I looked at a plane that had its -10 engines overhauled 5 years ago by a very reputable shop. The plane never flew for 5 years after the OH. The engines now have about 1.5 hours on them. The seller has hinted that the engines were run on the ground every 90 days during that 5 year period, but there seem to be no logs substantiating that.

I am not looking for advice on this particular plane - it has enough other issues that disqualify it.

I am looking for information on what 331 storage requirements are.

I am looking for information on whether ground runs are sufficient to avoid the engines being deemed stored.

If the engines have been improperly stored, what inspections are required?

If the engines have been improperly stored, what are the likely downsides? The airplane was not in a desert climate.

Do 331s have a calendar year overhaul limit, e.g. 7,000 hours or 70 years?

Is there a calendar limit for hot section inspections?

There are definite requirements for periods of inactivity. Below are the basics I found on the Standard Aero site.



Store Your TFE731 Engines Properly or it Could be Costly

By Eric Thompson, Engines Product Director, StandardAero

During a recession, a lengthy corporate merger or company budget crunch it may be tempting to ground your aircraft and stash it in storage for a while in hopes of saving a few dollars. Unfortunately, that could damage your engines and prove extremely costly to rectify.

For an engine to work properly, critical parts, particularly the main shaft bearings, have to be exercised and lubricated regularly. Over time, moisture collects, causing corrosion and pitting.

The easiest, least costly approach is simply to operate the engines once a month and document it in your logbook. If you have to store your aircraft beyond 30 days, you’ll need to take these specific manufacturer recommended steps to preserve your TFE731 engine.

For stored or inactive engines, Honeywell’s Light Maintenance Manual requires specific steps. Here are the highlights.

On-wing Preservation

Less than six months: Motor the engine every 30 days.

More than six months: The fuel system must be preserved and the engine motored every 30 days.

To preserve the fuel system:

Disconnect fuel control discharge line between oil temperature regulator (fuel/oil cooler) and fuel control; and connect a line to the fuel control discharge port to drain overboard.
Disconnect fuel supply line at inlet connection on fuel pump and add preservation fluid at 2 to 5 psi pressure.
Turn off the power to the ignition system. Set to idle. Motor the engine until clean fluid flows from overboard drain line.
Stop engine, disconnect fuel supply lines from fuel inlet port on fuel pump and cap inlet port. Allow residual oil to drain from fuel control and lines, then disconnect overboard drain line and reconnect fuel line between fuel control and fuel/oil cooler.
Wipe all fuel and oil from the engine. Apply warning tags to indicate preservation procedures have been performed and that the engine shall not be operated except as noted until de-preservation procedures are performed.
Install inlet and tailpipe plugs.
Store digital electronic engine control in air-tight bag with desiccant.
Every 4 weeks, remove plugs and motor engines to N1 rotation.
Off-wing Preservation for More Than 30 Days

When the engine is removed from the aircraft, follow the same procedures as if storing on-wing for more than six months, plus:

Drain engine oil.
Wrap engine in first barrier material and seal all openings.
Add outer barrier with four bags of desiccant and two humidity indicator cards. Install humidity indicator plug into barrier. Seal seams.
Cut opening into the barrier and vacuum out the air. Seal opening with a heat gun.
Record preservation in the Engine Log Book.
Every 30 days, check the humidity indicator plug and humidity indicator cards. If the indicator plug or card changes from blue to pink, bag must be opened and engine inspected for rust or corrosion. If rust or corrosion is evident, take appropriate corrective action. Preserve the engine again.
Every two years, remove an engine from preservation storage, service with oil and operate to N1 rotation. Ensure fuel control power lever is in cutoff position prior to motoring. Preserve engine again and store.
Note: Never spray the compressor section with any corrosion-preventive compound. Engine lubricating oil is a satisfactory corrosion preventive.

For exact instructions, refer to the Honeywell maintenance manual for your specific engine model.

Improperly Stored Engines Land on the DEL List

If an engine is not maintained per the light maintenance manual, a condition report must be submitted to Honeywell to determine the work scope needed to return the engine to service. The engine’s serial number is placed on Honeywell’s Damaged Engine Review Board list until you comply with the instructions.

There are no set instructions for returning to service an engine that has not been properly preserved. It is left to Honeywell’s engineering discretion. If, during their review, they find that the main shaft bearings are suspect, you’ll be required to have the engine completely disassembled and inspected.

Fuel system parts as well as all of the accessory and transfer gearbox bearings among other things may need to be replaced. Service plans and engine programs very rarely cover this expensive procedure, which can run roughly $200,000, so the cost comes out of your pocket.

If you even suspect the aircraft will be down for a few weeks, take precautions ahead of time and prepare the engine properly. It could save you a lot of time and money.

I have never heard of a calendar limit for HSI or OH on the TPE331 series of engines.

5 years is a long time.

Erwin,

Thanks for the info. 5 years is a long time.

30 days is awfully short. When the time comes to sell your plane, could you document that your engines have been run at least every 30 days since their last inspection?

I expect that the bulk of the TPE331 fleet has violated the 30-day requirement. As a practical matter, I would guess that the engines can endure some 30-60 gaps every few years.

Enduring 5 years is a whole different story.

Did you say where the plane (engines) have been?
Kinda interested to hear more personally.
Pm if you like.

My recollection is that Honeywell considers an engine that doesn't run for 30 days to be "inactive" and that triggers certain maintenance actions. Sorry, I don't have that info.


My understanding is that they are. If the oil temperature gets in the green, and runs for 5 minutes, I think that is sufficient.


Don't know, requires talking to an engine shop.


I'd worry mostly about gear box corrosion. I'd be less worried about the hot section. A TPE331 engine shop could say more.


Seems to be entirely hour based.


Hour based.

Turbine engines tolerate idleness far better than piston. It would not surprise me if the engines operate fine. I would run the engine for 10-15 minutes, do an oil change, run it again for 2-3 hours, do a SOAP sample, and see what you have. A good ground run will tell you if the engine has serious problems and the SOAP will indicate if you have corrosion in the gear box.

I wonder who overhauls a pair of -10 engines and then doesn't use them? Weird.

Mike C.

Proving the e wry 30 day run isn't hard - turbine aircraft have cycle logs so you can tell/prove they were run every 30 days.

As Mike said, failure to do so is a real issue with respect to Honeywell. This is more Han something like running a piston LOP despite what Lycomu g or Continental recommend. The 30 day issue is in the inspection /maintenance manual and thus not optional for turbine aircraft.

Unless he plane you are looking pat is so cheap that the purchase plus cost of two fill verbals at the high end of the cost window (probably budget 550-600K for both engines) is a good deal, I'd run away from this plane.

What the he** are you guys talking about? The 30 day thing in Erwin's example is for the TFE731, not the TPE331. They're two completely different things.

Good catch Adam, I was nearly asleep when I posted last night.

The same applies to the TPE331 series I have been told.

I have been told many engines go over 30 days and it takes a lot more to get on the DEL list.

Adam,
TPE331-10 has the same 30 day requirement. If the engine isn't run for more than 30 days and not "stored" correctly, the maintenance manual requires a special inspection. As this is an inspection and not an overhaul, even if you operate part 91 it is not waiver able...falls in the same category as your HSI or gear box inspection.

I'm sure there are people who go over the 30 day interval and don't do the inspection. That works great until something happens and you have an insurance claim. At that point the plane was not operated and maintained in accordance with the published guidance and the claim may be denied. When I had my claim last year, the insurance guy went through my maintenance, operating and training logs with a fine toothed comb. Questions about when x had been done last as he and I then looked to find the vent in the logs (it was there).

Even part 91, the rules for maintenance and record keeping are very different when one goes to a turboprop engine...the 30 day inspection rule if the engine isn't stored properly (and return to service inspection if it is stored correctly) is not unique to TPE engines.

My recollection is that the reason for the "run at least once every 30 days" has to,do with the seals. Since the engine bearings are dry sump style (oil goes in and out of them), failure to run the engine often enough can result in the seals drying out and thus the bearings not staying sealed. Result is catastrophic failure as that engine spools up to 40,000 rpm with unlubricated bearings. This is NOT the same issue as pickling a piston engine to help prevent corrosion.

The requirement to run at least once every 30 days is in the maintenance manual and was covered during transition training when I started flying my plane. Requirement for a cycle log is also in th manual. If you don't have one, there is a math formula to generat number of cycles based on hours flown, but it has a penalty (meaning you get charged for more cycles) and since there engine components which are cycle count limited, you end up having to replace them early, hence every operator I know keeps a cycle log (my plane came with complete cycle logs dating back to delivery in 1979 along with the logbooks). I would consider a turboprop/turbine plane that didn't come with complete cycle logs to have "incomplete logbooks".

Anyone have links or attachments for the 30-day rule?

My understanding is that a ground run would not be entered in the cycle log. From Honeywell's TPE331 Training Handbook:

"One cycle is defined as:
•Engine start, Takeoff
• Landing Engine shutdown
Accomplishing ten engine ground runs would result in no cycle being recorded.The basis of this cycle relates to
the thermal shock the turbine section is subjected to. Ground operation for maintenance actions was taken
into account when cycle limits were established."


So, I guess there would be no harm in logging a ground run in the cycle log and not counting it as a cycle, but a ground run is not a cycle. I think a separate ground run log would be better.

Is anyone logging ground runs in order to comply with the 30-day activity rule??

I never have, but I never went more than 30 days without flying.

I think it is more nuanced than that. One must log cycles, but I just log cycles annually in the maintenance log. I am the only one who flies my airplane, so I just track cycles via my pilot log and tally them annually into the maintenance log. I figure anything that simplifies record keeping makes it more likely to get done.

And for the TPE engine, the cycle-hour conversion formula is one hour equals one cycle. Which in my experience is remarkably accurate to my actual use.