[Federal Register Volume 64, Number 218 (Friday, November 12, 1999)]
[Proposed Rules]
[Pages 61533-61540]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-29476]


 ========================================================================
 Proposed Rules
                                                 Federal Register
 ________________________________________________________________________
 
 This section of the FEDERAL REGISTER contains notices to the public of 
 the proposed issuance of rules and regulations. The purpose of these 
 notices is to give interested persons an opportunity to participate in 
 the rule making prior to the adoption of the final rules.
 
 ========================================================================
 

  Federal Register / Vol. 64, No. 218 / Friday, November 12, 1999 / 
Proposed Rules  

[[Page 61533]]


=======================================================================
-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-NM-235-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 727 Series Airplanes 
Modified in Accordance With Supplemental Type Certificate SA1444SO, 
SA1509SO, SA1543SO, or SA1896SO

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

-----------------------------------------------------------------------

SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 727 series 
airplanes that have been converted from a passenger to a cargo-carrying 
(``freighter'') configuration. This proposal would require, among other 
actions, installation of a fail-safe hinge, redesigned main deck cargo 
door warning and power control systems, and 9g cargo barrier. This 
proposal is prompted by the FAA's determination that the main deck 
cargo door hinge is not fail-safe; that certain main deck cargo door 
control systems do not provide an adequate level of safety; and that 
the main deck cargo barrier is not structurally adequate during an 
emergency landing. The actions specified by the proposed AD are 
intended to prevent structural failure of the main deck cargo door 
hinge or failure of the cargo door system, which could result in the 
loss or opening of the cargo door while the airplane is in flight, 
rapid decompression, and structural damage to the airplane; and to 
prevent failure of the main deck cargo barrier during an emergency 
landing, which could injure occupants.

DATES: Comments must be received by December 27, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 97-NM-235-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location by appointment only between the hours of 9 a.m. and 3 p.m., 
Monday through Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Paul Sconyers, Associate Manager, 
Airframe and Propulsion Branch, ACE-117A, FAA, Small Airplane 
Directorate, Atlanta Aircraft Certification Office, One Crown Center, 
1895 Phoenix Boulevard, Suite 450, Atlanta, Georgia 30349; telephone 
(770) 703-6076; fax (770) 703-6097.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule.
    The proposals contained in this notice may be changed in light of 
the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    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 97-NM-235-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules 
Docket No. 97-NM-235-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    Supplemental Type Certificate (STC) SA1509SO specifies a design for 
a cargo door, associated cargo door cutout, and door systems. STC 
SA1543SO specifies a design for a Class ``E'' cargo interior with a 
cargo restraint barrier net. STC's SA1444SO and SA1896SO specify a 
design for both of these subject areas. (All of these STC's are held by 
Pemco.) As discussed in notice of proposed rulemaking (NPRM), Rules 
Docket No. 97-NM-81-AD [the final rule, AD 98-26-21, amendment 39-
10964, was published in the Federal Register on January 12, 1999 (64 FR 
2061)], which is applicable to certain Boeing Model 727 series 
airplanes that have been converted from a passenger to a cargo-carrying 
(``freighter'') configuration, the FAA has conducted a design review of 
Boeing Model 727 series airplanes modified in accordance with STC's 
SA1590SO and SA1543SO and has identified several potential unsafe 
conditions. [Results of this design review are contained in ``FAA 
Freighter Conversion STC Review, Report Number 1, dated September 23-
26, 1996,'' (hereinafter referred to as ``the Design Review Report''), 
which is included in the Rules Docket for this NPRM.] This NPRM 
proposes corrective action for three of those potential unsafe 
conditions that relate to the following three areas: main deck cargo 
door hinge, main deck cargo door systems, and main deck cargo barrier.

Main Deck Cargo Door Hinge

    In order to avoid catastrophic structural failure, it has been a 
typical industry approach to design outward opening cargo doors 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 resulting loads). Another potential design approach is safe-life, 
where the critical structure is shown by analyses and/or tests to be 
capable of withstanding the repeated loads of variable magnitude 
expected in service for a specific service life. Safe-life is usually 
not used on critical structure because it is difficult to account for 
manufacturing or in-service accidental damage. For this reason, plus 
the fact

[[Page 61534]]

that none of the STC holders have provided data in support of this 
approach, the safe-life approach will not be discussed further 
regarding the design and construction of the main deck cargo door 
hinge.
    Structural elements such as the main deck cargo door hinge are 
subject to severe in-service operating conditions that could result in 
corrosion, binding, or seizure of the hinge. These conditions, in 
addition to the normal operational loads, can lead to early and 
unpredictable fatigue cracking. If a main deck cargo door hinge is not 
a fail-safe design, a fatigue crack could initiate and propagate 
longitudinally undetected, which could lead to a complete hinge 
failure. A possible consequence of this undetected failure is the 
opening of the main deck cargo door while the airplane is in flight. 
Service experience indicates that the opening of a cargo door while the 
airplane is in flight can be extremely hazardous in a variety of ways 
including possible loss of flight control, severe structural damage, or 
rapid decompression, any of which, could lead to loss of the airplane.
    The design of the main deck cargo door hinge must be in compliance 
with Civil Air Regulations (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 principal 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 SA1509SO, 
SA1444SO, or SA1896SO is supported by latches along the bottom of the 
door and one continuous hinge along the top. This single-piece hinge is 
considered a critical structural element for this STC. A crack that 
initiates and propagates longitudinally along the hinge line of the 
continuous hinge will eventually result in failure of the entire hinge, 
because there is no segmenting of the hinge to interrupt the crack 
propagation and 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.
    As discussed in the Design Review Report, an inspection of one 
Boeing Model 727 series airplane modified in accordance with STC's 
SA1509SO and SA1543SO revealed a number of fasteners with both short 
edge margins and short spacing in the cargo door cutout external 
doublers. Some edge margins were as small as one fastener diameter. 
Fasteners that are placed too close to the edge of a structural member 
or spaced too close to an adjacent fastener can result in inadequate 
joint strength and stress concentrations, which may result in fatigue 
cracking of the skin. If such defects were to exist in the structure of 
the door or the fuselage to which the main deck cargo door hinge is 
attached, the attachment of the hinge could fail, and consequently 
cause the door to open while the airplane is in flight.
    Since unsafe conditions have been identified that are likely to 
exist or develop on other products of this same type design, this 
proposed AD would require, within 250 flight cycles after the effective 
date of the AD, a one-time detailed visual inspection of the external 
surface of the main deck cargo door hinge (both fuselage and door side 
hinge elements) to detect cracks, and repair, if necessary. 
Accomplishment of this inspection will ensure that the subject 
airplanes are not in immediate risk of hinge failure.
    In addition, the proposed AD would require a detailed visual 
inspection of the mating surfaces of both the hinge and the door skin 
and external fuselage doubler underlying the hinge to detect cracks or 
other discrepancies (e.g., double or closely drilled holes, corrosion, 
chips, scratches, or gouges). The proposed AD also would require 
installation of a main deck cargo door hinge that complies with the 
applicable requirements of CAR part 4b, including fail-safe 
requirements. Accomplishment of this detailed visual inspection will 
ensure the integrity of the door and fuselage structure to which the 
hinge is attached. The proposed compliance time for this inspection and 
installation is within 36 months or 4,000 flight cycles after the 
effective date of this AD, whichever occurs first. The compliance time 
is based on the FAA's assessment of the reasonable amount of time to 
redesign, manufacture, and install a fail-safe hinge. This time is in 
consideration of the 18-month time period estimated by the Boeing 727 
industry working group, which includes operators, affected STC holders, 
and engineering organizations, to develop FAA-approved redesigns. These 
actions would be required to be accomplished in accordance with a 
method approved by the FAA.

Main Deck Cargo Door Systems

    In early 1989, two transport airplane accidents were attributed to 
cargo doors coming open during flight. The first accident involved a 
Boeing 747 series airplane in which the cargo door separated from the 
airplane, and damaged the fuselage structure, engines, and passenger 
cabin. The second accident involved a McDonnell Douglas DC-9 series 
airplane in which the cargo door opened but did not separate from its 
hinge. The open door disturbed the airflow over the empennage, which 
resulted in loss of flight control and consequent loss of the airplane. 
Although cargo doors have opened occasionally without mishap during 
takeoff, these two accidents serve to highlight the extreme potential 
dangers associated with the opening of a cargo door while the airplane 
is in flight.
    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 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.
    The ATA task force made its recommendations in the ``ATA Cargo Door 
Task Force Final Report,'' dated May 15, 1991 (hereinafter referred to 
as ``the ATA Final Report''). On March 20, 1992, the FAA issued a 
memorandum to the Director-Airworthiness and Technical Standards of ATA 
(hereinafter referred to as ``the FAA Memorandum''), acknowledging 
ATA's recommendations and providing additional guidance for purposes of 
assessing the continuing airworthiness of existing designs of outward 
opening doors. The FAA Memorandum was not intended to upgrade the 
certification basis of the various airplanes, but rather to identify 
criteria to evaluate potential unsafe conditions demonstrated on in-
service airplanes. Appendix 1 of this AD contains the specific 
paragraphs from the FAA Memorandum that set forth the criteria to which 
the outward opening doors should be shown to comply.
    Applying the applicable requirements of CAR part 4b and design 
criteria

[[Page 61535]]

provided by the FAA Memorandum, the FAA has reviewed the original type 
design of major transport airplanes, including Boeing 727 airplanes 
equipped with outward opening doors, for any design deficiency or 
service difficulty. Based on that review, the FAA identified unsafe 
condition and issued, among others, the following AD's:
     For certain McDonnell Douglas Model DC-9 series airplanes: 
AD 89-11-02, amendment 39-6216 (54 FR 21416, May 18, 1989);
     For all Boeing Model 747 series airplanes: AD 90-09-06, 
amendment 39-6581 (55 FR 15217, April 23, 1990);
     For certain McDonnell Douglas Model DC-8 series airplanes: 
AD 93-20-02, amendment 39-8709 (58 FR 471545, October 18, 1993);
     For certain Boeing Model 747-100 and -200 series 
airplanes: AD 96-01-51, amendment 39-9492 (61 FR 1703, January 23, 
1996); and
     For certain Boeing Model 727-100 and -200 series 
airplanes: AD 96-16-08, amendment 39-9708 (61 FR 41733, August 12, 
1996).
    Using the criteria specified in the ATA Final Report and the FAA 
Memorandum as evaluation guides, the FAA conducted an engineering 
design review and inspection of an airplane modified in accordance with 
STC's SA1509SO and SA1543SO (held by Pemco). The FAA identified a 
number of unsafe conditions with the main deck cargo door systems of 
these STC's. The FAA design review team determined that the design data 
of these STC's design data did not include a safety analysis of the 
main deck cargo door systems.
    As specified in the criteria contained in Appendix 1 of this AD, 
for powered lock systems on the main deck cargo door, it must be shown 
by safety analysis that inadvertent opening of the door after it is 
fully closed, latched, and locked is extremely improbable.
    However, the FAA is aware of two events in which the main deck 
cargo door open during flight. These events occurred on FedEx 
passenger/freighter conversion STC's in October 1996, and March 1995. 
These events are referenced in the Design Review Report.
    The FAA has reviewed the design drawings of the main deck cargo 
door systems installed on Boeing Model 727 series airplanes modified in 
accordance with STC's SA1444SO, SA1509SO, and SA1896SO, and has 
determined that the design of the door systems is nearly identical to 
that installed on the subject FedEx passenger/freighter conversion 
STC's. Therefore, the door opening events disclosed by FedEx are likely 
to occur on airplanes modified in accordance with STC SA1444SO, 
SA1509SO, or SA1896SO.
    For airplanes modified in accordance with STC SA1444SO, SA1509SO, 
SA1543SO, or SA1896SO, the FAA considers the following four specific 
design deficiencies of the main deck cargo door systems to be unsafe:

1. Indication System

    The main deck cargo door indication system for the STC's SA1509SO, 
SA1444SO, and SA1896SO uses a warning light at the door operator's 
control panel and a light at the flight engineer's panel. Both of these 
lights indicate the status of the cargo door latch and lock positions, 
but do not indicate either the door open or closed status. All three 
conditions (i.e., door closed, latched, and locked) must be monitored 
directly so that the door indication system cannot display either 
``latched'' before the door is closed or ``locked'' before the door is 
latched. If a sequencing error caused the door to latch and lock 
without being fully closed, the subject indication system, as designed, 
would not alert the door operator or the flight engineer of this 
condition. As a result, the airplane could be dispatched with the main 
deck cargo door unsecured, which could lead to the cargo door opening 
while the airplane is in flight and possible loss of the airplane.
    The light on the flight engineer's panel is labeled ``MAIN CARGO'' 
and is displayed in red since it indicates an event that requires 
immediate pilot action. However, if the flight engineer is temporarily 
away from his station, a door unsafe warning indication could be missed 
by the pilots. In addition, the flight engineer could miss such an 
indication by not scanning the panel. As a result, the pilots and 
flight engineer could be unaware of, or misinterpret, an unsafe 
condition and could fail to respond in the correct manner. Therefore, 
an indicator light must be located in front of and in plain view of 
both pilots since one of the pilot's stations is always occupied during 
flight operations.
    The main deck cargo door indication system of STC's SA1509SO, 
SA1444SO, and SA1896SO does not have a level of reliability that is 
considered adequate for safe operation. Many components are exposed to 
the environment during cargo loading operations and may be contaminated 
by precipitation, dirt, and grease, or damaged by foreign objects or 
cargo loading equipment. As a result, wires, switches, and relays can 
fail, jam, or short circuit and cause a loss of indication or a false 
indication to the door operator and flight crew. The design logic of 
the indication system (i.e., lights which extinguish when the door is 
locked) will, in the event of a single point failure that would 
extinguish the light, result in an erroneous ``safe'' indication 
regardless of actual door status.
    The design of STC's SA1509SO, SA1444S0, and SA1896S0 has a ``Press-
to-Test'' red warning light on the main deck cargo door control panel 
located near the L-1 door. The design of the monitoring system of the 
main deck cargo door does not include separate lights to provide the 
door operator with door close, latch, and lock status. The electrical 
wiring design of the close, latch, and lock sensors of the door 
monitoring system are wired in parallel instead of in series. In 
parallel, two sensors could be sensing ``unsafe'' and the third sensor 
could be sensing ``safe.'' If this situation were to occur, the sensors 
would not illuminate the red warning light on the door control panel or 
at the flight engineer's panel. Therefore, the ``Press-to-Test'' 
feature is adequate to check the light bulb functionality, but is not 
adequate to check the cargo door close, latch, and lock functions and 
status without annunciator lights for those three functions.

2. Means to Visually Inspect the Locking Mechanism

    The single view port of the main deck cargo door installed in 
accordance with STC's SA1444SO, SA1509SO, and SA1896SO is included to 
allow the flight crew to conduct a visual inspection of the door 
locking mechanism. This view port is used in conjunction with the door 
warning system and should provide a suitable ``back-up'' in the event 
that the main deck cargo door warning system malfunctions.
    The door locking mechanism is an assembly comprised of multiple 
lock pins (one for each of the door latches) connected by linkages to a 
common lock shaft. Although an indicator flag attached to the lock 
shaft can be seen through the view port when the shaft is in the 
``locked'' position, a failure between the shaft and the pins could go 
undetected, because this flag is attached to the lock shaft and not the 
actual lock pins. If such a failure goes undetected, the airplane may 
be dispatched with the main deck cargo door warning system inoperative 
and the door not fully closed, latched, and locked, which could lead to 
a main deck cargo door opening while the airplane is in flight and 
possible loss of the airplane. Therefore, the FAA finds that the

[[Page 61536]]

subject view port is not a suitable back-up when the cargo door warning 
system malfunctions.
    As discussed in the ATA Final Report and the FAA Memorandum, there 
must be a means of directly inspecting each lock or, at a minimum, the 
locks at each end of the lock shaft of certain designs, such that a 
failure condition in the lock shaft would be detectable.

3. Means to Prevent Pressurization to an Unsafe Level

    Boeing 727-100 and -200 airplanes modified in accordance with STC 
SA1444SO, SA1509SO, or SA1896SO are configured to utilize the existing 
pressurization outflow valve for the purpose of preventing fuselage 
pressurization of the airplane to an unsafe level in the event that the 
main deck cargo door is not closed, latched, and locked. The FAA design 
review of these modified Boeing 727-200 airplanes (documented in the 
Design Review Report) identified single point failures in the door 
control/outflow valve interface that could result in the valve not 
sensing and responding to an unsafe door condition. In addition, the 
FAA found no data to substantiate that the outflow valve location and 
size could prevent pressurization to an unsafe level. With the current 
design, it is possible that the outflow valve may not perform its 
intended function when utilized for the purpose of preventing 
pressurization of the airplane in the event of an unsecured door. This 
condition could result in cabin pressurization forcing an unsecured 
door open while the airplane is in flight and possible loss of the 
airplane.
    In some cases, neither Boeing 727-100 airplanes nor Boeing 727-200 
airplanes modified in accordance with the STC SA1444SO or SA1509SO have 
any means of preventing pressurization in the event that the main deck 
cargo door is not closed, latched, and locked, and therefore, have a 
higher risk of a cargo door opening while the airplane is in flight and 
possible loss of the airplane.

4. Powered Lock Systems

    The main deck cargo door control system for STC's SA1444SO, 
SA1509SO, and SA1896SO that utilizes electrical interlock switches is 
designed to remove door control power (electrical and hydraulic) prior 
to flight and to prevent inadvertent door openings. As discussed 
previously, the door system design of the subject STC's is nearly 
identical to the FedEx design. The FedEx door opening events, discussed 
previously, indicate the likelihood that there may be latent and/or 
single point failures that can restore or continue to allow power to 
the door controls and cause inadvertent door openings. The failure 
modes may be found in the electrical portion of the door control panel, 
which, in turn, activates the door control hydraulics. The potential 
for the occurrence of these failure conditions is increased by the 
harsh operating environment of freighter airplanes. Door system 
components are routinely exposed to precipitation, dirt, grease, and 
foreign object intrusion, all of which increase the likelihood of 
damage. As a result, wires, switches, and relays have a greater 
potential to fail or short circuit in such a way as to allow the cargo 
door to be powered open without an operator's command and regardless of 
electrical interlock positions.
    A systems safety analysis would normally evaluate and resolve the 
potential for these types of unsafe conditions. However, the design 
data for STC's SA1444SO, SA1509SO, and SA1896SO do not include a 
systems safety analysis to specifically identify these failure modes 
and do not show that an inadvertent opening is extremely improbable. 
The need for a system safety analysis is identified in the ATA Final 
Report and the FAA Memorandum.
    Since unsafe conditions have been identified that are likely to 
exist or develop on other products of this same type design, this 
proposed AD would require, within 60 days after the effective date, 
revising the Limitations Section of the FAA-approved Airplane Flight 
Manual (AFM) Supplement to provide the flight crew with procedures for 
ensuring that all power is removed from the main deck cargo door prior 
to dispatch of the airplane, and that the main deck cargo door is 
closed, latched, and locked prior to dispatch of the airplane; and 
installing any associated placards.
    In addition, the proposed AD would require, within 36 months after 
the effective date of the AD, incorporation of redesigned main deck 
cargo door systems (e.g., warning/monitoring, power control, view 
ports, and means to prevent pressurization to an unsafe level if the 
main deck cargo door is not closed, latched, and locked), including any 
associated procedures and placards that comply with the applicable 
requirements of CAR part 4b and design criteria of the ATA Final Report 
and the FAA Memorandum. Design data provided in support of the door 
systems re-design should include a Systems Safety Analysis and 
Instructions for Continued Airworthiness that are acceptable to the 
FAA. Accomplishment of the incorporation of redesigned main deck cargo 
door systems will prevent rapid decompression and/or structural damage 
to the airplane as a result of loss or opening of the cargo door while 
the airplane is in flight. The compliance time is based on the FAA's 
assessment of the reasonable amount of time to incorporate redesigned 
main deck cargo door systems. This time is in consideration of the 18-
month time period estimated by the Boeing 727 industry working group, 
which includes operators, affected STC holders, and engineering 
organizations, to develop FAA-approved redesigns.
    These actions would be required to be accomplished in accordance 
with a method approved by the FAA.

Cargo Restraint Barrier

    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 727 passenger airplane was designed to 
these criteria which 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 the 727 passenger airplane is converted to carry cargo on the 
main deck, a cargo barrier is required, since most cargo containers and 
the 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 cargo barrier, it is 
probable that the loads associated with an emergency landing would 
cause the cargo to be unrestrained and impact the occupants of the 
airplane, which could result in serious injury or death.
    The structural inadequacy of the cargo barrier was evident to the 
FAA during its review in October 1996 of a Boeing 727 modified in 
accordance with STC SA1543SO. The observations revealed that the design 
of the net restraint barrier floor attachment and circumferential 
supporting structure

[[Page 61537]]

does not provide adequate strength to withstand the 9g forward inertia 
load generated by the main deck cargo mass, nor does it provide a load 
path to effectively transfer the loads from the restraint barrier to 
the fuselage structure of the airplane. These observations are 
supported by data contained in ``ER 2785, Structural Substantiation of 
the 50k 9g Bulkhead Restraint System in Support of STC SA1543SO PN 53-
1292-401 for the 9g Bulkhead 53-1980-300 Assembly with Upper Attachment 
Structure, Lower Attachment Structure, Floor Shear Web Structure, Seat 
Track Splice Fittings, Seat Tracks, and Seat Track Splices,'' dated 
September 29, 1996, by M. F. Daniel. Although this report was specific 
to STC SA1543SO, the FAA has determined that the data are applicable to 
airplane modified in accordance with STC ST00015AT because the design 
principles for attachment of the barriers in both STC's are the same. 
The report reveals that the structural deficiencies were found in the 
net attach plates and floor attachment structure of the cargo barrier. 
The data show large negative margins of safety, which indicate that the 
inertia load capability of the cargo barrier is closer to 2g than the 
required 9g in the forward direction. From these analyses, it is 
evident that the cargo restraint barrier would not be capable of 
preventing serious injury to the occupants during an emergency landing 
event with the full allowable cargo load.
    Since unsafe conditions have been identified that are likely to 
exist or develop on other products of this same type design, this 
proposed AD would require installation of a main deck cargo barrier 
that complies with the applicable requirements of CAR part 4b. 
Accomplishment of the installation will prevent serious injury to the 
occupants in the event of an emergency landing. The proposed compliance 
time for the installation is within 36 months or 4,000 flight cycles 
after the effective date of the AD, whichever occurs first. This 
compliance time is based on the FAA's assessment of the reasonable 
amount of time to redesign, manufacture, and install the cargo barrier. 
This time is consistent with estimates by affected STC holders and 
operators that necessary redesigns can by developed and approved by the 
FAA within 12 to 18 months from August 1998.

Regulatory Evaluation Summary

    The regulations proposed herein would not have substantial direct 
effects 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, in 
accordance with Executive Order 12612, it is determined that this 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    This analysis examines the cost of a proposed AD that would require 
the installation of a fail-safe hinge, redesigned main deck cargo door 
warning and power control systems, and a 9g cargo barrier on Boeing 
Model 727 series airplanes that have been modified in accordance with 
STC's held by Pemco. As discussed above, the FAA has determined that 
the main deck cargo door hinge is not fail-safe, that certain main deck 
cargo door control systems do not provide an adequate level of safety, 
and that the main deck cargo barrier is not structurally adequate 
during a minor crash landing.
    Approximately 62 U.S.-registered Boeing Model 727 series airplanes 
would be affected by the proposed AD. The following discussion 
addresses, in sequence, the actions in this proposed AD and the 
estimated cost associated with each of these actions. An analysis of 
the costs is also available in Rules Docket No. 97-NM-235-AD.

1. Main Deck Cargo Door Hinge

    Since unsafe conditions have been identified that are likely to 
exist or develop on other modified Boeing Model 727 series airplanes, 
paragraph (a) of the proposed AD would require, within 250 flight 
cycles after the effective date of this AD, a one-time detailed visual 
inspection to detect cracks of the external surface of the main deck 
cargo door hinge. Pemco estimates that this inspection would take 1.5 
work hours. At a mechanic's burdened labor rate of $60 per work hour, 
the cost per airplane would be $90, or $5,580 for the fleet of 62 
affected Boeing Model 727 series airplanes.
    Paragraph (b)(1) of the proposed AD would require, within 36 months 
or 4,000 cycles after the effective date of this AD, a detailed visual 
inspection of the mating surfaces of both the hinge and the door skin 
and external fuselage doubler underlying the hinge. The FAA estimates 
that compliance with this inspection would take 200 hours at a cost of 
$12,000 per airplane, or $744,000 for the affected fleet.
    Paragraph (b)(2) of the proposed AD would require installation of a 
fail-safe door hinge. The compliance time for this installation also 
would be 36 months or 4,000 cycles after the effective date of this AD. 
Pemco estimates the cost to design and certificate such a hinge is 
$20,000, that the parts for a fail-safe door hinge would cost $8,000, 
and installation would take 300 hours. Total compliance costs for this 
proposed provision for the affected fleet of 62 airplanes would be $1.6 
million.
    Paragraph (c) of the proposed AD would require that, if any crack 
or discrepancy is detected during the inspections required by paragraph 
(a) or (b)(1) of the proposed AD, repairs must be made prior to further 
flight. The cost of these repairs is not attributable to this proposed 
AD.
    For purposes of this analysis, the FAA assumes an effective date of 
July 1, 2000. The cost to comply with proposed paragraphs (a) through 
(c) over the 36-month compliance period is $2.4 million, or $2.0 
million discounted to present value at 7 percent. The FAA assumes that 
the installation of the main deck cargo door hinge [paragraph (b)(1)] 
would be accomplished at the same time as the detailed visual 
inspection of fastener holes [paragraph (b)(2)]. The FAA also assumes 
that operators of airplanes modified under Pemco AD's would perform 
these two activities uniformly throughout the 36-month period. Finally, 
the certification cost for the main deck cargo door hinge would be 
incurred within the first 6 months after the effective date of this AD.

2. Main Deck Cargo Door Systems

    Paragraph (d) of the proposed AD would require, within 60 days 
after the effective date, revising the Limitations Section of the FAA-
approved Airplane Flight Manual (AFM) Supplement to provide the flight 
crew with procedures for ensuring that all power is removed from the 
main deck cargo door prior to dispatch of the airplane, and that the 
main deck cargo door is closed, latched, and locked prior to dispatch 
of the airplane. In addition, paragraph (d) of the proposed AD would 
require the installation of any associated placards.
    The Pemco door system design as provided by STC's SA1444SO, 
SA1896SO, and SA1509SO is nearly identical to that of FedEx. Therefore 
it is likely that the cost associated with the inspection of the door 
are the same based on FedEx's assumptions. FedEx assumes that an 
external inspection of the flushness of the cargo door, combined with 
an ``enhanced B-check'' would be an acceptable means to the FAA to 
ensure that the cargo door is secured prior to dispatch. Based on this 
assumption, FedEx estimates, before a redesigned door system is 
installed [see proposed paragraph (f) below], that it would take a 
mechanic 30 minutes to inspect for flushness of the main deck cargo 
door prior to dispatch. Using these

[[Page 61538]]

estimates for compliance for airplanes with Pemco STC's, and, assuming 
each affected airplane flies 1 flight per day, 260 days per year, the 
estimated cost per inspection would be $30, or $7,800 per airplane per 
year until the door system is changed, a total of $865,800 over 36 
months.
    B-checks on these Boeing Model 727 series airplanes occur 
approximately twice a year. FedEx estimates the incremental cost for 
maintenance during this ``enhanced B-check'' is $11,700 per year until 
the door system is changed. Assuming incorporation of the redesigned 
door system occurs uniformly over the 36-month period, the total cost 
to operators of Pemco-modified Boeing Model 727 series airplanes would 
be $1.3 million. In addition, Pemco estimates the setup costs for the 
daily inspection (i.e., procedure materials for the mechanics to 
perform the inspection and training requirements) would be $50,000.
    Paragraph (e) of the proposed AD would require, within 36 months 
after the effective date of this AD, incorporation of a redesigned main 
deck cargo door system. Pemco estimates that the development and 
certification of the system would cost $138,800. Modification parts 
would cost $10,000 per airplane and labor costs would be $18,000 per 
airplane. The FAA assumes that operators would incorporate the 
redesigned main deck cargo door system during regularly scheduled 
maintenance but that, on average, each airplane in the affected fleet 
would be out of service for 3 additional days at a cost of $18,300. The 
total costs of installing a redesigned main deck cargo door system, 
including certification, parts, labor, and down time would be $3.0 
million over the 36-month period.
    The total estimated cost to comply with proposed requirements for 
the main deck cargo door system is $5.2 million or $4.6 million, 
discounted to present value.

3. Main Deck Cargo Barrier

    Paragraph (f) of the proposed AD would require, within 36 months or 
4,000 flight cycles after the effective date of this AD, installation 
of a main deck cargo barrier that complies with the applicable 
requirements of CAR part 4b. Pemco estimates that development and 
certification of a 9g barrier would cost $126,500, while parts would 
cost $25,000 and labor would cost $18,000 per airplane for 300 hours of 
labor at $60 per hour burdened rate.
    The FAA assumes that operators would install 9g barriers in their 
affected fleets uniformly over the 36-month compliance period. The 
total non-discounted cost would be $2.8 million, or $2.4 million 
discounted to present value.

4. Alternative Methods of Compliance (AMOC) and Special Flight Permits

    Paragraph (g) of the proposed AD would allow an AMOC or adjustment 
of compliance time that provides an acceptable level of safety if 
approved by the Manager of the Atlanta ACO. The FAA is unable to 
determine the cost of an AMOC, but assumes it would be less than the 
cost of complying with the proposed provisions in paragraphs (a) 
through (f) of the proposed AD.
    Paragraph (h) of the proposed AD would allow special flight permits 
in accordance with the regulations to operate an affected airplane to a 
location where the requirements of the proposed AD could be 
accomplished.

5. Total Cost of the Proposed AD

    The FAA estimates that the total compliance cost of the proposed AD 
would be $10.4 million, or $9.0 million discounted to present value.
    The Regulatory Flexibility Act (RFA) of 1980 establishes ``as a 
principle of regulatory issuance that agencies shall endeavor, 
consistent with the objective of the rule and of applicable statutes, 
to fit regulatory and informational requirements to the scale of the 
business, organizations, and governmental jurisdictions subject to 
regulation. To achieve that principle, the RFA requires agencies to 
solicit and consider flexible regulatory proposals and to explain the 
rationale for their actions. The RFA covers a wide-range of small 
entities, including small businesses, not-for-profit organizations, and 
small governmental jurisdictions.
    Agencies must perform a review to determine whether a proposed or 
final rule will have a significant economic impact on a substantial 
number of small entities. If the determination is that it will, the 
Agency must prepare a regulatory flexibility analysis as described in 
the RFA. However, if an agency determines that a proposed or final rule 
is not expected to have a significant economic impact on a substantial 
number of small entities, section 605(b) of the RFA provides that the 
head of the agency may so certify and an RFA is not required. The 
certification must include a statement providing the factual basis for 
this determination, and the reasoning should be clear.
    Six of the 11 operators that would be affected by this proposed AD 
are small, that is, they employ fewer than 1,500 persons. The estimated 
total cost of the proposed AD is $10.4 million, or approximately 
$167,700 for each of the 62 affected airplanes.
    Therefore, the FAA has determined that the proposed rule would have 
a significant impact on a substantial number of small entities and a 
regulatory flexibility analysis is required.
    Under Section 63(b) of the RFA, the analysis must address:
    1. Reasons why the agency is promulgating the rule;
    2. The objectives and legal basis for the rule;
    3. The kind and number of small entities to which the rule will 
apply;
    4. The projected reporting, recordkeeping, and other compliance 
requirements of the rule; and
    5. All federal rules that may duplicate, overlap, or conflict with 
the rule. These elements of the RFA are addressed below.
A. Reasons Why Agency Action is Being Considered
    The FAA has determined that the main deck cargo door hinge is not 
fail-safe; that certain main deck cargo door control systems do not 
provide an adequate level of safety; and the main deck cargo barrier is 
not structurally adequate during a minor crash landing.
    The actions specified in the proposed AD are intended to prevent 
structural failure of the main deck cargo door hinge or failure of the 
cargo door system, which could result in the loss or opening of the 
cargo door while the airplane is in flight, and consequent rapid 
decompression and/or structural damage to the airplane; and to prevent 
failure of the main deck cargo barrier during an emergency landing, 
which could injure occupants.
B. Statement of Objective and Legal Basis
    Under the United States Code (U.S.C.), the FAA Administrator is 
required to consider the following matter, among others, as being in 
the public interest: assigning, maintaining, and enhancing safety and 
security as the highest priorities in air commerce. [See 49 U.S.C. 
Sec. 44101(d).] 49 U.S.C. Sec. 44701(a) provides broad rulemaking 
authority to ``promote safe flight of civil aircraft in air commerce.'' 
Accordingly, this proposed AD will amend Title 14 of the Code of 
Federal Regulations to require operators of Boeing Model 727 series 
airplanes that have been converted from a passenger-to a cargo-carrying 
configuration to correct the identified unsafe conditions.

[[Page 61539]]

C. Kind and Number of Small Entities
    The RFA requires the FAA to determine whether or not a rule 
significantly affects a substantial number of small entities. This 
determination is typically based on small entity size and cost 
thresholds that vary depending on the affected industry. The entities 
affected by the rule are those operating U.S.-registered converted 
Boeing Model 727 series airplanes. The FAA has determined that 
approximately 6 of the 11 entities are small, i.e., employ fewer than 
1,500 persons. Two small entities operate 1 affected airplane each, 1 
small entity operates 2 affected airplanes, 1 small entity operates 7 
affected airplanes, and 2 small entities operate 9 affected airplanes 
each. Assuming the total costs of the proposed rule are divided equally 
among the affected fleet of 62 airplanes, the costs per airplane would 
be about $167,700. Therefore, the FAA has determined that this proposed 
AD would significantly affect a substantial number of small entities.
D. Projected Reporting, Recordkeeping, and Other Compliance 
Requirements
    With two minor exceptions, the rule will not mandate additional 
reporting or recordkeeping. The proposed AD would require operators to 
report results of the visual inspection of the main deck cargo door 
hinge and the visual inspection of the fastener holes common to the 
main deck cargo door hinge and underlying door and fuselage structure. 
The cost of these reports is negligible.
E. Overlapping, Duplicative, or Conflicting Federal Rules
    The rule will not overlap, duplicate, or conflict with existing 
Federal rules.
F. Analysis of Alternatives
    The FAA acknowledges that the rule will impose a financial 
requirement on small entities. Therefore, the agency considered 
alternatives to the proposed rule. These alternatives are:
     Exclude small entities; and
     Extend the compliance date for small entities.
    The FAA has determined that the option to exclude small entities 
from the requirements of the rule is not justified. The unsafe 
condition that exists on an affected Boeing Model 727 series airplane 
operated by a small entity is as potentially catastrophic as that on an 
affected Boeing Model 727 series airplane operated by a large entity.
    The FAA also considered options to extend the compliance period for 
small operators. The Boeing 727 Freighter Industry Working Group, which 
includes all affected U.S. operators (including small entities), 
provided input on the incorporation of corrective actions for the door 
hinge, door systems, and 9g barrier issues. The FAA initially proposed 
a compliance time of 28 months, consistent with a related AD dealing 
with the cargo floor structure on the same airplanes. The Industry 
Working Group requested an extension to 36 months. Following review of 
the Working Group's request, the FAA finds 36 months to be an 
acceptable compliance time. Therefore, the FAA has, in fact, considered 
and accepted this alternative and has accommodated small entity 
concerns about compliance time.
    Title II of the Unfunded Mandates Reform Act of 1995 (the Act), 
enacted as Pub. L. 104-4 on March 22, 1995, requires each Federal 
agency, to the extent permitted by law, to prepare a written assessment 
of the effects of any Federal mandate in a proposed or final agency 
rule that may result in the expenditure by State, local, and tribal 
governments, in the aggregate, or by the private sector, of $100 
million or more (adjusted annually for inflation) in any one year. 
Section 204(a) of the Act, 2 U.S.C. 1534(a), requires the Federal 
agency to develop an effective process to permit timely input by 
elected officers (or their designees) of State, local, and tribal 
governments on a proposed ``significant intergovernmental mandate.'' A 
``significant intergovernmental mandate'' under the Act is any 
provision in a Federal agency regulation that would impose an 
enforceable duty upon State, local, and tribal governments, in the 
aggregate, of $100 million (adjusted annually for inflation) in any one 
year. Section 203 of the Act, 2 U.S.C. 1533, which supplements section 
204(a), provides that before establishing any regulatory requirements 
that might significantly or uniquely affect small governments, the 
agency shall have developed a plan that, among other things, provides 
for notice to potentially affected small governments, if any, and for a 
meaningful and timely opportunity to provide input in the development 
of regulatory proposals.
    This proposed AD does not contain any Federal intergovernmental or 
private sector mandate. Therefore, the requirements of Title II of the 
Unfunded Mandates Reform Act of 1995 do not apply.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (14 CFR part 39) as 
follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

Boeing: Docket 97-NM-235-AD.
    Applicability: Model 727 series airplanes that have been 
converted from a passenger to a cargo-carrying (``freighter'') 
configuration in accordance with Supplemental Type Certificate (STC) 
SA1444SO, SA1509SO, SA1543SO, or SA1896SO; certificated in any 
category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
otherwise modified, altered, or repaired in the area subject to the 
requirements of this AD. For airplanes that have been modified, 
altered, or repaired so that the performance of the requirements of 
this AD is affected, the owner/operator must request approval for an 
alternative method of compliance in accordance with paragraph (g) of 
this AD. The request should include an assessment of the effect of 
the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if the unsafe condition has not been 
eliminated, the request should include specific proposed actions to 
address it.

    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent structural failure of the main deck cargo door hinge 
or failure of the cargo door system, which could result in the loss 
or opening of the cargo door while the airplane is in flight, rapid 
decompression, and structural damage to the airplane; and to prevent 
failure of the main deck cargo barrier during an emergency landing, 
which could injure occupants; accomplish the following:

Actions Addressing the Main Deck Cargo Door Hinge

    (a) Within 250 flight cycles after the effective date of this 
AD, perform a detailed visual inspection of the external surface of 
the main deck cargo door hinge (both fuselage and door side hinge 
elements) to detect cracks.

    Note 2: For the purposes of this AD, a detailed visual 
inspection is defined as: ``An intensive visual examination of a 
specific structural area, system, installation, or assembly to 
detect damage, failure, or irregularity. Available lighting is 
normally supplemented with a direct source of good lighting at 
intensity deemed appropriate by the inspector. Inspection aids such 
as mirror,

[[Page 61540]]

magnifying lenses, etc., may be used. Surface cleaning and elaborate 
access procedures may be required.''

    (b) Within 36 months or 4,000 flight cycles after the effective 
date of this AD, whichever occurs first, accomplish paragraphs 
(b)(1) and (b)(2) of this AD.
    (1) Perform a detailed visual inspection of the mating surfaces 
of both the hinge and the door skin and external fuselage doubler 
underlying the hinge to detect cracks or other discrepancies (e.g., 
double or closely drilled holes, corrosion, chips, scratches, or 
gouges). The detailed visual inspection shall be accomplished in 
accordance with a method approved by the Manager, Atlanta Aircraft 
Certification Office (ACO), FAA, Small Airplane Directorate. The 
requirements of this paragraph may be accomplished prior to or 
concurrently with the requirements of paragraph (b)(2) of this AD.
    (2) Install a main deck cargo door hinge that complies with the 
applicable requirements of Civil Air Regulations (CAR) part 4b, 
including fail-safe requirements, in accordance with a method 
approved by the Manager, Atlanta ACO.
    (c) If any crack or discrepancy is detected during the detailed 
visual inspection required by either paragraph (a) or (b)(1) of this 
AD, prior to further flight, repair in accordance with a method 
approved by the Manager, Atlanta ACO.

Actions Addressing the Main Deck Cargo Door Systems

    (d) Within 60 days after the effective date of this AD, revise 
the Limitations Section of the FAA-approved Airplane Flight Manual 
(AFM) Supplement by inserting therein the procedures specified in 
paragraphs (d)(1) and (d)(2) of this AD, and install any associated 
placards. The AFM revision procedures and installation of any 
associated placards shall be accomplished in accordance with a 
method approved by the Manager, Atlanta ACO.
    (1) Procedures to ensure that all power is removed from the main 
deck cargo door prior to dispatch of the airplane. And
    (2) Procedures to ensure that the main deck cargo door is 
closed, latched, and locked prior to dispatch of the airplane.
    (e) Within 36 months after the effective date of this AD, 
incorporate redesigned main deck cargo door systems (e.g., warning/
monitoring, power control, view ports, and means to prevent 
pressurization to an unsafe level if the main deck cargo door is not 
closed, latched, and locked), including any associated procedures 
and placards, that comply with the applicable requirements of CAR 
part 4b and criteria specified in Appendix 1 of this AD; in 
accordance with a method approved by the Manager, Atlanta ACO.

    Note 3: The design data submitted for approval should include a 
Systems Safety Analysis and Instructions for Continued Airworthiness 
that are acceptable to the Manager, Atlanta ACO.

Actions Addressing the Main Deck Cargo Barrier

    (f) Within 36 months or 4,000 flight cycles after the effective 
date of this AD, whichever occurs first, install a main deck cargo 
barrier that complies with the applicable requirements of CAR part 
4.b, in accordance with a method approved by the Manager, Atlanta 
ACO.

    Note 4: The maximum main deck total payload that can be carried 
is limited to the lesser of the approved cargo barrier weight limit, 
weight permitted by the approved maximum zero fuel weight, weight 
permitted by the approved main deck position weights, weight 
permitted by the approved main deck running load or distributed load 
limitations, or approved cumulative zone or fuselage monocoque 
structural loading limitations (including lower hold cargo).

    Note 5: Installation of a Ventura Aerospace Inc. cargo barrier 
STC ST00848LA is an approved means of compliance with the 
requirements of paragraph (f) of this AD.

    (g) An alternative method of compliance or adjustment of the 
compliance time contained in this proposal that provides an 
acceptable level of safety may be used if approved by the Manager, 
Atlanta ACO. Operators shall submit their requests through an 
appropriate FAA Principal Maintenance Inspector, who may add 
comments and then send it to the Manager, Atlanta ACO.

    Note 6: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Atlanta ACO.

    (h) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.

Appendix 1

    Excerpt from an FAA Memorandum to the Director-Airworthiness and 
Technical Standards of ATA, dated March 20, 1992.
    ``(1) Indication System:
    (a) The indication system must monitor the closed, latched, and 
locked positions, directly.
    (b) The indicator should be amber unless it concerns an outward 
opening door whose opening during takeoff could present an immediate 
hazard to the airplane. In that case the indicator must be red and 
located in plain view in front of the pilots. An aural warning is 
also advisable. A display on the master caution/warning system is 
also acceptable as an indicator. For the purpose of complying with 
this paragraph, an immediate hazard is defined as significant 
reduction in controllability, structural damage, or impact with 
other structures, engines, or controls.
    (c) Loss of indication or a false indication of a closed, 
latched, and locked condition must be improbable.
    (d) A warning indication must be provided at the door operators 
station that monitors the door latched and locked conditions 
directly, unless the operator has a visual indication that the door 
is fully closed and locked. For example, a vent door that monitors 
the door locks and can be seen from the operators station would meet 
this requirement.
    (2) Means to Visually Inspect the Locking Mechanism:
    There must be a visual means of directly inspecting the locks. 
Where all locks are tied to a common lock shaft, a means of 
inspecting the locks at each end may be sufficient to meet this 
requirement provided no failure condition in the lock shaft would go 
undetected when viewing the end locks. Viewing latches may be used 
as an alternate to viewing locks on some installations where there 
are other compensating features
    (3) Means to Prevent Pressurization:
    All doors must have provisions to prevent initiation of 
pressurization of the airplane to an unsafe level, if the door is 
not fully closed, latched and locked.
    (4) Lock Strength:
    Locks must be designed to withstand the maximum output power of 
the actuators and maximum expected manual operating forces treated 
as a limit load. Under these conditions, the door must remain 
closed, latched and locked.
    (5) Power Availability:
    All power to the door must be removed in flight and it must not 
be possible for the flight crew to restore power to the door while 
in flight.
    (6) Powered Lock Systems:
    For doors that have powered lock systems, it must be shown by 
safety analysis that inadvertent opening of the door after it is 
fully closed, latched and locked, is extremely improbable.''

    Issued in Renton, Washington, on November 4, 1999.
D. L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-29476 Filed 11-10-99; 8:45 am]
BILLING CODE 4910-13-U