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Meridian - PT6A-42A Engine Troubles

2020 was a sorry year in the life of this particular Meridian owner. Initially avionic issues with appalling support from the Piper supply chain (Separate post) and the subject of this post: multiple issues with the supposedly bullet proof PT6A.

I should say at the outset that the aircraft/engine was always operated with care and consideration with zero exceedances and I am confident there was nothing I could have done differently that would have changed the outcome.

Oil analysis for a pre-buy inspection showed traces of bearing type material plus Aluminium. PT6 specialist Euravia recommended engine removal and strip. They did the strip and discovered several issues with the engine.

Issue 1
The entire auxiliary gearbox (AGB) was damaged. Every gear, bearing and shaft from the starter drive onwards was trashed. Diagnosis was Electrical Discharge Damage (EDD) and evidence is easily seen as fluting and erosion on shafts and bearings. I only saw photos and a video of the strip due to early COVID restrictions but it was clear it was EDD after reference to P&W supplied example photos

Very few people have heard of EDD but it has caused PT6s to fail in flight. None in a Meridian but about 20 instances in PC12s and Kingairs.

It is caused by the most innocuous fault you can imagine. A simple build-up of carbon dust in the starter generator causes some of the generator output to find an alternate path through the AGB and usually exits to aircraft ground through No1 main engine bearing. All parts in the path get fluting due to the erosion caused by the current. There are ZERO cockpit indications or any other indication until it’s detected in an oil sample or eventually main engine bearing seizure. Currents as little as 0.5A leaking through secondary paths to ground can cause this. But even if it was 20A you wouldn’t see it as an abnormal cockpit reading as the path is outside the current sensing path for the ammeter.

Fortunately, the damage to my engine was limited to the AGB. But the requirement once this is detected is mandatory overhaul of all accessories that have oil running through them. So prop governor, torque limiter, over-speed governor and obviously starter generator were all overhauled as well. Starter gen was examined first and no fault found other than brush dust build-up so conclusion was that leakage through carbon build-up was the cause. As are most cases apparently.

The aircraft had flown just 75 hours since the Starter Gen had been last cleaned as standard part of maintenance programme…..

Issue 2
And of course once engine is on a bench and stripped, other investigations had to take place to identify the source of Aluminium. Those were due to lumps missing from the internal surfaces of the main oil pump and scavenge pump. No idea why as this appeared disconnected from the EDD.

Issue 3
This one I knew was a latent problem and had been identified the previous year at the Event inspection. This was corrosion on the surface of the propeller gear box housing. It didn’t look too bad and Piper Germany applied protective paint to prevent further corrosion. Alas when inspected on the bench, the corrosion was too deep and the approved repair using Epoxy wasn’t suitable – a new part required at $25k.

Hot Section Inspection
And while it’s there maybe a do a hot section as well? This was fortunately ok.

All added up by the time engine was refitted and serviceable to about £180k including fresh Events, coincidental prop overhaul and rectification of usual annual stuff.

Euravia in the UK were absolutely amazing given it was at the start of the first COVID wave and no-one had learned how to work/cope. They discounted the parts as much as they could and did the Hot Section free of charge. But it was their customer care that was outstanding and how it should be. I think I was the first private customer they had and they quickly realised this was coming straight out of my pocket. I dread to think emotionally how it would have been if they were the usual disinterested maintenance company we seem to accept as typical

Having said that, Aerotech in Coventry were also heros and Rob and his team did a great job in difficult COVID services getting it all put back together again. I really wish I had used Aerotech from the beginning of ownership but I continued with Piper Germany it being a D registered aircraft.

Anyway, I sold the aircraft in December 2020 secure in the knowledge that the buyer had just got the bargain of a lifetime with the engine as known a quantity as any 1400 hour PT6 could be.

Emotionally it was touch and go if I continued flying – irrationally I felt for the first time in 35 years that flying had let me down and I wanted out. As “therapy” and to keep interest I undertook a highly risky aircraft purchase of buying an unseen C185 within a couple of weeks. But that’s another story ……………..

Lydd

@PhilG you left us waiting for more news on your Cessna 185! The Cessna 185 should be less fiscally painful! On the balance of probabilities you may be selling it for a nice profit in a few years.

Oxford (EGTK), United Kingdom

Hello Robert, yes I will post on my bought unseen C185. COVID travel restrictions and BREXIT combine to make a force and decision process that no rational human would normally take.

Funny thing is the risky bit is working out ok, the bit I thought was secure is causing some issues. More in the post.

Lydd

Thanks for sharing that. Incredibly scary, and I understand the feeling of wanting to give up flying. I’m glad you didn’t – as an addict, I always hate it when others manage to quit.

EGTF, LFTF

Sure enough, 180k is a lot of money, but isn‘t it something that an operator of a turbine aircraft HAS to expect, or at least somehow be prepared for, anytime? Isn‘t it the equivalent to 50k for the operator of a big bore piston single, which many of us have already been hit with, even at a point in time where it wasn‘t really expected.
Just surprised that this event almost had you quit flying…

Mainz (EDFZ) & Egelsbach (EDFE), Germany

Stuff like this always have scared me of the turbines. However, the rest always attracts me.

LDZA LDVA, Croatia

Sure enough, 180k is a lot of money, but isn‘t it something that an operator of a turbine aircraft HAS to expect, or at least somehow be prepared for, anytime? Isn‘t it the equivalent to 50k for the operator of a big bore piston single

Really? 50k is a bit excessive for an SR22, or at least one would hope, and if someone who doesn’t have one suggested that every SR22 owner needs to have 50k to blow away anytime he would be jumped on by loads of people including a load who have never owned an SR22

For a TP, it will depend on the details, and whether it is on a maint programme. At the TBM level I think most of them are but at the PA46 level probably no.

To what extent does a Meridian log the exceedances? I have heard complaints from TBM850 owners that the G1000 logs everything whereas the older systems didn’t and that resulted in a lot less worry

I have known a number of people who gave up flying after a bad experience. A number have given up when a friend got killed in a crash.

Electrical Discharge Damage (EDD)

How exactly does this work?

Normally, heavy-draw equipment bolted to an engine (alternator, starter, etc) does use the engine body to carry the return current but there is a heavy strap from the engine to the firewall. The only way to get an alternative return path is if the said equipment becomes unbolted and the drive shaft remains more or less in place.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

For a TP, it will depend on the details, and whether it is on a maint programme

How do these programmes work in cases like this? Would they cover these repairs?

Biggin Hill

Sure enough, 180k is a lot of money, but isn‘t it something that an operator of a turbine aircraft HAS to expect, or at least somehow be prepared for, anytime?

Well no it it isn’t something to expect because it is actually quite rare. Everything you read (and I did a lot of reading before the Meridian) suggests that investing in turbines is investing in reliability compared to those fragile piston engines. Of course every turbine operator is aware of the potential costs, but these super expensive events with low time, cosseted turbine engines are quite rare.

It happened to me and I was simply unlucky – I think I am the only Meridian owner that has had this in the whole world wide fleet though. So not unreasonable going back 4 years not to anticipate a £180k bill.

Lydd

How exactly does this work?

Armature leakage. Carbon debris build-up from the brushes provides a path for the current to travel between the commutator and the shaft. The TRW starter gen MM has a cleaning procedure that has to be followed.

T28
Switzerland
34 Posts
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