It seems modern fighter aircraft are rather sensitive to what you put in their fuel tanks.
According to local media, the fuel used by the German Tornado fleet appears to have been mixed with ‘too much bio-diesel’.
According to news site Frankfurter Allgemeine, this was noticed during a routine check last Monday:
“The tolerance values are minimally exceeded,” said Colonel Kristof Conrath of the Tactical Air Force Squadron 51. “It’s not that the aircraft would fall from the sky. For safety reasons, all tanks of the aircraft must be flushed.”
It is understood that this breakdown is particularly annoying for the Luftwaffe, as training of new Tornado pilots is already three months behind.
There's more at the link.
I didn't know that the Luftwaffe was using biodiesel in its jet aviation fuel - presumably as an additive, just as we're using ethanol as a gasoline additive in the USA.
Automobiles are a bit sensitive to what's in their tanks, too. My father served in the Royal Air Force during World War II. At the start of the war in 1939, the RAF began to switch to 100-octane fuel for its high-performance aircraft engines (previously it had used 87-octane). Gasoline rationing was introduced at about the same time for all civilian vehicles. He used to tell us stories of how airmen, who couldn't get enough gasoline coupons to make the trip to London and back, would "borrow" a few gallons of 100-octane fuel from the bowser to top up their tanks. The engines of the time simply couldn't handle the hotter combustion temperatures of the aircraft fuel, and would burn out their valves, leading to drunken airmen stranded by the side of the road in the small hours of the morning, unable to get back to base. Misuse of "official" fuel was considered a serious offense, so many of them simply accepted the punishment for being late to return from liberty - then proceeded to repair their engines using RAF maintenance facilities as well! He used to laugh about that.