Peter wrote:
Wiki says the Mirage is piston (“Malibu Mirage”). The Meridian is a TP (turboprop) and was marketed as “Malibu Meridian”.Hence how would “running costs are not very different between a Meridian and a Mirage” be possible?
I assume the idea behind this is that although the turbine engine is much more expensive in purchase and overhaul its more simple in many ways (less moving parts) and requires less unscheduled maintaince than a piston. PT6-35 on the jetprop has 4000 hours TBO from what I can read, and that should actually be possible to reach and even continue beyond. TBO for the TIO-540 is 2000 hours if it doesn’t need work before. The fuel flow is much higher for the turbine but with the higher avgas prices in Europe vs JET A1 then the difference becomes smaller. On top of this the Jetprop/Meridian cruises faster and therefore has less flight hours for a given distance.
Yes see e.g. here. Based on knowing many owners I would be amazed if any piston PA46 made 1k hrs before changing cylinders.
A PT6 is much more reliable.
Also whether you get duty free fuel varies. In the UK you do not (there is a self declaration system).
Peter wrote:
any piston PA46 made 1k hrs before changing cylinders.
That’s indeed very unlikely. 800h is feasible. If you treat your cylinders as consumables (and get away from the “traumatising” aspect of thinking about changing them as a “top overhaul”), the cost per hour isn’t dramatic at all though.
While a thumbs up on a PT6 if you are looking for more dependability in a single engine, there are a few arguments for the defence for a Continental 520 or Lycoming 540:
- for a typical profile of 100-500nm sectors and 80-120 hours p.a. the piston is fine – an aircraft with relatively low usage and sector distance tend to be good candidates for piston – air ambulance that use Cessna 421 might be a good example
- quite likely that a turbo charged piston, even if operated correctly and with good inter coolers, will require a few cylinders being overhauled en route to TBO, but this is a relatively straightforward maintenance item with a reasonable budget – having a sensible SOP on engine management usually works, and perhaps sticking to mid teens on FL
- the maintenance budget, even adjusted for longer TBO of a turbine, is lower
- fuel consumption is much lower
- keeping your batteries up to scratch on the PT6 is a go no-go, and ham fisted hot starts do occur, perhaps as often as the odd cylinder overhaul – no prize to guess which costs more
The reliability of a PT6 is the main argument for. Also on the horizon is the supply of Avgas. It would be interesting to run an NTSB search on how many PA-46 piston have had in flight engine failures.
AOPA NTSB last five years only shows one engine failure on the PA-46
https://www.aopa.org/asf/ntsb/narrative.cfm?ackey=1&evid=20170731X62912
…and helpfully none of the turbine PA-46 have had an engine failure in the AOPA NTSB database
There’s definitely been PT6 issues in the PA46 (rollbacks), don’t know why they don’t appear on the databases… In the piston there’s been more than 1 but thanks to an excellent glide ratio and focused training, they can be handled safely
Peter wrote:
Based on knowing many owners I would be amazed if any piston PA46 made 1k hrs before changing cylinders.
An exchanged cylinder is not very expensive for this kind of plane (in the “5 flight hrs.” cost range). So no real factor. One cylinder every 500hrs. would add less than 1 Percent to hourly cost.
When comparing piston to turbine Malibu one also has to keep in mind, that no PT6 makes it to TBO w/o hot section inspection at halftime. That is a 40k ticket – you can buy lots of cylinders for 40k…
Real world cost comparison between Piston and Turbine Malibu depends extremely on mission profile. If you use your Malibu as long to mid range IFR workhorse, than cost per NM are truly comparable: The higher fuel flow is compensated by cheaper Jetfuel and (most important) faster climb with longer part of the flight at high altitude cruise speed.
But, there are also other mission profiles esp. if you are a private owner:
- You might want to operate your Malibu VFR at lower altitudes
- You might operate under airspace structures that do not allow the “Turbine optimized profile” of climbing at max roc to cruise altitude esp. if you fly on Z-flightplans from non instrument airports.
- You might fly less than 200hrs/year in a piston so that the “saved time” in a turbine leads to subcritical yearly hours and therefore increases hourly cost due to fixed cost.
In short: If you use a Malibu more like a typical privately owned piston plane with the added comfort of a pressurized cabin and the luxury of going over the Alps at FL220 w/o oxygen for this 2-3 trips to the mediterranean per year but also a couple of <200NM pizza flights, the piston will be significantly cheaper in hourly cost than the turbine.
If you treat your cylinders as consumables (and get away from the “traumatising” aspect of thinking about changing them as a “top overhaul”), the cost per hour isn’t dramatic at all though.
How about the downtime?
It takes quite a lot of work to access the bottom of a cylinder, before you can change it. Well, unless it is #2 on an IO540 which is easy 
You will spend hours just removing the baffles. Then you have to remove some portion of the exhaust system. I’ve seen it.
And then you have to fly a more careful mission profile because you have done major engine work. It’s not a picnic.
I reckon there must be a lot of people who get a 50/80 compression test and just fly with it, in the hope that nothing big will come off in flight.
At the same time I don’t want to start another “turbo v. non turbo” thread – one is here – because they represent very different camps which by definition shall never mix And on the PA46 piston you don’t get the choice. All the piston ones eat cylinders for breakfast, according to the owners.
RobertL18C wrote:
It would be interesting to run an NTSB search on how many PA-46 piston have had in flight engine failures.
Feels like one every 3-4 years globally – compared to about 10 PA-46 accidents that is in the ballpark of 2-3% of all Malibu accidents.
Peter wrote:
How about the downtime?
…
I reckon there must be a lot of people who get a 50/80 compression test and just fly with it, in the hope that nothing big will come off in flight
For commercial operators downtime is a big thing – for private ones not so much as the plane is often on the ground for multiple days anyways.
Plus: A 50/80 compression is bad for power, but not an indicator of an upcoming catastrophic failure (if compression has degraded gradually over time and not dropped from one flight to another). Therefore waiting with the replacement of the cylinder until you don’t need the plane anyways for a week is perfectly safe.
