§29.952 Fuel system crash resistance

Unless other m eans acceptable to the Agency are employed to minimise the hazard of fuel fires to occupant s fol lowing an otherwise survivable impact (crash landing), the fuel systems must incorporate t he desi gn feat ures of this paragraph. These system s m ust be shown to be capable of sustaining the static a nd dynam ic deceleration loads of th is p aragraph, co nsidered as u ltimate loads acting alone, m easured at the system component’s cent re of gravi ty wi thout st ructural damage to the system components, fuel tanks, or their attachm ents that w ould leak fuel to an ignition source. (a) Drop test requirements. Each t ank, or t he most critical tank, must be drop-tested as follows: (1) The drop height m ust be at l east 15.2m (50 ft). (2) The drop im pact surface must be non deforming. (3) The tan ks must b e filled with water to 80% of the normal, full capacity. (4) The tank m ust be enclosed in a surrounding st ructure represent ative of the installation unless it can be established that the surrounding structure is free of project ions or other desi gn feat ures l ikely t o contribute to rupture of the tank. (5) The t ank m ust drop freely and impact in a horizontal position ± 10°. (6) After the drop test, there must be no leakage. (b) Fuel tank load factors. Except for fuel tanks located so that tank rupture with fuel release to either significant ignition sources, such as engines, heaters, and au xiliary p ower u nits, o r occupants is extremely remote, each fuel tank must be designed and i nstalled t o ret ain i ts contents under the followi ng ultimate inertial load factors, acting alone. (1) For fuel tanks in the cabin – (i) Upward – 4 g. (ii) Forward – 16 g. (iii) Sideward – 8 g. (iv) Downward – 20 g. (2) For fuel t anks l ocated above or behind the crew or passenger compartment that, if l oosened, coul d i njure an occupant in an emergency landing – (i) Upward – 1.5 g. (ii) Forward – 8 g. (iii) Sideward – 2 g. (iv) Downward – 4 g. (3) For fuel tanks in other areas – (i) Upward –1.5 g. (ii) Forward – 4 g. (iii) Sideward – 2 g. (iv) Downward – 4 g. (c) Fuel line self-sealing breakaway couplings. Self-sealing breakaway coupl ings m ust be i nstalled unless hazardous relative m otion of fuel system components to each other or to local rotorcraft structure is demonstrated to be extremely improbable or unless other means are provided. The couplings or equivalent devices must be installed at all fuel tank-to-fuel lin e co nnections, tan k-to-tank in terconnects, and at ot her poi nts i n t he fuel system where local structural deformation could lead to release of fuel. (1) The design and const ruction of self-sealing breakaway couplings m ust incorporate the following design features: (i) The load necessary to separate a breakaway coupling must be between 25 and 50% of the minimum ultimate failure load (u ltimate stren gth) o f the weakest component in the fluid-carrying line. The separation l oad m ust i n no case be less than 1334 N (300 pounds), regardl ess of the size of the fluid line. (ii) A breakaway coupling m ust separate whenever its u ltimate lo ad (as defined i n sub-paragr aph (c) (1) (i) ) is applied in the failure modes most likely to occur. (iii) All breakaway coupling must incorporate desi gn provi sions to visually ascertain th at th e co upling is locked together (leak-free) and i s open duri ng normal installation and service. (iv) All breakaway couplings must incorporate desi gn provi sions t o prevent uncoupling or uni ntended cl osing due t o operational shocks, vi brations, or accelerations. (v) No breakaway coupling design may allow the release of fuel once the coupling has perform ed i ts i ntended function. (2) All individual breakaway couplings, coupling fuel feed sy stems, or equi valent means must be designed, tested, installed, and maintained so in advertent fu el sh utoff in flig ht is improbable in accordance with CS 29.955 (a) and must comply with th e fatig ue ev aluation requirements of CS 29.571 without leaking. (3) Alternate, equivalent m eans to the use of breakaway couplings m ust not create a survivable impact-induced load on the fuel line to wh ich it is in stalled g reater th an 25 to 50% of the ultimate lo ad (stren gth) o f th e weak est component in t he l ine and m ust com ply wi th the fat igue requi rements of CS 29.571 without leaking. (d) Frangible or deformable structural attachments. Unless hazardous relative m otion of fuel t anks and fuel sy stem components to local rotorcraft structure is dem onstrated to be extremely im probable in an otherwise survivable impact, frangi ble or l ocally deform able attachments of fuel tanks and fuel sy stem components to l ocal rot orcraft st ructure m ust be used. The attachment of fuel tanks and fuel system components t o l ocal rot orcraft structure. whether frangible or locally deformable, must be designed such that its sep aration o r relativ e lo cal deformation will occur without rupture or local tearout of t he fuel t ank or fuel system component that will cause fuel leakage. The ultimate strength of frangible or deform able attachments must be as follows: (1) The load required to separate a frangible attachment from its support structure, or deform a locally deformable attachment relative to its support st ructure, m ust be between 25 an d 5 0% o f th e m inimum u ltimate load (u ltimate stren gth) o f the weakest component in t he at tached sy stem. In no case may the load be less than 1334 N (300 pounds). (2) A frangible or locally deformable attachment m ust sep arate o r locally deform as intended whenever its u ltimate load (as d efined in sub-paragraph (d)(1)) is applied in the modes most likely to occur. (3) All frangible or locally deform able attachments m ust co mply with the fatigue requirements of CS 29.571. (e) Separation of fuel and ignition sources. To provi de m aximum crash resi stance, fuel m ust be located as far as practicable from all occupiable areas and from all potential ignition sources. (f) Other basic mechanical design criteria. Fuel tanks, fuel lines , electrical wires and electrical devices m ust be desi gned, const ructed, and installed, as far as practicable, to be crash resistant. (g) Rigid or semi-rigid fuel tanks. Rig id o r semi-rigid fuel tank or bl adder wal ls m ust be impact and tear resistant.