Decompression Regulations
The FAA regulations for sudden pressure loss have evolved since the initial
release (amendment 0) of the Federal Air Regulations (FAR). Section 25.365
contains the rules governing decompression requirements for transport
aircraft. To date this section, 25.365, has been revised 4 times since its' initial release
to add specific hole requirements, add definition for regions of the aircraft
that must be considered, and to define decompression loads as ultimate.
Excerpts from the various amendments are shown below.
In addition to FAR revisions there have been airworthiness directives (AD's)
that have further added decompression design requirements for aircraft. To
date there are over 200 AD's the address some aspect of the aircraft design or
continued airworthiness, the great majority of these address maintenance
inspections/actions however there are many that require aircraft design
changes. Notable among AD's that require design changes are shown below.
Excerpts from the amendments and AD's that are shown below present the
evolution of decompression regulations, official copies of these amendments or
AD's must be obtained from the FAA (http://www1.faa.gov/certification/aircraft/).
Coming soon ... a time line presenting significant decompression events
in aviation and the corresponding regulatory changes and amendments.
AMENDMENTS
AMENDMENT 25-0 (2/1/65):
Pressurized cabin loads.
For each pressurized compartment for occupants, the following apply:
(a) The airplane structure must be strong enough to withstand the flight loads combined with pressure differential loads from zero up to the maximum relief valve setting.
(b) The external pressure distribution in flight, and stress concentrations and fatigue effects must be accounted for.
(c) If landings may be made with the cabin pressurized, landing loads must be combined with pressure differential loads from zero up to the maximum allowed during landing.
(d) The airplane structure must be strong enough to withstand the pressure differential loads corresponding to the maximum relief valve setting multiplied by a factor of 1.33, omitting other loads.
(e) If a pressurized cabin has two or more compartments separated by partitions, bulkheads, or floors, the structure supporting the prescribed flight and grounds loads (and any other structure that, if it failed, could interfere with continued safe flight and landing) must be designed to withstand the effects of sudden release of pressure in any compartment through an opening resulting from the failure or penetration of an external door, window, or windshield panel, or from structural fatigue or penetration of the fuselage in this compartment, unless it is shown that the probability of failure or penetration is extremely remote.
(f) In determining the probability of failure or penetration and probable size of openings, the fail-safe features of the design may be considered if possible improper operation of closure devices and inadvertent door openings are also considered. The pressure relief provided by intercompartment venting may also be considered.
(g) Reasonable design precautions must be taken to minimize the probability of parts becoming detached and injuring occupants while in their seats.
AMENDMENT 25-54 (10/14/80):
Pressurized cabin loads.
For each pressurized compartment for occupants, the following apply:
(a) The airplane structure must be strong enough to withstand the flight loads combined with pressure differential loads from zero up to the maximum relief valve setting.
(b) The external pressure distribution in flight, and stress concentrations and fatigue effects must be accounted for.
(c) If landings may be made with the cabin pressurized, landing loads must be combined with pressure differential loads from zero up to the maximum allowed during landing.
(d) The airplane structure must be strong enough to withstand the pressure differential loads corresponding to the maximum relief valve setting multiplied by a factor of 1.33, omitting other loads.
[(e) Partitions, bulkheads, and floors in pressurized cabins must be designed to withstand the effects of a sudden release of pressure through an opening in any compartment at any approved operating altitude resulting from any of the following conditions (to be considered as ultimate conditions):
(1) The penetration of the cabin by a portion of an engine following an engine disintegration;
(2) An opening in any passenger or cargo compartment given by the equation--
where,
 = maximum opening in square feet, not to exceed 20 square feet.
AS = maximum cross sectional area of pressurized shell normal to the longitudinal axis, in square feet; and
(3) The maximum opening caused by airplane or equipment failures not shown to be extremely improbable.]
(f) In determining the probability of failure or penetration and probable size of openings, the fail-safe features of the design may be considered if possible improper operation of closure devices and inadvertent door openings are also considered. The pressure relief provided by intercompartment venting may also be considered.
(g) Reasonable design precautions must be taken to minimize the probability of parts becoming detached and injuring occupants while in their seats.
Amdt. 25-54, Eff. 10/14/80
AMENDMENT 25-71 (5/10/90):
Pressurized [compartment] loads.
[For airplanes with one or more pressurized compartments the following apply:]
(a) The airplane structure must be strong enough to withstand the flight loads combined with pressure differential loads from zero up to the maximum relief valve setting.
(b) The external pressure distribution in flight, and stress concentrations and fatigue effects must be accounted for.
[(c) If landings may be made with the compartment pressurized, landing loads must be combined with pressure differential loads from zero up to the maximum allowed during landing.]
(d) The airplane structure must be strong enough to withstand the pressure differential loads corresponding to the maximum relief valve setting multiplied by a factor of 1.33, omitting other loads.
[(e) Any structure, component, or part, inside or outside a pressurized compartment, the rupture of which could interfere with continued safe flight and landing, must be designed to withstand the effects of a sudden release of pressure through an opening in any compartment at any operating altitude resulting from each of the following conditions:
(1) The penetration of the compartment by a portion of an engine following an engine disintegration;
(2) Any operating in any pressurized compartment up to the size HO in square feet; however, small compartments may be combined with an adjacent pressurized compartment and both considered as a single compartment for openings that cannot reasonably be expected to be confined to the compartment. The size HO must be computed by the following formula:
Ho=PAS
where,
Ho = Maximum opening in square feet, need not exceed 20 square feet.
As = Maximum cross-sectional area of the pressurized shell normal to the longitudinal axis, in square feet; and
(3) The maximum opening caused by airplane or equipment failures not shown to be extremely improbable.
(f) In complying with paragraph (e) of this section, the fail-safe features of the design may be considered in determining the probability of failure or penetration and probable size of openings, provided that possible improper operation of closure devices and inadvertent door openings are also considered. Furthermore, the resulting differential pressure loads must be combined in a rational and conservative manner with 1-g level flight loads and any load arising from emergency depressurization conditions. These loads may be considered as ultimate conditions; however, any deformations associated with these conditions must not interfere with continued safe flight and landing. The pressure relief provided by intercompartment venting may also be considered.
(g) Bulkheads, floors, and partitions in pressurized compartments for occupants must be designed to withstand the conditions specified in paragraph (e) of this section. In addition, reasonable design precautions must be taken to minimize the probability of parts becoming detached and injuring occupants while in their seats.]
Amdt. 25-71, Eff. 5/10/90
AMENDMENT 25-72(8/20/90):
Pressurized compartment loads.
[For airplanes with one or more pressurized compartments the following apply:]
(a) The airplane structure must be strong enough to withstand the flight loads combined with pressure differential loads from zero up to the maximum relief valve setting.
(b) The external pressure distribution in flight, and stress concentrations and fatigue effects must be accounted for.
(c) If landings may be made with the compartment pressurized, landing loads must be combined with pressure differential loads from zero up to the maximum allowed during landing.
(d) The airplane structure must be strong enough to withstand the pressure differential loads corresponding to the maximum relief valve setting multiplied by a factor of 1.33, omitting other loads.
(e) Any structure, component, or part, inside or outside a pressurized compartment, the rupture of which could interfere with continued safe flight and landing, must be designed to withstand the effects of a sudden release of pressure through an opening in any compartment at any operating altitude resulting from each of the following conditions:
(1) The penetration of the compartment by a portion of an engine following an engine disintegration;
(2) Any operating in any pressurized compartment up to the size HO in square feet; however, small compartments may be combined with an adjacent pressurized compartment and both considered as a single compartment for openings that cannot reasonably be expected to be confined to the compartment. The size HO must be computed by the following formula:
Ho=PAs
where,
Ho = Maximum opening in square feet, need not exceed 20 square feet.
As = Maximum cross-sectional area of the pressurized shell normal to the longitudinal axis, in square feet; and
(3) The maximum opening caused by airplane or equipment failures not shown to be extremely improbable.
(f) In complying with paragraph (e) of this section, the fail-safe features of the design may be considered in determining the probability of failure or penetration and probable size of openings, provided that possible improper operation of closure devices and inadvertent door openings are also considered. Furthermore, the resulting differential pressure loads must be combined in a rational and conservative manner with 1-g level flight loads and any load arising from emergency depressurization conditions. These loads may be considered as ultimate conditions; however, any deformations associated with these conditions must not interfere with continued safe flight and landing. The pressure relief provided by intercompartment venting may also be considered.
(g) Bulkheads, floors, and partitions in pressurized compartments for occupants must be designed to withstand the conditions specified in paragraph (e) of this section. In addition, reasonable design precautions must be taken to minimize the probability of parts becoming detached and injuring occupants while in their seats.
Amdt. 25-72; Eff. 8/20/90
AMENDMENT 25-87 (7/5/96):
Pressurized compartment loads.
For airplanes with one or more pressurized compartments the following apply:
(a) The airplane structure must be strong enough to withstand the flight loads combined with pressure differential loads from zero up to the maximum relief valve setting.
(b) The external pressure distribution in flight, and stress concentrations and fatigue effects must be accounted for.
(c) If landings may be made with the compartment pressurized, landing loads must be combined with pressure differential loads from zero up to the maximum allowed during landing.
[(d) The airplane structure must be designed to be able to withstand the pressure differential loads corresponding to the maximum relief valve setting multiplied by a factor of 1.33 for airplanes to be approved for operation to 45,000 feet or by a factor of 1.67 for airplanes to be approved for operation above 45,000 feet, omitting other loads.]
(e) Any structure, component or part, inside or outside a pressurized compartment, the failure of which could interfere with continued safe flight and landing, must be designed to withstand the effects of a sudden release of pressure through an opening in any compartment at any operating altitude resulting from each of the following conditions:
(1) The penetration of the compartment by a portion of an engine following an engine disintegration:
(2) Any opening in any pressurized compartment up to the size HO in square feet; however, small compartments may be combined with an adjacent pressurized compartment and both considered as a single compartment for openings that cannot be reasonably be expected to be confined to the small compartment. The size HO must be computed by the following formula
Ho = PAs
where--
Ho = Maximum opening in square feet, need not exceed 20 square feet.
As=Maximum cross-sectional area of the pressurized shell normal to the longitudinal axis, in square feet; and
(3) The maximum opening caused by airplane or equipment failures not shown to be extremely improbable.
(f) In complying with paragraph (e) of this section, the fail-safe features of the design may be considered in determining the probability of failure or penetration and probable size of openings, provided that possible improper operation of closure devices and inadvertent door openings are also considered. Furthermore, the resulting differential pressure loads must be combined in a rational and conservative manner with 1-g level flight loads and any loads arising from emergency depressurization conditions. These loads may be considered as ultimate conditions; however, any deformations associated with these conditions must not interfere with continued safe flight and landing. The pressure relief provided by intercompartment venting may also be considered.
(g) Bulkheads, floors, and partitions in pressurized compartments for occupants must be designed to withstand the conditions specified in paragraph (e) of this section. In addition, reasonable design precautions must be taken to minimize the probability of parts becoming detached and injuring occupants while in their seats.
Amdt. 25-87, Eff. 7/5/96
AD's
AD 75-15-05
75-15-05 MCDONNELL DOUGLAS, LOCKHEED, BOEING, AND AIRBUS INDUSTRIE: Amendment 39-2262 as amended by Amendment 39-2739. Applies to McDonnell Douglas Model DC-10 Series, Lockheed Model L-1011 Series, Boeing Model B-747 Series, and Airbus Industrie Model A-300 Series airplanes certificated in all categories.
Unless already accomplished, compliance is required on or before December 31, 1977, or in accordance with a schedule of accomplishment approved by the Chief, Aircraft Engineering Division, FAA Western Region, for McDonnell Douglas Model DC-10 Series and Lockheed Model L-1011 Series airplanes; the Chief, Engineering and Manufacturing Branch, FAA Northwest Region, for Boeing Model B-747 Series airplanes, or the Chief, Aircraft Certification Staff, FAA Europe, Africa, and Middle East Region, for Airbus Industrie Model A-300 Series airplanes, but not later than December 31, 1978.
To improve the capability of the passenger and crew compartment floors to withstand, without collapse, an in-flight depressurization caused by the sudden opening of a large hole in the lower deck cargo compartment, comply with paragraphs (a) or (b) as appropriate:
(a) Incorporate the modification specified in paragraph (a)(1), taking into consideration the factors specified in paragraphs (a)(2) and (a)(3):
(1) Provide additional venting capability or an increase in floor strength, or both, as necessary, to prevent floor collapse caused by the decompression effects resulting from a sudden large in-flight opening in any portion of any lower deck cargo compartment.
(2) The size of openings to be considered must include the maximum size opening expected in service, but the maximum size opening considered may not have an area of less than 20 square feet.
(3) Each compartment and ambient condition pressure differential expected in service must be considered.
(4) In showing compliance with paragraphs (a)(1), (a)(2), and (a)(3), damage to the floor is permitted if the degree of damage will not preclude continued safe flight and landing, or result in injury to occupants.
(b) For the all-cargo version of each of the above airplanes, it is satisfactory to comply with paragraph (a)(2) by showing that continued safe flight and landing is assured and that no injury to any occupant results in lieu of showing no floor collapse. Appropriate limitations must be added to the flight manual for the particular airplane approved under the all-cargo provisions.
(c) The modification and determinations required under paragraphs (a) and (b) of this AD must be approved by the Chief, Aircraft Engineering Division, FAA Western Region, for McDonnell Douglas Model DC-10 Series and Lockheed Model L-1011 Series airplanes; the Chief, Engineering and Manufacturing Branch, FAA Northwest Region, for Boeing Model B-747 Series airplanes; or the Chief, Aircraft Certification Staff, FAA Europe, Africa, and Middle East Region, for Airbus Industrie Model A-300 Series airplanes.
Amendment 39-2262 became effective August 11, 1975.
This amendment 39-2739 becomes effective November 3, 1976.
AD 99-02-06
AD 99-02-06, Amendment 39-10995; This amendment adopts a new airworthiness directive (AD), applicable to certain Fokker Model F.28 Mark 0100 series airplanes, that requires modification of the aft cabin sidewall area to improve decompression venting and, for certain airplanes, modification of the aft wardrobe/stowage area door and installation of decompression panels to improve decompression venting. This amendment is prompted by issuance of mandatory continuing airworthiness information by a foreign civil airworthiness authority. The actions specified by this AD are intended to prevent damage to the cabin floor in the event of sudden decompression in the cargo compartment, which could result in injury to passengers, reduced structural integrity of the airplane, and the loss of airplane systems.
AD 96-22-07
Amendment 39-9796; AD 96-22-07. This amendment adopts a new airworthiness directive (AD), applicable to certain Jetstream Model 4100 series airplanes, that requires replacement of the existing decompression panel on the aft bulkhead of the toilet compartment with a modified decompression panel. This amendment is prompted by a report that a decompression panel that does not meet flammability requirements was installed on these airplanes during manufacture. The actions specified by this AD are intended to prevent injury to the crew and passengers and damage to the airplane structure due to the incapability of the decompression panel to contain a fire.
AD 2001-26-01
Amendment 39-12565; AD 2001-26-01 This amendment adopts a new airworthiness directive (AD), applicable to certain McDonnell Douglas Model DC-8 series airplanes that have been converted from a passenger-to a cargo-carrying ("freighter") configuration. This amendment requires, among other actions, modification of the main deck cargo door structure and fuselage structure; modification of a main deck cargo door hinge; modification of the main deck cargo floor; and installation of a main deck cargo 9g crash barrier; as applicable. The actions specified by this AD are intended to prevent opening of the cargo door while the airplane is in flight or collapse of the main deck cargo floor, and consequent rapid decompression of the airplane including possible loss of flight control or severe structural damage. These actions are intended to address the identified unsafe condition.
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