Source: https://www.federalregister.gov/documents/2000/09/27/00-24749/airworthiness-directives-mcdonnell-douglas-model-dc-8-series-airplanes
Timestamp: 2018-04-24 04:08:53
Document Index: 533104317

Matched Legal Cases: ['art 25', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4', 'art 4']

58185-58192 (8 pages)
1. Main Deck Cargo Door and Associated Fuselage Structure.
2. Main Deck Cargo Door Hinge.
1. Capability of the Unmodified Floor
2. 9g Crash Barrier.
https://www.federalregister.gov/d/00-24749 https://www.federalregister.gov/d/00-24749
Start Preamble Start Printed Page 58186
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain McDonnell Douglas Model DC-8 series airplanes that have been converted from a passenger-to a cargo-carrying (“freighter”) configuration. This proposal would require, 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. These actions are necessary 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.
Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-280-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal holidays. Comments may be submitted via fax to (425) 227-1232. Comments may also be sent via the Internet using the following address: 9-anm-nprmcomment@faa.gov. Comments sent via fax or the Internet must contain “Docket No. 2000-NM-280-AD” in the subject line and need not be submitted in triplicate. Comments sent via the Internet as attached electronic files must be formatted in Microsoft Word 97 for Windows or ASCII text.
Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this notice must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 2000-NM-280-AD.” The postcard will be date stamped and returned to the commenter.
Any person may obtain a copy of this notice of proposed rulemaking (NPRM) by submitting a request to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-280-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.
Supplemental Type Certificate (STC) SA1063SO (originally issued to Aeronautical Engineers, Inc. (AEI)) specifies a design for installation of a main deck cargo door, associated door cutout in the fuselage, and door hydraulic and indication systems on McDonnell Douglas Model DC-8 series airplanes. STC SA1377SO (originally issued to AEI) specifies a design for installation of a Class E compartment with a 9g crash barrier and cargo handling system on McDonnell Douglas Model DC-8 series airplanes. The FAA has conducted a design review of Model DC-8 series airplanes modified in accordance with STC's SA1063SO and SA1377SO and has conducted discussions regarding the design with the STC holder. From the design review and these discussions, the FAA has identified several potential unsafe conditions. (Results of this design review are contained in “DC-8 Cargo Modification Review Team Review of AEI Supplemental Type Certificates SA1063SO—Installation of a Cargo Door and SA1377SO—Installation of a Cargo Interior, Final Report, dated July 30, 1999,” hereinafter referred to as “the Design Review Report,” which is included in the Rules Docket for this NPRM.)
On August 9, 2000, the FAA issued airworthiness directive (AD) 2000-13-03 R1, amendment 39-11865 (65 FR 49735, August 15, 2000), which identifies corrective action for the unsafe conditions that relate to the hydraulic and indication systems of the main deck cargo door and provides for a means to prevent pressurization to an unsafe level if the main deck cargo door is not closed, latched, and locked.
In the preamble of the NPRM for AD 2000-13-03 R1, the FAA indicated that further rulemaking action was being considered to address the potential unsafe conditions on Model DC-8 series airplanes modified in accordance with STC SA1063SO that relate to the main deck cargo door hinge and fuselage structure in the area modified by installation of a main deck cargo door. In addition, the FAA indicated that further rulemaking action was being considered to address the potential unsafe conditions on Model DC-8 series airplanes modified in accordance with STC SA1377SO that relate to the unreinforced main deck floor, 9g crash barrier, and fire/smoke detection system. The FAA now has determined that further rulemaking action is indeed necessary, and this NPRM follows from that determination. Start Printed Page 58187
The FAA is considering further rulemaking to address the remaining potential unsafe condition on Model DC-8 series airplanes modified in accordance with STC SA1377SO that relates to the fire/smoke detection system.
As a result of these cargo door opening accidents, the Air Transport Association (ATA) of America formed a task force, including representatives of the FAA, to review the design, manufacture, maintenance, and operation of airplanes fitted with outward opening cargo doors, and to make recommendations to prevent inadvertent cargo door openings while the airplane is in flight. A design working group was tasked with reviewing 14 Code of Federal Regulations (CFR) part 25.783 (and its accompanying Advisory Circular (AC) 25.783-1, dated December 10, 1986) with the intent of clarifying its contents and recommending revisions to enhance future cargo door designs. This design group also was tasked with providing specific recommendations regarding design criteria to be applied to existing outward opening cargo doors to ensure that inadvertent openings would not occur in the current transport category fleet of airplanes.
For certain Boeing Model 747-100 and −200 series airplanes: AD 96-01-51, amendment 39-9492 (61 FR 1703, January 23, 1996);
For certain McDonnell Douglas Model DC-8 series airplanes: AD 2000-13-03 R1, amendment 39-11865, (65 FR 49735, August 15, 2000).
In late 1997, the FAA informed the STC holders and operators of Model DC-8 series airplanes that it was embarking on a review of Model DC-8 series airplanes that have been converted from a passenger-to a cargo-carrying (“freighter”) configuration by STC. The FAA proposed at a subsequent industry sponsored meeting in early 1998, that DC-8 operators and STC holders work together to identify and address potential safety concerns. This suggestion to the affected industry resulted in the creation of the DC-8 Cargo Conversion Joint Task Force (JTF) (hereinafter referred to as “the JTF”).
Using the certification basis of the airplane (i.e., CAR part 4b), the FAA, in collaboration with the JTF, conducted an engineering design review, inspected an airplane modified in accordance with STC's SA1063SO and SA1377SO, and identified a number of design features of these STC's that are unsafe.
For airplanes modified in accordance with STC SA1063SO, the FAA considers the following two specific design deficiencies to be unsafe:
The FAA, in collaboration with structural engineering representatives of the JTF, has identified several areas of the main deck cargo door and door jamb structure of STC SA1063SO that require modification to meet type design requirements. These areas include the addition of structural elements to augment and, in some places, to add the structural capability necessary to safely support design loads. When taken individually, these areas do not necessarily represent an unsafe condition. However, the critical load condition for each of the elements is the same, so that all of the elements could fail at the same time. Therefore, the FAA has determined that the potential of concurrent failure of several structural elements presents an unsafe condition for the airplane, and that these elements require modification to Start Printed Page 58188ensure the safety of the airplane. The modifications include:
Replacement of some of the latch mechanism bolts with increased strength bolts; and
Replacement of the existing bolts that attach the latches to the door with increased strength bolts.
As part of its continuing work to maintain the structural integrity of older transport category airplanes, in the early 1980's, the FAA concluded that the incidence of fatigue cracking may increase as these airplanes continue in service. In light of this, and as a result of increased utilization, longer operational lives, and the levels of safety expected of the currently operated transport category airplanes, the FAA has determined that a damage tolerance assessment of the structural modifications associated with STC SA1063SO is necessary to ensure the structural integrity for all airplanes in the affected fleet. This damage tolerance assessment is to identify any principal structural elements (PSE), including the associated inspection threshold, inspection method, and repetitive inspection interval, to ensure continued operational safety of the airplane. The PSE information must be identified in any method of compliance presented to address the requirements of the proposed AD.
In order to avoid catastrophic structural failure of outward opening cargo doors, a typical industry approach has been to design them and their attaching structure to be fail safe (i.e., designed so that if a single structural element fails, other structural elements are able to carry the redistributed load).
The design of the main deck cargo door hinge for STC SA1063SO must be in compliance with CAR part 4b, including CAR part 4b.270, which requires, in part, that catastrophic failure or excessive structural deformation, which could adversely affect the flight characteristics of the airplane, is not probable after fatigue failure or obvious partial failure of a single critical structural element. One common feature of a fail-safe hinge design is a division of the hinge into multiple segments such that, following failure of any one segment, the remaining segments would support the redistributed load.
The main deck cargo door installed in accordance with STC SA1063SO is supported by latches along the bottom of the door and a two-segment hinge along the top. This two-segment hinge is considered a critical structural element for this STC. A crack that initiates and propagates longitudinally along either segment of the hinge will eventually result in failure of the entire hinge, because the remaining segment of the hinge is unable to support the redistributed loads. Failure of the entire hinge can result in the opening of the main deck cargo door while the airplane is in flight.
For airplanes modified in accordance with STC SA1377SO, the FAA considers the following two specific design deficiencies to be unsafe:
Based on the results of the FAA's and JTF's structural evaluation of the main deck cargo floor, the FAA has determined that the unmodified main deck cargo floor is not capable of safely supporting the main deck zone loading (cargo weight) currently allowed by STC SA1377SO. There are several methods to address the unsafe condition. The floor beams and their attachment to the fuselage frames and struts, which support the floor beams on either side of the fuselage, could be modified to support the currently acceptable main deck zone loading. It is also possible to limit the main deck zone loading to a level that the main deck cargo floor can be supported safely without modification. A further possibility is to modify the main deck cargo floor beams to a configuration compatible with the desired level of zone loading.
In assessing the load carrying capability of the main deck cargo floor for STC SA1377SO, the manner in which the load is applied to the floor, as well as the magnitude of that load, must be considered. For example, it is possible to directly place the cargo onto the floor and secure it to the floor in a safe manner. However, most operators utilize a cargo handling system installed in the airplane that allows the use of unit load devices (ULD), such as pallets and containers. Together, the cargo handling system and ULD's expedite loading and unloading of the airplanes. Technical Standard Order (TSO) TSO-C90c, dated April 3, 1992, identifies both the ultimate loads that the ULD's produced under the TSO must support, and the number and location of restraints necessary to carry those loads. The TSO requires identification of the type and size of the ULD's. Although this TSO is the most common method of approval for ULD's, it is not the only means of approving ULD's. ULD designs also may be approved as part of a type certificate or STC. Therefore, the total cargo weight, distribution of cargo weight in the airplane, and restraint requirements for ULD's must be identified in any method of compliance presented to address the requirements of the proposed AD.
During evaluations of Model 727 and DC-8 series airplanes converted to a freighter configuration by STC, the FAA found instances where the existing venting capability of certain airplanes had been compromised by installation of the Class E compartment. In some cases, the vent area was decreased or restricted during modification. The FAA also found that the available design data for the main deck cargo floor for STC SA1377SO do not demonstrate the adequacy of the venting system of the modified DC-8 airplanes. The FAA is concerned about the venting between Start Printed Page 58189the main cabin floor and the baggage compartments below the main deck cargo floor in the event of a rapid decompression. If the vent area of the original type design has been decreased or restricted during modification, the loads on the main deck cargo floor may be increased to an unsafe level during a rapid decompression event. The increased loads on the main deck cargo floor could lead to collapse of the floor beams. Collapse of the main deck cargo floor could restrict the motion of the flight and engine control cables routed through the floor beams or could cause the failure of those cables, which could result in reduced controllability of the airplane or loss of control. Rapid decompression of the airplane could result from a sufficiently large failure in the fuselage pressure boundary either above or below the main deck cargo floor, such as inadvertent opening of the cargo door.
In order to ensure the safety of occupants during emergency landing conditions, the FAA first established in 1934 a set of inertia load factors used to design the structure for restraining items of mass in the fuselage. Because the airplane landing speeds have increased over the years as the fleet has transitioned from propeller to jet design, inertia load factors were changed as specified in CAR part 4b.260. Experience has shown that an airplane designed to this regulation has a reasonable probability of protecting its occupants from serious injury in an emergency landing. The DC-8 passenger airplane was designed to these criteria that specified an ultimate inertia load requirement of 9g in the forward direction. These criteria were applied to the seats and structure restraining the occupants, including the flight crew, as well as other items of mass in the fuselage.
When a Model DC-8 series airplane is converted from a passenger-to a cargo-carrying (“freighter”) configuration, a 9g crash barrier is required, since most cargo containers and container-to-floor attaching devices are not designed to withstand emergency landing loads. In fact, the FAA estimates that the container-to-floor attaching devices will only support approximately 1.5g's to 3g's in the forward direction. Without a 9g crash barrier, it is probable that the loads associated with an emergency landing would cause the cargo to become unrestrained and impact the occupants of the airplane, which could result in serious injury to the occupants.
The structural inadequacy of the 9g crash barrier was evident to the FAA during its review in October 1998 of a McDonnell Douglas Model DC-8 modified in accordance with STC SA1377SO. The observations revealed that the design of the crash barrier floor attachment and circumferential supporting structure neither provide adequate strength to withstand the 9g forward inertia load generated by the main deck cargo mass, nor provide a load path to effectively transfer the loads from the crash barrier to the fuselage structure of the airplane.
Since an unsafe condition has been identified that is likely to exist or develop on other products of this same type design, the proposed AD would require, for airplane modified by STC SA1063SO, the following five actions:
For airplanes modified by STC SA1377SO, this proposed AD would require the following four actions:
1. An inspection and evaluation of the cargo handling system to determine if the side restraints provide the support required by the ULD; and modification of the vertical side restraint to provide the support appropriate to the ULD's compatible with the cargo handling system, if necessary.
2. Modification of the main deck cargo floor to safely carry the applicable
FAA-approved payload limits for above and below the main deck cargo floor. The modification must comply with the applicable requirements of CAR part 4b for the FAA-approved payload distribution.
3. An inspection and evaluation of the venting system of the main deck cargo floor to determine if the system limits decompression loads to a level that can be carried by the floor structure without failure; and modification of the venting system, as necessary, to limit the decompression loads to a level that can be supported successfully by the existing floor structure, if necessary.
4. Installation of a main deck cargo 9g crash barrier that complies with the applicable requirements of CAR part 4b.
AD 98-26-18, amendment 39-10961 (64 FR 1994, January 12, 1999); Start Printed Page 58190
The original floor beams for the DC-8 passenger airplanes have a deeper cross section, which reduces internal stresses for the same applied bending moment, than those for Model 727 series airplanes. Additionally, DC-8 passenger airplanes utilize intermediate “struts” between the main deck cargo floor beams and fuselage frames below the floor to help support the floor beams, which decreases the unsupported span. A shorter unsupported span helps reduce the bending moment for a given applied load. The amount of design data available to the FAA for review of each of the DC-8 STC's (i.e., SA1063SO, SA10377SO, SA1802SO, SA1832SO, SA1862SO, and SA00309AT) was greater than that available when the FAA issued the subject Model 727 NPRM's and AD's. Additionally, the JTF has assisted the FAA in engineering review of this greater volume of data and in the creation of additional data necessary for substantiation of the existing designs. Based on the data available for review, the margins of safety of the DC-8 floor beams indicate a lower level of immediate concern than those margins indicated for the 727 floor beams when the 727 AD's and NPRM's were proposed. Therefore, the FAA has determined that the type of restrictions and interim floor loading and side vertical restraint that were applied to the 727 are not required for the subject DC-8 STC's.
To address the safety concerns of Boeing Model 727 series airplanes that have been modified to freighters by STC, the FAA issued AD's 98-26-19, 98-26-20, 98-26-21, and 98-26-22 to address the capability of the main deck cargo floor and then issued NPRM Rules Dockets 97-NM-232-AD, 97-NM-233-AD, 97-NM-234-AD, and 97-NM-235-AD to address the door indicating system and related systems issues; means to prevent pressurization to an unsafe level if the door is not closed, latched, and locked; door hinge; and 9g crash barrier. Because there have been events involving the cargo door opening in flight on the modified DC-8 series airplanes, the FAA has issued the following AD's to address the door indication system and other related systems issues for those airplanes:
This DC-8 NPRM, and NPRM Rules Dockets 2000-NM-281-AD, 2000-NM-282-AD, and 2000-NM-283-AD would address the structures issues, including the main deck cargo floor, as discussed previously.
There are approximately 15 Model DC-8 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 11 airplanes of U.S. registry would be affected by this proposed AD. The following table shows the estimated cost impact for airplanes affected by this AD. The average labor rate is $60 per work hour. The estimated maximum total cost for all airplanes affected by this proposed AD is $2,192,520, or $199,320 per airplane.
SA1063SO Modification of main deck cargo door structure and fuselage structure 205 700 $143,000, or $13,000 per airplane.
The regulations proposed herein would not have a substantial direct effect on the States, on the relationship between the national Government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, it is determined that this proposal Start Printed Page 58191would not have federalism implications under Executive Order 13132.
McDonnell Douglas: Docket 2000-NM-280-AD.
(a) For airplanes that have been converted from a passenger- to a cargo-carrying (“freighter”) configuration in accordance with STC SA1063SO: Accomplish the actions specified in paragraphs (a)(1) and (a)(2) of this AD in accordance with a method approved by the Manager, Los Angeles Aircraft Certification Office (ACO), FAA.
(b) For airplanes that have been converted from a passenger- to a cargo-carrying (“freighter”) configuration in accordance with STC SA1377SO: Within 2 years or 2,000 flight cycles after the effective date of this AD, whichever occurs first, perform an inspection and evaluation of the cargo handling system to determine if the side restraints provide the support required by the unit load device (ULD), in accordance with a method approved by the Manager, Los Angeles ACO. If any vertical side restraint does not provide the required support, within 2 years or 2,000 flight cycles after the effective date of this AD, whichever occurs first, modify the vertical side restraint to provide the support appropriate to the ULD's compatible with the cargo handling system, in accordance with a method approved by the Manager, Los Angeles ACO.
(c) For airplanes that have been converted from a passenger- to a cargo-carrying (“freighter”) configuration in accordance with STC SA1377SO: Within 3 years or 4,000 flight cycles after the effective date of this AD, whichever occurs first, modify the main deck cargo floor to safely carry the applicable FAA-approved payload limits for above and below the main deck cargo floor. The modification and payload distribution shall be accomplished in accordance with a method approved by the Manager, Los Angeles ACO. The modification must comply with the applicable requirements of CAR part 4b for the FAA-approved payload distribution.
(d) For airplanes that have been converted from a passenger- to a cargo-carrying (“freighter”) configuration in accordance with STC SA1377SO, except for those airplanes that have been modified in accordance with paragraph (c) of this AD: Within 1 year or 1,000 flight cycles after the effective date of this AD, whichever occurs first, perform an inspection and evaluation of the venting system of the main deck cargo floor to determine if the system limits decompression loads to a level that can be carried by the floor structure without failure, in accordance with a method approved by the Manager, Los Angeles ACO.
(g) For airplanes that have been converted from a passenger- to a cargo-carrying (“freighter”) configuration in accordance with STC SA1063SO: Within 3 years or 4,000 flight cycles after the effective date of this AD, whichever occurs first, accomplish the Start Printed Page 58192actions specified in paragraphs (g)(1) and (g)(2) of this AD in accordance with a method approved by the Manager, Los Angeles ACO.
[FR Doc. 00-24749 Filed 9-26-00; 8:45 am]