This is a notable claim by Friedrich Merz, head of the CDU party and a member of the German parliament:
„Ich bereue nicht, dass ich zur Hochzeit von Christian Lindner geflogen bin. Um es mal auf den Punkt zu bringen: Mit meinem Kleinflugzeug verbrauche ich weniger Sprit als jeder #Dienstwagen eines Mitglieds der #Bundesregierung. Und deswegen fliege ich.“
Translation (via deepl.com):
"I have no regrets about flying to Christian Lindner's wedding. To put it in a nutshell: With my small plane I use less fuel than any #servicecar of a member of the #federalgovernment. And that's why I fly."
I'm very skeptical about this claim with regard to fuel usage. Aviation fuels cannot easily compared to fuel used for cars. Thus, it is hard to say what "uses more fuel" actually means. A literal reading would probably compare those fuels by volume in litres. Whilst I'd appreciate debunking or verifying the claim on that basis, I'd also be interested in how the carbon footprint stacks up (car vs plane) to be able to judge if — even if the literal claim would be true — it might be misleading.
Another thing to consider: How many electric cars are available for members of parliament. If an electric car had been available, this would debunk the literal claim immediately, but again, a comparison based on the carbon footprint (what kind of energy mix was available that day to [re-]charge the car) would be interesting.
Also relevant for discussion: The route via plane might be shorter than via car (although not necessarily). Answers should focus an the general claim (car vs. plane) but also consider the special circumstances of this route. I have not been able to find the actual flight data recording of the route.
The aircraft in question seems to be an DA62 (Source, in German).