Extract from: "The emergency and abnormal situations project"; last seen via NASA, - use Google search
"The Transportation Safety Board (TSB) of Canada studied 15 in-flight fires that occurred over 31 years (TSB, 2003). The Board determined that the average amount of time between the detection of an on-board fire and the point at which the aircraft ditched, conducted a forced landing, or crashed was 17 minutes. Seventeen minutes is not a lot of time to complete a diversion from cruise altitude, and half of these flights had less than that amount of time".
NB SR111 (MD11) crashed 17 min after the first detection of smoke.
Quotes from TSB investigation / safety recommendations re SR 111: “Appropriate regulatory authorities take action to ensure that industry standards reflect a philosophy that when odour / smoke from an unknown source appears in an aircraft, the most appropriate course of action is to prepare to land the aircraft expeditiously.”
“Appropriate regulatory authorities ensure that emergency checklist procedures for the condition of odour / smoke of unknown origin be designed so as to be completed in a timeframe that will minimize the possibility of an in-flight fire being ignited or sustained.”