By Vincent Wigmans

Regularly we receive questions from European registered aircraft owners about flying on an on-condition program. But what does on-condition flying mean? In short, it means, flying with an aircraft that has parts installed that are outside their overhaul limitations. To give an example, all piston engine manufacturers recommend a lifetime for their engines. This engine lifetime is given in days and hours. Mostly this lifetime is calculated around the 2000 hours or 12 years, whatever comes first. When a piston engine reached the end of its normal lifecycle you can expect some wear to the cylinders, pistons, bearings etc. But what if the aircraft engine reached 12 years but has only 800 hours on it. Then it can be that the engine is in a condition, suitable to continue in service for some years.

Several European CAA’s have accepted in the past that you can continue flying under an on-condition maintenance program. You needed to set up an additional monitoring program, which must be approved by your local CAA, with additional tasks to make sure the engine condition is good. Mostly these additional items described that you must fly a minimum of hours per month, perform additional analyzed oil samples and perform an additional on-condition inspection every six months. These inspections were necessary to determine and monitor any change of the condition of the engine. Flying on-condition was only possible in a non-commercial operation. These programs did not apply to US registered aircraft, which makes it attractive for aircraft owners to switch to an N-reg. 


Recently, EASA Part-ML has been implemented. These rules apply to EASA member state registered aircraft and are following more the FAA system, therefore the advantage to switch to an N-reg is limited. EASA Part-ML is applicable to privately owned and operated aircraft not exceeding, 2730 kg. The major advantage of EASA Part-ML is that aircraft owners get more flexibility in maintenance. 

Under EASA Part-ML, the aircraft owner can declare an Aircraft Maintenance Program (AMP) for their aircraft. This can be based on the Aircraft Maintenance Manual (AMM) or the Minimum Inspection Program from EASA (MIP). If you declare that your aircraft will be maintained i.a.w. the AMM, then you do not have to create a customized AMP. 

All Airworthiness Limitations from the AMM (Chapter 4) incl. Airworthiness Directives (AD) are mandatory, items that are recommended (Chapter 5) can receive some deviations, this must also be translated to the AMP of the aircraft. These deviations cannot be less restrictive than the MIP and therefore on-condition means now days to inspect the items at least every 100 hours or annually, whichever occurs first. In any case, when you prepare to deviate from a recommended maintenance interval, a risk-based approach should be taken. If aircraft maintenance is not your core business, you can also decide to hire a professional to prepare an AMP for you.

For further questions, please feel free to contact us at You can also call us at +31 (0)15 820 0999.