MOC VTOL.2330
Fire Protection in designated fire zones
n/a
1. Definitions and Terminology
In accordance with VTOL.2400, the aircraft lift/thrust system installation includes each component that is necessary for lift/thrust, affects lift/thrust safety, or provides auxiliary power to the aircraft.
Three types of Fire Zone can be found in electric lift/thrust systems. Among them there is the Designated Fire Zone, as defined in CS 29.1181, which should not be confused with the generic term designated fire zone used in the Special Condition VTOL encompassing zones of different fire risks.
For the purpose of this MOC, the following definitions are provided:
(a) Electrical Energy Storage System
The Electrical Energy Storage System (EESS) consists of the battery necessary for the propulsion of VTOL capable aircraft and its associated management system.
(b) Fire zones for the lift/thrust system
(2) Fire Withstanding Zone, FWZ
(3) Designated Fire Zone, DFZ (reserved)
(c) Explosive Fire Zone
The term is related to EESS (Electrical Energy System Storage) supplying an electric engine or powerplant installation and defined by a volume surrounding an EESS including or not an electrical lift/thrust unit. This volume contains the effect of a flame and/or sparks, heat, hot parts ejection, explosive behaviour of accumulated gases and prevents overpressure and its effects.
(d) Designated Fire Zone
The Designated Fire Zone encompasses the zones defined in CS 29.1181(a) regarding fires fed by a significant amount of flammable fluids.
(e) Fire withstanding Zone
Is a volume surrounding one or several electric lift/thrust units not containing a hazardous quantity of flammable fluids that could be open or closed and able to withstand the effect of a flame and/or sparks, arcing, heat, and hot parts ejection. It is assumed that a lift/thrust unit basically presents a fire hazard, which means that a fire withstanding zone will provide the minimum zonal fire protection.
(f) Closed Volume
A closed volume is a volume designed for the complete retention/ containment of fire – it does not preclude from draining or ventilation features that do not impact the fire containment capabilities of the volume or zone.
(g) Open Volume
An open volume is a volume designed for the partial retention/ containment of fire. The concept of open volume is applied on the FWZ. It prevents fire propagation by an appropriate choice of materials.
(h) Fire withstanding capability (Electrical lift/thrust unit fire)
The fire withstanding capability is the capability required of a Fire Withstanding Zone for electric lift/thrust unit installation, for a fire not confined in a Designated Fire Zone as defined in CS 29.1181(a).
This capability can be shown:
(1) by the test in section 3(e)(4) of this MOC, or
(2) following a fire threat characterisation of the electrical lift/thrust unit proposed by the applicant and accepted by the Agency. This characterisation should be performed using the representative design, material characteristics, power, etc. and should then be used to demonstrate the zone’s robustness against a fire threat.
(i) Explosive fire capability (Electrical Energy Storage System fire)
The explosive fire capability is the capability required to contain a thermal runaway of the propulsion batteries as defined in the accepted standards or means of compliance.
2. Applicability and Scope
This MOC VTOL.2330 will be developed in an incremental approach according to the following steps:
(a) Step 1: Air cooled engine with rechargeable batteries as electrical energy storage system that are not liquid cooled,
(b) Step 2: Air cooled engine with liquid cooled battery (oil, glycol water, etc…),
(c) Step 3: Other energy storage technologies (e.g. fuel cells, capacitors) or hybrid propulsion. For instance: liquid cooled engine with liquid cooled battery.
The MOC at hand provides guidance and methods for addressing the fire protection of the installation of electric propulsion systems in VTOL using rechargeable batteries as electrical energy storage system that are not liquid cooled [step 1]. Some provisions for steps 2 and 3 have already been included in this step 1 for clarity purpose, especially the definition of Designated Fire Zone in the VTOL context, and will be completed in the subsequent steps. For different energy storage technologies (e.g. fuel cells, capacitors) or hybrid propulsion systems this MOC is not yet applicable and will be completed [steps 2 and 3].
The certification of electric engines and propellers is not part of this MOC.
This MOC does not cover or replace applicable regulations for qualification, handling, storage, transport, and disposal of batteries.
It is applicable to VTOL capable Aircraft in Category Basic and Enhanced.
This MOC can also be followed to demonstrate compliance with VTOL.2325 and VTOL.2440, where applicable.
3. Protection against the effects of fire
(a) Fire protection of flight controls, lift/thrust unit mounts, and other flight structure: Flight controls, lift/thrust unit mounts and other flight structure located in the Fire Withstanding Zone, the Designated Fire Zone, the Explosive Fire Zone or in adjacent areas subject to the effects of fire, heat or arc-faults should be constructed of materials or shielded to withstand the effects of fire, so that they can perform their essential function at the most adverse operating condition.
(b) Areas adjacent to a Fire Withstanding Zone, a Designated Fire Zone or an Explosive Fire Zone: Components, electrical lines and fittings (including fire detection components, if any), located in an area adjacent to a Fire Withstanding Zone, a Designated Fire Zone or an Explosive Fire Zone should be constructed of such materials and located such that if a portion of the lift/thrust unit or EESS is subject to fire, heat or arc-faults, the following is ensured:
(1) continued safe flight and landing, for Category Enhanced VTOL capable aircraft, or
(2) controlled emergency landing, for Category Basic VTOL capable aircraft.
(c) Drainage and ventilation of Fire Withstanding Zone, Designated Fire Zone and Explosive Fire Zone:
(1) There should be a complete drainage of each part of each Fire Withstanding Zone or Explosive Fire Zone if any presence of fluids can occur.
(2) The drainage means should be:
(iii) effective under conditions expected to prevail when drainage is needed; and
(iv) arranged so that no discharged fluids or gases, smoke, soot, particulate will cause an additional hazard.
(3) In the absence of efficient draining, especially in case of a limited amount of fluids in EESS, these fluids can be contained within the zone, which then should be capable of resisting the increased fire threat.
(4) Each Fire Withstanding Zone or Explosive Fire Zone should be ventilated/exhausted to prevent the accumulation of hazardous gases, smoke, soot, particulate.
(5) No ventilation opening may be where it would allow the entry of fluids, of hazardous gases, smoke, soot, particulate or flame from other zones.
(6) The ventilation means should be:
(v) effective under conditions expected to prevail when ventilation is needed, and
(vi) arranged so that no discharge of gases, smoke, soot, particulate or flame will cause an additional hazard or impinge occupants or persons on the ground (refer to Hazard Areas, as defined in paragraph (d) of MOC VTOL.2400(c)(3)).
(d) Disconnect mechanism
(1) For each EESS there should be a means to quickly disconnect, either manually by the flight crew or automatically, and isolate the battery from the main electrical circuit during operation.
(2) For each lift/thrust unit there should be a means to quickly disconnect, either manually by the flight crew or automatically, and isolate the engine from the main electrical circuit during operation.
(3) If a manual disconnection means for a lift/thrust unit is implemented, it should be ensured that the connection can be re-established in flight.
(1) Each lift/thrust unit, should be isolated by a Fire Withstanding Wall, barrier, shroud, or equivalent means (for example, an air gap), from personnel compartments, structures, flight controls, and any other parts that may be affected by the lift/thrust unit fire and propagate it.
(2) Each element in the Fire Withstanding Zone, including its wall, barrier and shroud should be:
(i) constructed of self-extinguishing materials in order to prevent fire propagation. If an Open Fire Withstanding Volume is chosen, a minimum distance to materials not part of the zone should be established to prevent fire propagation.
(ii) constructed so that no hazardous quantity of fumes, flames, heat, arc or spark, and fluids, including liquid metal, can pass from any lift/thrust unit compartment to other parts of the VTOL capable aircraft, and
(3) In meeting this paragraph, account should be taken of the probable path of a fire as affected by the airflow in normal flight and vertical take-off and landing.
(4) Fire withstanding wall, barrier, and shroud - including any adhesives, resins, sealer coatings, grommets, bushings or fittings that make up the barrier assembly and installation - should be made of material shown to be flame resistant as per Appendix F of CS-23 Amdt. 4 when exposed to the following tests or their equivalent:
(i) Vertical tests of section (d) for 60 seconds, during which:
(A) the average burn length should not exceed 15cm (6 inches), and
(B) the average flame time after removal of the flame should not exceed 15 seconds, and
(C) drippings from the test specimen should not continue to flame for an average of 3 seconds after falling, and
(D) at no time should the flame penetrate (pass through) the material during application of the flame or subsequent to its removal.
(ii) 45-degree flame tests of section (f), during which the flame should not penetrate (pass through) the material during application of the flame or subsequent to its removal.
(f) Explosive firewall
(1) Each EESS should be isolated by an Explosive Firewall, shroud, or equivalent means, from personnel compartments, structures, flight controls, and any other parts that may be affected by fire, heat, sparks, ejected parts and pressure caused by the EES.
(2) Each opening in the Explosive Firewall should be sealed with close-fitting as grommets, bushings, or fittings able to withstand the heat and pressure created by a thermal runaway of the battery.
(3) Each Explosive Firewall and shroud should be:
(i) constructed of materials capable of withstanding the effects of a flame and/or sparks, heat, pressure and hot parts ejection, not allowing backside burning, backside ignition, or significantly high temperatures that can result in additional fire hazard,
(ii) constructed so that no hazardous quantity of fluid, gases, smoke, soot, particulate, liquid metal or flame can pass from any Explosive Fire Zone to other parts of the VTOL capable aircraft, and
(4) The conditions in (f)(3)(i) and (ii) should be fulfilled for the complete duration of an accepted Thermal Runaway Test as per MOC VTOL.2440.
(5) In meeting this paragraph, account should be taken of the probable path of a fire as affected by the airflow in normal flight and vertical take-off and landing.
(g) Detection systems
(1) Detection systems include but are not limited to: quick-acting fire, gases, overtemperature / undervoltage / overpressure sensors.
(2) For each EESS and lift/thrust unit, approved, quick-acting detectors should be provided in numbers and locations to ensure prompt detection of faults potentially leading to fire.
(3) Each detector should be constructed and installed to withstand any loads to which it would be subjected in operation.
(4) No detector should be affected by any oil, water, other fluids, or fumes, soot and corrosive gas that might be present.
(5) There should be a means to allow flight crew members to check the functioning of each detector system electrical circuit.
(6) The wiring and other components of each detector system in an electrical energy storage system compartment should have appropriate characteristics for the associated fire zone.
(7) No detector system component for any fire zone (FWZ, DFZ or EFZ) should pass through any other fire zone, unless–
(i) It is protected against the possibility of false warnings resulting from fires in zones through which it passes; or
(ii) The zones involved are simultaneously protected by the same detector and extinguishing systems.
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