(j) Components of the emergency lighting system, including batteries, wiring relays, lamps, and switches must be capable of normal operation after having been subjected to the inertia forces listed in § 25.561(b).
(k) The emergency lighting system must be designed so that after any single transverse vertical separation of the fuselage during crash landing-
(1) Not more than 25 percent of all electrically illuminated emergency lights required by this section are rendered inoperative, in addition to the lights that are directly damaged by the separation;
(2) Each electrically illuminated exit sign required under § 25.811(d)(2) remains operative exclusive of those that are directly damaged by the separation; and
(3) At least one required exterior emergency light for each side of the airplane remains operative exclusive of those that are directly damaged by the separation.
b. Guidance.
(1) Advisory Circular 20-38A, “Measurement of Cabin Interior Emergency Illumination in Transport Airplanes,” dated 2/8/66, provides guidance material for the minimum measurements required by this paragraph. (Amendment 25-15)
(2) Paragraph (b)(1). The wording “a passenger seating configuration, excluding pilot seats, of 10 seats or more,” which was promulgated with the intent of being consistent with Amendment 23-10 to part 23, does not directly address seats intended for use by observers or flight attendants. Seats approved for use by observers or flight attendants are not included in the passenger seating configuration. Seats that have dual approval for occupancy by either crew/observers or passengers will be included in the passenger seating configuration and must be provided emergency lighting as required by this section. (Amendment 25-32)
(3) Paragraph (c). (Amendment 25-15)
(i) Required illumination levels for main aisles also apply to cross aisles that are required to meet § 25.807(a)(7)(v). Cross aisles that are in excess of those required need not be provided with emergency lighting. (Amendment 25-15)
(ii) When measuring the illumination levels required by this paragraph, the interior color scheme (sidewalls, seat covers, floor covering, etc.) should be evaluated for its reflective contribution to the illumination level. This may be accomplished by negating the contribution of reflected light and demonstrating the minimum illumination levels independent of reflected light. If the reflective contribution is known, subsequent interiors of different reflectivity may be analyzed to show the effect on illumination levels is not detrimental. (Amendment 25-15)
(4) Paragraph (e). Normal electrical power is interpreted to mean the engine driven generators. (Amendment 25-15)
(5) Paragraph (e)(1). The emergency lighting switch in the cabin cannot turn off the system once it is activated. This switch should activate the system, however, even if the switch in the cockpit is “off.” (Amendment 25-46)
(6) Paragraph (f)(1). The illumination level at an overwing escape route where the evacuee would take his first step outside the airplane may be measured with the exit unobstructed. It is not necessary to consider an evacuee standing in the exit opening when measuring illumination levels. Transient blocking of the wing contact area illumination as an evacuee passes through the exit is acceptable provided no adverse effects are observed during the demonstration required by § 25.803(c). (Amendment 25-15)
(7) Paragraphs (g)(1) and (g)(2)(ii). With one or more landing gear legs collapsed, the resultant position of the assist means should be evaluated so that it does not obscure the illumination at the point of evacuees first ground contact. Under such conditions the likely point of contact may change, depending upon the specific collapsed landing gear case. The emergency lighting system must provide for these changes. (Amendment 25-32)
(8) Paragraph (g). Illumination of the overwing escape path or an assist means at any exit should be automatically activated as part of the airplane emergency lighting system, or by the action of opening the exit. The required exterior lighting at an exit may not be dependent on the operation of another exit. (Amendment 25-15)
(9) Paragraph (h). When the airplane is exposed to the critical minimum and maximum ambient temperatures such that the airplane is in equilibrium, the airplane environmental systems may be used to condition the airplane prior to boarding passengers. The temperature of the power supplies may be determined following a reasonable conditioning period to obtain operation voltage when the airplane is at the critical outside ambient temperature. The illumination may then be measured assuming ten-minute operation from these initial conditions.
If an applicant is unable to furnish what initial conditions are, it is acceptable to use Radio Technical Commission for Aeronautics Document No. RTCA/DO-160B, titled "Environmental Conditions and Test Procedures for Airborne Equipment," for low and high temperature tests.
An additional alternate set of satisfactory environmental conditions may be found in AC 25.812-1A, “Floor Proximity Emergency Escape Path Marking,” dated 5/22/89.
(Amendment 25-15)
(10) Paragraph (k). A transverse separation is considered to occur at any fuselage station, irrespective of the perceived likelihood that a separation could occur there. “Separation” in this context refers to all degrees of fuselage separation such that the emergency lighting system is interrupted, and not just separations that result in two distinct segments of fuselage.
(Amendment 25-15)
(11) Paragraph (k)(1). This paragraph is based on the number of electrically illuminated lights required to meet the illumination levels of this section. Exit signs which are
383 not used to contribute to cabin illumination and subsystems provided in accordance with paragraph (g)(2) do not apply to this paragraph. However, an applicant should not be penalized for providing lights in excess of the number required. (Amendment 25-15)
(12) Paragraph (k)(2). “Directly damaged,” as used in this paragraph, refers to a sign that is located at the same station as a transverse fuselage separation, or between the frames bounding the separation location, and therefore rendered inoperative. The sign is also considered inoperative if the separation occurs at the same station as any part of the power supply. The sign should remain operative unless it is “directly damaged” or the separation renders the exit unopenable. Therefore, the power supply should be located at a station between the frames that make up the exit, or in the case of a sign beside the exit, the power supply may also be at the same fuselage station as any part of the sign. (Amendment 25-15)
396. AMENDMENT 25-58, Effective November 26, 1984.
a. Regulation.
(a) An emergency lighting system, independent of the main lighting system, must be installed. However, the sources of general cabin illumination may be common to both the emergency and the main lighting systems if the power supply to the emergency lighting system is independent of the power supply to the main lighting system. The emergency lighting system must include:
[(1) Illuminated emergency exit marking and locating signs, sources of general cabin illumination, interior lighting in emergency exit areas, and floor proximity escape path marking.]
(2) Exterior emergency lighting.
(b) Emergency exit signs-
(1) For airplanes that have a passenger seating configuration, excluding pilot seats, of 10 seats or more must meet the following requirements:
(i) Each passenger emergency exit locator sign required by § 25.811(d)(1) and each passenger emergency exit marking sign required by § 25.811(d)(2) must have red letters at least 1½-inches high on an illuminated white background, and must have an area of at least 21 square-inches excluding the letters. The lighted background-toletter contrast must be at least 10:1. The letter height to stroke-width ratio may not be more than 7:1 nor less than 6:1. These signs must be internally electrically illuminated with a background brightness of at least 25 foot-lamberts and a high-tolow background contrast no greater than 3:1.
(ii) Each passenger emergency exit sign required by § 25.811(d)(3) must have red letters at least 1½-inches high on a white background having an area of at least 21
384 square-inches excluding the letters. These signs must be internally electrically illuminated or self-illuminated by other than electrical means and must have an initial brightness of at least 400 microlamberts. the colors may be reversed in the case of a sign that is self-illuminated by other than electrical means.
(2) For airplanes that have a passenger seating configuration, excluding pilot seats, of nine seats or less, that are required by § 25.811(d)(1), (2), and (3) must have red letters at least 1-inches high. These signs may be internally electrically illuminated, or self-illuminated by other than electrical means, with an initial brightness of at least 160 microlamberts. The colors may be reversed in the case of a sign that is selfilluminated by other than electrical means.
(c) General illumination in the passenger cabin must be provided so that when measured along the centerline of main passenger aisle(s), and cross aisle(s) between main aisles, at seat armrest height and at 40-inch intervals, the average illumination is not less than 0.05 foot-candle and the illumination at each 40-inch interval is not less than 0.01 foot-candle. A main passenger aisle(s) is considered to extend along the fuselage from the most forward passenger emergency exit or cabin occupant seat, whichever is farther forward, to the most rearward passenger emergency exit or cabin occupant seat, whichever is farther aft.
(d) The floor of the passageway leading to each floor-level passenger emergency exit, between the main aisles and the exit openings, must be provided with illumination that is not less than 0.02 foot-candle measured along a line that is within six-inches of and parallel to the floor and is centered on the passenger evacuation path.
[(e) Floor proximity emergency escape path marking must provide emergency evacuation guidance for passengers when all sources of illumination more than 4 feet above the cabin aisle floor are totally obscured. In the dark of the night, the floor proximity emergency escape path marking must enable each passenger to-
(1) After leaving the passenger seat, visually identify the emergency escape path along the cabin aisle floor to the first exits or pair of exits forward and aft of the seat;
and
(2) Readily identify each exit from the emergency escape path by reference only to markings and visual features not more than 4 feet above the cabin floor.] [(f)] Except for subsystems provided in accordance with paragraph [(h)] of this section that serve no more than one assist means, are independent of the airplane's main emergency lighting system, and are automatically activated when the assist means is erected, the emergency lighting system must be designed as follows:
(1) The lights must be operable manually from the flight crew station and from a point in the passenger compartment that is readily accessible to a normal flight attendant seat.
(2) There must be a flight crew warning light which illuminates when power is on in the airplane and in the emergency lighting control device is not armed.
(3) The cockpit control device must have an "on," "off," and "armed" position so that when armed in the cockpit or turned on at either the cockpit or flight attendant station the lights will either light or remain lighted upon interruption (except and interruption caused by a transverse vertical separation of the fuselage during crash landing) of the airplane's normal electric power. There must be a means to safeguard against inadvertent operation of the control device from the "armed" or "on" positions.
[(g)] Exterior emergency lighting must be provided as follows:
(1) At each overwing emergency exit the illumination must be-
(i) Not less than 0.03 foot-candle (measured normal to the direction of the incident light) on a two-square-foot area where an evacuee is likely to make is first step outside the cabin;
(ii) Not less than 0.05 foot-candle (measured normal to the direction of the incident light) for a minimum width of 42-inches for a Type A overwing emergency exit and of 2 feet for all other overwing emergency exits along the 30 percent of the slip-resistant portion of the escape route required in § 25.803(e) that is farthest fro the exit; and Note: The reference to § 25.803(e) above applies to § 25.803 at Amendment 25-46.
However, Amendment 25-72 relocated this requirement from § 25.803(e) to § 25.810(c) at Amendment 25-72.
(iii) Not less than 0.03 foot-candle on the ground surface with the landing gear extended (measured normal to the direction of the incident light) where an evacuee using the established escape route would normally make first contact with the ground.
(2) At each non-overwing emergency exit not required by § 25.809(f) to have descent assist means the illumination must be not less than 0.03 foot-candle (measured normal to the direction of the incident light) on the ground surface with the landing gear extended where an evacuee is likely to make his first contact with the ground outside the cabin.
Note: The reference to § 25.809(f) above applies to § 25.809 at Amendment 25-47.
However, Amendment 25-72 relocated this requirement from § 25.809(f) to § 25.810(a) at Amendment 25-72.
386 [(h)] The means required in §§ 25.809(f)(1) and (h) and to assist the occupants in descending to the ground must be illuminated so that the erected assist means is visible from the airplane.
Note: The references to §§ 25.809(f)(1) and (h) above applies to Amendment 25-47 of § 25.809. Amendment 25-72 relocated these requirements from §§ 25.809(f)(1) and (h) to §§ 25.810(a) and (d) at Amendment 25-72.
(1) If the assist means is illuminated by exterior emergency lighting, it must provide illumination of not less than 0.03 foot-candle (measured normal to the direction of the incident light) at the ground end of the erected assist means where an evacuee using the established escape route would normally make first contact with the ground, with the airplane in each of the attitudes corresponding to the collapse of one or more legs of the landing gear.
(2) If the emergency lighting subsystem illuminating the assist means serves no other assist means, is independent of the airplane's main emergency lighting system, and is automatically activated when the assist means is erected, the lighting provisions-
(i) May not be adversely affected by stowage; and
(ii) Must provide illumination of not less than 0.03 foot-candle (measured normal to the direction of incident light) at the ground end of the erected assist means where an evacuee would normally make first contact with the ground, with the airplane in each of the attitudes corresponding to the collapse of one or more legs of the landing gear.
[(i)] The energy supply to each emergency lighting unit must provide the required level of illumination for at least 10 minutes at the critical ambient conditions after emergency landing.
[(j)] If storage batteries are used as the energy supply for the emergency lighting system, they may be recharged from the airplane's main electric power system:
Provided, That, the charging circuit is designed to preclude inadvertent battery discharge into charging circuit faults.
[(k)] Components of the emergency lighting system, including batteries, wiring relays, lamps, and switches must be capable of normal operation after having been subjected to the inertia forces listed in § 25.561(b).
[(l)] The emergency lighting system must be designed so that after any single transverse vertical separation of the fuselage during crash landing-
(1) Not more than 25 percent of all electrically illuminated emergency lights required by this section are rendered inoperative, in addition to the lights that are directly damaged by the separation;
(2) Each electrically illuminated exit sign required under § 25.811(d)(2) remains operative exclusive of those that are directly damaged by the separation; and
(3) At least one required exterior emergency light for each side of the airplane remains operative exclusive of those that are directly damaged by the separation
b. Guidance. NOTE: This change replaced the existing paragraph (e) with a new paragraph
(e) and relettered existing paragraphs (e) through (k) as (f) through (l).
(1) Advisory Circular 20-38A, “Measurement of Cabin Interior Emergency Illumination in Transport Airplanes,” dated 2/8/66, provides guidance material for the minimum measurements required by this paragraph. (Amendment 25-15)
(2) Paragraph (b)(1). The wording “a passenger seating configuration, excluding pilot seats, of 10 seats or more,” which was promulgated with the intent of being consistent with Amendment 23-10 to part 23, does not directly address seats intended for use by observers or flight attendants. Seats approved for use by observers or flight attendants are not included in the passenger seating configuration. Seats that have dual approval for occupancy by either crew/observers or passengers will be included in the passenger seating configuration and must be provided emergency lighting as required by this section. (Amendment 25-32)
(3) Paragraph (c). (Amendment 25-15)
(i) Required illumination levels for main aisles also apply to cross aisles that are required to meet § 25.807(a)(7)(v). Cross aisles that are in excess of those required need not be provided with emergency lighting. (Amendment 25-15)
(ii) When measuring the illumination levels required by this paragraph, the interior color scheme (sidewalls, seat covers, floor covering, etc.) should be evaluated for its reflective contribution to the illumination level. This may be accomplished by negating the contribution of reflected light and demonstrating the minimum illumination levels independent of reflected light. If the reflective contribution is known, subsequent interiors of different reflectivity may be analyzed to show the effect on illumination levels is not detrimental. (Amendment 25-15)
(4) Paragraph (e). The floor proximity emergency escape path marking system is included as part of the emergency lighting system when determining compliance with the separation requirements of paragraph (l). (Amendment 25-58)
(5) Paragraph (e). Refer to AC 25.812-1A, “Floor Proximity Emergency Escape Path Marking,” dated 5/22/89 and AC 25.812-2, “Floor Proximity Emergency Escape Path Marking Systems Incorporating Photoluminescent Elements,” dated 7/24/97. (Amendment 25-58)
(6) Paragraph (f). Normal electrical power is interpreted to mean the engine driven generators. (Amendment 25-15)
(7) Paragraph (f)(1). The emergency lighting switch in the cabin cannot turn off the system once it is activated. This switch should activate the system, however, even if the switch in the cockpit is “off.” (Amendment 25-46)
(8) Paragraph (g)(1). The illumination level at an overwing escape route where the evacuee would take his first step outside the airplane may be measured with the exit unobstructed. It is not necessary to consider an evacuee standing in the exit opening when measuring illumination levels. Transient blocking of the wing contact area illumination as an evacuee passes through the exit is acceptable provided no adverse effects are observed during the demonstration required by § 25.803(c). (Amendment 25-15)
(9) Paragraphs (h)(1) and (h)(2)(ii). With one or more landing gear legs collapsed, the resultant position of the assist means should be evaluated so that it does not obscure the illumination at the point of evacuees first ground contact. Under such conditions the likely point of contact may change, depending upon the specific collapsed landing gear case. The emergency lighting system must provide for these changes. (Amendment 25-32)
(10) Paragraph (h). Illumination of the overwing escape path or an assist means at any exit should be automatically activated as part of the airplane emergency lighting system, or by the action of opening the exit. The required exterior lighting at an exit may not be dependent on the operation of another exit. (Amendment 25-15)
(11) Paragraph (i). When the airplane is exposed to the critical minimum and maximum ambient temperatures such that the airplane is in equilibrium, the airplane environmental systems may be used to condition the airplane prior to boarding passengers. The temperature of the power supplies may be determined following a reasonable conditioning period to obtain operation voltage when the airplane is at the critical outside ambient temperature. The illumination may then be measured assuming ten-minute operation from these initial conditions. If an applicant is unable to furnish what initial conditions are, it is acceptable to use Radio Technical Commission for Aeronautics Document No. RTCA/DO-160B, titled "Environmental Conditions and Test Procedures for Airborne Equipment," for low and high temperature tests. An additional alternate set of satisfactory environmental conditions may be found in AC 25.812-1A, “Floor Proximity Emergency Escape Path Marking,” dated 5/22/89.
(Amendment 25-15)
(12) Paragraph (l). A transverse separation is considered to occur at any fuselage station, irrespective of the perceived likelihood that a separation could occur there. “Separation” in this context refers to all degrees of fuselage separation such that the emergency lighting system is interrupted, and not just separations that result in two distinct segments of fuselage.
(Amendment 25-15)
(13) Paragraph (l)(1). This paragraph is based on the number of electrically illuminated lights required to meet the illumination levels of this section. Exit signs which are not used to contribute to cabin illumination and subsystems provided in accordance with paragraph (h)(2) do not apply to this paragraph. However, an applicant should not be penalized for providing lights in excess of the number required. (Amendment 25-15)
(14) Paragraph (l)(2). “Directly damaged,” as used in this paragraph, refers to a sign that is located at the same station as a transverse fuselage separation, or between the frames bounding the separation location, and therefore rendered inoperative. The sign is also considered inoperative if the separation occurs at the same station as any part of the power supply. The sign should remain operative unless it is “directly damaged” or the separation renders the exit unopenable. Therefore, the power supply should be located at a station between the frames that make up the exit, or in the case of a sign beside the exit, the power supply may also be at the same fuselage station as any part of the sign. (Amendment 25-15)
397. AMENDMENT 25-88, Effective December 9, 1996.
a. Regulation.
(a) An emergency lighting system, independent of the main lighting system, must be installed. However, the sources of general cabin illumination may be common to both the emergency and the main lighting systems if the power supply to the emergency lighting system is independent of the power supply to the main lighting system. The emergency lighting system must include:
(1) Illuminated emergency exit marking and locating signs, sources of general cabin illumination, interior lighting in emergency exit areas, and floor proximity escape path marking.
(2) Exterior emergency lighting.
(b) Emergency exit signs-
(1) For airplanes that have a passenger seating configuration, excluding pilot seats, of 10 seats or more must meet the following requirements:
(i) Each passenger emergency exit locator sign required by § 25.811(d)(1) and each passenger emergency exit marking sign required by § 25.811(d)(2) must have red letters at least 1½-inches high on an illuminated white background, and must have an area of at least 21 square-inches excluding the letters. The lighted background-toletter contrast must be at least 10:1. The letter height to stroke-width ratio may not be more than 7:1 nor less than 6:1. These signs must be internally electrically illuminated with a background brightness of at least 25 foot-lamberts and a high-tolow background contrast no greater than 3:1.
(ii) Each passenger emergency exit sign required by § 25.811(d)(3) must have red letters at least 1½-inches high on a white background having an area of at least 21 square-inches excluding the letters. These signs must be internally electrically illuminated or self-illuminated by other than electrical means and must have an
390 initial brightness of at least 400 microlamberts. The colors may be reversed in the case of a sign that is self-illuminated by other than electrical means.
(2) For airplanes that have a passenger seating configuration, excluding pilot seats, of nine seats or less, that are required by § 25.811(d)(1), (2), and (3) must have red letters at least 1-inch high on a white background at least 2-inches high. These signs may be internally electrically illuminated, or self-illuminated by other than electrical means, with an initial brightness of at least 160 microlamberts. The colors may be reversed in the case of a sign that is self-illuminated by other than electrical means.
(c) General illumination in the passenger cabin must be provided so that when measured along the centerline of main passenger aisle(s), and cross aisle(s) between main aisles, at seat armrest height and at 40-inch intervals, the average illumination is not less than 0.05 foot-candle and the illumination at each 40-inch interval is not less than 0.01 foot-candle. A main passenger aisle(s) is considered to extend along the fuselage from the most forward passenger emergency exit or cabin occupant seat, whichever is farther forward, to the most rearward passenger emergency exit or cabin occupant seat, whichever is farther left.
(d) The floor of the passageway leading to each floor-level passenger emergency exit, between the main aisles and the exit openings, must be provided with illumination that is not less than 0.02 foot-candle measured along a line that is within six-inches of and parallel to the floor and is centered on the passenger evacuation path.
(e) Floor proximity emergency escape path marking must provide emergency evacuation guidance for passengers when all sources of illumination more than 4 feet above the cabin aisle floor are totally obscured. In the dark of the night, the floor proximity emergency escape path marking must enable each passenger to-
(1) After leaving the passenger seat, visually identify the emergency escape path along the cabin aisle floor to the first exits or pair of exits forward and aft of the seat;
and
(2) Readily identify each exit from the emergency escape path by reference only to markings and visual features not more than 4 feet above the cabin floor.
(f) Except for subsystems provided in accordance with paragraph (h) of this section that serve no more than one assist means, are independent of the airplane's main emergency lighting system, and are automatically activated when the assist means is erected, the emergency lighting system must be designed as follows:
(1) The lights must be operable manually from the flight crew station and from a point in the passenger compartment that is readily accessible to a normal flight attendant seat.
(2) There must be a flight crew warning light which illuminates when power is on in the airplane and the emergency lighting control device is not armed.
(3) The cockpit control device must have an "on," "off," and "armed" position so that when armed in the cockpit or turned on at either the cockpit or flight attendant station the lights will either light or remain lighted upon interruption (except an interruption caused by a transverse vertical separation of the fuselage during crash landing) of the airplane's normal electric power. There must be a means to safeguard against inadvertent operation of the control device from the "armed" or "on" positions.
(g) Exterior emergency lighting must be provided as follows:
(1) At each overwing emergency exit the illumination must be-
(i) Not less than 0.03 foot-candle (measured normal to the direction of the incident light) on a two-square-foot area where an evacuee is likely to make his first step outside the cabin;
[(ii) Not less than 0.05 foot-candle (measured normal to the direction of incident light) along the 30 percent of the slip-resistant portion of the escape route required in § 25.810(c) that is farthest from the exit for the minimum required width of the escape route; and]
(iii) Not less than 0.03 foot-candle on the ground surface with the landing gear extended (measured normal to the direction of the incident light) where an evacuee using the established escape route would normally make first contact with the ground.
(2) At each non-overwing emergency exit not required by § 25.809(f) to have descent assist means the illumination must be not less than 0.03 foot-candle (measured normal to the direction of the incident light) on the ground surface with the landing gear extended where an evacuee is likely to make his first contact with the ground outside the cabin.
Note: The reference to § 25.809(f) above applies to § 25.809 at Amendment 25-47.
However, Amendment 25-72 relocated this requirement from § 25.809(f) to § 25.810(a) at Amendment 25-72.
(h) The means required in §§ 25.809(f)(1) and (h) to assist the occupants in descending to the ground must be illuminated so that the erected assist means is visible from the airplane.
Note: The references to §§ 25.809(f)(1) and (h) above applies to § 25.809 at Amendment 25-47. However, Amendment 25-72 relocated these requirements from §§ 25.809(f)(1) and (h) to §§ 25.810(a) and (d) at Amendment 25-72.
(1) If the assist means is illuminated by exterior emergency lighting, it must provide illumination of not less than 0.03 foot-candle (measured normal to the direction of the incident light) at the ground end of the erected assist means where an evacuee using the established escape route would normally make first contact with the ground, with the airplane in each of the attitudes corresponding to the collapse of one or more legs of the landing gear.
(2) If the emergency lighting subsystem illuminating the assist means serves no other assist means, is independent of the airplane's main emergency lighting system, and is automatically activated when the assist means is erected, the lighting provisions-
(i) May not be adversely affected by stowage; and
(ii) Must provide illumination of not less than 0.03 foot-candle (measured normal to the direction of incident light) at the ground end of the erected assist means where an evacuee would normally make first contact with the ground, with the airplane in each of the attitudes corresponding to the collapse of one or more legs of the landing gear.
(i) The energy supply to each emergency lighting unit must provide the required level of illumination for at least 10 minutes at the critical ambient conditions after emergency landing.
(j) If storage batteries are used as the energy supply for the emergency lighting system, they may be recharged from the airplane's main electric power system:
Provided, That, the charging circuit is designed to preclude inadvertent battery discharge into charging circuit faults.
(k) Components of the emergency lighting system, including batteries, wiring relays, lamps, and switches must be capable of normal operation after having been subjected to the inertia forces listed in § 25.561(b).
(l) The emergency lighting system must be designed so that after any single transverse vertical separation of the fuselage during crash landing-
(1) Not more than 25 percent of all electrically illuminated emergency lights required by this section are rendered inoperative, in addition to the lights that are directly damaged by the separation;
(2) Each electrically illuminated exit sign required under § 25.811(d)(2) remains operative exclusive of those that are directly damaged by the separation; and
(3) At least one required exterior emergency light for each side of the airplane remains operative exclusive of those that are directly damaged by the separation.