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My TBM700 neighbour that...

I am based at a sizeable turboprop service centre and apparently when the TBM850 came along, some of the owners started complaining about the engine costing them more money.

It was because the 850 (G1000) logs the engine temperatures, whereas on the 700 (EFIS40, no engine data logging) you could do what you like and so long as the engine didn't crack, etc, nobody would find out.

Shoreham EGKA, United Kingdom

Sebastian G and achimha, that would of course make sense and is a similar limit (1650F). It is however very definitely listed in the POH as an EGT limit.

All this hot start stuff is overblown. Of course you have to monitor things as the consequences are dire, but so long as you have a good battery, and we make sure we always do, it is unbelievably rare to get a hot start on a PT6. We have operated Kingairs for around 10 years and never had one, so I can't understand why these TBM guys are getting so bothered.

Same comments for Williams FJ44 engines.

Darley Moor, Gamston (UK)

I doubt hot starts are at all common. One pilot I know says that unless (a) our battery is shagged and (b) you are really not paying any attention, it is very hard to do it.

But you can overtemp the TBM PT6 during flight. On the 700 this is not logged. On the 850 it is.

Shoreham EGKA, United Kingdom

Well, logged or not, if you cruise with the ITT's too high you are in for an expensive hot section inspection or overhaul!

Darley Moor, Gamston (UK)

Are you sure actual individual over-temping events are an issue, and not the overall temperature trend?

As I understand it, the performance of the hot section degrades over time. Engine output is regulated via torque, so the engine has to work harder and harder to achieve rated output. The average ITT increases, up to the point where the engine needs an overhaul to maintain rated power without approaching/exceeding limits [or probably well before that]

So with trend monitoring, you might need an overhaul earlier than if on a fixed schedule, even if the ITT is always kept well within limits, just simply because of deterioration of the hot section.

Biggin Hill

On the subject of turbine maintenance, it's worth going onto YouTube and having a look at the AgentJayZ channel. He's a freelance turbine mechanic in northern Canada, and works on pretty much every turbine engine, from classics such as afterburning J-79 engines, the Orenda type 14, the Orenda Irquois (which would have gone in the Avro Arrow), turboshaft engines (including one in a speed boat), industrial engines like the GE LM1500 and LM2500. It's very easy to spend hours watching the videos.

Andreas IOM

The Garrett's normally need more power than the PT6's, as they have to spin up the gearing as well. However, they are slightly more efficient. The new upcoming Kestrel (a real looker) will have the Garrett (or Honeywell as they're now called). I've heard they cost about the same to maintain, but that there are perhaps more used parts and replacement engines to be had in Garrett-world, as they used to power so many early turbine twins.

The Garrets are not "slightly more efficient", I would call it "vastly" or at least "significantly" The issue in Europe is that there are very few maintenance shops that service Garrets. It doesn't help that the manufacturer charges a lot of money every year for shops to have the right to service them. And not to forget, the Garret turbines make a lot of noise.

The CEO of one of the big turbine manufacturers is my hangar neighbor and I had an interesting chat with him. He said that the market for turboprops is a very small one and is not growing at all. The GA market is kind of non-existent from his point of view and therefore there is almost no R&D on turboprop and GA turbines these days. Everything is focused on the big stuff.

The fixed pitched PA28's I've flown have a EGT gauge (which obviously rises as you lean) but the 'red line' (a needle) can be 'positioned' (set) by pressing ones thumb on the centre red bit and turning!!!! - I never understood the point of a 'red line' that was so easy to 're-position'.

The Arrow I've been flying more recently has the same gauge with the same 'easy set' red needle - think I'm right there, will check when next in the aircraft.

Easy adjustable 'red needle' - seems odd to me.

Regret no current medical
Sandtoft EGCF, North England, United Kingdom
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