Summary
The FAA proposes to supersede an existing airworthiness directive (AD) that applies to all Short Brothers Model SD3-30 and SD3- 60 series airplanes equipped with certain fire extinguishers. The existing AD currently requires replacement of the covers for fire extinguisher adapter assemblies that are installed on certain bulkheads with new covers that swivel to lock the extinguishers in place; and replacement of nozzles and triggers on these fire extinguishers with better fitting nozzles and stronger triggers. The existing AD also currently requires the installation of new fire extinguisher point placards and a revision of the Airplane Flight Manual (AFM) to instruct the flightcrew in the use of the new covers for these adapter assemblies. This proposed AD would also require modification of the fire extinguishing point adapter assembly of the forward and aft baggage bays as applicable. This proposed AD also would add airplanes to the applicability. For these new airplanes, thisproposed AD would require a revision to the AFM for instructions on using the new fire extinguisher adapter. This proposed AD is prompted by reports of individuals experiencing fire extinguishant blowback when the extinguishant discharges through the fire extinguishing point adapters. We are proposing this AD to prevent fire extinguishant blowback, which could result in injury to a person using the fire extinguisher in the event of a fire.