Disclosed herein is a flame retardant thermoplastic resin composition including a polycarbonate resin, a branched acrylic copolymer, and a flame retardant. In this regard, a representative door assembly for a gas turbine engine includes: a door configured for alignment with an exit area of a nozzle and operative to variably open and close the nozzle exit area such that gas directed along a gas path defined, at least in part, by the nozzle exit area is regulated. The doping agent is an organic sulphonic acid which is allowed to absorb into the fibres in an aqueous medium, and after that a monomer corresponding to the polymer is brought into contact with the fibres and polymerised. The processor is further configured, in the event of a detected failure of Data Back End, to generate one or more authentication data sets in response to the request using the data stored in the memory, and send the generated data set to the Authentication Centre Front End via the interface. The locking elements and the support element are easily attached to the modular elements via rivets screws or similar fasteners.