin hub. Propeller overhaul usually 3K. New propeller- 9K Props under 10 years since last overhaul normally pass overhaul.

During the Pre-Purchase inspection all of these items are scrutinized and itemized in order of relevance. Exhaust, mags, prop, starter, alternator will all be inspected and tested.

If you’re looking for your first used plane, or looking to add one to the collection, keep Propellerhead in mind. We have performed pre-buy inspections all over the country. Give us a call or inquire right here on the site to schedule a pre-buy inspection with one of our qualified mechanics.

-Bill