AMC1 31TGB.67 On-board power units

ED Decision 2013/011/R

For this AMC, it is assumed that only power units are used which conform to the state-of-the-art industrial standard. The safe operation of the balloon is not directly dependent on the proper function of the power unit. For all other designs, the Agency is consulted for more detailed requirements.

Power units of industrial standard used on-board of the balloon in addition comply with the following:

(a)     General

The power unit is designed and installed so that under all normal operating conditions and reasonably foreseeable in service emergency situations, it does not endanger the aircraft, its occupants, or third parties.

(b)     Ventilation

The occupants are accommodated in adequately ventilated areas where:

(1)     the carbon monoxide partial pressure does not exceed 1/20 000; and

(2)     fuel vapour is not present in harmful concentrations.

(c)      Fire extinguishers

(1)     Unless the power unit has a fire extinguishing system by itself, there is at least one manual fire extinguisher within reach of an occupant.

(2)     The following applies to manual fire extinguishers. The type and quantity of the fire extinguishing substance is appropriate to the fire extinguisher's application area. Fire extinguishers:

(i)      conform to EN3 or an equivalent specification acceptable to the Agency;

(ii)     have a minimum capacity of 2 kg when using dry powder, unless the capacity is otherwise determined by the applicant; and

(iii)     be at least of comparable effect when the extinguishing means is other than ‘dry powder’.

(3)     Fire extinguishers in compartments intended for persons are designed to minimise the risk of toxicity caused by use of the fire extinguishing substance.

(d)     Gondola

The following applies to the gondola when an on-board power unit is carried:

(1)     The material used is at least fire retardant.

(2)     Pipes, tanks or equipment that carries fuel, oil or flammable liquids are not to be placed in the gondola unless they are reasonably shielded, insulated, or otherwise protected so that fracture or failure of such parts causes no danger.

(e)     Electrical earth connection

(1)     In order to prevent the occurrence of potential differences between components of the power unit and other electrically conductive parts of the balloon which cannot be ignored on account of their mass, such conductive parts are conductively interconnected.

(2)     The cross-sectional area of bonding connectors, if made from copper, is not less than 1·33 mm².

(f)      Fire protection for control system and structure

Control systems, suspension units or other structures in the power unit compartment which are added to the design by the applicant are made of fireproof material or shielded to withstand the effect of a fire.

(g)     Fire protection

(1)     The power unit is adequately separated from the balloon's structure by fireproof bulkheads or ventilated bays.

(2)     Areas in which combustible liquids can accumulate as a result of a leaking tank have an adequate drain pipe. Collected leaking liquids cannot reach other locations in and under the craft which pose a potential risk of fire.

(3)     Precautionary measures are to be taken to reduce as far as possible the risk of fire as a result of a hard landing of the gondola.

(h)     Power unit installation

(1)     Each power unit is supported so that the loads resulting from the weight of the unit are not concentrated.

(2)     There are pads, if necessary, to prevent chafing between each unit and its supports.

(3)     Materials employed for supporting the unit or padding the supporting members are non-absorbent or treated to prevent the absorption of fuel.

(4)     Each installation is ventilated and drained to prevent accumulation of flammable fluids and vapours.

(i)      Fuel tank expansion space

(1)     Each external fuel tank added to the design by the applicant has an expansion space of sufficient capacity, but of not less than 2 % of the tank capacity, to prevent spillage of fuel onto the surfaces of the power unit and the balloon's structure due to thermal expansion or manoeuvre unless the design of the venting system precludes such spillage.

(2)     It is not possible to fill the expansion space inadvertently with the power unit in any normal ground attitude.

(j)      Exhaust system, general

(1)     The exhaust system ensures safe disposal of exhaust gases without fire hazard or carbon monoxide contamination in any personnel compartment.

(2)     Each exhaust system part with a surface hot enough to ignite flammable fluids or vapours is located or shielded so that leakage from any system carrying flammable fluids or vapours will not result in a fire caused by impingement of the fluids or vapours on any part of the exhaust system, including shields for the exhaust system.

(3)     All parts of the exhaust system are located sufficiently far from or separated from adjacent parts of the balloon's structure by fireproof shielding.

(4)     No exhaust gases will discharge dangerously near any oil or fuel system drain.

(5)     Each exhaust system component added to the design by the applicant is ventilated to prevent points of excessively high temperature.

(k)     Firewalls

(1)     The power unit is isolated from the rest of the balloons structure by a firewall, shroud, or equivalent means.

(2)     The firewall or shroud is constructed so that no hazardous quantity of liquid, gas or flame can pass from the power unit compartment to other parts of the balloon.

(3)     The firewall and shroud is fireproof and protected against corrosion or deterioration. The following materials are accepted as fireproof, when used in firewalls or shrouds, without being tested:

(i)      stainless steel sheet, 0·38 mm thick;

(ii)     mild steel sheet (coated with aluminium or otherwise protected against corrosion) 0·5 mm thick;

(iii)     steel or copper base alloy firewall fittings.

(4)     Other materials such as fire protection paint and/or putty are only used if they conform to the FAA Advisory Circular No. 20-135 or equivalent accepted specifications.