Document ID: FAA-2013-0109-0001
Agency: faa
Document Type: Proposed Rule
Title: Harmonization of Airworthiness Standards: Miscellaneous Structures Requirements
Posted Date: 2013-03-01T05:00Z

[Federal Register Volume 78, Number 41 (Friday, March 1, 2013)]
[Proposed Rules]
[Pages 13835-13843]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2013-04812]

 ========================================================================
 Proposed Rules
                                                 Federal Register
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 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.
 
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 

  Federal Register / Vol. 78, No. 41 / Friday, March 1, 2013 / Proposed 
Rules  

[[Page 13835]]

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2013-0109; Notice No. 25-137]
RIN 2120-AK13

Harmonization of Airworthiness Standards--Miscellaneous 
Structures Requirements

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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

SUMMARY: The FAA proposes to amend certain airworthiness regulations 
for transport category airplanes, based on recommendations from the 
Aviation Rulemaking Advisory Committee (ARAC). Adopting this proposal 
would eliminate regulatory differences between the airworthiness 
standards of the FAA and European Aviation Safety Agency (EASA). This 
proposal would not add new requirements beyond what manufacturers 
currently meet for EASA certification and would not affect current 
industry design practices. This proposal would revise the structural 
test requirements necessary when analysis has not been found reliable; 
clarify the quality control, inspection, and testing requirements for 
critical and non-critical castings; add control system requirements 
that consider structural deflection and vibration loads; expand the 
fuel tank structural and system requirements regarding emergency 
landing conditions and landing gear failure conditions; add a 
requirement that engine mount failure due to overload must not cause 
hazardous fuel spillage; and revise the inertial forces requirements 
for cargo compartments by removing the exclusion of compartments 
located below or forward of all occupants in the airplane.

DATES: Send comments on or before May 30, 2013.

ADDRESSES: Send comments identified by docket number FAA-2013-0109 
using any of the following methods:
     Federal eRulemaking Portal: Go to http://www.regulations.gov and follow the online instructions for sending your 
comments electronically.
     Mail: Send comments to Docket Operations, M-30; U.S. 
Department of Transportation (DOT), 1200 New Jersey Avenue SE., Room 
W12-140, West Building Ground Floor, Washington, DC 20590-0001.
     Hand Delivery or Courier: Take comments to Docket 
Operations in Room W12-140 of the West Building Ground Floor at 1200 
New Jersey Avenue SE., Washington, DC, between 9 a.m. and 5 p.m., 
Monday through Friday, except Federal holidays.
     Fax: Fax comments to Docket Operations at (202) 493-2251.
    Privacy: The FAA will post all comments it receives, without 
change, to http://www.regulations.gov, including any personal 
information the commenter provides. Using the search function of the 
docket Web site, anyone can find and read the electronic form of all 
comments received into any FAA dockets, including the name of the 
individual sending the comment (or signing the comment for an 
association, business, labor union, etc.). DOT's complete Privacy Act 
Statement can be found in the Federal Register published on April 11, 
2000 (65 FR 19477-19478), as well as at http://DocketsInfo.dot.gov.
    Docket: Background documents or comments received may be read at 
http://www.regulations.gov at any time. Follow the online instructions 
for accessing the docket or go to the Docket Operations in Room W12-140 
of the West Building Ground Floor at 1200 New Jersey Avenue SE., 
Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, 
except Federal holidays.

FOR FURTHER INFORMATION CONTACT: For technical questions concerning 
this action, contact Todd Martin, Airframe and Cabin Safety Branch, 
ANM-115, Transport Airplane Directorate, Aircraft Certification 
Service, Federal Aviation Administration, 1601 Lind Avenue SW., Renton, 
WA 98057-3356; telephone (425) 227-1178; facsimile (425) 227-1232; 
email Todd.Martin@faa.gov.
    For legal questions concerning this action, contact Sean Howe, 
Office of the Regional Counsel, ANM-7, Federal Aviation Administration, 
1601 Lind Avenue SW., Renton, Washington 98057-3356; telephone (425) 
227-2591; facsimile (425) 227-1007; email Sean.Howe@faa.gov.

SUPPLEMENTARY INFORMATION: 

Authority for This Rulemaking

    The FAA's authority to issue rules on aviation safety is found in 
Title 49 of the United States Code. Subtitle I, Section 106 describes 
the authority of the FAA Administrator. Subtitle VII, Aviation 
Programs, describes in more detail the scope of the agency's authority.
    This rulemaking is promulgated under the authority described in 
Subtitle VII, Part A, Subpart III, Section 44701, ``General 
Requirements.'' Under that section, the FAA is charged with promoting 
safe flight of civil aircraft in air commerce by prescribing 
regulations and minimum standards for the design and performance of 
aircraft that the Administrator finds necessary for safety in air 
commerce. This regulation is within the scope of that authority. It 
prescribes new safety standards for the design and operation of 
transport category airplanes.

I. Background

    Part 25 of Title 14, Code of Federal Regulations (14 CFR) 
prescribes airworthiness standards for type certification of transport 
category airplanes, for products certified in the United States. Book 1 
of the EASA Certification Specifications and Acceptable Means of 
Compliance for Large Aeroplanes (CS-25) prescribes the corresponding 
airworthiness standards for products certified in Europe. While part 25 
and CS-25 Book 1 are similar, they differ in several respects. The 
necessity of meeting two sets of certification requirements raises the 
cost of developing new transport category airplanes with little to no 
increase in safety. Therefore, the FAA tasked ARAC through the Loads 
and Dynamics Harmonization Working Group (LDHWG) and the General 
Structures Harmonization Working Group (GSHWG) to review existing 
structures regulations and recommend changes that would eliminate 
differences between the U.S. and European airworthiness standards, 
while maintaining or improving the level of safety in the current 
regulations. This proposed rule is a result of this harmonization 
effort.

[[Page 13836]]

    The LDHWG and GSHWG developed recommendations, which EASA has 
incorporated into CS-25 with some changes. The FAA agrees with the ARAC 
recommendations as adopted by EASA, and we propose to amend part 25 
accordingly. The proposals are not expected to be controversial and 
should reduce certification costs to industry without adversely 
affecting safety. The complete analyses for the proposed changes made 
in response to ARAC recommendations can be found in the ARAC 
recommendation reports, located in the docket for this rulemaking.

II. Overview of Proposed Rule

    The FAA proposes to amend the airworthiness regulations described 
below. This action would harmonize part 25 requirements with the 
corresponding requirements in EASA CS-25 Book 1.
    1. Section 25.307(a), ``Proof of structure,'' would be revised to 
allow a ``sufficient'' level of structural testing, in some cases less 
than ultimate, when analysis has not been shown to be reliable.
    2. Section 25.621, ``Casting factors,'' would be revised to clarify 
the--
     Definition of critical casting and
     Quality control, inspection, and testing requirements for 
critical and non-critical castings.
    3. Section 25.683, ``Operation tests,'' would be revised to add a 
requirement that--
     The control system must remain free from jamming, 
friction, disconnection, and permanent damage in the presence of 
structural deflection and
     Under vibration loads, no hazard may result from 
interference or contact of the control system with adjacent elements.
    4. Section 25.721, ``Landing Gear--General,'' would be revised to--
     Expand the landing gear failure conditions to include side 
loads, in addition to up and aft loads, and expand this requirement to 
include nose landing gear in addition to the main landing gear,
     Specify that the wheels-up landing conditions are assumed 
to occur at a descent rate of 5 feet per second,
     Add a sliding-on-ground condition, and
     Require the engine mount be designed so that, when it 
fails due to overload, this failure does not cause the spillage of 
enough fuel to constitute a fire hazard.
    5. Section 25.787, ``Stowage compartments,'' would be revised to 
expand the inertia forces requirements for cargo compartments by 
removing the exclusion of compartments located below or forward of all 
occupants in the airplane.
    6. Section 25.963, ``Fuel tanks: general,'' would be revised to--
     Require that fuel tanks be designed so that no fuel is 
released in or near the fuselage, or near the engines, in quantities 
that would constitute a fire hazard in otherwise survivable emergency 
landing conditions,
     Define fuel tank pressure loads for fuel tanks located 
within and outside the fuselage pressure boundary and near the fuselage 
or near the engines, and
     Specify the wheels-up landing conditions and landing gear 
and engine mount failure conditions that must be considered when 
evaluating fuel tank structural integrity.
    7. Section 25.994, ``Fuel system components,'' would be revised to 
specify the wheels-up landing conditions to be considered when 
evaluating fuel system components.

III. Discussion of the Proposal

A. Section 25.307(a), ``Proof of Structure''

    Section 25.307(a) currently requires that applicants for a type 
design conduct strength testing unless structural analysis has been 
shown to be reliable. When analysis has not been shown to be reliable, 
the regulation states that the FAA ``may require ultimate load tests in 
cases where limit load tests may be inadequate.''
    Rather than specifying ``limit load'' or ``ultimate load,'' the 
GSHWG proposed that the harmonized requirement state that 
substantiating load tests must be made that are ``sufficient'' to 
verify structural behavior up to the load levels required by Sec.  
25.305 (strength and deformation). Where it is justified, these test 
load levels may be less than ultimate.
    We propose to revise Sec.  25.307(a) to state that, when analysis 
has not been shown to be reliable, tests must be conducted to 
``sufficient'' load levels. Normally, testing to ultimate load levels 
is required, but when previous relevant test evidence can be used to 
support the analysis, then a lower level of testing may be accepted. 
The proposed rule would allow this intermediate level of testing. While 
the rule has changed, the intent remains the same: to ensure that the 
structure will not have any structural deformation under limit load or 
any failure under ultimate load.
    This action would harmonize Sec.  25.307(a) with the corresponding 
EASA standard.

B. Section 25.621, ``Casting Factors''

    Section 25.621 currently requires classification of structural 
castings as either critical or non-critical, and depending on 
classification, specifies inspection requirements, test requirements, 
and casting factors for strength and deformation. These casting factors 
are applied in addition to the factor of safety required by Sec.  
25.303, ``Factor of safety.'' The application of factors of safety to 
castings is necessary because the casting process can be inconsistent. 
Castings are subject to variability in mechanical properties due to 
this casting process, which can result in imperfections (such as voids) 
within the cast part.
    We propose to revise Sec.  25.621 to define ``critical casting'' 
and to clarify the quality control, inspection, and testing 
requirements for critical and non-critical castings. The proposed rule 
would specify the inspection and testing requirements based on the 
casting factor chosen by the applicant--from 1.0 to 2.0 or greater.
    Section 25.621 currently requires that critical castings in 
structural applications have a minimum casting factor of 1.25. A 
casting factor of 1.0 would be allowed by the proposed rule, as 
described below, because casting technology has improved since the 
current Sec.  25.621 was adopted, and much higher quality castings can 
be produced using improved foundry methods. The proposed rule would 
require the following for critical castings:
     A visual and special non-destructive inspections. The 
special non-destructive inspections would be limited to specified areas 
of the casting where defects are likely to occur.
     A casting factor of 1.5 or greater would be allowed 
provided that one casting undergoes static testing and is shown to meet 
the relevant strength and deformation requirements. A casting factor of 
1.25 or greater would be allowed provided that three castings undergo 
static testing and are shown to meet the relevant strength and 
deformation requirements.
     A casting factor of 1.0 or greater would be allowed 
provided that one casting undergoes static testing and is shown to meet 
the relevant strength and deformation requirements, and it is 
demonstrated that a process is in place to ensure the castings produced 
have material variation equivalent to those of wrought alloy products 
of similar composition. Draft Advisory Circular (AC) 25.621-X, 
``Casting Factors,'' will be published concurrently with this NPRM. 
This draft AC outlines a process for using a casting factor of 1.0,

[[Page 13837]]

including any changes to that process that may occur over time. The 
proposed rule requires ``process monitoring,'' which is intended to 
mean continuous process monitoring for the entire production lifecycle.
    The proposed rule would also specify quality control, inspection, 
and testing requirements for non-critical castings with casting factors 
ranging from 1.0 to 2.0 or greater.

C. Section 25.683, ``Operation Tests''

    Section 25.683 currently requires the airplane control system to be 
free from jamming, excessive friction, and excessive deflection when 
subjected to pilot effort and control system loads. We propose to 
revise Sec.  25.683 by adding a requirement to substantiate that, in 
the presence of deflections of the airplane structure due to maneuver 
loads, the control system can be exercised and remain free from 
jamming, friction, disconnection, and any form of permanent damage. In 
addition, we propose adding a requirement to substantiate that, under 
vibration loads, no interference or contact of the control system with 
adjacent elements can result in hazard.
    Since control systems are typically attached or routed through 
adjacent aircraft structure, it is necessary to ensure that deflections 
of that adjacent structure do not adversely affect the safe operation 
of the control system through interference, jamming, or induced 
loading. Also, the control system design should be such that the 
effects of vibration loads in normal flight and ground operating 
conditions will not affect the safe operation of the control system.
    These actions would harmonize Sec.  25.683 with the corresponding 
EASA standard.

D. Section 25.721, ``Landing Gear--General (Emergency Landing 
Conditions)''

    Section 25.721(a) currently requires that the main landing gear 
system be designed so that if it fails due to overloads during takeoff 
and landing, the failure does not cause the spillage of enough fuel to 
constitute a fire hazard. This is intended to protect fuel tanks from 
rupture and puncture due to the failure of the landing gear and its 
supports. This requirement applies only to fuel systems inside the 
fuselage for airplanes with 9 seats or less, and all fuel systems for 
airplanes with 10 seats or more. We propose to revise Sec.  25.721(a) 
to:
    1. Apply to the nose landing gear as well as the main landing gear,
    2. Clarify that landing gear failure is assumed,
    3. Expand the failure conditions to include side loads, in addition 
to up and aft loads, and
    4. Remove the exception for airplanes with less than 10 seats.
    We propose revising Sec.  25.721(a) to apply to the nose gear as 
well as the main landing gear because nose gear failures can also 
impact fuel tanks. We would also clarify that landing gear failure is 
assumed by stating that the design must consider such failures ``when'' 
they occur, rather than ``if'' they occur. This clarification is needed 
because in some past cases, applicants relied on over-designing the 
landing gear beyond ultimate strength requirements rather than showing 
safe separation in the event of failure.
    We would expand the failure conditions to consider side loads to 
ensure that a comprehensive range of failure conditions are considered. 
Lastly, we would remove the exception for airplanes with less than 10 
seats.
    This exception in Sec.  25.721 was originally introduced at 
Amendment 25-32 (37 FR 3969, February 24, 1972). In the preamble to 
that final rule, the FAA determined that:

[C]ertain of the requirements in proposed Secs. 25.562, 25.721, 
25.787, 25.807, and 25.812 are inappropriate and unnecessary, or are 
unnecessarily severe, for transport category airplanes that have 
maximum passenger seating configurations, excluding pilots seats, of 
nine seats or less. In those instances, the proposed requirements 
have been revised to provide exceptions and to include requirements 
for such airplanes that provide a level of safety for such airplanes 
equivalent to that for airplanes with larger passenger seating 
configurations.

    This exception is appropriate for certain cabin safety provisions 
that necessitate the egress of large numbers of passengers. However, 
the FAA believes that for the hazards associated with fuel fires, there 
is no technical justification for limiting the applicability of any of 
the fuel tank protection provisions based on the passenger seating 
capacity.
    Section 25.721(b) currently states that airplanes must be able to 
land on a paved runway, with any one or more landing gear legs not 
extended, without failures that result in spillage of enough fuel to 
constitute a fire hazard. This condition is not intended to treat a 
collapsed gear condition, but is intended to cover cases in which one 
or more gear legs do not extend for whatever reason, and the airplane 
must make a controlled landing on a paved runway in this condition. The 
current requirement applies only to airplanes with 10 seats or more. We 
propose to revise Sec.  25.721(b) to:
    1. Specify that the wheels-up landing conditions are assumed to 
occur at a descent rate of 5 feet per second,
    2. Clarify the combinations of retracted landing gear that must be 
considered,
    3. Add a sliding-on-ground condition, and
    4. Remove the exception for airplanes with less than 10 seats.
    At the time Sec.  25.721(b) was adopted by Amendment 25-32 (37 FR 
3969, February 24, 1972), Sec.  25.561 contained a landing descent 
speed of ``5 feet per second'' as an alternative criterion that could 
allow a reduction in the specified vertical emergency landing design 
load factor. Amendment 25-64 (53 FR 17646, May 17, 1988) removed this 
alternative to make the specified vertical design load factor the 
minimum design condition. However, the 5-feet-per-second descent speed 
contained in Sec.  25.561 had become, by design practice and 
interpretation, the design descent velocity for the wheels-up landing 
conditions addressed in Sec. Sec.  25.721 and 25.994. By removing it, 
the quantitative definition of the wheels-up landing condition on a 
paved runway was lost. We propose to revise Sec.  25.721(b) to re-
establish the 5-feet-per-second descent rate for the ``minor crash 
landing'' condition.
    We would add a sliding-on-ground condition to ensure that the 
wheels-up landing conditions are evaluated beyond the initial impact. 
The exception for airplanes with less than 10 seats would be removed 
from Sec.  25.721(a) and (b) as noted above.
    We propose to replace Sec.  25.721(c) with a new requirement that 
the engine mount and pylon be designed so that, when it fails due to 
overload, the failure mode is not likely to cause the spillage of 
enough fuel to constitute a fire hazard. Service experience has shown 
that landing gear malfunctions can lead to the airplane landing on the 
engine nacelles for some configurations. This can result in the engine 
nacelle breaking away, creating much the same fuel tank rupture 
potential as the landing gear breaking away.
    These actions would harmonize Sec.  25.721 with the corresponding 
EASA standard.

E. Section 25.787(a), ``Stowage Compartments''

    Section 25.787(a) currently requires that cargo compartments be 
designed to the emergency landing conditions of Sec.  25.561(b), but 
excludes compartments located below or forward of all occupants in the 
airplane. We propose

[[Page 13838]]

to revise Sec.  25.787(a) to include compartments located below or 
forward of all occupants in the airplane. This change would ensure 
that, in these compartments, inertia forces in the up and aft direction 
will not injure passengers, and inertia forces in any direction will 
not cause penetration of fuel tanks or lines, or cause other hazards. 
This action would harmonize Sec.  25.787(a) with the corresponding EASA 
standard.
    The LDHWG originally recommended that Sec.  25.561(c) be revised to 
achieve this objective of addressing cargo compartments below or 
forward of airplane occupants. However, when evaluating the LDHWG 
recommendation, EASA determined that CS 25.787 already addressed the 
issue and noted that Sec.  25.787(a) and CS 25.787(a) were different in 
this regard. Separately, ARAC also tasked the Cabin Safety 
Harmonization Working Group with reviewing Sec.  25.787, and that group 
also recommended that the FAA harmonize Sec.  25.787(a) with CS 
25.787(a). The FAA agrees that the change should be made to Sec.  
25.787(a), rather than Sec.  25.561.

F. Section 25.963(d), ``Fuel Tanks: General (Emergency Landing 
Conditions)''

    Section 25.963(d) currently requires that fuel tanks within the 
fuselage contour be able to resist rupture and retain fuel under the 
inertia forces defined in Sec.  25.561. In addition, these tanks must 
be in a protected position so that exposure of the tanks to scraping 
action with the ground is unlikely. We propose to revise Sec.  
25.963(d), as described below, based on recommendations provided by the 
LDHWG.
    1. The introductory sentence to Sec.  25.963(d) would require that, 
``so far as it is practicable,'' fuel tanks be designed, located and 
installed so that no fuel is released in or near the fuselage, or near 
the engines, in quantities that would constitute a fire hazard in 
``otherwise survivable emergency landing conditions.'' This is 
considered a general requirement, while more specific criteria are 
provided in Sec.  25.963(d)(1) through (d)(5). The term ``practicable'' 
here means that any feasible or workable design should be considered in 
order to protect the fuel tanks. The phrase ``otherwise survivable 
emergency landing conditions'' is not specifically quantified. However, 
past events should be considered in developing a robust fuel tank 
design.
    2. Section 25.963(d)(1) through (d)(3) would define fuel tank 
pressure loads for fuel tanks located within and outside the fuselage 
pressure boundary, and near the fuselage or near the engines, as 
described below.
    The LDHWG recommended revising Sec.  25.963(d) to delete the 
reference to Sec.  25.561 for emergency landing load factors, which are 
used to develop the fuel tank pressure loads. The emergency landing 
load factors of Sec.  25.561(b)(3) are based upon the restraint of 
fixed mass items, and the response of a fluid during emergency landings 
is different and much more complex to quantify. The proposed 
requirements for fuel tanks both within and outside of the fuselage 
pressure boundary have been simply formulated in terms of equations 
with factors that are justified based upon the satisfactory service 
experience of the existing fleet.
    The current regulation addresses only fuel tanks within the 
fuselage contour, although the FAA has issued special conditions to 
require fuel inertia loading conditions on horizontal tail tanks 
outside the fuselage contour.
    The LDHWG determined that the safety record for fuel tank rupture 
caused solely by fuel inertia loads is excellent. Manufacturers' 
records of accidents and serious incidents involving large transport 
airplanes showed no event where fuel inertia pressure caused 
significant loss of fuel. Fuel losses that did occur were mainly caused 
by direct impact and external-object punctures.
    Nevertheless, a fuel inertia criterion for wing fuel tanks is 
needed to ensure that future designs meet the same level of safety 
achieved by the current fleet. The wing fuel tanks of many current 
aircraft types were designed to a simple criterion in which fuel 
pressure was calculated using an inertia head equal to the local 
geometrical stream-wise distance between the fuel tank solid 
boundaries. Service experience has shown this criterion produces fuel 
tank designs with an acceptable level of safety. Therefore, it is 
appropriate that the future airworthiness standards for fuel tanks 
should require a similar level of design fuel pressure for similar fuel 
tank designs.
    For fuel tanks within the fuselage pressure boundary, the current 
fuel inertia load criterion, as generally applied, covers up to a full 
fuel tank, an inertia head equal to maximum pressure head, and inertia 
load factors equal to those of Sec.  25.561(b)(3). This level of 
rupture resistance for fuel tanks is justified based upon occupant 
survivability considerations. Therefore, the LDHWG recommended, and the 
FAA concurs, that the current minimum level of rupture resistance 
should be retained for fuel tanks within the fuselage pressure 
boundary. For fuel tanks outside the fuselage pressure boundary, the 
design load factors for the inboard and outboard (lateral) loading 
conditions and forward loading conditions are proposed as one-half of 
those for fuel tanks within the fuselage. The design load factors for 
the up, down, and aft loading conditions would be the same for all fuel 
tanks.
    When EASA adopted the LDHWG recommendations, it noted an objection 
that had been raised by the Joint Aviation Authorities (JAA) Power 
Plant Study Group (PPSG). The PPSG did not agree with the LDHWG 
recommendation regarding fuel tank pressure loads for fuel tanks ``near 
the fuselage or near the engines,'' which had been specifically 
addressed by Joint Aviation Regulation. In response to the PPSG 
objection, EASA added criteria for fuel tanks near the fuselage and 
near the engines. We agree with these criteria and propose to add the 
same to Sec.  25.963(d).
    3. Section 25.963(d)(4) would require that the effects of crushing 
and scraping actions with the ground not cause fuel spillage, or 
generate temperatures that would constitute a fire hazard under the 
conditions specified in proposed Sec.  25.721(b). By reference to Sec.  
25.721(b), this rule would require consideration of the 5 feet-per-
second wheels-up landing criteria and subsequent sliding on the ground. 
The potential effects of crushing and scraping, including thermal 
effects, must be evaluated for these minor crash landing conditions.
    4. Section 25.963(d)(5) would require that fuel tank installations 
be such that the tanks will not rupture as a result of an engine pylon 
or engine mount or landing gear tearing away as specified in proposed 
Sec.  25.721(a) and (c). This requirement would be largely redundant to 
the proposed Sec.  25.721(a) and (c), but is included in Sec.  
25.963(d) for completeness.
    These actions would harmonize Sec.  25.963(d) with the 
corresponding EASA standard with the following two exceptions:
    CS 25.963(d) requires that fuel tanks be designed and located so 
that no fuel is released in quantities ``sufficient to start a serious 
fire'' in otherwise survivable emergency landing conditions. The 
proposed rule would require that no fuel is released in quantities 
``that would constitute a fire hazard.'' The two phrases have the same 
intent and meaning, and the latter phrase is consistent with the 
wording in CS 25.721/Sec.  25.721, CS 25.963(d)(4)/Sec.  25.963(d)(4), 
and CS 25.994/Sec.  25.994.
    The fuel tank pressure criteria in CS 25.963(d) vary depending on 
whether the fuel tank is ``within the fuselage

[[Page 13839]]

contour'' or ``outside the fuselage contour.'' The proposed rule would 
be more specific by referring to ``those parts of fuel tanks within the 
fuselage pressure boundary or that form part of the fuselage pressure 
boundary'' versus ``those parts of fuel tanks outside the fuselage 
pressure boundary.'' The proposed wording is clearer and has the same 
intent and meaning as that specified in CS 25.963(d).

G. Section 25.994, ``Fuel System Components''

    Section 25.994 currently requires that fuel system components in an 
engine nacelle or in the fuselage be protected from damage that could 
result in spillage of enough fuel to constitute a fire hazard as a 
result of a wheels-up landing on a paved runway. We propose to revise 
Sec.  25.994 to specify that the wheels-up landing conditions that must 
be considered are those defined in proposed Sec.  25.721(b). This 
action would harmonize Sec.  25.994 with the corresponding EASA 
standard.
    As noted previously, the 5-feet-per-second descent speed contained 
in an earlier amendment to Sec.  25.561 had become, by design practice 
and interpretation, the design descent velocity for the wheels-up 
landing conditions addressed in Sec. Sec.  25.721 and 25.994. In fact, 
Advisory Circular (AC) 25.994-1, ``Design Considerations to Protect 
Fuel Systems During a Wheel-Up Landing,'' dated July 24, 1986, 
specifically referred to Sec.  25.561 for the design conditions, which 
at that time contained the 5-feet-per-second landing descent criteria.

H. Advisory Material

    The FAA is developing three new proposed ACs to be published 
concurrently with the proposed regulations in this NPRM. The proposed 
ACs would provide guidance material for acceptable means, but not the 
only means, of demonstrating compliance with proposed Sec. Sec.  
25.307, 25.561, 25.621, 25.721, 25.963, and 25.994. We will accept 
public comments to the following proposed ACs on the ``Aviation Safety 
Draft Documents Open for Comment'' Internet Web site at http://www.faa.gov/aircraft/draft_docs/:
     AC 25-X, ``Fuel Tank Strength in Emergency Landing 
Conditions.'' (AC 25-X would provide guidance for the fuel tank 
structural integrity requirements of Sec. Sec.  25.561, 25.721, and 
25.963.)
     AC 25.307-X, ``Proof of Structure.''
     AC 25.621-X, ``Casting Factors.''

IV. Regulatory Notices and Analyses

A. Regulatory Evaluation

    Proposed changes to Federal regulations must undergo several 
economic analyses. First, Executive Order 12866 and Executive Order 
13563 direct that each Federal agency shall propose or adopt a 
regulation only upon a reasoned determination that the benefits of the 
intended regulation justify its costs. Second, the Regulatory 
Flexibility Act of 1980 (Pub. L. 96-354) requires agencies to analyze 
the economic impact of regulatory changes on small entities. Third, the 
Trade Agreements Act (Pub. L. 96-39) prohibits agencies from setting 
standards that create unnecessary obstacles to the foreign commerce of 
the United States. In developing U.S. standards, the Trade Act requires 
agencies to consider international standards and, where appropriate, 
that they be the basis of U.S. standards. Fourth, the Unfunded Mandates 
Reform Act of 1995 (Pub. L. 104-4) requires agencies to prepare a 
written assessment of the costs, benefits, and other effects of 
proposed or final rules that include a Federal mandate likely to result 
in the expenditure by State, local, or tribal governments, in the 
aggregate, or by the private sector, of $100 million or more annually 
(adjusted for inflation with base year of 1995). This portion of the 
preamble summarizes the FAA's analysis of the economic impacts of this 
proposed rule.
    Department of Transportation Order DOT 2100.5 prescribes policies 
and procedures for simplification, analysis, and review of regulations. 
If the expected cost impact is so minimal that a proposed or final rule 
does not warrant a full evaluation, this order permits that a statement 
to that effect and the basis for it be included in the preamble if a 
full regulatory evaluation of the cost and benefits is not prepared. 
Such a determination has been made for this proposed rule. The 
reasoning for this determination follows.
    The FAA proposes to amend certain airworthiness standards for 
transport category airplanes. Adopting this proposal would eliminate 
regulatory differences between the airworthiness standards of the FAA 
and EASA. This proposal would not add new requirements beyond what 
manufacturers currently meet for EASA certification and would not 
affect current industry design practices. Meeting two sets of 
certification requirements raises the cost of developing new transport 
category airplanes with little to no increase in safety. In the 
interest of fostering international trade, lowering the cost of 
manufacturing new transport category airplanes, and making the 
certification process more efficient, the FAA, EASA, and several 
industry working groups came together to create, to the maximum extent 
possible, a single set of certification requirements that would be 
accepted in both the United States and Europe. Therefore, as a result 
of these harmonization efforts, the FAA proposes to amend the 
airworthiness regulations described in section II of this NPRM, 
``Overview of the Proposed Rule.'' This action would harmonize part 25 
requirements with the corresponding requirements in EASA CS-25 Book 1.
    Currently, all manufacturers of transport category airplanes, 
certificated under part 25 are expected to continue their current 
practice of compliance with the EASA certification requirements in CS-
25 Book 1. Since future certificated transport airplanes are expected 
to meet CS-25 Book 1, and this rule simply adopts the same EASA 
requirements, manufacturers will incur minimal or no additional cost 
resulting from this proposed rule. Therefore, the FAA estimates that 
there are no additional costs associated with this proposed rule.
    In fact, manufacturers could receive cost savings because they will 
not have to build and certificate transport category airplanes to two 
different authorities' certification specifications and rules.
    The FAA, however, has not attempted to quantify the cost savings 
that may accrue from this rule, beyond noting that while they may be 
minimal, they contribute to a potential harmonization savings. The 
agency concludes that because the compliance cost for this proposed 
rule is minimal and there may be harmonization cost savings, further 
analysis is not required.
    The FAA has, therefore, determined that this proposed rule is not a 
``significant regulatory action'' as defined in section 3(f) of 
Executive Order 12866, and is not ``significant'' as defined in DOT's 
Regulatory Policies and Procedures.

B. Regulatory Flexibility Determination

    The Regulatory Flexibility Act of 1980 (Pub. L. 96-354) (RFA) 
establishes ``as a principle of regulatory issuance that agencies shall 
endeavor, consistent with the objectives of the rule and of applicable 
statutes, to fit regulatory and informational requirements to the scale 
of the businesses, organizations, and governmental jurisdictions 
subject to regulation. To achieve this principle, agencies are required 
to solicit and

[[Page 13840]]

consider flexible regulatory proposals and to explain the rationale for 
their actions to assure that such proposals are given serious 
consideration.'' 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 rule will 
have a significant economic impact on a substantial number of small 
entities. If the agency determines that it will, the agency must 
prepare a regulatory flexibility analysis as described in the RFA.
    However, if an agency determines that a 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 a regulatory flexibility analysis is not 
required. The certification must include a statement providing the 
factual basis for this determination, and the reasoning should be 
clear.
    The FAA believes that this rule would not have a significant 
economic impact on a substantial number of small entities for the 
following reason. The net effect of this rule is minimum regulatory 
cost relief as the proposed rule would adopt those EASA requirements 
that industry already complies with. Moreover, manufacturers of part 25 
airplanes are not small entities. Because those manufacturers already 
meet or expect to meet this CS-25 standard as well as the existing CFR 
requirement, the net effect of this proposed rule is regulatory cost 
relief.
    Because manufacturers of transport category airplanes are not small 
entities, this proposed rule is expected to have minimal to no 
additional costs, and could be cost-relieving, as the acting FAA 
Administrator, I certify that this proposed rule would not have a 
significant economic impact on a substantial number of small entities.

C. International Trade Impact Assessment

    The Trade Agreements Act of 1979 (Pub. L. 96-39), as amended by the 
Uruguay Round Agreements Act (Pub. L. 103-465), prohibits Federal 
agencies from establishing standards or engaging in related activities 
that create unnecessary obstacles to the foreign commerce of the United 
States. Pursuant to these Acts, the establishment of standards is not 
considered an unnecessary obstacle to the foreign commerce of the 
United States, so long as the standard has a legitimate domestic 
objective, such the protection of safety, and does not operate in a 
manner that excludes imports that meet this objective. The statute also 
requires consideration of international standards and, where 
appropriate, that they be the basis for U.S. standards. The FAA has 
assessed the potential effect of this proposed rule and determined that 
it is in accord with the Trade Agreements Act as the rule uses European 
standards as the basis for United States regulation.

D. Unfunded Mandates Assessment

    Title II of the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-
4) requires each Federal agency to prepare a written statement 
assessing the effects of any Federal mandate in a proposed or final 
agency rule that may result in an expenditure of $100 million or more 
(in 1995 dollars) in any one year by State, local, and tribal 
governments, in the aggregate, or by the private sector; such a mandate 
is deemed to be a ``significant regulatory action.'' The FAA currently 
uses an inflation-adjusted value of $143.1 million in lieu of $100 
million. This proposed rule does not contain such a mandate; therefore, 
the requirements of Title II of the Act do not apply.

E. Paperwork Reduction Act

    The Paperwork Reduction Act of 1995 (44 U.S.C. 3507(d)) requires 
that the FAA consider the impact of paperwork and other information 
collection burdens imposed on the public. The FAA has determined that 
there would be no new requirement for information collection associated 
with this proposed rule.

F. International Compatibility and Cooperation

    (1) In keeping with U.S. obligations under the Convention on 
International Civil Aviation, it is FAA policy to conform to 
International Civil Aviation Organization (ICAO) Standards and 
Recommended Practices to the maximum extent practicable. The FAA has 
reviewed the corresponding ICAO Standards and Recommended Practices and 
has identified no differences with these proposed regulations.
    (2) Executive Order (EO) 13609, Promoting International Regulatory 
Cooperation, (77 FR 26413, May 4, 2012) promotes international 
regulatory cooperation to meet shared challenges involving health, 
safety, labor, security, environmental, and other issues and reduce, 
eliminate, or prevent unnecessary differences in regulatory 
requirements. The FAA has analyzed this action under the policy and 
agency responsibilities of Executive Order 13609, Promoting 
International Regulatory Cooperation. The agency has determined that 
this action would eliminate differences between U.S. aviation standards 
and those of other civil aviation authorities by creating a single set 
of certification requirements for transport category airplanes that 
would be acceptable in both the United States and Europe.

G. Environmental Analysis

    FAA Order 1050.1E identifies FAA actions that are categorically 
excluded from preparation of an environmental assessment or 
environmental impact statement under the National Environmental Policy 
Act in the absence of extraordinary circumstances. The FAA has 
determined this rulemaking action qualifies for the categorical 
exclusion identified in paragraph 312f of Order 1050.1E and involves no 
extraordinary circumstances.

V. Executive Order Determinations

A. Executive Order 13132, Federalism

    The FAA has analyzed this proposed rule under the principles and 
criteria of Executive Order 13132, Federalism. The agency has 
determined that this action would not have a substantial direct effect 
on the States, or the relationship between the Federal Government and 
the States, or on the distribution of power and responsibilities among 
the various levels of government, and, therefore, would not have 
Federalism implications.

B. Executive Order 13211, Regulations That Significantly Affect Energy 
Supply, Distribution, or Use

    The FAA analyzed this proposed rule under Executive Order 13211, 
Actions Concerning Regulations that Significantly Affect Energy Supply, 
Distribution, or Use (May 18, 2001). The agency has determined that it 
would not be a ``significant energy action'' under the executive order 
and would not be likely to have a significant adverse effect on the 
supply, distribution, or use of energy.

VI. Additional Information

A. Comments Invited

    The FAA invites interested persons to participate in this 
rulemaking by submitting written comments, data, or views. The agency 
also invites comments relating to the economic, environmental, energy, 
or federalism impacts that might result from adopting the proposals in 
this document. The most helpful comments reference a specific portion 
of the proposal, explain the reason for any recommended

[[Page 13841]]

change, and include supporting data. To ensure the docket does not 
contain duplicate comments, commenters should send only one copy of 
written comments, or if comments are filed electronically, commenters 
should submit only one time.
    The FAA will file in the docket all comments it receives, as well 
as a report summarizing each substantive public contact with FAA 
personnel concerning this proposed rulemaking. Before acting on this 
proposal, the FAA will consider all comments it receives on or before 
the closing date for comments. The FAA will consider comments filed 
after the comment period has closed if it is possible to do so without 
incurring expense or delay. The agency may change this proposal in 
light of the comments it receives.
    Proprietary or Confidential Business Information: Commenters should 
not file proprietary or confidential business information in the 
docket. Such information must be sent or delivered directly to the 
person identified in the FOR FURTHER INFORMATION CONTACT section of 
this document, and marked as proprietary or confidential. If submitting 
information on a disk or CD ROM, mark the outside of the disk or CD 
ROM, and identify electronically within the disk or CD ROM the specific 
information that is proprietary or confidential.
    Under 14 CFR 11.35(b), if the FAA is aware of proprietary 
information filed with a comment, the agency does not place it in the 
docket. It is held in a separate file to which the public does not have 
access, and the FAA places a note in the docket that it has received 
it. If the FAA receives a request to examine or copy this information, 
it treats it as any other request under the Freedom of Information Act 
(5 U.S.C. 552). The FAA processes such a request under Department of 
Transportation procedures found in 49 CFR part 7.

B. Availability of Rulemaking Documents

    An electronic copy of rulemaking documents may be obtained from the 
Internet by--
    1. Searching the Federal eRulemaking Portal at http://www.regulations.gov,
    2. Visiting the FAA's Regulations and Policies Web page at http://www.faa.gov/regulations_policies, or
    3. Accessing the Government Printing Office's Web page at http://www.gpo.gov/fdsys/.
    Copies may also be obtained by sending a request to the Federal 
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence 
Avenue SW., Washington, DC 20591, or by calling (202) 267-9680. 
Commenters must identify the docket or notice number of this 
rulemaking.
    All documents the FAA considered in developing this proposed rule, 
including economic analyses and technical reports, may be accessed from 
the Internet through the Federal eRulemaking Portal referenced in item 
(1) above.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.

The Proposed Amendment

    In consideration of the foregoing, the Federal Aviation 
Administration proposes to amend chapter I of title 14, Code of Federal 
Regulations as follows:

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

0
1. The authority citation for part 25 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, and 44704.

0
2. Amend Sec.  25.307 by revising paragraph (a) to read as follows:

Sec.  25.307  Proof of structure.

    (a) Compliance with the strength and deformation requirements of 
this subpart must be shown for each critical loading condition. 
Structural analysis may be used only if the structure conforms to that 
for which experience has shown this method to be reliable. In other 
cases, substantiating tests must be made to load levels that are 
sufficient to verify structural behavior up to loads specified in Sec.  
25.305.
* * * * *
0
3. Amend Sec.  25.621 by revising paragraphs (a), (c), and (d) to read 
as follows:

Sec.  25.621  Casting factors.

    (a) General. For castings used in structural applications, the 
factors, tests, and inspections specified in paragraphs (b) through (d) 
of this section must be applied in addition to those necessary to 
establish foundry quality control. The inspections must meet approved 
specifications. Paragraphs (c) and (d) of this section apply to any 
structural castings, except castings that are pressure tested as parts 
of hydraulic or other fluid systems and do not support structural 
loads.
    (b) * * *
    (c) Critical castings. Each casting whose failure could preclude 
continued safe flight and landing of the airplane or could result in 
serious injury to occupants is considered a critical casting. Each 
critical casting must have a factor associated with it for showing 
compliance with strength and deformation requirements, and must comply 
with the following criteria associated with that factor:
    (1) A casting factor of 1.0 or greater may be used, provided that--
    (i) It is demonstrated, in the form of process qualification, proof 
of product, and process monitoring that, for each casting design and 
part number, the castings produced by each foundry and process 
combination have coefficients of variation of the material properties 
that are equivalent to those of wrought alloy products of similar 
composition. Process monitoring must include testing of coupons cut 
from the prolongations of each casting (or each set of castings, if 
produced from a single pour into a single mold in a runner system) and, 
on a sampling basis, coupons cut from critical areas of production 
castings. The acceptance criteria for the process monitoring 
inspections and tests must be established and included in the process 
specifications to ensure the properties of the production castings are 
controlled to within levels used in design.
    (ii) Each casting receives:
    (A) Inspection of 100% of its surface, using visual and liquid 
penetrant, or equivalent, inspection methods; and
    (B) Inspection of structurally significant internal areas and areas 
where defects are likely to occur, using radiographic, or equivalent, 
inspection methods.
    (iii) One casting undergoes a static test and is shown to meet the 
strength and deformation requirements of Sec.  25.305(a) and (b).
    (2) A casting factor of 1.25 or greater may be used, provided 
that--
    (i) Each casting receives:
    (A) Inspection of 100% of its surface, using visual and liquid 
penetrant, or equivalent inspection methods; and
    (B) Inspection of structurally significant internal areas and areas 
where defects are likely to occur, using radiographic, or equivalent, 
inspection methods.
    (ii) Three castings undergo static tests and are shown to meet:
    (A) The strength requirements of Sec.  25.305(b) at an ultimate 
load corresponding to a casting factor of 1.25; and
    (B) The deformation requirements of Sec.  25.305(a) at a load of 
1.15 times the limit load.
    (3) A casting factor of 1.50 or greater may be used, provided 
that--
    (i) Each casting receives:
    (A) Inspection of 100% of its surface, using visual and liquid 
penetrant, or equivalent, inspection methods; and

[[Page 13842]]

    (B) Inspection of structurally significant internal areas and areas 
where defects are likely to occur, using radiographic, or equivalent, 
inspection methods.
    (ii) One casting undergoes a static test and is shown to meet:
    (A) The strength requirements of Sec.  25.305(b) at an ultimate 
load corresponding to a casting factor of 1.50; and
    (B) The deformation requirements of Sec.  25.305(a) at a load of 
1.15 times the limit load.
    (d) Non-critical castings. For each casting other than critical 
castings, as specified in paragraph (c) of this section, the following 
apply:
    (1) A casting factor of 1.0 or greater may be used, provided that 
the requirements of (c)(1) of this section are met, or all of the 
following conditions are met:
    (i) Castings are manufactured to approved specifications that 
specify the minimum mechanical properties of the material in the 
casting and provides for demonstration of these properties by testing 
of coupons cut from the castings on a sampling basis.
    (ii) Each casting receives:
    (A) Inspection of 100% of its surface, using visual and liquid 
penetrant, or equivalent, inspection methods; and
    (B) Inspection of structurally significant internal areas and areas 
where defects are likely to occur, using radiographic, or equivalent, 
inspection methods.
    (iii) Three sample castings undergo static tests and are shown to 
meet the strength and deformation requirements of Sec.  25.305(a) and 
(b).
    (2) A casting factor of 1.25 or greater may be used, provided that 
each casting receives:
    (i) Inspection of 100% of its surface, using visual and liquid 
penetrant, or equivalent, inspection methods; and
    (ii) Inspection of structurally significant internal areas and 
areas where defects are likely to occur, using radiographic, or 
equivalent, inspection methods.
    (3) A casting factor of 1.5 or greater may be used, provided that 
each casting receives inspection of 100% of its surface using visual 
and liquid penetrant, or equivalent, inspection methods.
    (4) A casting factor of 2.0 or greater may be used, provided that 
each casting receives inspection of 100% of its surface using visual 
inspection methods.
    (5) The number of castings per production batch to be inspected by 
non-visual methods in accordance with paragraphs (d)(2) and (d)(3) of 
this section may be reduced when an approved quality control procedure 
is established.
0
4. Amend Sec.  25.683 by redesignating the introductory text as 
paragraph (a), redesignating paragraphs (a), (b), and (c) as paragraphs 
(a)(1), (a)(2), and (a)(3) respectively, and adding paragraphs (b) and 
(c) to read as follows:

Sec.  25.683  Operation tests.

    (a) It must be shown by operation tests that when portions of the 
control system subject to pilot effort loads are loaded to 80% of the 
limit load specified for the system and the powered portions of the 
control system are loaded to the maximum load expected in normal 
operation, the system is free from--
    (1) Jamming;
    (2) Excessive friction; and
    (3) Excessive deflection.
    (b) It must be shown by analysis and, where necessary, by tests 
that in the presence of deflections of the airplane structure due to 
the separate application of pitch, roll, and yaw limit maneuver loads, 
the control system, when loaded to obtain these limit loads and 
operated within its operational range of deflections, can be exercised 
about all control axes and remain free from--
    (1) Jamming;
    (2) Excessive friction;
    (3) Disconnection, and
    (4) Any form of permanent damage.
    (c) It must be shown that under vibration loads in the normal 
flight and ground operating conditions, no hazard can result from 
interference or contact with adjacent elements.
0
5. Revise Sec.  25.721 to read as follows:

Sec.  25.721  General.

    (a) The landing gear system must be designed so that when it fails 
due to overloads during takeoff and landing, the failure mode is not 
likely to cause spillage of enough fuel to constitute a fire hazard. 
The overloads must be assumed to act in the upward and aft directions 
in combination with side loads acting inboard and outboard. In the 
absence of a more rational analysis, the side loads must be assumed to 
be up to 20% of the vertical load or 20% of the drag load, whichever is 
greater.
    (b) The airplane must be designed to avoid any rupture leading to 
the spillage of enough fuel to constitute a fire hazard as a result of 
a wheels-up landing on a paved runway, under the following minor crash 
landing conditions:
    (1) Impact at 5 feet-per-second vertical velocity, with the 
airplane under control, at Maximum Design Landing Weight--
    (i) With the landing gear fully retracted and, as separate 
conditions,
    (ii) With any other combination of landing gear legs not extended.
    (2) Sliding on the ground, with--
    (i) The landing gear fully retracted and with up to a 20[deg] yaw 
angle and, as separate conditions,
    (ii) Any other combination of landing gear legs not extended and 
with 0[deg] yaw angle.
    (c) For configurations where the engine nacelle is likely to come 
into contact with the ground, the engine pylon or engine mounting must 
be designed so that when it fails due to overloads (assuming the 
overloads to act predominantly in the upward direction and separately, 
predominantly in the aft direction), the failure mode is not likely to 
cause the spillage of enough fuel to constitute a fire hazard.
0
6. Amend Sec.  25.787 by revising paragraph (a) to read as follows:

Sec.  25.787  Stowage compartments.

    (a) Each compartment for the stowage of cargo, baggage, carry-on 
articles, and equipment (such as life rafts), and any other stowage 
compartment, must be designed for its placarded maximum weight of 
contents and for the critical load distribution at the appropriate 
maximum load factors corresponding to the specified flight and ground 
load conditions, and to the emergency landing conditions of Sec.  
25.561(b)(3) where the breaking loose of the contents of such 
compartments could--
    (1) Cause direct injury to occupants;
    (2) Penetrate fuel tanks or lines or cause fire or explosion hazard 
by damage to adjacent systems; or
    (3) Nullify any of the escape facilities provided for use after an 
emergency landing.

If the airplane has a passenger-seating configuration, excluding pilot 
seats, of 10 seats or more, each stowage compartment in the passenger 
cabin, except for under seat and overhead compartments for passenger 
convenience, must be completely enclosed.
* * * * *
0
7. Amend Sec.  25.963 by revising paragraph (d) to read as follows:

Sec.  25.963  Fuel tanks: general.

* * * * *
    (d) Fuel tanks must, so far as it is practicable, be designed, 
located, and installed so that no fuel is released in or near the 
fuselage, or near the engines, in quantities that would constitute a 
fire hazard in otherwise survivable emergency landing conditions, and--
    (1) Fuel tanks must be able to resist rupture and retain fuel under 
ultimate hydrostatic design conditions in which

[[Page 13843]]

the pressure P within the tank varies in accordance with the formula:

P = K[rho]gL

Where

P = fuel pressure at each point within the tank.
[rho] = typical fuel density.
g = acceleration due to gravity.
L = a reference distance between the point of pressure and the tank 
farthest boundary in the direction of loading.
K = 4.5 for the forward loading condition for those parts of fuel 
tanks outside the fuselage pressure boundary.
K = 9 for the forward loading condition for those parts of fuel 
tanks within the fuselage pressure boundary, or that form part of 
the fuselage pressure boundary.
K = 1.5 for the aft loading condition.
K = 3.0 for the inboard and outboard loading conditions for those 
parts of fuel tanks within the fuselage pressure boundary, or that 
form part of the fuselage pressure boundary.
K = 1.5 for the inboard and outboard loading conditions for those 
parts of fuel tanks outside the fuselage pressure boundary.
K = 6 for the downward loading condition.
K = 3 for the upward loading condition.

    (2) For those parts of wing fuel tanks near the fuselage or near 
the engines, the greater of the fuel pressures resulting from 
paragraphs (d)(2)(i) and (d)(2)(ii) of this section must be used:
    (i) The fuel pressures resulting from paragraph (d)(1) of this 
section, and
    (ii) The lesser of the two following conditions:
    (A) Fuel pressures resulting from the accelerations as specified in 
Sec.  25.561(b)(3) considering the fuel tank full of fuel at maximum 
fuel density. Fuel pressures based on the 9.0g forward acceleration may 
be calculated using the fuel static head equal to the streamwise local 
chord of the tank. For inboard and outboard conditions, an acceleration 
of 1.5g may be used in lieu of 3.0g as specified in Sec.  25.561(b)(3), 
and
    (B) Fuel pressures resulting from the accelerations as specified in 
Sec.  25.561(b)(3) considering a fuel volume beyond 85% of the maximum 
permissible volume in each tank using the static head associated with 
the 85% fuel level. A typical density of the appropriate fuel may be 
used. For inboard and outboard conditions, an acceleration of 1.5g may 
be used in lieu of 3.0g as specified in Sec.  25.561(b)(3).
    (3) Fuel tank internal barriers and baffles may be considered as 
solid boundaries if shown to be effective in limiting fuel flow.
    (4) For each fuel tank and surrounding airframe structure, the 
effects of crushing and scraping actions with the ground should not 
cause the spillage of enough fuel, or generate temperatures that would 
constitute a fire hazard under the conditions specified in Sec.  
25.721(b).
    (5) Fuel tank installations must be such that the tanks will not 
rupture as a result of an engine pylon or engine mount or landing gear, 
tearing away as specified in Sec.  25.721(a) and (c).
* * * * *
0
8. Revise Sec.  25.994 to read as follows:

Sec.  25.994  Fuel system components.

    Fuel system components in an engine nacelle or in the fuselage must 
be protected from damage that could result in spillage of enough fuel 
to constitute a fire hazard as a result of a wheels-up landing on a 
paved runway under each of the conditions prescribed in Sec.  
25.721(b).

    Issued in Washington, DC, on February 14, 2013.
Dorenda D. Baker,
Director, Aircraft Certification Service.
[FR Doc. 2013-04812 Filed 2-28-13; 8:45 am]
BILLING CODE 4910-13-P