As were many in the aviation industry, officials at Diamond Aircraft were "surprised" by ExxonMobil's letter to its network of fuel suppliers warning against using jet fuel in piston-driven diesel aviation engines. Unlike most others, however, Diamond's brain trust has a vital stake in the issue, since their twin-engine DA42 Twin Star is powered by Thielert diesel engines. Notwithstanding the debacle over Thielert's insolvency and the resulting chaos surrounding support of DA42 powerplants, ExxonMobil's position confounded Diamond because the DA42 engines were certified by the FAA to operate on jet fuel and not certified to run on conventional diesel fuel. In a letter to Diamond aircraft operators, the company said it was unaware of any service difficulties resulting from the use of jet fuel. It further explained that it was aware of the safety issues cited by ExxonMobil-lack of established standards for ignition quality, freeze point and lubricity-but that all those concerns had been addressed during the certification processes, and the engines had still passed regulatory muster.