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(a) The aircraft must be designed to minimise the risk of fire initiation due to:
(1) anticipated heat or energy dissipation or system failures or overheat that are expected to generate heat sufficient to ignite a fire;
(2) ignition of flammable fluids, gases or vapours; and
(3) fire-propagating or -initiating system characteristics (e.g. oxygen systems).
(4) a survivable emergency landing.
(b) The aircraft must be designed to minimise the risk of fire propagation by:
(1) providing adequate fire or smoke awareness and extinguishing means when practical;
(2) application of self-extinguishing, flame-resistant, or fireproof materials that are adequate to the application, location and certification level; or
(3) specifying and designing designated fire zones that meet the specifications of VTOL.2330.
MOC VTOL.2325(a)(4) Fire Protection - Energy storage crash resistance
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1. Introduction and scope
VTOL.2325 (a)(4) requires that the energy storage system and its installation in the aircraft are designed to minimise the risk of post-crash fires in survivable emergency landings. The ultimate goal is to provide occupants with sufficient time to evacuate or be extracted from the aircraft following such events.
The similarity of VTOL capable aircraft and small rotorcraft justifies the consideration of the design and test criteria as being comparable and therefore applicable. These criteria, mainly contained in CS 27.952 Amdt. 6 and CS 27.561 Amdt. 6, have proven to be successful in a large number of accidents in preventing or delaying the onset of post-crash fires, thus maximising the occupant escape time after survivable emergency landings.
The main concern in small rotorcraft are crash-induced fuel leaks that quickly come in contact with ignition sources during or after impact. It is recognised that there are many possible energy sources in VTOL capable aircraft (fuel, electricity, gas) that require the need to consider other forms of fire initiation. However, they do not invalidate the defined emergency landing conditions for which the design needs to show its capability to minimise the risk of fire initiation.
The following accepted means of compliance with VTOL.2325(a)(4) therefore builds on the design and test criteria contained in CS 27.952 Amdt. 6 and CS 27.561 Amdt. 6, complementing or adapting them, whenever necessary to account for different energy sources.
In addition, this MOC also constitutes an accepted means of compliance with VTOL.2430(a)(6) regarding the energy retention capability of the energy storage and distribution system during a survivable emergency landing on land. Specific considerations for the demonstration of compliance with VTOL.2430(a)(6) of VTOL capable aircraft intended to be used for operations on water, emergency flotation or ditching as per VTOL.2310 or over water are provided in MOC VTOL.2430(a)(6).
2. Energy Storage crash resistance
(c) In addition, no harmful amounts of liquids or toxic fumes or gases should enter an occupied area or the evacuation path.
Each energy storage system, or the most critical energy storage system, should be subject to a drop-test using the following methodology:
(a) the drop height should be at least 15.2 m (50 ft);
(b) the drop impact surface should be non-deforming;
(c) the energy storage system should be charged or filled to its most critical condition expected during a crash;
(d) the energy storage system should be enclosed in a surrounding structure representative of the installation unless it can be established that the surrounding structure is free of projections or other design features likely to contribute to rupture of the energy storage system;
(e) the energy storage system should drop freely in an orientation that is representative of a typical installation on the aircraft and impact in a horizontal position ±10°with regards to the horizontal axis of the VTOL; and
(f) after the drop test there should be no risk of post-crash fire or other harmful release within a time frame compatible with the rescue of seriously injured occupants.
(1) For liquid or gaseous fuels: no leakage of flammable fluids or gases.
(2) For batteries:
(i) structural damage should not lead to a fire, leakage of harmful fluids, fumes or gases; or
(ii) any fire or leakage of harmful fluids, fumes or gases should be contained for at least 15 minutes in non-occupied areas and outside the evacuation path.
(3) Any projectile release should not lead to serious injury to occupants or persons on ground.
4. Energy storage system load factors
(a) Except for energy storage systems located so that structural damage to the energy storage that could cause fire, leakage of harmful or flammable fluids or gases, or toxic fumes in occupied areas or the evacuation path is extremely remote, each energy storage system should be designed and installed to retain its contents under the following ultimate inertial load factors, acting alone.
(b) For energy storage systems in the cabin:
(1) Upward – 4 g.
(2) Forward – 16 g. (18 g for CTOL)
(3) Sideward – 8 g.
(4) Downward – 20 g.
(5) Rearward – 1.5 g.
(c) For energy storage systems located above or adjacent the crew or passenger compartment that, if loosened, could injure an occupant in an emergency landing:
(1) Upward – 1.5 g.
(2) Forward – 12 g.
(3) Sideward – 6 g.
(4) Downward – 12 g.
(5) Rearward – 1.5 g.
(d) For energy storage systems in other areas:
(1) Upward – 1.5 g.
(2) Forward – 4 g.
(3) Sideward – 2 g.
(4) Downward – 4 g.
5. Energy storage system isolation means
(a) For liquid or gaseous fuel systems, self-sealing isolation means should be installed unless hazardous relative motion of energy storage system components to each other or to local aircraft structure is demonstrated to be extremely improbable or unless other means are provided.
(b) The isolations means, such as a fuses, couplings or equivalent devices should be installed where structural deformation could lead to a hazard to the occupants due to high energy release or release of harmful amount of fluids or gases.
(2) a breakaway coupling should separate whenever its ultimate load (as defined in sub-paragraph 5(c)(1)) is applied in the failure modes most likely to occur;
(3) all breakaway couplings should incorporate design provisions to visually ascertain that the coupling is locked together (leak-free) and is open during normal installation and service;
(4) all breakaway couplings should incorporate design provisions to prevent uncoupling or unintended closing due to operational shocks, vibrations, or accelerations; and
(5) no breakaway coupling design may allow the release of liquid or gaseous fuel once the coupling has performed its intended function.
(d) For electrical energy storage systems:
(i) automatic, unless this is demonstrated to be impractical, in which case other means acceptable to the Agency may be employed.
(ii) indicated to the flight crew and rescue personnel.
(e) All individual isolation means, such as fuses, emergency stop, breakaway couplings, coupling fuel feed systems, or equivalent means should be designed, tested, installed and maintained so that inadvertent activation in flight is minimised to the maximum extent practicable. It should be ensured that the isolation means are not degrading beyond an acceptable level in accordance with the reliability requirements for systems and the fatigue requirements for structural installations.
6. Frangible or deformable structural attachments
(a) Frangible or locally deformable attachments of energy storage system components to local aircraft structure should be used unless hazardous relative motion of energy storage system components to local aircraft structure is demonstrated to be extremely improbable in an otherwise survivable impact.
(b) The attachment of energy storage system components to local aircraft structure, whether frangible or locally deformable, should be designed such that separation or relative local deformation of the attachment of energy storage system components will occur without rupture or local tear-out of energy storage system components that will could cause leakage or high energy release.
(d) A frangible or locally deformable energy storage system components attachment should separate or locally deform as intended whenever its ultimate load (as defined in sub-paragraph 6(c)) is applied in the modes most likely to occur.
(e) All frangible or locally deformable energy storage system components attachments should comply with the fatigue requirements of CS 27.571 Amdt. 6.
7. Separation of flammable fluids or gases and ignition sources
To provide maximum crash resistance, flammable fluids or gases should be located as far as practicable from all occupiable areas and from all potential ignition sources.
8. Other basic mechanical design criteria
Battery system components, electrical wires, and electrical devices should be designed, constructed and installed, as far as practicable, to be crash resistant.
9. Rigid or semi-rigid fuel tanks
Rigid or semi-rigid fuel tank or bladder walls should be impact and tear resistant.
MOC VTOL.2325(b)(1) and (b)(2) Fire Protection: fire extinguishers and design of interiors
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1. Category Basic
(f) Fire Extinguishers: CS 23.851(a), (b)(1), (c) Amdt. 4 are accepted as a means of compliance
(g) Compartment interiors: CS 27.853 Amdt. 6 is accepted as a means of compliance.
(h) Cargo and baggage compartment: CS 27.855 Amdt. 6 is accepted as a means of compliance.
2. Category Enhanced
For Category Enhanced the means of compliance accepted for Category Basic should be completed with the following provisions:
(a) Compartment interiors: CS 29.853(a), (b) and (d) Amdt. 7 are accepted as a means of compliance.
(b) Baggage compartment:
A baggage compartment that is located where the presence of a fire would not easily be discovered by a pilot while at his station should:
(1) Have ceiling and sidewall liners and floor panels constructed of materials that have been subjected to and meet the 45° angle test of Appendix F to CS-23 Amdt. 4. The flame should not penetrate (pass through) the material during application of the flame or subsequent to its removal. The average flame time after removal of the flame source should not exceed 15 s, and the average glow time should not exceed 10 s. The compartment should be constructed to provide fire protection that is not less than that required of its individual panels; or
(2) Be constructed and sealed to contain any fire within the compartment or have a device to ensure detection of fires or smoke by a crew member while at his station and to prevent the accumulation of harmful quantities of smoke, flame, extinguishing agents, and other noxious gases in any crew or passenger compartment.
3. Category Basic and Enhanced: Detection and extinguishing systems in designated fire zones
(a) Detection Systems:
It is accepted that adequate fire or smoke awareness for the designated fire zones is provided by the installation of detection systems that follow Section 3(g) in MOC VTOL.2330.
(b) Extinguishing Systems:
Following CS requirements are accepted as means to comply with VTOL.2325(b)(1) regarding adequate extinguishing means for Designated Fire Zones in accordance with section 1(d) of MOC VTOL.2330:
(1) CS 27.1194 Amdt. 6 “Other surfaces”
(2) CS 29.1195 Amdt. 6 “Fire extinguishing systems”
(3) CS 29.1197 Amdt. 6 “Fire extinguishing agents”
(4) CS 29.1199 Amdt. 6 “Extinguishing agent containers”
(5) CS 29.1201 Amdt. 6“Fire extinguishing system materials”
For extinguishing systems in Fire Withstanding Zones and Explosive Fire Zones (refer to definitions in sections 1(c) and 1(e) of MOC VTOL.2330), specific means of compliance should be agreed with the Agency taking into consideration the intended operation and existing technologies.
VTOL.2330 Fire Protection in designated fire zones
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(a) Flight critical systems, lift/thrust unit mounting, and other structures within or adjacent to designated fire zones must be capable of withstanding the effects of a fire.
(b) A fire or other release of stored energy in a designated fire zone must not preclude continued safe flight and landing for Category Enhanced, or a controlled emergency landing for Category Basic.
(c) Terminals, equipment, and electrical cables used during emergency procedures must be fire-resistant.
MOC VTOL.2330 Fire Protection in designated fire zones
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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.
VTOL.2335 Lightning Protection
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Unless it is shown that exposure to lightning is unlikely, the aircraft must be protected against catastrophic effects of lightning.
MOC VTOL.2335 Lightning Protection
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(a) In order to demonstrate that the exposure to lightning is “unlikely”, the same operational limitations as defined in MOC VTOL.2515 “Electrical and electronic system lightning protection” are accepted.
(b) CS 27.610 Amdt. 6 is accepted as a means of compliance.
(c) As an alternative to CS 27.610 Amdt. 6, paragraph 17.1 of ASTM F3061/F3061M-19 “Standard Specification for Systems and Equipment in Small Aircraft” is also accepted as a means of compliance.
VTOL.2340 Design and construction information
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The following design and construction information must be established:
(a) operating limitations, procedures and instructions necessary for the safe operation of the aircraft;
(b) the need for instrument markings or placards;
(c) any additional information necessary for the safe operation of the aircraft; and
(d) inspections or maintenance to assure continued safe operation.