Did they say what actually failed?
An alternator should not fail that easily. The only affected part is the slip rings and I can’t see those failing – assuming the brushes were not worn out. The rectifier won’t fail just because it has some crap on it.
Peter wrote:
Did they say what actually failed?
It’s been a while so I don’t really remember. They did say the whole alternator was full of the same kind of stuff you had, all electric connectors had been damaged and also the voltage regulator (external) needed to be replaced. The alternator at that time was sitting so that it was directly exposed to the airflow.
the voltage regulator (external) needed to be replaced
I think they did a fair bit of revenue generation 
In GA, most alternators are exposed, and when they aren’t exposed themselves they have a cooling air pipe like mine has.
Peter wrote:
I think they did a fair bit of revenue generation
Nope.
About 2 weeks after my flight, the airplane was on a flight with a pilot of mine when they lost all electrics gradually over about 20 minutes. He correctly did load shedding and landed at our maintenance base without further incident (thanks to the fact that both Gear and Flaps are manual…) Further checks showed initially that the voltage regulator to be faulty and they discovered (in my presence) that there was dirt on the alternator. So we decided to send both voltage regulator and alternator for assessment and possible overhaul while a loaner alternator and new voltage regulator was installed.
What the overhauler came back with I told you. The regulator was damaged beyond repair, as they said as a consequence of the alternator not working properly, the alternator showed irregular output and power spikes on the bench, so it was disassembled and found full of sticky dirt to the extent, that it was beyond economical repair. They said they never have seen something like this in decades of working with those alternators.
I was able to purchase the loaner alternator which has been working since.
We also had a close inspection of other exposed parts of the engine but found only some sticky dirt, which we cleaned. The engine was overhauled about 6 months later for other reasons at rougly 2500 hours TSN.
I recently closed of the engine intake with a cowl closure, which now protects those parts fully.
Is there such a thing a cheap (perhaps disposable) volcanic ash detector that could be used in flight?
The regulator was damaged beyond repair, as they said as a consequence of the alternator not working properly
I don’t buy that – it makes no sense electrically. The most current which the regulator will ever pass is the field current, and it needs to handle that at a 100% duty cycle.
Was the regulator ventilated with outside air?
Is there such a thing a cheap (perhaps disposable) volcanic ash detector that could be used in flight?
Never heard of one. All the kit seems quite complicated. I saw a BAE146 plane fitted out with a load of it.
Update after an Annual:
Instrument filters were clean. However in the TB20 the vacuum system air is drawn from the cockpit, not from the engine section. I am sure these filters are a big con; experience from many years ago suggests they are good for 10-20 years.
Landing gear was OK too, but this was retracted for most of that flight.
Quite a bit of muck inside the engine compartment – like somebody was chucking bits of food at the exhaust system, etc, and these got toasted on impact. Took a bit of cleaning but looks OK now especially after ACF50
dublinpilot wrote:
Is there such a thing a cheap (perhaps disposable) volcanic ash detector that could be used in flight?
I don’t think there is, nothing official anyway.
However, I wonder. During the islandic volcano crisis, we were repeatedly asked to provide “proof” to the press that the ash was there, even though it was visible to the educated eye and we had it on the LIDAR stations which were in use then. Until one guy had a brilliant idea and called the phenology department. And yes, they had a measuring station up a rather high mountian. Two phonecalls later, we got the pic (need to ask if it is still someplace) of the station’s pollen catcher: It was totally dark brown. That pic went on the national news that night and stopped all discussions in Switzerland about the authenticity of the threat.
So I wonder: How about putting a strip of double sided sticky tape someplace in the airflow and look at it after the flight. I’d say,someplace near but not directly on the engine inlet. And obviously somewhere it won’t do damage if it becomes loose and flies off.
What that would do is most definitly catch any volcanic ash or other dirt in the atmosphere. VA is very easy to identify by color and smell.
I was thinking the same as @arj1…
like somebody was chucking bits of food at the exhaust system, etc, and these got toasted on impact.
That doesn’t really fit my perception of „semi permanent cloud of volcanic ash around Sicily“.
Simply put, how can ash get toasted, melting… again?
TB20 the vacuum system air is drawn from the cockpit
And the air drawn from the cockpit is coming from… let me guess… outside?
