§29.1103 Induction systems ducts and air duct systems

(a) Each i nduction sy stem duct upst ream of the fi rst st age of t he engi ne supercharger and of the au xiliary p ower u nit co mpressor m ust have a drain to prevent the hazardous accum ulation of fuel and m oisture in the ground attitude. No drain may discharge where it might cause a fire hazard. (b) Each duct m ust be st rong enough to prevent induction sy stem fai lure from norm al backfire conditions. (c) Each duct connect ed t o com ponents between wh ich relativ e m otion co uld ex ist m ust have means for flexibility. (d) Each duct within any fire zone for which a fi re-extinguishing sy stem i s requi red m ust be at least: (1) Fireproof, if i t passes t hrough any firewall; or (2) Fire resistant, for ot her duct s, except that ducts for auxiliary power units must be fireproof within the auxiliary power unit fire zone. (e) Each auxiliary power unit induction system duct must be fireproof for a sufficient distance u pstream o f th e auxiliary power unit compartment to prevent hot gas reverse flow from burning through auxiliary power unit ducts and entering any other com partment or area of the rotorcraft in which a hazard would be created resulting from t he ent ry of hot gases. The materials used to form the remainder of the induction system duct and pl enum chamber of t he auxiliary power unit must b e cap able o f resistin g the maximum heat conditions likely to occur. (f) Each auxiliary power unit induction system duct m ust be const ructed of m aterials t hat will not absorb or trap hazardous quantities of flammable fluids that could be ignited in the event of a surge or reverse flow condition.