Menu Sign In Contact FAQ
Welcome to our forums

Engine calendar life, where mandatory?

Hello everyone,

Could someone explain how the TBO for piston engine work ? We see manufacturers requirements of the type TBO 1500 hours or 12 years. Is it in the sense "whichever comes first" ? How should I read that as a prospective aircraft owner ?

I would be interested to know if there are national differences as well.

Is it in the sense "whichever comes first" ?


How should I read that as a prospective aircraft owner ?

It depends on the regulatory climate in the country where you are based.

In the USA, the UK, and I think most countries in Europe, you are allowed to run the "old" Lycoming or Continental engines past 12 years, and you can run them to 2000hrs, and then run them after that "on condition" (which basically means compression figures above certain limits, etc).

The scenarios where they can't be run past 12 years are generally when carrying paying passengers.

There are also other types of engine in use in aviation, where there may well be a hard "X years life" limit or a hard "X hours life" limit. What about the Rotax/Thielert/Austro engines?

Shoreham EGKA, United Kingdom

Thank you for your answer.

Since I fly in Switzerland, I found the related Technical amendements on the Swiss authorities website

As long as it's private flying under 5700kg , the TBO are recommendations only. However they seem to request the engine and propeler below manufacturer TBO at time of first registration.

However they seem to request the engine and propeler below manufacturer TBO at time of first registration.

That is not unusual.

In the UK, you cannot initially register a plane on the G-reg if the engine is over 12 years, as far as I know.

This affects even people who were G-reg, then went N-reg, then went past 12 years on the engine, then want to go back to G-reg, and they can't! But there is rarely a good reason to do that anyway...

Shoreham EGKA, United Kingdom

To add a little bit to this in the Canadian context, I will offer the following:

The national regulations are what you must do. You must only do what the manufacturer says, if the national regulations tell you that you must. The national regulations may allow you to treat that manufacturer's numbers as recommendations only. The national regulations may also give their own "hard times", irrespective of what the manufacturer says.

About 20 years ago, I participated in some of this rule making at Transport Canada, and outcome (in part) is as follows:

Variable Pitch Propellers (amended 2007/12/30; previous version) Except for aircraft that are operated under a special certificate of airworthiness in the owner-maintenance or amateur-built classification, all variable pitch propellers shall be overhauled at the following intervals: (amended 2007/12/30; no previous version)

(a) Where the manufacturer has made recommendations regarding the air time between overhauls, overhaul at the interval recommended or every ten years, whichever comes first; (amended 2000/12/01; previous version)

(b) Where the manufacturer has not made any recommendations regarding TBO, the propeller(s) shall be overhauled at the following intervals: (amended 2000/12/01; previous version)

(i) in the case of propellers installed on turbine engines: 2,000 hours air time or ten years, whichever comes first; (amended 2000/12/01; previous version)

(ii) in the case of double acting propellers installed on piston engines: 2,000 hours air time or ten years, whichever comes first, or; (amended 2000/12/01; previous version)

(iii) in the case of single acting propellers installed on piston engines: 1,500 hours air time or ten years, whichever comes first. (amended 2000/12/01; previous version)

Information Note:

The ten year overhaul intervals mentioned in (a) and (b), start either from its initial date of installation following manufacture, from its last five year corrosion inspection or its last overhaul, whichever occurred last. (amended 2000/12/01; previous version)

6. Fixed Pitch and Ground Adjustable Propellers

(a) Fixed pitch wooden propellers shall be checked for tightness after the first 25 hours of air time following their installation and at each subsequent inspection. (amended 2007/12/30; no previous version)

(b) At intervals of not more than 5 years, the propeller shall be removed from the aircraft and inspected for corrosion or other defects over its entire surface, including the hub faces and the mounting hole bores. While the propeller is removed, it shall also be checked for correct dimensions. However, if defects which require repairs beyond those recommended as field repairs by the propeller manufacturer are found, the propeller shall be repaired by an organization approved for the overhaul of propellers. (amended 2007/12/30; previous version)

Information Note: (amended 1998/09/01; no previous version)

The dimensional check requirement does not include a check on blade twist. The dimensional check refers to changes in blade dimension resulting from repairs, particularly cropping of the tips. It is intended to ensure that the blade diameter remains within service limits.


All piston and turbine engines installed in aeroplanes and helicopters operated pursuant to CAR 406, in large aircraft operated pursuant to CAR 604, and in aircraft operated pursuant to Part VII, shall be overhauled at the intervals recommended by the engine manufacturer, or in accordance with an alternative hard time interval or an engine on-condition maintenance program approved in accordance with Appendix D.

Information Note: No hard time, including calendar time, between overhauls need be observed in the case of small aircraft reciprocating engines in non-commercial private operation


The accuracy of mechanical drag cup type tachometers, for fixed wing propeller driven aircraft, shall be checked on site annually, and be accurate to within the tolerances established by the aircraft manufacturer or, where no tolerance has been specified by the aircraft manufacturer, to within +- 4% of engine RPM at mid-point of the cruise range.

As you can see engines were relaxed from manufacturer's TBO's for non commercial aircraft, where propellers and tachometers were captured, where they had not previously been. Most of this was calendar, as we recognized that GA aircraft tend to calendar out before they time out. TC and our group recognized that some manufacturer's did not state any requirement for TBO or condition checks, so they had to be regulated somehow.

I can tell you that these numbers were all arrived at with consensus for Transport Canada staff, and industry (of whom I was one). This was certainly not a case where numbers were pulled from the air, and applied for no good reason. The industry experience with long term condition, maintenance and history of these items played a large role in the selection of times. Happily, Transport Canada staff recognized that industry held more valuable experience with these numbers than TC staff did, so they listened, and generally applied what we recommended. No-one in the room thought these items should not be regulated....

Sometimes regulation seems to come at random from on high. In this case, it was very much a regulator and industry partnership, and no one from industry was excluded from the meeting - a one plane owner could attend if they wanted, and would be heard.

Home runway, in central Ontario, Canada

How should I read that as a prospective aircraft owner? I would be interested to know if there are national differences as well.

On N-register, my aircraft are well maintained by me and my mechanics based on inspected condition and our careful and continuous on-site assessment of engineering data, plus a personal risk assessment for my private use. Exactly the same way I maintain my other eleven vehicles :-) My aircraft get probably four maintenance hours per flight flight hour. However, on N-register no legally mandated TBO or calendar life limit applies to any component of my aircraft, except as dictated by an AD. If that were to change in the future, and if my aircraft were subject to non-AD operational time or calendar time overhaul limits, I would re-register the aircraft in N-register Experimental Exhibition Category. If that proved impractical for any reason, I'd sell the aircraft.


for Switzerland that is exactly the rule. On Import, the engine and prop must be within limits. Therafter, you can fly them until they are out of tolerance. My engine had 2500 hours before it had to be done.

The moment however you fly commercial, the engine will go on revision every 12 years and the prop whenever it's time is up, no matter if you are way below TBO. I believe it is possible to get extensions to TBO but not to calendar time.

Private flying however, once you have the plane in Switzerland, you do not have to dismantle a perfectly serviceable engine or prop, you just need to increase controls after the TBO limit has passed.

Best regards Urs

LSZH, Switzerland

I understand new legislation comes up in EASA-land that regulates the issue of on-condition maintenance. I will post a link once I get the info. Now, the process of adoption in all individual countries (or not) is unclear to me. I thought that this compulsory adoption was the whole point of EASA.

My aircraft is registered in Holland, and the Dutch CAA says that I need to have my props inspected next year (6 year calendar interval), but my service center here in Spain is looking at the rules in Belgium. These props are in excellent condition, only having seen daylight during flight, 500 hrs on them.. If Belgium is more relaxed about On Condition maintenance than Holland is, I may consider reregistering. But then again, if new EASA legislation will rule soon anywhere....

This seems like an excellent forum to ask for some expert advice. Thanks in advance..

Private field, Mallorca, Spain

What about changing to N-reg instead of trying (and probably failing) to find a EASA-country that is more flexible towards On Condition maintenance?

Would it make any sense financially to make the change to N-reg, when talking about the DA42? On Condition rules for engine and props and hoses/pipes instead of replacement? I know there is the cost of a Trust, and the conversion to an N-licence, and of course the general tendency in Europe to get rid of all things N, but am still interested to look at this option.

Thanks in advance for your feedback.

Aart DA42.332 PH-CCD LESB (Palma de Mallorca, Spain) CPL/IR/ME/FI

Private field, Mallorca, Spain

In short: yes, it does make sense.

Mainz (EDFZ), Germany
75 Posts
Sign in to add your message

Back to Top