c. Background. This rule was carried forward from § 4b.230(b) of the Civil Air Regulations (CAR) with minor changes. Amendment 25-23 made additional minor changes, but the basic requirements remain the same. Amendment 25-91 made some editorial conforming changes related to dynamic landing conditions and lateral drift.
d. Acceptable Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of Amendment 25-23, 35 FR 5673, April 8, 1970; and Amendment 25-91, 62 FR 40702, July 29, 1997.
e. References. None.
351 - 361. [RESERVED]
362. SECTION 25.477 - LANDING GEAR ARRANGEMENT.
a. Rule Text.
Sections 25.479 through 25.485 apply to airplanes with conventional arrangements of main and nose gears, or main and tail gears, when normal operating techniques are used.
b. Intent of Rule. This rule identifies the landing gear configurations for which these rules apply. It acknowledges that there may be nonconventional arrangements of landing gears.
c. Background. This rule was carried forward from § 4b.230(b)(3) of the Civil Air Regulations (CAR).
d. Acceptable Compliance Methods. Compliance with this requirement may be shown by test(s) and/or analysis.
e. References. Special Conditions (SC) have been issued for non-conventional landing gear arrangements. Reference SC 25-77-NW-4 for the Boeing 747 and reference SC 25-18-WE-7 for the DC-10.
363 - 369. [RESERVED] 363
370. SECTION 25.479 - LEVEL LANDING CONDITIONS.
a. Rule Text.
(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 § 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 § 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 § 25.25.473(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.
[Amdt. 25-23, 35 FR 5673, Apr. 8, 1970; Amdt. 25-91, 62 FR 40702, Jul. 29, 1997
b. Intent of Rule. The purpose of this rule is to ensure that the airplane, landing gear and its supporting structure are able to withstand any load distributions likely to occur in service.
c. Background. This rule was carried forward from § 4b.231 of the Civil Air Regulations (CAR) with minor editorial changes. A minor editorial change was also made by Amendment 25-23.
Amendment 25-91 made some editorial conforming changes related to dynamic landing conditions and lateral drift.
d. Acceptable Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of Amendment 25-23, 35 FR 5673, April 8, 1970; and Amendment 25-91, 62 FR 40702, July 29, 1997.
e. References. None.
371 - 380. [RESERVED]
381. SECTION 25.481 - TAIL DOWN LANDING CONDITIONS.
a. Rule Text.
(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 § 25.473 with -
(1) VL1 equal to VSO (TAS) at the appropriate landing weight and in standard sea level conditions; and
(2) VL2 equal to VSO (TAS) at the appropriate landing weight and altitudes in a hot day temperature of 41 degrees F. above standard.
The combination of vertical and drag components specified in § 25.479(c)(1) and
(3) is considered to be acting at the main wheel axle centerline.
(3) The combination of vertical and drag components is considered to be acting at the main wheel axle centerline.
(b) For the tail-down landing condition for airplanes with tail wheels, the main and tail wheels are assumed to contact the ground simultaneously, in accordance with figure 3 of Appendix A. Ground reaction conditions on the tail wheel are assumed to act - 365
(1) Vertically; and
(2) Up and aft through the axle at 45 degrees to the ground line.
(c) For the tail down landing condition for airplanes with nose wheels, the airplane is assumed to be at an attitude corresponding to either the stalling angle or the maximum angle allowing clearance with the ground by each part of the airplane other than the main wheels, in accordance with figure 3 of Appendix A, whichever is less.
[Amdt. 25-91, 62 FR 40705, Jul. 29, 1997]
b. Intent of Rule. The purpose of this rule is to ensure the airplane, landing gear and its supporting structure are able to withstand any load distributions likely to occur in service.
c. Background. This rule was carried forward from § 4b.232 of the Civil Air Regulations (CAR) with only editorial changes.
d. Acceptable Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of Amendment 25-91, 62 FR 40705, July 29, 1997.
e. References. None.
382 - 389. [RESERVED]
390. SECTION 25.483 - ONE GEAR LANDING CONDITIONS.
a. Rule Text.
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 § 25.479(d)(1), and
(b) Each unbalanced external load must be reacted by airplane inertia in a rational or conservative manner.
[Amdt. 25-91, 62 FR 40705, Jul. 29, 1997]
b. Intent of Rule. The purpose of this rule is to ensure the airplane, landing gear and its supporting structure are able to withstand any load distributions likely to occur in service.
c. Background. This rule was carried forward from § 4b.233 of the Civil Air Regulations (CAR).
The title was changed from “One-wheel landing conditions” to “One-gear landing conditions” in Amendment 25-91.
d. Acceptable Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of Amendment 25-91, 62 FR 40705, July 29, 1997.
e. References. None.
391 - 398. [RESERVED]
399. SECTION 25.485 - SIDE LOAD CONDITIONS.
a. Rule Text.
In addition to § 25.479(d)(2) the following conditions must be considered:
(a) For the side load condition, the airplane is assumed to be in the level attitude with only the main wheels contacting the ground, in accordance with figure 5 of Appendix A.
(b) Side loads of 0.8 of the vertical reaction (on one side) acting inward and 0.6 of the vertical reaction (on the other side) acting outward must be combined with one-half of the maximum vertical ground reactions obtained in the level landing conditions. These loads are assumed to be applied at the ground contact point and to be resisted by the inertia of the airplane. The drag loads may be assumed to be zero.
[Amdt. 25-91, 62 FR 40705, Jul. 29, 1997]
b. Intent of Rule. The purpose of this rule is to ensure the airplane, landing gear and its supporting structure are able to withstand any load distributions likely to occur in service.
c. Background. This rule was carried forward from § 4b.234 of the Civil Air Regulations (CAR) unchanged, except for the title. Amendment 25-91 added the requirement for the lateral drift in determining the side loads.
d. Acceptable Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of Amendment 25-91, 62 FR 40705, July 29, 1997.
e. References. None.
400 - 409. [RESERVED] 367
410. SECTION 25.487 - REBOUND LANDING CONDITION.
a. Rule Text.
(a) The landing gear and its supporting structure must be investigated for the loads occurring during rebound of the airplane from the landing surface.
(b) With the landing gear fully extended and not in contact with the ground, a load factor of 20.0 must act on the unsprung weights of the landing gear. This load factor must act in the direction of motion of the unsprung weights as they reach their limiting positions in extending with relation to the sprung parts of the landing gear.
b. Intent of Rule. The purpose of this rule is to ensure that the landing gear and its supporting structure are capable of withstanding the loads exerted as the unsprung mass of the gear extends to the limits of its stroke during airplane rebound conditions.
c. Background. This rule was carried forward from § 4b.234A of the Civil Air Regulations (CAR).
d. Acceptable Compliance Methods. Compliance with this requirement may be shown by test(s) and/or analysis.
e. References. None.
411 -420. [RESERVED]
421. SECTION 25.489 - GROUND HANDLING CONDITIONS.
a. Rule Text.
Unless otherwise prescribed, the landing gear and airplane structure must be investigated for the conditions in §§ 25.491 through 25.509 with the airplane at the design ramp weight (the maximum weight for ground handling conditions).
No wing lift may be considered. The shock absorbers and tires may be assumed to be in their static position.
[Amdt. 25-23, 35 FR 5673, Apr. 8, 1970] b Intent of Rule. The purpose of this rule is to establish the conditions under which ground handling conditions are to be evaluated.
c. Background. This rule was carried forward from § 4b.235 of the Civil Air Regulations (CAR).
Amendment 25-23 changed "design takeoff weight" to "design ramp weight."
d. Acceptable Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of Amendment 25-23, 35 FR 5673, April 8, 1970.
e. References. None.
422 - 434. [RESERVED]
435. SECTION 25.491 - TAXI, TAKEOFF, AND LANDING ROLL.
a. Rule Text.
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.
[Amdt. 25-91, 62 FR 40702, Jul. 29, 1997]
b. Intent of Rule. The purpose of this rule is to ensure that the landing gear and airplane structure will not be damaged during operations on any rough surfaces (e.g., ramps, taxiways, runways) likely to be encountered in service.
c. Background. This rule was carried forward from § 4b.235(a) of the Civil Air Regulations (CAR). Amendment 25-91 clarified the title and intent to include the taxi and landing roll as well as the takeoff run.
d. Acceptable Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of Amendment 25-91, 62 FR 40702, July 29, 1997.
e. References. None.
436 - 446. [RESERVED] 370
447. SECTION 25.493 - BRAKED ROLL CONDITIONS.
a. Rule Text.
(a) An airplane with a tail wheel is assumed to be in the level attitude with the load on the main wheels, in accordance with figure 6 of Appendix A. The limit vertical load factor is 1.2 at the design landing weight and 1.0 at the design ramp weight. A drag reaction equal to the vertical reaction multiplied by a coefficient of friction of 0.8, must be combined with the vertical ground reaction and applied at the ground contact point.
(b) For an airplane with a nose wheel the limit vertical load factor is 1.2 at the design landing weight, and 1.0 at the design ramp weight. A drag reaction equal to the vertical reaction, multiplied by a coefficient of friction of 0.8, must be combined with the vertical reaction and applied at the ground contact point of each wheel with brakes. The following two attitudes, in accordance with figure 6 of Appendix A, must be considered:
(1) The level attitude with the wheels contacting the ground and the loads distributed between the main and nose gear. Zero pitching acceleration is assumed.
(2) The level attitude with only the main gear contacting the ground and with the pitching moment resisted by angular acceleration.
(c) A drag reaction lower than that prescribed in this section may be used if it is substantiated that an effective drag force of 0.8 times the vertical reaction cannot be attained under any likely loading condition.
(d) An airplane equipped with a nose gear must be designed to withstand the loads arising from the dynamic pitching motion of the airplane due to sudden application of maximum braking force. The airplane is considered to be at design takeoff weight with the nose and main gears in contact with the ground, and with a steady-statevertical load factor of 1.0. The steady-state nose gear reaction must be combined with the maximum incremental nose gear vertical reaction caused by the sudden application of maximum braking force as described in paragraphs (b) and (c) of this section.
(e) In the absence of a more rational analysis, the nose gear vertical reaction prescribed in paragraph (d) of this section must be calculated according to the following formula:
WT Ø fmAE øV = B +N Œ œA + B º A + B + mE ß Where:
VN = Nose gear vertical reaction.
WT = Design takeoff weight.
A = Horizontal distance between the c.g of the airplane and the nose wheel.
B = Horizontal distance between the c.g. of the airplane and the line joining the centers of the main wheels.
E = Vertical height of the c.g. of the airplane above the ground in the 1.0 g. static condition.
µ = Coefficient of friction of 0.80.
f = Dynamic response factor; 2.0 is to be used unless a lower factor is substantiated. In the absence of other information, the dynamic response factor f may be defined by the equation:
( ) - pxf = 1 + exp
Ł
Where:
? is the effective critical damping ratio of the rigid body pitching mode about the main landing gear effective ground contact point.
[Amdt. 25-23, 35 FR 5673, Apr. 8, 1970; Amdt. 25-91, 61 FR 40712, Aug. 5, 1996]
b. Intent of Rule. The purpose of this rule is to ensure that the landing gear and airplane structure are able to withstand any braked roll conditions likely to occur in service.
c. Background. This rule was carried forward from § 4b.235(b) of the Civil Air Regulations (CAR). Amendment 25-23 changed "design takeoff weight" to "design ramp weight.”
ł- 21 x 372
d. Acceptable Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of Amendment 25-23, 35 FR 5673, April 8, 1970.
e. References. None.
448 - 458. [RESERVED]
459. SECTION 25.495 - TURNING.
a. Rule Text.
In the static position, in accordance with figure 7 of Appendix A, the airplane is assumed to execute a steady turn by nose gear steering, or by application of sufficient differential power, so that the limit load factors applied at the center of gravity are 1.0 vertically and 0.5 laterally. The side ground reaction of each wheel must be 0.5 of the vertical reaction.
b. Intent of Rule. The purpose of this rule is to ensure that the landing gear and supporting structure are able to withstand any likely turning conditions.
c. Background. This rule was carried forward from § 4b.235(c) of the Civil Air Regulations (CAR).
d. Acceptable Compliance Methods. Compliance with this requirement may be shown by test(s) and/or analysis.
e. References. None.
460 - 468. [RESERVED]
469. SECTION 25.497 - TAIL-WHEEL YAWING.
a. Rule Text.
(a) A vertical ground reaction equal to the static load on the tail wheel, in combination with a side component of equal magnitude, is assumed.
(b) If there is a swivel, the tail wheel is assumed to be swiveled 90o to the airplane longitudinal axis with the resultant load passing through the axle.
(c) If there is a lock, steering device, or shimmy damper, the tail wheel is also assumed to be in the trailing position with the side load acting at the ground contact point.
b. Intent of Rule. The purpose of this rule is to ensure that the airplane, the tail wheel, and its supporting structure are able to withstand any load likely to be encountered in service.
c. Background. This rule was carried forward from § 4b.235(f) of the Civil Air Regulations (CAR).
d. Acceptable Compliance Methods. Compliance with this requirement may be shown by test(s) and/or analysis.
e. References. None.
470 - 477. [RESERVED]
478. SECTION 25. 499 - NOSE-WHEEL YAW AND STEERING.
a. Rule Text.
(a) A vertical load factor of 1.0 at the airplane center of gravity, and a side component at the nose wheel ground contact equal to 0.8 of the vertical ground reaction at that point are assumed.
(b) With the airplane assumed to be in static equilibrium with the loads resulting from the use of brakes on one side of the main landing gear, the nose gear, its attaching structure, and the fuselage structure forward of the center of gravity must be designed for the following loads:
(1) A vertical load factor at the center of gravity of 1.0.
(2) A forward acting load at the airplane center of gravity of 0.8 times the vertical load on one main gear.
(3) Side and vertical loads at the ground contact point on the nose gear that are required for static equilibrium.
(4) A side load factor at the airplane center of gravity of zero.
(c) If the loads prescribed in paragraph (b) of this section result in a nose gear side load higher than 0.8 times the vertical nose gear load, the design nose gear side load may be limited to 0.8 times the vertical load, with unbalanced yawing moments assumed to be resisted by airplane inertia forces.
(d) For other than the nose gear, its attaching structure, and the forward fuselage structure, the loading conditions are those prescribed in paragraph (b) of this section, except that - 374