"06/23/1967 Mohawk Airlines
BAC-111-204AF Blossburg, Pennsylvania The airplane crashed after an in-flight fire destroyed the pitch control systems. All 34 people aboard were killed. A malfunctioning nonreturn valve allowed hot engine bleed air to flow back through an open air delivery valve, through the APU and into an acoustic blanket lined section of the fuselage. This caused flexible hoses with hydraulic fluid to ignite and lead to an uncontrollable fire". Beware of check valves!!
"09/06/1971 Pan International
BAC-111 Hasloh, Germany The aircraft collided with a bridge, shearing off both wings, after a double engine failure occurred during takeoff. The water-injection system to cool the engines during takeoff was inadvertently filled with kerosene instead of water".
30 years ago, an operator in the plant I worked filled up antifoam liquid from a drum similar to an oil drum into the hydraulic governor of a large steam turbine. We found out when the governor started misbehaving!!
Source of plane accidents : http://planecrashinfo.com/unusual.htm