The 4 stroke engines are certified according to CS-22 Subpart H[1] for use in motorgliders, CS-LSA[2] and CS-VLA[3] type of aircraft.

Those with the casing of air-cooled beetle engines, and those with the largely similar, but stronger Wasserboxer casing used in late VW vans before the Volkswagen Transporter (T4).

Even though the Wasserboxer engine is water-cooled, this involves only the cylinders and the top.

This makes it possible to convert the Wasserboxer "back" to an air-cooled engine.

The benefits of this conversion is the added strength, and the size of the Wasserboxer casing will accept larger cylinders.