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Calendar time for engine overhauls

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Calendar time for engine overhauls

Old 20th Apr 2021, 02:17
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Calendar time for engine overhauls

Hi all,

Looking into the costs associated with aircraft ownership. I know engines need to be overhauled according to the hourly limits imposed in the POH, but what are the rules (in Australia) surrounding calendar time limits? Scenario: I want to buy an entry level hour builder while I work toward CPL, I have found several aircraft that have in excess of 800 hours left to run before they're due for their overhaul, but they're still on the original engines from, say, 1970 so "beyond calendar time". Do I need an overhaul?

I've had some people tell me that my purpose is private, not charter, so I can fly these aircraft without an overhaul. But others have said that flight training would count as air work and therfore require an overhaul.

Can anyone shed some light here?

Thanks.
phlegm is offline  
Old 20th Apr 2021, 10:27
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The TBO hours and the calendar hours are manufactures recommendations. Most NAAs require that these recommendations are followed when the aeroplane is used for anything other than private use. However, there is usually a 20% extension available whatever the use and this period is known as 'on condition'. This is overseen by a licenced engineer and requires, typically, an inspection every 50 hours. When the aeroplane is used for private use only there are no limits to the on condition period, including a 12 year limitation.

If by example you bought a C150: the TCM 0-200 engine has a TBO of 1800 hours + 20% extension so totaling 2160 hours for professional use. What is most important for your situation is that the aircraft has been well maintained and that all ADs have been fully complied with. A survey is most important to confirm that the condition of the engine and the aeroplane generally is unlikely to require expensive maintenance in the foreseeable future. It is wise as a buyer to value the aeroplane based on the manufacturers TBO recommendations. It will be rarely viable to do any major repairs to a time expired engine. The only reasonable option could be a total rebuild/overhaul or a replacement. The seller of course will see it differently and may wax lyrical over the known reliability of the engine and that it could go on forever.
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Old 20th Apr 2021, 11:55
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What FF said, plus...

Though a calendar requirement for overhaul may not be applicable, you also don't want an engine which has sat idle for long periods. If the engine was built in the '70's, has been overhauled once or twice since, and used fairly regularly 50 hours or so a year, it's probably a better choice. If it has sat idle for months since the last overhaul (otherwise than having been properly preserved), be cautious - corrosion.

Cylinders should be considered long period consumable. They could need repair/replacement during the whole engine overhaul interval. For my experience, if one cylinder needs work approaching 1000 hours in service, you may as well have them all done.

For your reference, I bought my C150M in 1987, with 1700 hours since the second overhaul (so very close to the third), god a deal, 'run out engine. I flew it and checked it and the engine was good, the owner had taken care of it, and flown regularly. That was just when Canada was changing to engine on condition (my buying strategy). I put the engine on that program. I flew five hundred hours or so, overhauled all four cylinders, and the accessories, looked in to check the cam lobes, and kept flying. At 3600 hours since overhaul, I found some metal in the oil filter, so I disassembled it for inspection. The metal had come from the alternator drive, so non critical. The only defect in the engine itself was that one crankshaft bearing surface was 0.0008" undersize on the power side. I had the crankshaft ground ten under, MPI'd and reinstalled it. I also had the cylinders and accessories all overhauled too. The engine shop told me that for another $1000 in replacement parts (mostly valves), the engine could be recorded as "overhauled" (to zero time) rather than "repaired", so I did that.

I've flown it another 1000 hours since that overhaul, doing accessories as required along the way. I have just overhauled the cylinders again, and it runs very nicely. But frequent use, regular oil changes and maintenance are key to keeping your engine in good shape - rather than numbers in a log book!
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Old 22nd Apr 2021, 11:39
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Thanks both of you!

Originally Posted by Fl1ingfrog View Post
The TBO hours and the calendar hours are manufactures recommendations. Most NAAs require that these recommendations are followed when the aeroplane is used for anything other than private use
Do you know if flight training would still count as "private use"? I'm just worried that it might fall under air work and therefore require an overhaul.
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Old 22nd Apr 2021, 12:00
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If you are just hour building for a 200 hr cpl (and obviously hold an rpl or ppl) this would be private operations.
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Old 22nd Apr 2021, 16:26
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Do you know if flight training would still count as "private use"?
It most likely will depend upon how the airplane is registered. If it's a privately registered plane, being flown by the owner, or lent to someone else, it's private use. If it's a commercially registered plane, that commercial designation invokes the hours/calendar limitation on the engine, no matter by whom or how the plane is being flown.
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Old 22nd Apr 2021, 18:32
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It most likely will depend upon how the airplane is registered. If it's a privately registered plane, being flown by the owner, or lent to someone else, it's private use. If it's a commercially registered plane, that commercial designation invokes the hours/calendar limitation on the engine, no matter by whom or how the plane is being flown.
The 'Transport' and 'Private' designations no longer apply in the UK nor the EU and haven't for many years. A UK aeroplane is issued with a Certificate of Airworthiness whatever the purpose. The maintenance required though is dependent on the aircraft use. If the aircraft is used for gain (this doesn't only mean payments) then the aircraft must be maintained by a licenced engineer and a 'Release to Service' issued. If used solely for private use then many items of maintenance can be done by the owner and recorded in the log book/s, a Release to Service is not required for this.

With regards to engine hours a Release to Service can be issued up to the plus 20% (if allowed) on condition. I'm not sure about the 12 year calendar limit, this has been an issue for debate for some time now. It raised its head some years ago regarding imports. The CAA would not issue a C of A for engines of 12 years old. I'm not sure whether this has been resolved for ongoing use.

Perhaps someone knows what the Australian regulations are for certain.
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