Derailer AKA derailleur is the mechanical thingy that moves the chain sideways to change gears on bicycles with external gear.
Mehrabpur derailment happened in 2007.
Matsukawa derailment happened in 1949.
Circumvesuviana derailment happened in 2010.
Jajapur derailment happened in 2009.
Rudine derailment happened on 2009-07-24.
Spanish River derailment happened in 1910.
Minot train derailment happened in 2002.
Brooks derailment happened on 2007-01-16.
Merano derailment happened on 2010-04-12.
King's Cross derailment happened in 2003.
Fiesch derailment happened on 2010-07-23.
Valencia Metro derailment happened in 2006.