NHTSA Preliminary Evaluation PE17004

On July 7, 2017, the Office of Defects Investigation (ODI) received a report from an executive officer of the State of Iowa's Bureau of Finance, Facilities, Operations & Transportation Services, informing ODI of numerous seat back pan weld failures (pan material fatiguing at weld points) in multiple 2011 model year (MY) Navistar IC school buses.In August 2017, ODI engineers found similar failures when they visited an Arlington, Virginia public school facility to inspect buses ranging from MY 2011 to 2015. The first MY2011 bus inspected demonstrated the same issue (broken back seat pan welds) as reported on the Iowa buses. MY2012 - MY2015 buses did not demonstrate the failed seat back pan issue. NHTSA discovered that these buses had a different seat back pan design.ODI opened this investigation to better understand the potential risk of injury and evaluate passengercompartmentalization in the event of a crash involving a subject vehicle containing broken seat back pan welds. Navistar conducted sled testing at the Transportation Research Center of Ohio (TRC) to better understand if broken seat back pan welds could lead to a loss of passenger compartmentalization in a crash. ODI engineers were present and observed all tests done by the manufacturer.Although the test results indicated that passengers would remain compartmentalized, upon further review, ODI became concerned that the test manikin's necks seemed to over-extend when their heads struck the seat back frame and the torso pushed into the seat back pan. There was a concern that injuries may occur as a result of the broken seat back pan welds, allowing the passenger torso to push further into the seat back than if good welds were in place. Upon NHTSA's request, Navistar ran additional sled tests with instrumented test manikins to measure injury potential in the head, neck, and chest. The tests were conducted using Federal Motor Vehicle Standard (FMVSS) 208 as a guide and reference as there are not specific standa