NHTSA Preliminary Evaluation PE17008

During the review of Motor Coach Industries (MCI) Early Warning Reporting (EWR) 2016 Q4 data, field reports were identified that described fires on 2 buses from different regions of the country.These fires were alleged to have occurred as a result of a loose clamp allowing the tailpipe to separate from the exhaust after treatment assembly.During exhaust after treatment regeneration high temperature gases were directed at the plastic rear bumper.Prior to the fires, there were no indications (such as soot trails) that the clamps were loose.When contacted, the fleet maintenance manager stated all maintenance schedules and DOT inspections had been performed without a failure citation of the exhaust systems. MCI addressed the issue by installing additional brackets to the pipe on all the other buses in the fleet ensuring the tailpipe stayed intact should the clamp lose torque.In correspondence with another fleet using the same style bus, the fleet safety manager described having loose clamps resulting in fires.The MCI fix for the second fleet was to install a shield at the rear bumper to deflect the high temperature exhaust gases in the event of the tailpipe separated from the exhaust after treatment system.This fix was different from the first fleet.During review of communications submitted in March 2017, the Office of Defects Investigation (ODI) identified MCI Service Bulletin No. 309 regarding a maintenance procedure of the exhaust system Torca Accuseal clamp.This bulletin instructed that a new clamp must be utilized after any service or maintenance is performed in which the existing clamp was loosened or removed.ODI requested further information on this bulletin and received warranty claims showing loose tailpipes.MCI has taken the position that fires at the clamp location were due to improper maintenance by the fleets.After analysis of data, provided by MCI to ODI in response to an information request letter, ODI found there was not an increasing number (claim rate