[Federal Register Volume 62, Number 135 (Tuesday, July 15, 1997)]
[Proposed Rules]
[Pages 37778-37788]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-18358]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-NM-81-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 727 Series Airplanes 
Modified in Accordance with Supplemental Type Certificate SA1444SO, 
SA1509SO, SA1543SO, SA1896SO, SA1740SO, or SA1667SO

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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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 limiting the 
payload on the main cargo deck by revising the Limitations Sections of 
all Airplane Flight Manuals (AFM), AFM Supplements, and Airplane Weight 
and Balance Supplements for these airplanes. This proposal also 
provides for the submission of data and analysis that substantiates the 
strength of the main cargo deck, or modification of the main cargo 
deck, as optional terminating action for these payload restrictions. 
This proposal is prompted by the FAA's determination that unreinforced 
floor structure of the main cargo deck is not strong enough to enable 
the airplane to safely carry the maximum payload that is currently 
allowed in this area. The actions specified by the proposed AD are 
intended to prevent failure of the floor structure, which could lead to 
loss of the airplane.

DATES: Comments must be received by August 22, 1997.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 97-NM-81-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.

FOR FURTHER INFORMATION CONTACT: Steven C. Fox, Senior Aerospace 
Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington; 
telephone (425) 227-2777; fax (425) 227-1181.

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-81-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-103, Attention: Rules 
Docket No. 97-NM-81-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has issued supplemental type certificates (STC) for 
converting certain Boeing Model 727 and 747 series airplanes from a 
passenger to a cargo-carrying (``freighter'') configuration. These 
freighter conversions entail such modifications as removal of the 
passenger interior, the installation of systems to handle cargo 
containers (such as pallets and other unit load

[[Page 37779]]

devices), the installation of a side cargo door for the main cargo 
deck, and alterations to such systems as the hydraulic, electrical, and 
smoke detection systems that are associated with the transport of 
cargo. When a conversion is completed, the weight permitted to be 
carried (``payload'') on the main cargo deck is significantly greater 
than the payload allowed in that same area when the airplane was in its 
original passenger configuration.
    On December 27, 1995, the FAA issued Airworthiness Directive (AD) 
96-01-03, amendment 39-9479 (61 FR 116, January 3, 1996). The FAA took 
this action after determining that Model 747 passenger airplanes 
converted to freighters under certain STC's are not structurally 
capable of safely carrying the payload allowed on the main cargo deck. 
This condition is due to structural deficiencies in the floor beams of 
this deck, as well as in the fuselage structure surrounding the side 
cargo door for this area. That AD requires operators of those Model 747 
freighters to reduce the maximum payload that can be carried on the 
main cargo deck in order ``[t]o prevent collapse of the aft fuselage 
due to inadequate strength in the airplane structure and subsequent 
separation of the aft fuselage from the airplane.'' Model 747 
freighters affected by AD 96-01-03 were converted under STC's held by 
GATX/Airlog Company (``GATX'') when that AD was issued. GATX had 
acquired the original STC's from Hayes International Corporation 
(Hayes).
    During its investigation of the circumstances that led to the 
issuance of AD 96-01-03, the FAA determined that similar unsafe 
conditions were likely to be found on certain Model 727 series 
airplanes that had been converted to freighters in a comparable manner. 
The bases for these concerns were that similar procedures and design 
methods had been used on both the 727 and 747 models, and that these 
STC's could be traced back to the same companies.

Actions Subsequent to AD 96-01-03

    In response to those concerns, the FAA's Transport Airplane 
Directorate established a design review team of FAA engineers to 
identify any safety problems pertaining to certain interior and side 
cargo door STC's for Model 727 series airplanes, and to make 
recommendations for correcting any unsafe conditions.
    The design review team has determined that there are more than 10 
STC's for Model 727 freighters (``freighter STC's'' or ``Model 727 
freighter STC's'') that need to be reviewed. These freighter STC's are 
individually held by Aeronautical Engineers, Inc. (AEI), ATAZ, Inc. 
(ATAZ), Federal Express Corporation (FedEx), and Pemco Aeroplex, Inc. 
(Pemco). The STC's held by Pemco are SA1444SO, which pertains to the 
cargo door and cargo compartment interior on Model 727-100 series 
airplanes; SA1509SO, which pertains to the cargo door on Model 727-100 
and -200 series airplanes; SA1543SO, which pertains to the cargo 
compartment interior of Model 727-100 and -200 series airplanes; 
SA1896SO, which pertains to the cargo door and cargo compartment 
interior of Model 727-100 series airplanes; SA1740SO, which pertains to 
the cargo/passenger compartment interior of Model 727-100 series 
airplanes; and SA1667SO, which pertains to provisions for a ninth cargo 
pallet on Model 727-100 series airplanes. Over 300 Model 727 series 
airplanes of both U.S. and foreign registry have been modified in 
accordance with these STC's, and more than 32 operators worldwide use 
these freighters.
    In reviewing these freighter STC's, the design review team applied 
the standards of Civil Air Regulations (CAR) part 4b, applicable to the 
original Boeing Model 727 airplane. These federal standards establish 
minimum safety requirements. A design which does not meet these 
standards is presumed to be unsafe.
    Between September 1996 and February 1997, members of the design 
review team made four visits to inspect Model 727 series airplanes that 
were in the process of being converted or already had been converted 
under these freighter STC's. Site visits were conducted at Pemco World 
Air Services in Dothan, Alabama (Pemco STC's); the Tramco repair 
station in Everett, Washington (FedEx STC's that had originally been 
developed by Hayes); and Professional Modification Services (PMS), 
Inc.'s, facility in Miami, Florida (AEI and ATAZ STC's).
    On all of the Model 727 series airplanes inspected during these 
site visits, the design review team observed that the original 
passenger floor beams, which now support the main cargo deck, had not 
been structurally reinforced by the STC modification for the heavier 
payloads these freighters are permitted to carry.
    These STC freighters typically are allowed to carry 8,000 pound 
containers (weight of the cargo and container) on the main cargo deck. 
Because these containers are 88 inches long, the running load (the 
weight that can be placed on a longitudinal section of the main cargo 
deck) is 90 pounds per inch (8,000 pounds divided by 88 inches). This 
running load of 90 pounds per inch is a safety concern because it is 
approximately 2.6 times higher than the maximum running load of 34.5 
pounds per inch allowed on these same floor beams when the airplane was 
in a passenger configuration.

FAA Structural Analysis of the Floor Beams of the Main Cargo Deck

    The design review team examined the documents that the current or a 
previous STC holder had submitted when seeking original FAA approval of 
the STC application. The team was unable to find any data to verify 
that the unreinforced floor structure of the main cargo deck can safely 
support the heavier freighter payloads.
    To independently evaluate whether these floor beams are strong 
enough to support the maximum payload permitted by the STC's, the 
design review team performed a limited structural analysis of the 
design of each main cargo deck viewed during its site visits.
    In analyzing the floor beams of the main cargo deck, the FAA 
engineers used the payload configuration defined in the weight and 
balance documents for each STC. (These STC freighters are operated in 
accordance with FAA-approved Weight and Balance Supplements, which 
specify the payload that can be carried onboard, as well as the maximum 
payload and assigned location for individual containers on the main 
cargo deck.) Most of the containers permitted in the Weight and Balance 
Supplements for these STC's weigh up to 8,000 pounds each.
    In its analysis, the design review team considered the different 
cargo handling system configurations observed on the STC freighters 
during the site visits; these systems include roller trays and 
container locks. The roller trays are attached to the floor of the main 
cargo deck, and enable cargo to be rolled forward and aft. These trays 
also support the weight of the cargo containers. The container locks, 
which hold a container in place, are spaced along the floor of the main 
cargo deck for all of these STC's but one; that STC also has side 
vertical cargo container restraints (``side restraints''). The analysis 
is based on the use of containers that are 88 inches by 125 inches, and 
the location of the horizontal center of gravity for the total payload 
in each container was within 8.8 inches from the geometric center of 
the base of the container for the forward and aft direction and 12.5 
inches from the geometric center of the base of the container for the 
left and right direction.

[[Page 37780]]

    The design review team used commonly accepted analytical methods in 
its structural analyses. This methodology, or an equivalent, was 
applicable when the STC application was originally submitted for 
approval, and it is applicable today. None of the floor analyses 
performed by the team involved the application of advanced technologies 
such as finite element modeling. The results of these structural 
analyses were consistent with data provided by Boeing, which had 
originally built these airplanes as passenger transports, and with some 
of the data provided by these STC holders.
    To evaluate the adequacy of the floor, the team determined that the 
most likely ``critical case'' (the conditions or circumstances that 
exert the greatest forces on the main cargo deck) would be the ``down 
gust'' conditions specified in CAR part 4b. Down gusts are downward 
vertical movements of air that occur in turbulence and storms. Down 
gusts exert a downward force on the entire airplane. As this force 
causes the airplane to accelerate downward, containers on the main 
cargo deck--because of inertia--are pulled upward. This upward force on 
the containers is transmitted through the container locks and into the 
floor beams. On these STC freighters, this upward force could bend 
these floor beams upward to failure, and the failure of even a single 
beam could result in loss of the airplane.
    Even if the floor beams of the main cargo deck only become 
deformed, the results could be catastrophic. Because flight control 
system cables and fuel lines pass through small holes in these floor 
beams, significant--although temporary--deformation of these beams 
could jam the cables or break fuel lines. Consequently, this could 
reduce controllability of the airplane, cause fuel starvation of one or 
more engines, or lead to a fire in the fuselage.
    The FAA also has determined that performance of the flight 
maneuvers defined in CAR part 4b would produce critical case forces on 
these STC freighters, and consequent deformation or failure of floor 
beams on the main cargo deck. These maneuvers would cause upward forces 
on the cargo containers relative to the floor. Because of the location 
of the container locks, the floor beams at the forward or aft edges of 
the containers would be more critically loaded, and consequently 
deflected upward.

Determining Floor Strength (The ``Margin of Safety'')

    The measure of the ability of the floor beams of the main cargo 
deck to support the stresses caused by various load cases (combinations 
of specific container weights with either wind gust conditions or 
airplane maneuvers) is its ``margin of safety.'' Because the floor must 
be designed to withstand the critical case stresses, the design review 
team calculated the margin of safety when the floor is subject to the 
turbulent ``down gust'' wind conditions defined in CAR part 4b.
    The equation for determining the margin of safety is:
    [GRAPHIC] [TIFF OMITTED] TP15JY97.003
    
    In this equation, ``Allowable Stress'' is the measure of the 
strength of a floor beam of the main cargo deck. ``Applied Stress'' is 
the stress level produced in that floor beam multiplied by a ``factor 
of safety'' of 1.5. The weight of the containers on the floor beam, 
flight conditions (for example, wind gusts or airplane maneuvers), and 
other forces, such as pressurization of the fuselage, all combine to 
create the ``applied stress'' level in that floor beam. CAR 4b.200(a) 
requires the inclusion of the 1.5 factor of safety in structural 
designs. (This factor is discussed in the ``Elimination of the 1.5 
Factor of Safety'' section of this preamble.)
    When the margin of safety is zero for all load cases, the structure 
meets the minimum requirements of CAR part 4b. A structure with a 
margin of safety greater than zero exceeds those standards. A structure 
with a margin of safety of less than zero does not meet these minimum 
requirements, and is presumed to be unsafe. If the margin of safety 
reaches -1 (the extreme case), the structure is not strong enough to 
withstand the stresses generated by any load case without failing.
    Using this equation, the design review team calculated margins of 
safety for the STC floor designs as ranging from approximately -0.55 to 
-0.63. Because of the large negative margins of safety that were 
calculated for the down gust condition (the most likely critical case), 
the FAA did not analyze other load cases.
    For the margins of safety to be positive for the ``down gust'' 
condition, the FAA determined that these STC freighters must be limited 
to less than 50% of the typical maximum payload of 8,000 pounds per 
container currently allowed by the STC's. From its analyses, the design 
review team determined that these main cargo decks are capable of 
supporting a maximum payload of approximately 3,000 pounds per 
container (a maximum running load of 34.5 pounds per inch) in all areas 
of the main cargo deck, except in the area adjacent to the side cargo 
door. In that side door area, containers would be restricted to a 
maximum payload of approximately 2,700 pounds per container (a maximum 
running load of 31.0 pounds per inch) due to structural configurations 
affecting the strength of the floor beams in this area. These running 
loads include payload in the lower lobe cargo compartments, and any 
other load applied to the bottom of the floor beams of the main cargo 
deck. [The Air Transport Association of America (ATA) recommended a 
maximum payload of 6,000 pounds per container. This recommendation, 
which is discussed in the ``ATA Recommendations for a Final Rule'' 
section of this preamble, is substantially above the safe payload 
limits calculated by the design review team, and would result in a 
negative margin of safety.]
    Typically, freighters converted under these STC's are allowed to 
carry 11 or 12 containers on the main cargo deck. Containers in most 
areas of this deck have a maximum payload of up to 8,000 pounds per 
container; over the wing and landing gear area, this maximum payload 
per container can be up to 10,000 pounds. Although it would seem that 
these STC freighters could carry up to a total of 100,000 pounds, the 
maximum payload is actually limited by the strength of the fuselage as 
well as the strength of the floor beams. Consequently, the current 
maximum payloads on these airplanes range from 54,000 pounds (for a 
Model 727-100 series airplane) to 62,000 pounds (for a Model 727-200 
series airplane), depending on the configuration of the freighter. The 
FAA's structural analysis shows that the maximum payload should be 
limited to approximately 35,000 pounds. This maximum payload is 
approximately 22% less than the average payload of 45,000 pounds that 
has been reported by some operators of these Model 727 STC freighters.
    The FAA has determined that none of these main cargo decks are 
strong enough for the current maximum payloads, and therefore are 
unsafe. Furthermore, these decks do not comply with the requirements of 
CAR part 4b.

Operational Factors Affecting Payload Limitation

    The FAA's structural analysis was based on the ``worst case'' 
conditions of the following operational factors: maximum operating 
speed limit, airplane in-flight weight, container orientation, and side 
restraints. The FAA realizes that if restrictions are placed on these 
factors, higher payloads can be allowed. Although the absolute effects 
of these restrictions would

[[Page 37781]]

require extensive analysis, the FAA has concluded that it is sufficient 
to estimate the effects of these factors if they are only to be applied 
for a limited amount of time. The FAA design review team determined 
that these restrictions would not violate other load cases.

 Maximum Operational Speed and In-Flight Weight

    Some of these STC freighters are allowed to fly at a maximum 
operational speed of 390 knots equivalent airspeed (KEAS). During 
turbulence, the forces experienced by the airplane are, in part, a 
function of the aircraft's speed, which consequently affects the forces 
on the floor beams. By reducing the maximum operational speed to 350 
knots indicated airspeed (KIAS), the forces on the floor beams during 
turbulence are reduced.
    The forces experienced by the airplane during turbulence also are a 
function of the weight of the aircraft. A heavy airplane has more 
inertia, and therefore is less affected by severe gusts than a lighter 
one. The FAA has estimated that a minimum operational in-flight weight 
of 100,000 pounds will reduce the gust loads on these airplanes and, 
therefore, reduce the floor beam loads. Some ways to ensure that the 
in-flight weight does not fall below a prescribed limit are to have a 
minimum cargo weight, a minimum quantity of ``tankered'' fuel, 
sufficient ballast, or a combination of these items.

 Container Orientation

    Typically, these STC freighters carry National Aerospace Standard 
(NAS) 3610 class II cargo containers, which have a fixed back wall; a 
partially or fully removable front wall; and are 88 inches by 125 
inches. Due to this method of construction, a large portion of the 
forces that a container experiences in ``down gust'' wind conditions or 
turbulence is carried by the container's back wall, which is its 
strongest element. When cargo containers are oriented back-to-back, a 
large portion of both container loads is carried by the same container 
locks. This places higher loads on the floor beam supporting these 
locks. By requiring the containers to be oriented with the door side of 
the container facing forward, however, a more uniform distribution of 
the loads is achieved.

 Side Restraints

    A better distribution of the container load is achieved by 
installing side restraints. The FAA estimates that there can be an 
increase in the maximum payload per container when FAA-approved side 
restraints are installed.
    The FAA estimates that the combined effect of this speed 
limitation, minimum in-flight weight, and container orientation would 
result in a total weight of no more than 8,000 pounds for any two 
adjacent containers that are each 88 inches by 125 inches. By 
installing FAA-approved side restraints, this estimated total weight 
for any two adjacent containers could be increased to 9,600 pounds. 
Under no circumstances, however, can the total weight of any individual 
container exceed 8,000 pounds.

Elimination of the 1.5 Factor of Safety

    At the request of industry, the FAA considered the consequences of 
elimination of the 1.5 factor of safety used in the ``Margin of 
Safety'' equation discussed above. By eliminating the 1.5 factor of 
safety, the FAA analysis determined that the proposed payload limits 
per container would increase by 50%. CAR 4b.200(a) requires that an 
airplane be designed with a certain amount of ``reserve structural 
strength'' to minimize the potential for complete structural failure of 
an airplane. This reserve is the ``1.5 factor of safety.'' Ordinarily, 
an applicant seeking to reduce or eliminate this requirement must file 
a request for an exemption. If the applicant uses an approach in its 
design that is comparable to the 1.5 factor of safety, the applicant 
can declare that this approach provides ``an equivalent level of 
safety.'' The applicant, however, must substantiate this declaration to 
the satisfaction of the FAA.
    The FAA has examined the consequences resulting from the 
elimination of the 1.5 factor of safety, and has concluded that this 
action would pose unacceptable hazards for these airplanes. The FAA's 
intent in issuing this proposed AD is to prevent a combination of 
circumstances that could result in catastrophic loss of a Model 727 
freighter converted under these STC's. Elimination of the 1.5 factor of 
safety in conjunction with the other measures discussed earlier to 
increase the allowable payload would be contrary to this intent.
    CAR part 4b refers to the critical load cases--the down gust and 
maneuver forces previously described in this preamble--as ``limit 
loads.'' CAR 4b.200 requires that these limit loads be multiplied by 
1.5 (the ``1.5 factor of safety''), thereby becoming ``ultimate loads'' 
as defined in CAR part 4b. CAR 4b.201(c) further requires that the 
structure be able to carry these ultimate loads (which provide a 
reserve of structural strength) without failure. Although it is 
anticipated that these STC freighters will not be routinely subjected 
to limit load forces, it sometimes happens during emergencies and 
unusual environmental conditions such as turbulence.

 Emergency Conditions

    In an emergency, the pilot may exceed critical case maneuver 
forces, and fly the STC freighter beyond the airspeed and flight 
maneuver limits for which the airplane is designed. The failure of an 
engine, avoidance of a collision, or the opening of a cargo door during 
flight are conditions that could necessitate these actions.
    Emergencies do occur. On February 5, 1997, a Model 727 passenger 
airplane was flying to John F. Kennedy International Airport in New 
York when an Air National Guard F-16 jet fighter approached close 
enough to activate the Model 727's collision avoidance system alarm. 
The pilot of the passenger airplane, following the system's emergency 
guidance, maneuvered the Model 727 into a steep dive and then a steep 
climb. Two flight attendants and a passenger were thrown down by these 
maneuvers. Although the actual maneuver forces for this incident are 
unknown, the 1.5 factor of safety may have provided structural strength 
to maneuver the airplane beyond the forces in CAR part 4b.
    In 1991, a pilot performed a flight maneuver that imposed forces of 
approximately 3g's (three times the force of gravity) on a Model 747 
freighter that was carrying a partial payload. The applicable federal 
regulations require Model 747 and 727 series airplanes to be designed 
for maneuvers imposing forces of up to 2.5g's. Had this freighter been 
carrying a full payload and the 1.5 factor of safety not been used in 
its design, FAA analysis indicates that this freighter would have been 
lost.

 Turbulence

    Airplanes may encounter severe turbulence that exerts wind gust 
forces beyond the critical case forces of CAR part 4b. AD 96-01-03 
describes an occasion in 1991 when wind gusts were so severe that an 
engine separated from a Model 747-100 freighter shortly after take-off.
    More recently, severe wind gusts on September 5, 1996, caused 
numerous passenger injuries and one fatality on a Model 747-400 series 
airplane. The FAA received reports indicating that those gusts produced 
downward accelerations of -1.15g's and upward accelerations of +2.09g's 
on that airplane in less than four seconds. Had a Model 727 STC 
freighter experienced

[[Page 37782]]

similar conditions while transporting close to the maximum payload, FAA 
analysis indicates that the floor beams of the freighter's main cargo 
deck would have collapsed.
    The FAA has received 87 reports of Model 727 series airplanes 
experiencing severe turbulence; these reports typically do not include 
events that have occurred in other countries. The majority of these 
events were unforeseen and resulted in injuries to the flight crew or 
passengers. Five of the reports document gusts causing airplane 
accelerations of at least +1.88g's upward and -1.5g's downward.

 Hazardous Deformation of the Main Cargo Deck

    CAR 4b.201(a) requires any structure on the freighter, including 
the floor beams, to be strong enough to withstand--without 
``detrimental permanent deformation''--the anticipated critical case 
forces that could be exerted upon it during its service life. CAR 
4b.201(b) requires that any structural deformations caused by these 
critical case or limit loads not interfere with the safe operation of 
the airplane. (The catastrophic consequences of deformation are 
discussed earlier in this preamble.) Using the 1.5 factor of safety in 
structural analysis takes deformation into account; without the 1.5 
factor of safety, the STC holder would be required to provide an 
analysis that demonstrates these floors would be free from detrimental 
deformation. Because these STC's lack a deformation analysis, the FAA 
would not consider a request for reducing the 1.5 factor of safety 
requirement unless such an analysis was conducted.

 Other Considerations

    Another reason that reserve structural strength is necessary is 
that aerodynamic and structural analysis theory is not precise: exact 
conditions or circumstances are indeterminable; therefore 
approximations must be made. In addition, the 1.5 factor of safety 
takes into account such considerations as the variations in the 
physical properties of materials, the range of fabrication tolerances, 
and corrosion or damage. For example, all Model 727 series airplanes 
must have enough structural reserve to cover the corrosion control 
activities mandated by AD 90-25-03, amendment 39-6787 (55 FR 49258, 
November 27, 1990). That AD, in order to control corrosion, permits up 
to 10% of the material thickness of a floor beam of the main deck to be 
removed by grinding without undertaking repair; the removal of this 
material further reduces the strength of the floor.
    The majority of these modified airplanes are nearing, or past, 
their design life of 20 years, 60,000 flights, or 50,000 hours of 
operation. As the airplanes age and are repeatedly flown, they 
accumulate fatigue damage and corrosion, which degrades the structural 
capability. Airplanes that are near or past their design life are part 
of the FAA's Aging Airplane Program and are subject to numerous AD's to 
correct unsafe conditions resulting from fatigue cracking and 
corrosion.
    During the time period allowed by the AD's to implement the 
corrective action, it is probable that many of these aging airplanes 
will continue to have fatigue cracks and corrosion. Because these 
airplanes have been built with a safety factor of 1.5, there is a 
sufficient structural strength margin to allow some finite time to 
implement the AD's to correct the unsafe conditions. Without this 
factor of safety, a new maintenance program would have to be developed 
for these airplanes to ensure that all of the Aging Airplane Program 
fatigue cracks and corrosion problems are continuously identified and 
immediately eliminated.

Service History of the Model 727 STC Freighters

    Although the modification of these airplanes commenced in 1983, the 
average modification date for these STC freighters is 1991. In fact, 
approximately 100 of these airplanes (one-third of the STC freighter 
fleet) have been modified in just the last three years.
    Most of these STC freighters fly only two flights each day, 
resulting in a low number of accumulated flights since conversion. A 
representative of the largest operator of these airplanes indicates 
that, on average, the airplanes carry only slightly more than half of 
the current maximum payload of 8,000 pounds per container. These 
circumstances may explain why the FAA has not received reports of 
adverse events relating to the structural strength of these floor 
beams.
    These floor beams, if overstressed, are not likely to give warning 
prior to total failure. The existing floor beams on these STC 
freighters are commonly made from 7075-T6511 aluminum alloy, and there 
is only a 10% difference between the stress level at which the floor 
beam permanently bends, and the stress level at which the beam breaks. 
Consequently, once the floor beams are stressed to the point of being 
permanently bent, it takes only a small amount of additional stress 
until the floor beams break, which could result in loss of the 
airplane.
    The FAA has concluded that the reported service history of these 
STC freighters does not demonstrate that these airplanes are safe.

Issuance of an AD is Appropriate Regulatory Action

    Because of the unsafe condition found on these STC freighters (the 
inadequate strength of the floor structure of the main cargo deck to 
carry the current maximum payloads), the FAA has determined that there 
are two ways in which it could proceed: Issuance of an AD to correct 
the unsafe condition of the floor, or suspension or revocation of these 
STC's.
    The Administrator of the FAA has the authority to issue an AD when 
``an unsafe condition exists in a product'' [14 CFR 39.1(a)], and 
``[t]hat condition is likely to exist or develop in other products of 
the same type design'' [14 CFR 39.1(b)]. When such a finding is made, 
the Administrator may, as appropriate, prescribe ``inspections and the 
conditions and limitations, if any, under which those products may 
continue to be operated'' (14 CFR 39.11). By using the AD process, the 
FAA can still allow these STC freighters to operate, although under 
restrictions which are necessary to eliminate the unsafe condition.
    Because the floor structures did not meet CAR part 4b certification 
standards at the time these STC's were originally issued, the 
Administrator of the FAA is empowered to suspend or revoke these STC's 
[49 U.S.C. 44709(b)]. If the Administrator were to take such action 
against these STC's, the order could result in the immediate grounding 
of these STC freighters.
    In consideration of the disruption of domestic and international 
commerce that would result from the suspension or revocation of these 
STC's, as well as the significant impacts on the domestic and 
international economy that such an action would have, the FAA has 
concluded that the issuance of an AD with restrictions on the maximum 
payloads on the main cargo deck is appropriate action. These payload 
restrictions will enable these freighters to continue operating, and 
remove the unsafe condition that currently exists in the floor beams of 
the main cargo deck.

FAA Meetings With STC Holders and Operators

    The FAA has met individually with each of the affected STC holders 
to discuss the FAA design review team's observations, analyses, and 
findings. In a letter sent prior to these meetings, the

[[Page 37783]]

FAA provided its preliminary conclusions to each STC holder. In 
addition, the agency asked the STC holder to submit data showing that 
unsafe conditions do not exist, and that the STC designs do meet 
applicable federal aviation regulations. If the FAA's findings and 
analyses could not be controverted, the STC holder was asked to specify 
what actions it would take to bring its designs into compliance. STC 
holders also were asked to propose actions that would enable these 
airplanes to operate safely while data or modifications were being 
developed.
    At its meeting with the FAA, Pemco did not present any information 
to contradict the FAA's analyses, or submit proposals to keep these 
planes operating safely. The FAA's meetings with the other 3 STC 
holders produced similar results.
    The FAA also has met jointly with the STC holders and the operators 
of the Model 727 freighters modified under these STC's. On February 14, 
1997, the FAA convened this meeting, which was attended by more than 75 
industry representatives, to discuss what the design review team had 
observed during its site visits and determined from its analyses of STC 
data. During this meeting the operators presented no technical data, 
but provided the FAA with information about the potential impacts on 
their businesses if the agency were to reduce the current maximum 
payload.

Industry Proposal for the Timing of an NPRM and FAA Response

    During the February 14 meeting, representatives of the affected 
operators and STC holders in attendance presented a proposal to the 
FAA. Generally, industry proposed that the FAA delay issuing an NPRM 
and imposing payload restrictions; in turn, industry, within 120 days 
from the end of February 1997, would test floor beams, perform 
analyses, redesign the floor structure, if necessary, and submit data 
to the FAA substantiating compliance with CAR part 4b. At the meeting, 
the FAA responded that its priority is the safety of these airplanes, 
and the burden is now on industry to establish the ability of these STC 
freighters to carry more than the 3,000 pounds per container being 
considered by the FAA.

ATA Recommendations for a Final Rule

    ATA followed up on the proposal at the February 14 meeting with a 
March 10, 1997, letter that contained recommendations in order ``to get 
the necessary design changes quickly incorporated while permitting the 
airlines to continue operating their aircraft.'' ATA proposed that a 
3,000 pound per pallet weight limit be gradually phased-in as follows:
    1. There would be at least 120 days after the effective date of the 
AD before any payload restrictions would be implemented. According to 
ATA, this period would enable STC holders or others to redesign the 
freighter floors and provide enough time for operators to procure parts 
to modify the floors.
    2. Initially, payload restrictions would be reduced from 8,000 
pounds per pallet to 6,000 pounds per pallet. These restrictions would 
be in effect for at least one year or the next ``C'' check, whichever 
occurs later, and operators would not be required to modify the floor 
beams during this time.
    3. Ultimately, the floor beams of the main cargo deck would not 
have to be modified until at least 16 months after the effective date 
of the AD. At that time, the payload per pallet would be reduced to 
3,000 pounds if an operator opted not to accomplish that modification.
    4. Airplanes would not be subject to any of these restrictions if 
operators can substantiate to the FAA that the floor beams are strong 
enough to support the existing payload per pallet.
    The FAA considered ATA's recommendations in developing this 
proposed action. The FAA determined that allowing these airplanes to 
continue to operate without restrictions for 120 days after the 
effective date of this AD, and allowing 16 months for modification of 
the floor structure of the main cargo deck would not address the unsafe 
condition in a timely manner. The FAA's analysis also determined that 
ATA's recommended payload limit of 6,000 pounds per container at all 
locations would result in negative margins of safety. The interim 
weight restrictions proposed by the FAA allow the carriage of a limited 
number of individual containers at or above the 6,000 pound per 
container payload suggested by ATA. In addition, the 120-day period of 
operation at the interim payloads proposed by the FAA (discussed below) 
does, in part, meet ATA's suggested time for allowing redesign of these 
STC freighter floors.

FAA Findings

    Based on the observations and analyses of its design review team, 
and information presented by affected STC holders and the operators of 
Model 727 series airplanes converted to freighters under these STC's, 
the FAA has found that:
    1. None of the floor beams of the main cargo deck on any of these 
STC's have been modified from the original passenger configuration to 
support the heavier payloads carried on a freighter.
    2. Based on the FAA's analyses, the floor structures of these STC 
freighters are not capable of withstanding the forces that would result 
from the current maximum payload when CAR part 4b conditions are 
encountered.
    3. When the maximum payload of a container is limited to 8,000 
pounds or 6,000 pounds (for all container positions) as proposed by 
ATA, the margins of safety for the floor beams of the main cargo deck 
are calculated as negative numbers and the structural strength of these 
beams is not sufficient to meet the requirements of CAR part 4b. When 
the maximum payload of a container is limited to approximately 3,000 
pounds, the margin of safety is calculated as a positive number and 
these floor beams meet the structural strength requirements of CAR part 
4b.
    4. The FAA estimates the combined effect of imposing operational 
restrictions on airplane weight, maximum operating speed, and 
orientation of containers reduces the forces exerted on the airplane in 
``down gust'' conditions, and will permit the maximum payload of a 
container to be increased on an interim basis. The installation of side 
restraints can permit a further temporary increase in payload.
    5. Typically, these STC freighters are modified by other STC's that 
change the maximum taxi, take-off, zero fuel, and landing weights of 
these airplanes. These weight changes permit the airplanes to carry 
more payload on the main cargo deck.
    No compatibility study has been performed showing that these weight 
changes are safe considering the existing freighter STC modifications 
and payload limits. In addition, no compatibility study has been done 
for the addition of auxiliary fuel tanks, engine changes, and other 
types of modifications that alter the basic loads on these airplanes.
    6. When these STC modifications were accomplished, each airplane 
was modified differently, due to different installer shop practices and 
the configuration of each airplane prior to modification. Subsequent 
modifications under other STC's that alter the structure were not shown 
to be compatible with the freighter modifications. The resulting 
airplane configuration can be significantly different between 
individual airplanes. Any modifications that are undertaken to bring 
these airplanes into compliance with CAR part 4b must be shown to be

[[Page 37784]]

compatible with the specific airplanes being modified.
    7. The elimination of the 1.5 factor would not eliminate the unsafe 
condition that occurs when these airplanes are carrying containers 
weighing more than the payloads specified in this proposed AD.

FAA Conclusions

    From these findings, the FAA has concluded that:
    1. The lack of strength in the floor structure of the main cargo 
deck must be corrected by reducing the payload carried on the main 
cargo deck. This reduced payload includes the payload in the lower lobe 
cargo compartments.
    2. Maximum payloads of approximately 2,700 pounds per container in 
the areas near the forward side cargo door and approximately 3,000 
pounds per container in all other areas of the main cargo deck provide 
an acceptable level of safety. It is estimated that operational 
restrictions on airplane weight, maximum operating speed, and 
orientation of containers, as well as the installation of FAA-approved 
side restraints, would allow safe operation with higher payloads during 
an interim period.
    3. Because these STC freighters are modified by other STC's that 
change the maximum taxi, take-off, zero fuel, and landing weights of 
these airplanes, and permit more payload on the main cargo deck, all of 
the airplanes' Airplane Flight Manuals (AFM's), AFM Supplements, and 
Weight and Balance Supplements would have to be revised to show the 
payload restrictions.

Additional AD Actions

    The FAA design review team's scope of review of these STC's was not 
limited to concerns about the strength of the floor structure that 
support the main cargo deck. The team also made inspections and 
gathered information about other areas where additional unsafe 
conditions may exist. Following this proposed rulemaking, additional 
rulemaking will be initiated to address these concerns. These concerns 
include the following structural, door systems, and STC certification 
and documentation issues:

 Structural Deficiencies

Lack of ``Fail-Safe'' Hinges on the Cargo Door
    The design review team saw single or double-piece hinge fittings on 
the side cargo doors of these STC freighters. Should a crack propagate 
along the hinge line where the hinge attaches either to the upper sill 
of the fuselage or to the door itself, the cargo door could separate 
from the airplane, and result in loss of the airplane.
Apparent Lack of Strength of the Structure Surrounding the Side Cargo 
Door
    To install a side cargo door for the main deck, an opening of 
approximately 7.5 feet by 11 feet (82.5 square feet) must be cut into 
the side of the fuselage. This opening requires that the cutout area 
and adjacent structural areas be substantially reinforced. If the 
fuselage structure that surrounds this cargo door is not strong enough 
to withstand the forces that may be exerted during flight, it could 
result in loss of the airplane.
    The design review team observed that reinforcing structures used in 
this area, such as longerons, frames, doublers and triplers, are 
discontinuous and appear to lack adequate load paths and strength. 
These discrepancies could result in a fuselage structure that does not 
meet the strength and deformation requirements of CAR 4b.201, proof of 
structure standards of CAR 4b.202, or fail safety requirements of CAR 
4b.270(b).
    In its examination of the data supporting these STC's, the design 
review team determined that the STC applicants used inadequate methods 
and/or incomplete analyses to substantiate that their modifications 
provide adequate strength in this area. The STC applicants typically 
did not substantiate the strength of numerous structural features, such 
as splices and runouts. The STC holders also used analytical approaches 
that failed to consider such impacts as redistribution of the forces in 
the fuselage, and localized stress effects such as ``buckling.''
Inadequate Cargo Restraint Barriers
    CAR 4b.260 requires that the restraint barrier in the cargo 
compartment of the main deck be strong enough to protect the occupants 
from injury when the freighter is carrying its maximum payload and 
emergency landing conditions occur (the ``9.0g standard'').
    Based on the observations and analyses of the design review team, 
the FAA has determined that the bulkhead restraint barriers on all of 
the observed STC freighters do not meet the 9.0g standard; three of the 
four STC holders have confirmed the FAA's finding.

 Deficiencies in Systems for the Side Cargo Door

    Because of cargo door-related accidents, industry and the FAA, 
during the early 1990s, conducted an extensive design review of cargo 
doors and agreed on new standards to eliminate safety deficiencies in 
certain cargo door systems. The FAA agreed to issue AD's requiring 
compliance with these standards, which are based on Amendment 54 to 14 
CFR 25.783, for those freighters that did not comply. These standards 
are not intended to upgrade the requirements of CAR part 4b after 
certification, but are to correct potentially unsafe conditions on 
airplanes already in service that were identified during the design 
review.
Inadequate Warning System for an ``Unsafe'' Door
    Freighters must have a warning system that directly alerts the 
pilot and co-pilot that the side cargo door is ``unsafe'' (open, 
unlatched, or unlocked). A ``safe'' cargo door is one that is verified 
to be closed, latched, and locked prior to taxiing for take-off.
    The design review team observed STC freighters that do not have a 
red cargo door warning light in plain view of both pilots. In the event 
that the cargo door is unsafe, pilots on those planes would not be 
directly warned; this situation could lead to pilot inaction or 
dispatch of the airplane, and consequent opening of this door during 
flight.
Improper Pressurization of the Fuselage When the Cargo Door is 
``Unsafe''
    The opening of a door during flight has caused several serious 
accidents. Some of those accidents have resulted in loss of life; 
others have resulted in loss of the airplane. Consequently, industry 
and the FAA adopted standards to prevent pressurization of the fuselage 
when the cargo door is unsafe. Typically, compliance with these 
standards involves installation of vent doors that close only when the 
cargo door is safe.
    In its examination of the associated cargo door related systems on 
these STC freighters, the design review team detected that the fuselage 
of some of these airplanes could be pressurized when the cargo door 
vent door is not closed. The team also found that some STC's did not 
have the required safety analysis that would verify the adequacy of the 
design's pressurization prevention system when the cargo door is 
unsafe.
Electrical/hydraulic System Deficiencies That Could Cause an ``Unsafe'' 
Cargo Door
    Electrical short circuits could transmit power to the electrical or 
hydraulic systems that operate the side cargo door, lead to opening of 
this door during flight, and could result in the loss of the airplane. 
To prevent this, all power to this door must be removed during flight,

[[Page 37785]]

and the flight crew must not be able to restore this power at any time 
during flight.
    CAR 4b.606 (which has been further refined by the cargo door 
standards agreed upon by industry and the FAA) requires STC holders to 
show that the design of the electrical system is adequate to prevent 
the side cargo door from opening during flight. These STC holders did 
not accomplish this analysis.
Inability to Visually Verify the Status of the Side Cargo Door
    When the system that warns the pilot and co-pilot about an 
``unsafe'' cargo door is not working correctly, the red warning light 
either will fail to light up during pre-flight testing of the system, 
or will light up when the side cargo door is actually ``safe.'' These 
STC's have a backup system that allows the flight crew to confirm that 
the door is actually safe.
    The cargo door standards to which industry and the FAA agreed 
require ``a visual means of directly inspecting the locks.'' The design 
review team observed that these backup systems enable the flight crew 
to view only a portion of the locking beam. Because a visual means of 
directly inspecting the locking mechanism of the door is not available, 
these STC's do not comply with these standards. When the entire locking 
mechanism cannot be visually inspected, a false report on the condition 
of the door may be given to the crew, and the airplane may be 
dispatched with an unsafe door.
Cargo Compartment Smoke Detection and Warning Systems
    CAR 4b.383(e)(2) requires that there be a means for the flight crew 
to check and assure the proper functioning of each smoke detector 
circuit. The FAA design review team and STC freighter operators have 
observed that some STC's contain electrical wiring designs that test 
only a portion of the smoke detection system--not the entire system as 
required--when a single button is pressed (the ``press to test'' 
feature). If the flight crew is not alerted that some smoke detectors 
are not functioning, the crew may not be able to respond to a cargo 
compartment fire in a timely manner.

 The Carriage of Supernumeraries

    Supernumeraries are non-flight crew personnel who are carried on 
board the airplane. For example, a supernumerary could be an airline 
employee who is not part of the flight crew, but is specially trained 
to handle cargo.
    These STC freighters have a cargo compartment that is used only for 
the carriage of cargo. Before supernumeraries can be carried, the STC 
holder or operator must apply to the FAA for an exemption from CAR 
4b.383(e), and from other federal regulations that pertain to seats, 
berths, and safety belts; emergency evacuation; ventilation; and fire 
protection. Such exemptions are granted only when the FAA determines 
that the design contains features that provide an acceptable level of 
safety for the supernumeraries.
    The FAA has become aware of numerous instances where STC holders 
have made provisions for the carriage of supernumeraries without 
applying for FAA exemptions and without demonstrating that the safety 
provisions for supernumeraries are acceptable.

 STC Data and Documentation Concerns

    When the FAA design review team evaluated data that STC applicants 
originally submitted to obtain FAA approval of these freighter STC's, 
the team found a number of deficiencies. Examples include data that is 
not adequately substantiated; payload limits in Weight and Balance 
documents that are inconsistent with the structural capability of the 
fuselage; structural analyses that lack the critical case; no analysis 
of the floor beams over the wing center section; and documented 
negative margins of safety that are unresolved.

 Unsubmitted Instructions for Continued Airworthiness

    Federal regulations require an STC holder to submit ``Instructions 
for Continued Airworthiness'' to the FAA for review. These instructions 
include maintenance procedures, maintenance manuals, and maintenance 
program requirements for the continued safety of the airplane converted 
under the STC. Only one of the four STC holders has complied with this 
requirement.

Future FAA Review of Other Transport Airplane Cargo Conversions

    The FAA's review of STC's and the safety of airplanes converted 
from a passenger to a cargo-carrying configuration will not be limited 
to just Model 727 and 747 series airplanes. Based on the discovery of 
unsafe conditions on both of these airplane models, the FAA intends to 
examine all transport category passenger airplanes that have been 
converted to a cargo-carrying configuration under STC's.
    The FAA urges STC holders and operators of these freighters to 
begin, as soon as possible, an examination of the data supporting the 
STC's. If problems such as those identified in the Model 727 and 747 
conversions are detected, corrective actions should be developed. Self-
examination of these conversions prior to formal FAA review may shorten 
the time needed for any corrective actions, and reduce the impacts on 
operators of these freighters.

Explanation of Requirements of Proposed Rule

    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 restrict the payload on the main cargo deck of Model 
727 series airplanes modified in accordance with STC SA 1444SO, 
SA1509SO, SA1543SO, SA1896SO, SA1740SO, or SA1667SO. This proposal 
would be accomplished by revisions to the Limitations Section of all 
FAA-approved AFM's, AFM Supplements, and Weight and Balance 
Supplements. Revision of all these documents would be required because 
these STC freighters have been modified by other STC's that change the 
maximum taxi, take-off, zero fuel and landing weights of these 
airplanes.
    The payload limits that are proposed are based on the use of 
containers that are 88 inches by 125 inches, and a horizontal center of 
gravity for the total payload in each container that is located within 
8.8 inches from the geometric center of the base of the container for 
the forward and aft direction and 12.5 inches from the geometric center 
of the base of the container for the left and right direction. The 
payload limits are also based on a requirement that all containers are 
loaded with the door side of the container facing forward.
    The proposal presents three options for payload limitations: one 
``baseline'' [paragraph (a)] and two ``interim'' [paragraphs (b) and 
(c)], depending upon the floor configuration and other operating 
limitations.
    Paragraph (a) would establish a payload limit of 3,000 pounds per 
container.
    For airplanes equipped with FAA-approved side restraints, paragraph 
(b) would provide for temporary payload limits in some areas of 9,600 
pounds for any two adjacent containers, with a limit of 8,000 pounds 
for any one container. These limits would be available when the 
following two conditions are met: the maximum operational airspeed does 
not exceed 350 KIAS and the minimum in-flight weight exceeds 100,000 
pounds.
    For airplanes that are not equipped with FAA-approved side 
restraints,

[[Page 37786]]

paragraph (c) would provide for a temporary payload limit in some areas 
of 8,000 pounds for any two adjacent containers. This limit also would 
be available when the following two conditions are met: the maximum 
operational airspeed does not exceed 350 KIAS and the minimum in-flight 
weight exceeds 100,000 pounds.
    Because the determination of the effects of operational limitations 
on payload is based on approximations, the resulting payload limits may 
be unconservative. Consequently, operation with these payload limits is 
only acceptable for a limited period of time. Continued use of these 
operational limits and the associated payload limits must be 
substantiated. The FAA has determined that an acceptable level of 
safety is provided if the time period is limited to no more than 120 
days, which would also allow sufficient time for an applicant to 
develop an acceptable analysis regarding the applicability of the 
operational limitations.
    At the February 14 meeting discussed above, the industry 
participants proposed to complete a redesign of the floor structure 
within 120 days from the end of February (by the end of June). The FAA 
bases the proposed 120-day interim period in paragraphs (b) and (c) on 
the following assumptions:
    1. Industry will fulfill this proposal;
    2. The final rule will not become effective before October 1, 1997, 
and thus allow additional time for the industry to modify the main 
cargo deck floor structure; and
    3. Operators and STC holders will work diligently in the meantime 
to avoid any disruptions to operations.
    In light of the seriousness of the unsafe conditions addressed by 
this proposal, the FAA considers that the 120-day interim period:
    1. Provides an acceptable level of safety;
    2. Minimizes exposure to any potential unconservatism in the 
determination of the payload limits;
    3. Provides an adequate opportunity for applicants to develop 
substantiation for continued use of operational limits to enhance 
payload limits; and
    4. Minimizes, for the interim period, the burdens on operators 
resulting from this AD.
    Should an operator desire to transport containers of other 
dimensions or use a different payload container center of gravity, it 
would have to apply to the FAA for appropriate payload limits.
    At any time, an applicant would be able to present a proposal to 
modify the floor structure or proposed weight and other limits, data, 
and analysis to the FAA to substantiate that floor structure of the 
main cargo deck (existing or modified) is in compliance with the 
requirements of CAR part 4b when supporting the proposed weight limits. 
When the FAA determines that these documents are acceptable, the 
operator would be able to operate its airplane at the payload limits 
substantiated by its data and analysis.

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.
    The FAA conducted a ``Cost Analysis and Initial Regulatory 
Flexibility Determination and Analysis'' to determine the regulatory 
impacts of this and three other proposed AD's to operators of all 244 
U.S.-registered Boeing Model 727-100 and -200 series passenger 
airplanes that have been converted to cargo-carrying configurations 
under 10 STC's held by four companies. This analysis is included in the 
docket for each AD. The FAA has determined that approximately 6 Model 
727-100 and 45 Model 727-200 series airplanes operated by 10 carriers 
were converted under Pemco STC's. (There were 15 Model 727 series 
airplanes for which the FAA could not identify the STC holder. It is 
possible that these airplanes were also converted under a Pemco STC. 
Their costs are not included here.)
    Assuming that operators of affected airplanes converted under Pemco 
STC's would comply with the restricted interim operating conditions set 
forth in the proposed rule, the FAA estimates in the analysis that each 
Model 727-100 series airplane modified under the Pemco STC's would lose 
approximately $32,504 in revenues during the 120-day interim period 
after the effective date of the proposed AD. Further, the FAA estimates 
that none of the modified Model 727-200 series airplanes would lose 
revenues during the interim period.
    Based on the ``Cost Analysis and Initial Regulatory Flexibility 
Determination and Analysis'' included in the docket, the FAA estimates 
that affected airplanes could be modified at a cost of $100,000 per 
airplane. The total cost, therefore, to modify the fleet of affected 
Model 727 series airplanes that were originally modified to Pemco STC's 
is $5.3 million. This assumes that modifications to the airplane are 
available and installed within the 120-day time period. If there are 
any delays in the availability or implementation of modifications, the 
revenue loss due to operation at the 3,000-pound payload limit would 
substantially increase the costs. The FAA solicits detailed cost 
information from the affected carrier concerning the proposed AD's 
compliance costs.
    The Regulatory Flexibility Act of 1980 (RFA) was enacted by 
Congress to ensure that small entities are not unnecessarily or 
disproportionately burdened by government regulations. The RFA requires 
a Regulatory Flexibility Analysis if a proposed rule would have a 
significant economic impact, either detrimental or beneficial, on a 
substantial number of small entities. The Regulatory Flexibility 
Analysis includes the consideration of alternative actions.
    FAA Order 2100.14A, Regulatory Flexibility Criteria and Guidance, 
establishes threshold cost values and small entity size standards for 
complying with RFA review requirements in FAA rulemaking actions. The 
Order defines ``small entities'' in terms of size thresholds, 
``significant economic impact'' in terms of annualized cost thresholds, 
and ``substantial number'' as a number which is not less than eleven 
and which is more than one-third of the small entities subject to the 
proposed or final rule.
    FAA Order 2100.14A sets the size threshold for small entities 
operating aircraft for hire at 9 aircraft and the annualized cost 
threshold at $69,000 for scheduled operations of airplanes with fewer 
than 60 seats and $5,000 for nonscheduled operations.
    Four of the 10 affected carriers operating 13 affected airplanes 
are considered small entities (i.e., each operates fewer than 9 
affected airplanes). The cost of the proposed AD greatly exceeds the 
threshold values defined in the FAA Order. The proposed AD does not 
affect a substantial number of small entities, however, because it is a 
number less than eleven. Therefore, this AD does not have a significant 
economic impact on a substantial number of small entities and a 
regulatory flexibility analysis is not required.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, will not have a significant

[[Page 37787]]

economic impact, positive or negative, on a substantial number of small 
entities under the criteria of the Regulatory Flexibility Act. A copy 
of the ``Cost Analysis and Initial Regulatory Flexibility Determination 
and Analysis'' prepared for this action is contained in the Rules 
Docket. A copy of it may be obtained by contacting the Rules Docket at 
the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Airplanes, 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-81-AD.

    Applicability: Model 727 series airplanes; modified in 
accordance with Supplemental Type Certificate SA1444SO, SA1509SO, 
SA1543SO, SA1896SO, A1740SO, or SA1667SO; 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 floor beams of the main 
cargo deck, which could lead to loss of the airplane, accomplish the 
following:
    (a) Except as provided in paragraphs (b), (c), and (d) of this 
AD, within 48 clock hours (not flight hours) after the effective 
date of this AD, accomplish the requirements of paragraph (a)(1) or 
(a)(2) of this AD, as applicable:
    (1) For airplanes on which only containers that are 88 inches by 
125 inches are transported: Revise the Limitations Section of all 
FAA-approved Airplane Flight Manuals (AFM) and AFM Supplements, and 
the Limitations Section of all FAA-approved Airplane Weight and 
Balance Supplements to include the following information. This may 
be accomplished by inserting a copy of this AD in all AFM's, AFM 
Supplements, and Weight and Balance Supplements.

``Limitations

    All containers must be oriented with the door side of the 
container facing forward.
    The location of the horizontal center of gravity for the total 
payload within each container shall not vary more than 8.8 inches 
from the geometric center of the base of the container for the 
forward and aft direction and 12.5 inches from the geometric center 
of the base of the container for the left or right direction.

Payload Limitations

    Do not exceed a total weight of 3,000 pounds per container on 
the main cargo deck, except in the area adjacent to the side cargo 
door. In that side door area (Body Station 440 to Body Station 660), 
containers are restricted to a maximum payload of 2,700 pounds per 
container. This payload limit includes the payload in the lower lobe 
cargo compartments and any other load applied to the bottom of the 
floor beams of the main cargo deck for the same body station 
location as the container on the main cargo deck.''
    (2) For airplanes on which any containers other than 88 inches 
by 125 inches are transported: Revise the Limitations Section of all 
FAA-approved AFM's and AFM Supplements, and the Limitations Section 
of all FAA-approved Airplane Weight and Balance Supplements in 
accordance with a method approved by the Manager, Standardization 
Branch, ANM-113, FAA Transport Airplane Directorate.

    Note 2: The weight restrictions to be approved under paragraph 
(a)(2) will be consistent with the applicable weight restrictions of 
paragraph (a)(1), (b), or (c) of this AD.

    (b) During the period ending 120 days after the effective date 
of this AD: For airplanes on which only containers that are 88 
inches by 125 inches are transported, and that are equipped with 
side vertical cargo container restraints that have been approved by 
the Manager, Standardization Branch, ANM-113, as an optional 
alternative to compliance with paragraph (a)(1) of this AD, revise 
the Limitations Section of all FAA-approved AFM's and AFM 
Supplements, and the Limitations Section of all FAA-approved 
Airplane Weight and Balance Supplements to include the following 
limitations. This may be accomplished by inserting a copy of this AD 
in all AFM's, AFM Supplements, and Weight and Balance Supplements.

``Limitations

    Maximum Operating Airspeed of Vmo equals 350 knots 
indicated airspeed (KIAS).
    Minimum in-flight weight: 100,000 pounds or greater. All 
containers must be oriented with the door side of the container 
facing forward.
    The location of the horizontal center of gravity for the total 
payload within each container shall not vary more than 8.8 inches 
from the geometric center of the base of the container for the 
forward and aft direction and 12.5 inches from the geometric center 
of the base of the container for the left or right direction.

Payload Limitations

    Do not exceed a total weight of 9,600 pounds for any two 
adjacent containers and a total weight of 8,000 pounds for any 
container, except that the total weight of all containers forward of 
Body Station 436 shall not exceed 4,000 pounds. This payload limit 
includes the payload in the lower lobe cargo compartments and any 
other load applied to the bottom of the floor beams of the main 
cargo deck for the same body station location as the container on 
the main cargo deck.''
    (c) During the period ending 120 days after the effective date 
of this AD: For airplanes on which only containers that are 88 
inches by 125 inches are transported, and that are NOT equipped with 
side vertical cargo container restraints that have been approved by 
the Manager, Standardization Branch, ANM-113, as an optional 
alternative to compliance with paragraph (a)(1) of this AD, revise 
the Limitations Section of all FAA-approved AFM's and AFM 
Supplements, and the Limitations Section of all FAA-approved 
Airplane Weight and Balance Supplements to include the following 
limitations. This may be accomplished by inserting a copy of this AD 
in all AFM's, AFM Supplements, and Weight and Balance Supplements.

``Limitations

    Maximum Operating Airspeed of Vmo equals 350 knots 
indicated airspeed (KIAS).
    Minimum in-flight weight: 100,000 pounds or greater. All 
containers must be oriented with the door side of the container 
facing forward.
    The location of the horizontal center of gravity for the total 
payload within each container shall not vary more than 8.8 inches 
from the geometric center of the base of the container for the 
forward and aft direction and 12.5 inches from the geometric center 
of the base of the container for the left or right direction.

Payload Limitations

    Do not exceed a total weight of 8,000 pounds for any two 
adjacent containers and the total weight of all containers forward 
of Body Station 436 shall not exceed 4,000 pounds. This payload 
limit includes the payload in the lower lobe cargo compartments and 
any other load applied to the bottom of the floor beams of the main 
cargo deck for the same body station location as the container on 
the main cargo deck.''
    (d) For airplanes that operate under the 350 KIAS requirements 
of paragraph (b) or (c) of this AD: A maximum operating airspeed 
limitation placard must be installed adjacent to the airspeed 
indicator and in full view of both pilots. This placard must state: 
``Limit Vmo to 350 KIAS.''
    (e) For airplanes complying with paragraph (b) or (c) of this 
AD, within 120 days after the effective date of this AD: Revise the 
Limitations Section of all FAA-approved AFM's and AFM Supplements, 
and the Limitations Section of all FAA-approved

[[Page 37788]]

Airplane Weight and Balance Supplements to include the following 
information. This may be accomplished by inserting a copy of this AD 
in all AFM's, AFM Supplements, and Weight and Balance Supplements.

``Limitations

    All containers must be oriented with the door side of the 
container facing forward.
    The location of the horizontal center of gravity for the total 
payload within each container shall not vary more than 8.8 inches 
from the geometric center of the base of the container for the 
forward and aft direction and 12.5 inches from the geometric center 
of the base of the container for the left or right direction.

Payload Limitations

    Do not exceed a total weight of 3,000 pounds per container on 
the main cargo deck, except in the area adjacent to the side cargo 
door. In that side door area (Body Station 440 to Body Station 660), 
containers are restricted to a maximum payload of 2,700 pounds per 
container. This payload limit includes the payload in the lower lobe 
cargo compartments and any other load applied to the bottom of the 
floor beams of the main cargo deck for the same body station 
location as the container on the main cargo deck.''
    (f) As an alternative to compliance with paragraphs (a), (b), 
(c), (d), and (e) of this AD: An applicant may submit a proposal to 
modify the floor structure or proposed new payload and other limits, 
and substantiating data and analyses to the Manager, Standardization 
Branch, ANM-113, in accordance with the procedures of paragraph (g) 
of this AD, showing that the floor structure of the main cargo deck 
is in compliance with the requirements of Civil Air Regulations 
(CAR) part 4b. If the FAA determines that these documents are 
acceptable and applicable to the specific airplane being analyzed 
and approves the proposed limits, prior to flight under these new 
limits, the operator must revise the Limitations Section of all FAA-
approved AFM's and AFM Supplements, and the Limitations Section of 
all FAA-approved Airplane Weight and Balance Supplements in 
accordance with a method approved by the Manager, Standardization 
Branch, ANM-113. Accomplishment of these revisions in accordance 
with the requirements of this paragraph constitutes terminating 
action for the requirements of this AD.
    (g) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be 
used if approved by the Manager, Standardization Branch, ANM-113. 
Operators shall submit their requests through an appropriate FAA 
Principal Maintenance Inspector who may add comments and then send 
it to the Manager, Standardization Branch, ANM-113.

    Note 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Manager, Standardization Branch, ANM-113.

    (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.

    Issued in Renton, Washington, on .July 8, 1997.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-18358 Filed 7-14-97; 8:45 am]
BILLING CODE 4910-13-U