ODI became aware of three bus fires that originated in the area of the transmission on the subject vehicles through media reports.Inspection of the vehicles indicated that the static parking brake, which is located behind the transmission, may have been applied as a result of an air leak while the vehicles were in motion.Under certain driving conditions, the parking brake can apply without the audible driver warning engaging.Parking brake application while the vehicle is in motion may result in a fire.To address the concerns of this investigation, Navistar has issued a recall (12V-479) that will add a switch to detect parking brake lever movement while the vehicle is in motion (in addition to the existing switch that monitors brake line air pressure) and set an additional warning light to warn the driver of application of the parking brake.Navistar's recall actions address the issues raised by this investigation and as a result this investigation is closed.