Getting an idle aircraft flying again

Q: We have a Piper Navajo PA-31-350 that has not flown in three to four years, but maintenance has been done on it continually. During intervals the engines were started and run up.

What are the requirements as to the engines (or the aircraft itself) if it has not flown for three or four years? Are there any Service Bulletins or Airworthiness Directives that I will need to look at?

I know the lifespan of the engines are either 1,800 or 2,000 hours, depending on maintenance provided, or 12 years, whichever comes first — I need some clarification.

Davidson Mourillon

A: This could be a rather difficult one to answer. There are so many factors of great importance surrounding a situation like this that it’s very difficult to be certain that everything that should be checked is checked.

First of all, the geographical location of this aircraft is important. It makes a big difference whether the aircraft is located in a hot, humid, salt air environment, or located in a high desert area where the climate is dry.

That being said, let’s see what we should give serious consideration before even thinking about putting this aircraft back into service.

Even though you say the aircraft hasn’t flown in three or four years, but the maintenance has been done, that doesn’t really tell me anything.

You mentioned also that the engines were started up and run and that, in itself, causes me great concern.

If aircraft engines are just simply started up and run on the ground for any length of time and then shut down, this is not good. Just running the engines up on the ground does not allow the engine oil temperature to get hot enough to boil off the condensation and other by-products of combustion. As a result, the most common result from this is corrosion in the cylinders.

This is a common result of not generating enough heat in the engine to boil off the condensation, so my recommendation before you do anything else is to conduct a very thorough borescope inspection of each cylinder.

Note: I’m assuming these engines are fitted with Lycoming Factory Nitrided cylinders and not field chrome plated cylinders?

During your borescope inspection, if you see any indications of corrosion in any or all of the cylinders, I’d suggest removing the cylinders for a closer inspection. This would also allow you access to inspect the camshaft and tappet body interface for any corrosion in that area.

Depending on your findings, if there are indications of corrosion in this area, the decision has been made for you and the engine will need to be removed from service.

If no corrosion is noted in the cam and tappet area, but only in the cylinders, you may be able to remove the corrosion by having the cylinders honed. If they can be honed, and maintained within the service limits of the cylinder bore diameter, then reinstalling them with all new piston rings would be acceptable.

My other concern would be with the fuel injection system, again because of the extended periods of inactivity. Consideration should be given to removing the entire fuel injection system and sending it to an approved facility for a complete flow bench test.

I’d suggest this test be conducted prior to requesting any overhaul of the components, because the system may meet all specifications as removed from the engine. The bench test gives you the advantage of knowing the entire system is performing to spec and will be reliable.

Always make certain you advise the facility that you want a bench test only so they don’t automatically assume you want the system completely overhauled.

With regard to any outstanding Lycoming Service Bulletins, Service Instructions, or FAA Airworthiness Directives, you should review the engine logbooks closely.

To save time doing your research on any of these items, you may want to contact any repair facility that maintains this type aircraft and ask them if they have a quick reference guide outlining all of the manufacturers and FAA AD Notes applicable to your specific aircraft and engine combination.

Most shops that maintain Piper Navajo PA-31-350s use such a guide while conducting 100 hour or annual inspections. These guides simply allow the shop to review what requirements have been issued since they last serviced the aircraft without going back to day one.

The Recommended Time Between Overhaul Periods for the TIO-540-J2BD or TIO-540-J2B on the Piper Navajo PA-31-350 is 1,800 hours or 12 calendar years as set forth in Lycoming Service Instruction 1009AW or its latest revision.

The only time this may be extended to 2,000 hours is if the engines were being used in “frequent” type service and accumulated 40 hours a month or more and had done so consistently since being placed in service.

I’ve offered a few ideas here for you to consider Davidson, but would also suggest you conduct a very thorough inspection of the entire airframe and engines before allowing this aircraft to return to service.

Common sense and good shop practices, coupled with experience when conducting the inspection, should provide adequate information that will allow you to make your decision.