[Federal Register Volume 62, Number 145 (Tuesday, July 29, 1997)]
[Rules and Regulations]
[Pages 40702-40706]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-19040]



[[Page 40701]]

_______________________________________________________________________

Part VI





Department of Transportation





_______________________________________________________________________



Federal Aviation Administration



_______________________________________________________________________



14 CFR Part 25



Revised Structural Loads Requirements for Transport Category Airplanes; 
Final Rule

  Federal Register  / Vol. 62, No. 145 / Tuesday, July 29, 1997 / Rules 
and Regulations  

[[Page 40702]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. 28312; Amdt. No. 25-91]
RIN 2120-AF70


Revised Structural Loads Requirements for Transport Category 
Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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

SUMMARY: This amendment revises the structural loads design 
requirements of the Federal Aviation Regulations (FAR) for transport 
category airplanes by incorporating changes developed in cooperation 
with the Joint Aviation Authorities (JAA) of Europe and the Aviation 
Rulemaking Advisory Committee (ARAC). This action makes some of the 
requirements more rational and eliminates differences between current 
U.S. and European requirements that impose unnecessary costs on 
airplane manufacturers. These changes are intended to achieve common 
airworthiness standards and language between the requirements of the 
U.S. regulations and the Joint Aviation Requirements (JAR) of Europe 
while maintaining at least the level of safety provided by the current 
regulations and industry practices.

EFFECTIVE DATE: August 28, 1997.

FOR FURTHER INFORMATION CONTACT: James Haynes, Airframe and Propulsion 
Branch, ANM-112, Transport Airplane Directorate, Aircraft Certification 
Service, FAA, 1601 Lind Avenue, SW., Renton, WA 98055-4056; telephone 
(206) 227-2131.

SUPPLEMENTARY INFORMATION:

Background

    The manufacturing, marketing and certification of transport 
airplanes is increasingly an international endeavor. In order for U.S. 
manufacturers to export transport airplanes to other countries the 
airplane must be designed to comply, not only with the U.S. 
airworthiness requirements for transport airplanes (14 CFR part 25), 
but also with the transport airworthiness requirements of the countries 
to which the airplane is to be exported, unless the importing country 
accepts the aircraft without findings of compliance with specified 
regulations.
    The European countries have developed a common airworthiness code 
for transport category airplanes that is administered by the JAA. This 
code is the result of a European effort to harmonize the various 
airworthiness codes of the European countries and is called the Joint 
Aviation Requirements (JAR)-25. It was developed in a format similar to 
14 CFR part 25. Many other countries have airworthiness codes that are 
aligned closely to part 25 or to JAR-25, or they use these codes 
directly for their own certification purposes.
    Although JAR-25 is very similar to part 25, there are differences 
in methodologies and criteria that often result in the need to address 
the same design objective with more than one kind of analysis or test 
in order to satisfy both part 25 and JAR airworthiness codes. These 
differences result in additional costs to the transport airplane 
manufacturers and additional costs to the U.S. and foreign authorities 
that must continue to monitor compliance with different airworthiness 
codes.
    In 1988, the FAA, in cooperation with the JAA and other 
organizations representing the U.S. and European aerospace industries, 
began a process to harmonize the airworthiness requirements of the 
United States and the European authorities. The objective was to 
achieve common requirements for the certification of transport category 
airplanes without a substantive change in the level of safety provided 
by the regulations and industry practices. Other airworthiness 
authorities such as Transport Canada have also participated in this 
process.
    In 1992, the harmonization effort was undertaken by the Aviation 
Rulemaking Advisory Committee (ARAC). A working group of industry and 
government structural loads specialists of Europe, the United States, 
and Canada was chartered by notice in the Federal Register (58 FR 
13819, March 15, 1993) to harmonize the design loads sections of 
Subpart C of part 25. The bulk of the harmonization tasks for Subpart C 
were completed by the working group and recommendations were submitted 
to FAA by letter dated February 2, 1995. The FAA concurred with the 
recommendations and proposed them in Notice of Proposed Rulemaking 
(NPRM) No. 95-14; which was published in the Federal Register on August 
29, 1995 (60 FR 44998).
    In establishing a design requirement for the nose gear, its 
attaching structure and the forward fuselage structure, Sec. 25.499(e) 
continues to require consideration of positioning the nose gear in any 
steerable position. The term ``any'' is continued from the current 
regulation. The term, and the requirements of the section, are 
understood in the engineering and regulated communities to require 
demonstration that the nose gear and associated structures will sustain 
the applicable loads throughout the full range of nose gear positions.

Discussion of Comments

    Comments were received from transport airplane manufacturers, 
industry associations and foreign airworthiness authorities. All of the 
commenters express support for the proposals in Notice No. 95-14 
although a few make some recommendations for changes. One comment 
believes the changes proposed for Sec. 25.415 could be a burden to some 
applicants with airplanes that are derived from models that were 
certified to earlier amendment levels of the FAR and JAR. To provide 
relief for these derivative airplanes, the commenter proposes a change 
to paragraph (b) of Sec. 25.415 which would allow the use of 
``realistic'' aerodynamic hinge moment coefficients for control 
surfaces in lieu of the prescribed coefficients of paragraph (b). The 
FAA does not agree that there is likely to be a burden for derivative 
airplanes since the proposed rule applies to new designs. In addition, 
the design gust speed does not create an increased requirement over 
existing design requirements. Part 24 and JAR-25 were identical in 
using 88 feet per second (about 52 knots) in defining hinge moment for 
ground gust conditions. However, JAR Sec. 25.519 prescribes a 65 knot 
wind speed for ground gusts during jacking and tie-down, and 
specifically requires application of those gusts to control surfaces. 
As a result, aircraft designs already have to meet the 65 knot rather 
than the 52 knot requirement. The ARAC recommends, with FAA and JAA 
concurrence, that ground gusts on control surfaces be addressed in just 
one section, Sec. 25.415, so Notice No. 95-14 proposes to revise this 
section to achieve the same effect as the Sec. 25.519 of JAR-25 by 
incorporating the 65-knot wind speed into Sec. 25.415. The net effect 
is that there is no change in the ground gust speed requirement for 
control surfaces over that already required by JAR-25.
    Furthermore, the use of rational aerodynamic hinge moment 
coefficients would necessitate a rational ground gust speed as well, 
and the 65 knot design gust speed is not necessarily a rational design 
speed for ground gusts. Jet blasts in airport operations and normal 
storm conditions often exceed 65 knots but service history has shown 
that the 65 knot design speed when combined with the conservative 
prescribed hinge moments of paragraph (b) provides a satisfactory 
design.

[[Page 40703]]

    One commenter recommends that the formulation of the requirement 
for hinge moments in Sec. 25.415 be changed to show the 65 knot wind 
speed explicitly rather than embedding this value into the multiplying 
constant. The FAA agrees that this has merit since the connection 
between the 65 knot wind speed of Secs. 25.415 and 25.519 could 
otherwise be missed in any future rulemaking actions. The rule is 
adopted with a change to show the 65 knot wind speed explicitly in the 
formula for control surface hinge moments.
    One commenter points out that the proposed revision to paragraph 
(a) of Sec. 25.481 references paragraphs 25.479(c)(1) and (2) for 
vertical and drag load conditions and that these latter paragraphs, as 
proposed, no longer specify those conditions. Notice 95-14 proposes to 
express the substance of Sec. 25.479(c)(1) and (2) in more general 
terms in Sec. 25.473(c). The commenter is correct. The rule is adopted 
with a change to delete the incorrect references.

Regulatory Evaluation Summaries

Regulatory Evaluation, Regulatory Flexibility Determination, and Trade 
Impact Assessment

    Changes to Federal regulations must undergo several economic 
analyses. First, Executive Order 12866 directs 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 requires agencies to analyze the 
economic effect of regulatory changes on small entities. Third, the 
Office of Management and Budget directs agencies to assess the effects 
of regulatory changes on international trade. In conducting these 
analyses, the FAA has determined that this rule:
    (1) Will generate benefits that justify its costs and is not a 
``significant regulatory action'' as defined in the Executive Order; 
(2) is not significant as defined in DOT's Regulatory Policies and 
Procedures; (3) will not have a significant impact on a substantial 
number of small entities; and (4) will not constitute a barrier to 
international trade. These analyses, available in the docket, are 
summarized below.

Regulatory Evaluation Summary

    Depending on airplane design, the rule could result in additional 
compliance costs for some manufacturers. If manufacturers choose to 
design to and justify a VD-VC magin of 0.05 Mach, 
there will be an increase in analysis costs of approximately $145,000 
per certification. The requirement in Sec. 25.473 to consider 
structural flexibility in the analysis of landing loads and the 
increase in the factor on the maximum static reaction on the nose gear 
vertical force in Sec. 25.499 could add compliance costs, but the FAA 
estimates that these will be negligible.
    The rule will also result in cost savings. Revisions in the 
conditions in which unchecked pitch maneuvers are investigated could 
reduce certification costs by as much as $10,000 per certification. The 
FAA estimates that the change in the speed margin between VB 
and VC from a fixed margin to a margin variable with 
altitude could result in substantial, though unquantified, cost savings 
to some manufacturers. Manufacturers that design small transport 
category airplanes with direct mechanical rudder control systems could 
realize a savings as a result of the modification in the rudder control 
force limit in Sec. 25.351. No comments were received on the costs or 
cost savings resulting from these changes.
    The primary benefit of the rule will be the cost savings associated 
with harmonization of the FAR with the JAR. In order to sell airplanes 
in a global marketplace, manufacturers usually certify their products 
under the FAR and the JAR. The cost savings from reducing the resources 
necessary to demonstrate compliance with non-harmonized design load 
requirements will outweigh any incremental costs of the rule, resulting 
in a net cost savings. These savings will be realized by U.S. 
manufacturers that market airplanes in JAA countries as well as by 
manufacturers in JAA countries that market airplanes in the U.S.
    The change to Sec. 25.335(b)(2) in the minimum speed margin for 
atmospheric conditions from 0.05 Mach to 0.07 Mach could produce safety 
benefits. The increase in the margin between VD/
MD and VC/MC is more conservative and 
will standardize training across international lines. Crews could 
cross-train and cross-fly and this standardization will enhance safety 
as well as result in more efficient training.

Regulatory Flexibility Determination

    The Regulatory Flexibility Act of 1980 (RFA) was enacted by 
Congress to ensure that small entities are not unnecessarily and 
disproportionally burdened by Federal regulations. The RFA requires a 
Regulatory Flexibility Analysis if a proposed or final rule would have 
a significant economic impact, either detrimental or beneficial, on a 
substantial number of small entities. FAA Order 2100.14A, Regulatory 
Flexibility Criteria and Guidance, establishes threshold cost values 
and small entity standards for complying with RFA review requirements 
in FAA rulemaking actions. The Order defines ``small entities'' in 
terms of size threshold, ``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.
    Order 2100.14A specifies a size threshold for classification as a 
small manufacturer as 75 or fewer employees. Since none of the 
manufacturers affected by this rule has 75 or fewer employees and any 
costs of the rule will be negligible, the rule will not have a 
significant economic impact on a substantial number of small 
manufacturers.

International Trade Impact Assessment

    The rule will not constitute a barrier to international trade, 
including the export of U.S. airplanes to foreign markets and the 
import of foreign airplanes into the U.S. Because the rule will 
harmonize with the JAR, it would, in fact, lessen restraints on trade.

Federalism Implications

    The regulations amended herein do not have a 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. Thus, in 
accordance with Executive Order 12612, it is determined that this rule 
does not have sufficient federalism implications to warrant the 
preparation of a Federalism Assessment.

International Compatibility

    In keeping with U.S. obligations under the Convention on 
International Civil Aviation, it is FAA policy to comply with 
International Civil Aviation Organization (ICAO) standards and 
recommended practices to the maximum extent practicable. The FAA has 
determined that this rule does not conflict with any international 
agreement of the United States.

Paperwork Reduction Act

    In accordance with the Paperwork Reduction Act of 1980 (Pub. L. 96-
511), there are no requirements for information collection associated 
with this rule.

[[Page 40704]]

Conclusion

    Because these changes to the structural loads requirements do not 
result in any substantial economic costs, the FAA has determined that 
this rule will not be significant under Executive Order 12866. Because 
there has not been significant public interest in this issue, the FAA 
has determined that this action is not significant under DOT Regulatory 
Policies and Procedures (44 FR 11034; February 25, 1979). In addition, 
since there are no small entities affected by this rulemaking, the FAA 
certifies that the rule will not have a significant economic impact, 
positive or negative, on a substantial number of small entities under 
the criteria of the Regulatory Flexibility Act, since none will be 
affected. A copy of the regulatory evaluation prepared for this project 
may be examined in the Rules Docket or obtained from the person 
identified under the caption FOR FURTHER INFORMATION CONTACT.

List of Subjects in 14 CFR Part 25

    Air transportation, Aircraft, Aviation safety, Safety.

The Amendments

    Accordingly, the Federal Aviation Administration (FAA) amends 14 
CFR part 25 of the Federal Aviation Regulations as follows:

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

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

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

    2. Section 25.331 is amended by revising the introductory text of 
paragraph (c) and paragraph (c)(1) to read as follows:


Sec. 25.331  Symmetric maneuvering conditions.

* * * * *
    (c) Pitch maneuver conditions. The conditions specified in 
paragraphs (c)(1) and (2) of this section must be investigated. The 
movement of the pitch control surfaces may be adjusted to take into 
account limitations imposed by the maximum pilot effort specified by 
Sec. 25.397(b), control system stops and any indirect effect imposed by 
limitations in the output side of the control system (for example, 
stalling torque or maximum rate obtainable by a power control system.)
    (1) Maximum pitch control displacement at VA. The 
airplane is assumed to be flying in steady level flight (point 
A1, Sec. 25.333(b)) and the cockpit pitch control is 
suddenly moved to obtain extreme nose up pitching acceleration. In 
defining the tail load, the response of the airplane must be taken into 
account. Airplane loads that occur subsequent to the time when normal 
acceleration at the c.g. exceeds the positive limit maneuvering load 
factor (at point A2 in Sec. 25.333(b)), or the resulting 
tailplane normal load reaches its maximum, whichever occurs first, need 
not be considered.
* * * * *
    3. Section 25.335 is amended by revising paragraphs (a)(2) and 
(b)(2) to read as follows:


Sec. 25.335  Design airspeeds.

* * * * *
    (a) * * *
    (2) Except as provided in Sec. 25.335(d)(2), VC may not 
be less than VB + 1.32 U REF (with 
UREF as specified in Sec. 25.341(a)(5)(i)). However 
VC need not exceed the maximum speed in level flight at 
maximum continuous power for the corresponding altitude.
* * * * *
    (b) * * *
    (2) The minimum speed margin must be enough to provide for 
atmospheric variations (such as horizontal gusts, and penetration of 
jet streams and cold fronts) and for instrument errors and airframe 
production variations. These factors may be considered on a probability 
basis. The margin at altitude where MC is limited by 
compressibility effects must not less than 0.07M unless a lower margin 
is determined using a rational analysis that includes the effects of 
any automatic systems. In any case, the margin may not be reduced to 
less than 0.05M.
* * * * *
    4. Section 25.345 is amended by revising paragraph (d) to read as 
follows:


Sec. 25.345  High lift devices.

* * * * *
    (d) The airplane must be designed for a maneuvering load factor of 
1.5 g at the maximum take-off weight with the wing-flaps and similar 
high lift devices in the landing configurations.
    5. Section 25.351 is revised to read as follows:


Sec. 25.351  Yaw maneuver conditions.

    The airplane must be designed for loads resulting from the yaw 
maneuver conditions specified in paragraphs (a) through (d) of this 
section at speeds from VMC to VD. Unbalanced 
aerodynamic moments about the center of gravity must be reacted in a 
rational or conservative manner considering the airplane inertia 
forces. In computing the tail loads the yawing velocity may be assumed 
to be zero.
    (a) With the airplane in unaccelerated flight at zero yaw, it is 
assumed that the cockpit rudder control is suddenly displaced to 
achieve the resulting rudder deflection, as limited by:
    (1) The control system on control surface stops; or
    (2) A limit pilot force of 300 pounds from VMC to 
VA and 200 pounds from VC/MC to 
VD/MD, with a linear variation between 
VA and VC/MC.
    (b) With the cockpit rudder control deflected so as always to 
maintain the maximum rudder deflection available within the limitations 
specified in paragraph (a) of this section, it is assumed that the 
airplane yaws to the overswing sideslip angle.
    (c) With the airplane yawed to the static equilibrium sideslip 
angle, it is assumed that the cockpit rudder control is held so as to 
achieve the maximum rudder deflection available within the limitations 
specified in paragraph (a) of this section.
    (d) With the airplane yawed to the static equilibrium sideslip 
angle of paragraph (c) of this section, it is assumed that the cockpit 
rudder control is suddenly returned to neutral.
    6. Section 25.363 is amended by revising the heading and paragraph 
(a) to read as follows:


Sec. 25.363  Side load on engine and auxiliary power unit mounts.

    (a) Each engine and auxiliary power unit mount and its supporting 
structure must be designed for a limit load factor in lateral 
direction, for the side load on the engine and auxiliary power unit 
mount, at least equal to the maximum load factor obtained in the yawing 
conditions but not less than--
    (1) 1.33; or
    (2) One-third of the limit load factor for flight condition A as 
prescribed in Sec. 25.333(b).
* * * * *
    7. Section 25.371 is revised to read as follows:


Sec. 25.371  Gyroscopic loads.

    The structure supporting any engine or auxiliary power unit must be 
designed for the loads including the gyroscopic loads arising from the 
conditions specified in Secs. 25.331, 25.341(a), 25.349, 25.351, 
25.473, 25.479, and 25.481, with the engine or auxiliary power unit at 
the maximum rpm appropriate to the condition. For the purposes of 
compliance with this section, the pitch maneuver in Sec. 25.331(c)(1) 
must be carried out until the positive limit maneuvering load factor 
(point A2 in Sec. 25.333(b)) is reached.

[[Page 40705]]

    8. Section 25.415 is amended by revising paragraph (a)(2) to read 
as follows:


Sec. 25.415  Ground gust conditions.

    (a) * * *
    (2) The control system stops nearest the surfaces, the control 
system locks, and the parts of the systems (if any) between these stops 
and locks and the control surface horns, must be designed for limit 
hinge moments H, in foot pounds, obtained from the formula, 
H=.0034KV2cS, where--

V=65 (wind speed in knots)
K=limit hinge moment factor for ground gusts derived in paragraph 
(b) of this section.
c=mean chord of the control surface aft of the hinge line (ft);
S=area of the control surface aft of the hinge line (sq ft);
* * * * *
    9. Section 25.473 is revised to read as follows:


Sec. 25.473  Landing load conditions and assumptions.

    (a) For the landing conditions specified in Sec. 25.479 to 
Sec. 25.485 the airplane is assumed to contact the ground--
    (1) In the attitudes defined in Sec. 25.479 and Sec. 25.481;
    (2) With a limit descent velocity of 10 fps at the design landing 
weight (the maximum weight for landing conditions at maximum descent 
velocity); and
    (3) With a limit descent velocity of 6 fps at the design take-off 
weight (the maximum weight for landing conditions at a reduced descent 
velocity).
    (4) The prescribed descent velocities may be modified if it is 
shown that the airplane has design features that make it impossible to 
develop these velocities.
    (b) Airplane lift, not exceeding airplane weight, may be assumed 
unless the presence of systems or procedures significantly affects the 
lift.
    (c) The method of analysis of airplane and landing gear loads must 
take into account at least the following elements:
    (1) Landing gear dynamic characteristics.
    (2) Spin-up and springback.
    (3) Rigid body response.
    (4) Structural dynamic response of the airframe, if significant.
    (d) The limit inertia load factors corresponding to the required 
limit descent velocities must be validated by tests as defined in 
Sec. 25.723(a)
    (e) The coefficient of friction between the tires and the ground 
may be established by considering the effects of skidding velocity and 
tire pressure. However, this coefficient of friction need not be more 
than 0.8.
    10. Section 25.479 is revised to read as follows:


Sec. 25.479  Level landing conditions.

    (a) In the level attitude, the airplane is assumed to contact the 
ground at forward velocity components, ranging from VL1 to 
1.25 VL2 parallel to the ground under the conditions 
prescribed in Sec. 25.473 with--
    (1) VL1 equal to VS0 (TAS) at the appropriate 
landing weight and in standard sea level conditions; and
    (2) VL2 equal to VS0 (TAS) at the appropriate 
landing weight and altitudes in a hot day temperature of 41 degrees F. 
above standard.
    (3) The effects of increased contact speed must be investigated if 
approval of downwind landings exceeding 10 knots is requested.
    (b) For the level landing attitude for airplanes with tail wheels, 
the conditions specified in this section must be investigated with the 
airplane horizontal reference line horizontal in accordance with Figure 
2 of Appendix A of this part.
    (c) For the level landing attitude for airplanes with nose wheels, 
shown in Figure 2 of Appendix A of this part, the conditions specified 
in this section must be investigated assuming the following attitudes:
    (1) An attitude in which the main wheels are assumed to contact the 
ground with the nose wheel just clear of the ground; and
    (2) If reasonably attainable at the specified descent and forward 
velocities, an attitude in which the nose and main wheels are assumed 
to contact the ground simultaneously.
    (d) In addition to the loading conditions prescribed in paragraph 
(a) of this section, but with maximum vertical ground reactions 
calculated from paragraph (a), the following apply:
    (1) The landing gear and directly affected attaching structure must 
be designed for the maximum vertical ground reaction combined with an 
aft acting drag component of not less than 25% of this maximum vertical 
ground reaction.
    (2) The most severe combination of loads that are likely to arise 
during a lateral drift landing must be taken into account. In absence 
of a more rational analysis of this condition, the following must be 
investigated:
    (i) A vertical load equal to 75% of the maximum ground reaction of 
Sec. 25.473 must be considered in combination with a drag and side load 
of 40% and 35% respectively of that vertical load.
    (ii) The shock absorber and tire deflections must be assumed to be 
75% of the deflection corresponding to the maximum ground reaction of 
Sec. 25.473(a)(2). This load case need not be considered in combination 
with flat tires.
    (3) The combination of vertical and drag components is considered 
to be acting at the wheel axle centerline.
    11. Section 25.481 is amended by revising paragraph (a) 
introductory text and by designating the undesignated text following 
paragraph (a)(2) as paragraph (a)(3) and revising it to read as 
follows:

Sec. 25.481  Tail down landing conditions.

    (a) In the tail-down attitude, the airplane is assumed to contact 
the ground at forward velocity components, ranging from VL1 
to VL2 parallel to the ground under the conditions 
prescribed in Sec. 25.473 with--
    (1) * * *
    (2) * * *
    (3) The combination of vertical and drag components is considered 
to be acting at the main wheel axle centerline.
* * * * *
    12. Section 25.483 is amended by revising the heading, introductory 
text, and paragraph (a) to read as follows:


Sec. 25.483  One-gear landing conditions.

    For the one-gear landing conditions, the airplane is assumed to be 
in the level attitude and to contact the ground on one main landing 
gear, in accordance with Figure 4 of Appendix A of this part. In this 
attitude--
    (a) The ground reactions must be the same as those obtained on that 
side under Sec. 25.479(d)(1), and
* * * * *
    13. Section 25.485 is amended by adding the introductory text to 
read as follows:

Sec. 25.485  Side load conditions.

    In addition to Sec. 25.479(d)(2) the following conditions must be 
considered:
* * * * *
    14. Section 25.491 is revised to read as follows:


Sec. 25.491  Taxi, takeoff and landing roll.

    Within the range of appropriate ground speeds and approved weights, 
the airplane structure and landing gear are assumed to be subjected to 
loads not less than those obtained when the aircraft is operating over 
the roughest ground that may reasonably be expected in normal 
operation.
    15. Section 25.499 is amended by revising the heading and paragraph 
(e) to read as follows:


Sec. 25.499  Nose-wheel yaw and steering.

* * * * *

[[Page 40706]]

    (e) With the airplane at design ramp weight, and the nose gear in 
any steerable position, the combined application of full normal 
steering torque and vertical force equal to 1.33 times the maximum 
static reaction on the nose gear must be considered in designing the 
nose gear, its attaching structure, and the forward fuselage structure.
    16. Section 25.561 is amended by revising paragraph (c) to read as 
follows:


Sec. 25.561  General.

* * * * *
    (c) For equipment, cargo in the passenger compartments and any 
other large masses, the following apply:
    (1) Except as provided in paragraph (c)(2) of this section, these 
items must be positioned so that if they break loose they will be 
unlikely to:
    (i) Cause direct injury to occupants;
    (ii) Penetrate fuel tanks or lines or cause fire or explosion 
hazard by damage to adjacent systems; or
    (iii) Nullify any of the escape facilities provided for use after 
an emergency landing.
    (2) When such positioning is not practical (e.g. fuselage mounted 
engines or auxiliary power units) each such item of mass shall be 
restrained under all loads up to those specified in paragraph (b)(3) of 
this section. The local attachments for these items should be designed 
to withstand 1.33 times the specified loads if these items are subject 
to severe wear and tear through frequent removal (e.g. quick change 
interior items).
* * * * *
    Issued in Washington D.C. on July 14, 1997.
Barry L. Valentine,
Acting Administrator.
[FR Doc. 97-19040 Filed 7-28-97; 8:45 am]
BILLING CODE 4910-13-M