BeechTalk - BT

Username Protected · **Posted:** 23 Apr 2022, 15:55

Recently, an aircraft in which I have interest popped up for sale on Controller. It's a late model (relatively) twin-turboprop with -135A engines, 1500 hours since new. After a couple of talks with the broker and the maintenance/avionics shop in which it sits, I've learned the airplane hasn't flown in four years. One of the maintenance shop representatives told me it's had a few "ground runs" but when I queried about logbook entries, he crawfished. I then asked him if the engines have been preserved as per the Pratt Maintenance Manual - He crawfished again.

He did say the airframe has been maintained on the calendar items and is within compliance of all inspections. It has all new Garmin avionics installed including a GFC600, it just hasn't moved in four years.

A call to my contact at Prime Turbines in Dallas revealed that, in his opinion, the engines will require a "light" overhaul - basically disassembly, cleaning and reassembly. If this is the case, I will walk away from the airplane.

Thoughts?

Username Protected · **Posted:** 23 Apr 2022, 17:09

General location of the airplane? Stored inside or outside? Intake & exhaust plugs installed in either case?

If inside with plugs in a low humidity environment, the fuel delivery system and the prop governors may be only things that would need an OH. A messed up spray pattern in the burner can could get expensive fast. Do they do a compressor wash on a PT6? Check the tanks for fungal growth too. I really can't see what a take down and clean would get you other than new gaskets. Unless someone was being a bit deceptive on why they stopped flying the plane. See if you can get a bore scope camera in the exhaust and see if the turbine blades are all cruddy. Could be a plane worth a few thousand to you to have inspected a bit closer.

Outside with no plugs in a humid environment? There will be additional problems evident other than the engines and like you I would be suspect of them as well.

Username Protected · **Posted:** 23 Apr 2022, 17:56

Username Protected wrote:

General location of the airplane? Stored inside or outside? Intake & exhaust plugs installed in either case?

The aircraft is in Tennessee. Stored inside. Plugs? I certainly would hope so but, no way to tell.

I plan to visually inspect the aircraft with my mechanic next week. If it passes the smell test, I'll engage Prime Turbines to do a borescope and logbook inspection.

Username Protected · **Posted:** 23 Apr 2022, 18:35

Username Protected wrote:

but when I queried about logbook entries, he crawfished. I then asked him if the engines have been preserved as per the Pratt Maintenance Manual - He crawfished again.

"crawfished"??? :scratch:

Username Protected · **Posted:** 23 Apr 2022, 18:53

Username Protected wrote:

but when I queried about logbook entries, he crawfished. I then asked him if the engines have been preserved as per the Pratt Maintenance Manual - He crawfished again.

"crawfished"??? :scratch:

Username Protected · **Posted:** 23 Apr 2022, 18:54

Username Protected wrote:

but when I queried about logbook entries, he crawfished. I then asked him if the engines have been preserved as per the Pratt Maintenance Manual - He crawfished again.

"crawfished"??? :scratch:

Username Protected · **Posted:** 23 Apr 2022, 19:44

I was going to say “waffled” but figured “crawfish” was better.

Username Protected · **Posted:** 23 Apr 2022, 19:58

No experience other than having flown behind PT6s for a couple thousands hours.
I was going to suggest; fuel/oil sample, borescope, wash and engine run.

Username Protected · **Posted:** 24 Apr 2022, 08:38

Why do they call it. “Light overhaul”?

Username Protected · **Posted:** 24 Apr 2022, 09:18

Username Protected wrote:

Why do they call it. “Light overhaul”?

Makes it easier to pay the invoice?
We had a Cheyenne II and used an indepenant service called Specialty Turbines out near Pittsburgh PA to manage the engines. This was nearly 20 yrs ago now.
They weren’t a shop but had relationships with nearly every shop. They would come out to us for MX and Service/inspections. Saved us money.

Username Protected · **Posted:** 24 Apr 2022, 09:21

I’m no engine guy, but I think he meant most components would be cleaned, inspected and reinstalled. There wouldn’t be a lot of replacement or damaged parts.

The maintenance guy at the shop holding the airplane scoffed at this when I told him.

I feel like I’m getting two answers to the question, “What happens to a PT6 when it doesn’t run?

1. There’s absolutely nothing wrong with those engines. Go fly ‘em.

2. Those engines are trashed because they haven’t moved in four years. They need to be overhauled.

Which one is correct?

Username Protected · **Posted:** 24 Apr 2022, 09:30

There’s nothing the matter with them. They aren’t that delicate.

Username Protected · **Posted:** 24 Apr 2022, 09:53

I can only comment from an appraisal perspective but the engines which have not been run in accordance within the manufacturer's recommended timeframes OR been placed in long-term storage have no value to the overall aircraft and are essentially run out - regardless of how much time is on them since the most recent overhaul or CZI.

While someone can claim that a ground-run or two was carried out, it is really an issue of what is in the logbooks for each engine. Recently, I've run across several turbine engines with no entries for several years. Those entries exist or they do not.

The real question to be answered is - Will an IA return these engines to service and put their name to it without an overhaul? Some no doubt will but that is quite a bit of liability to be taking on.

Good luck

Username Protected · **Posted:** 24 Apr 2022, 10:44

There was a thread on this years ago. Even had some official guidance as a pdf file if I remember correctly. Let me see if I can find it in a search.

Username Protected · **Posted:** 24 Apr 2022, 10:52

Well I found one, but I think there’s another thread as well. Here’s the best post from that one (original found here)

Quote:

I have worked on PT6A's since 1992 and I was with Pratt for over 10 years until recently. Years ago, I spoke to a senior Pratt engineer that writes the maintenance manual on the PT6A. He stated there is a limit for everything and that limit has to be set. They know this limit is often broken and overlooked (similar to the speed limit), but there must be limits. Yes, most engines over their TBO life have sat inactive for more than 30 days and have operated normally up to the next OH. However, Pratt must provide guidelines and in extreme cases, could deny warranty if an unscheduled event were to occur. I have pasted the Pratt guidelines below. I recommend to anyone to run the engines at least every 30 days. If the aircraft is inactive at a maintenance facility for more than 30 days, drain the engine oil and fuel from the FCU. Keep the desiccant in the inlet and exhaust area with inlet and exhaust covers on the engines.

Buy these desiccant boxes from Ebay. You can re-activate them in the microwave.
They are $20 each. Put one in the inlet area and one in the exhaust with lanyard and covers on.
http://www.ebay.com/itm/Dry-Packs-900-G ... 2a0afef699

There is more detail in the manual about preservation beyond 90 days. See manual language below my signature. Kind regards,

Greg Miller
greg.miller@utpparts.com
http://www.utpparts.com
704-660-9999

Pratt & Whitney maintenance manual ch 72-00-00 page 306

(1) Engines inactive 0 to 7 days.
(a) If the engine was operated in a salt laden environment, do a compressor and turbine desalination wash (Ref. 71-00-00, CLEANING).
(b) Engine may remain inactive with no preservation protection provided engine is sheltered, humidity is not excessively high and there is not extreme temperature changes that may produce condensation.
(c) Install inlet and exhaust covers.

(2) Engines inactive 8 to 28 days.
(a) Do 0 to 7 days procedures.
(b) Place desiccant bags and humidity indicator on wooden racks in engine exhaust duct only.
(c) Seal off all engine openings. Make sure exhaust cover has suitable window to monitor humidity indicators.
(d) Check relative humidity every two weeks if engine is stored outside, and every 28 days if engine is stored inside. Relative humidity should be maintained at 40%. If humidity indicator turns pink, replace desiccant bags and indicator.

(3) Engines inactive 29 to 90 days.
(a) Do 0 to 7 days, and 8 to 28 days procedures.
(b) Wash engine externally (Ref. 71-00-00, CLEANING).
(c) Do a compressor performance recovery/desalination wash and a turbine rinse.
(d) Examine all engine external protective coating, and touch-up/repair as necessary.
(e) Lubricate all linkages.
(f) Disconnect fuel inlet to oil-to-fuel heater and connect suitable oil supply line to oil-to-fuel heater fuel inlet. Blank off disconnected fuel supply line.(g) Disconnect fuel line at flow divider inlet to prevent preservation oil from entering fuel manifold, and loosen line as required to permit drainage into a suitable container.
CAUTION: UNDER NO CIRCUMSTANCES PERMIT PRESERVATIVE OIL TO ENTER ENGINE WHERE IT MAY COME INTO CONTACT WITH THERMOCOUPLE PROBE ASSEMBLY. OIL CONTAMINATION OF PROBES MAY CAUSE COMPLETE FAILURE OF THERMOCOUPLE SYSTEM.
(h) Supply preserving oil (PWC05-077) at 5 to 25 psig at least 16°C (60°F).
CAUTION: OBSERVE STARTER MOTOR OPERATING LIMITS (REF. STARTER MANUFACTURER’S MANUAL).
(i) With ignition system OFF, fuel condition lever to GROUND-IDLE and power control lever to TAKE-OFF, carry out normal motoring run until all preservative oil is displaced. During motoring run, move power control lever from TAKE-OFF to GROUND-IDLE and back to TAKE-OFF and fuel condition lever from GROUND-IDLE to OFF and back to GROUND-IDLE to displace fuel from system.
(j) After motoring run, check to see if preservative oil is coming from opened fuel line. If not, repeat motoring cycle until preservative oil flows from opened fuel line.
(k) Return power control lever to GROUND-IDLE and fuel condition lever to OFF. Reconnect fuel supply to oil-to-fuel heater and fuel line to flow divider inlet.
(l) Install caps, covers and plugs as necessary to prevent entry of foreign material and accumulation of moisture (Ref. Fig. 304).

_________________
Greg Miller
M4 Aviation Group
Aircraft & Engine Sales
+1 (704) 634-0185
greg@m4aviationgroup.com

PT6's Sitting for Four Years