Complex sentence: Lebouder flew it until it was damaged in an accident in 1975; though the damage was chiefly to the undercarriage and propeller, the Autoplane never flew again though the road vehicle survived.
Split into simpler sentences: Lebouder flew it until it was damaged in an accident in 1975. The damage was chiefly to the undercarriage and propeller but the Autoplane never flew again, though the road vehicle survived.