The FAA has issued a Special Airworthiness Information Bulletin regarding mufflers on reciprocating aircraft engines based upon a study conducted by Wichita State University which was completed last October. While the SAIB is not mandatory you should at least be aware of the highlights of the report (outlined below), the fact that the FAA is concerned and take a moment to download the checklists at the end of this post.
Exposure to carbon monoxide (CO), which is formed by the incomplete combustion of carbon-containing materials such as aviation fuels, is associated with headache, dizziness, fatigue, and at elevated doses, death. Exhaust system failures in general aviation (GA) aircraft can result in CO exposure. When this occurs in an aircraft, the end result could be an accident. A total of 71,712 accident cases between 1962 and 2007 were reviewed from the National Transportation Safety Board (NTSB) accident/incident database. The review of these cases revealed that the CO-related accidents occurred throughout the year; however, the accidents caused by leakage in the muffler or exhaust system were more prevalent in the colder months. Furthermore, it was shown that the majority of the mufflers’ CO-related accidents had muffler usage greater than 1000 hours. The FAA standard for CO in an aircraft cabin is no more than 50 ppm ; however, there is currently no requirement to monitor for CO in the cabin. Due to the colorless and odorless characteristics of CO, it is extremely difficult to determine if hazardous levels of CO are in the cabin without some type of CO detector technology. However, little guidance exists regarding suitable CO detector technology for use in GA aircraft. Additionally, if CO detectors are used in the cabin of GA aircraft, no guidance exists to recommend the best placement to detect CO quickly and accurately. Hazardous situations, such as CO exposure, which may arise as a result of inefficient exhaust system maintenance and inspection together with the complexity of the exhaust system, demand effective practices in inspecting GA aircraft exhaust systems. Familiarity with the signs and causes of exhaust system failures can facilitate the identification and prevention of exhaust system failures that may result in CO exposure. Accompanied by a thorough visual inspection, an air pressure test may increase the chance of identifying cracks, damage, and developing deterioration. Performing a thorough visual inspection together with an air pressure test and considering an appropriate muffler lifetime before replacement can be considered the primary prevention methods for CO exposure in GA aircraft. Finally, utilization of the exhaust system inspection and maintenance checklists for pilots and mechanics developed in this study may aid in the process of exhaust system inspections to reduce the likelihood of missing indicators that are related to exhaust system failures. To achieve consistent best practices in exhaust system inspection and maintenance, a pilot and mechanics checklist was prepared based upon the review of FAA guidance documents, service manuals, and the survey of best practices in inspection and maintenance of exhaust systems. The intention of the checklists is to increase the communication between the pilot and mechanics and to aid in the process of exhaust system inspections. The pilot checklist is to be completed by the pilot and given to the mechanic as the aircraft is brought in for inspection and/or maintenance. The pilot checklist is intended to identify if triggers have been met and that a more detailed inspection is warranted. The mechanic checklist is to be completed by the mechanic during the inspection process to identify any indicators of exhaust system problems that may warrant more detailed inspections. Thus, the checklists are to be used as an aid to determine if an exhaust system problem exists. You can download your own copy here of the Exhaust System Checklists. Until next time keep your wings straight and level Hersch! JetAviator7 What is the cause of most aviation accidents: Usually it is because someone does too much too soon, followed very quickly by too little too late. — Steve Wilson, NTSB investigator, Oshkosh, WI , August, 1996. ps: Don't forget to sign up for our newsletter "All Things Aviation" here!