Airworthiness Directives; Meggitt (Troy), Inc. Combustion Heaters

We are superseding Airworthiness Directive (AD) 81-09-09 for certain Meggitt (Troy), Inc. (previously known as Stewart Warner South Wind Corporation and as Stewart Warner South Wind Division) Model Series (to include all the variants) 921, 930, 937, 940, 944, 945, 977, 978, 979, 8240, 8253, 8259, and 8472 combustion heaters. AD 81-09-09 required repetitive inspections of the combustion heater; repetitive installation inspections of the combustion heater; and, for combustion heaters having 1,000 hours or more time-in-service (TIS), overhaul of the combustion heater. This new AD requires detailed repetitive inspections, repetitive pressure decay tests, and disable/removal of the combustion heater if necessary. This AD was prompted by an airplane accident and reports that the heater was malfunctioning. We are issuing this AD to correct the unsafe condition on these products.