Diesel exhaust fluid (DEF) is a urea-based chemical that is added to ground vehicle emissions systems to reduce nitrogen oxide (NOx) emissions. DEF is not designed, nor approved, for use in jet fuel. If it is inadvertently added to jet fuel, as has happened in several incidents over the last 2 years, DEF will react with certain chemical components to form crystalline deposits in the fuel system. The crystalline deposits can then accumulate on filters, engine fuel nozzles, and fuel metering components and result in a loss of engine power.