---
kind: "range"
citation: "14 C.F.R. §§ 25.491–25.509"
title: "14"
from: "25.491"
to: "25.509"
count: 8
url: "https://uscodex.org/cfr/14/25.491..25.509"
---

# §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.


# §25.493. Braked roll conditions.

- (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-state vertical 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)](#b) and [(c)](#c) of this section.
- (e) In the absence of a more rational analysis, the nose gear vertical reaction prescribed in [paragraph (d)](#d) of this section must be calculated according to the following formula:

# §25.495. Turning.


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.


# §25.497. Tail-wheel yawing.

- (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 90° 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.

# §25.499. Nose-wheel yaw and steering.

- (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)](#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)](#b) of this section, except that—
  - (1) A lower drag reaction may be used if an effective drag force of 0.8 times the vertical reaction cannot be reached under any likely loading condition; and
  - (2) The forward acting load at the center of gravity need not exceed the maximum drag reaction on one main gear, determined in accordance with [§ 25.493(b)](/cfr/14/25.493.md?p=b).
- (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.

# §25.503. Pivoting.

- (a) **The airplane is assumed to pivot about one side of the main gear with the brakes on that side locked.** The limit vertical load factor must be 1.0 and the coefficient of friction 0.8.
- (b) The airplane is assumed to be in static equilibrium, with the loads being applied at the ground contact points, in accordance with figure 8 of appendix A.

# §25.507. Reversed braking.

- (a) The airplane must be in a three point static ground attitude. Horizontal reactions parallel to the ground and directed forward must be applied at the ground contact point of each wheel with brakes. The limit loads must be equal to 0.55 times the vertical load at each wheel or to the load developed by 1.2 times the nominal maximum static brake torque, whichever is less.
- (b) For airplanes with nose wheels, the pitching moment must be balanced by rotational inertia.
- (c) For airplanes with tail wheels, the resultant of the ground reactions must pass through the center of gravity of the airplane.

# §25.509. Towing loads.

- (a) The towing loads specified in [paragraph (d)](#d) of this section must be considered separately. These loads must be applied at the towing fittings and must act parallel to the ground. In addition—
  - (1) A vertical load factor equal to 1.0 must be considered acting at the center of gravity;
  - (2) The shock struts and tires must be in their static positions; and
  - (3) **With <I>W</I><I>T</I> as the design ramp weight, the towing load, <I>F</I><I>TOW,</I> is—**
    - (i) 0.3 WT for WT less than 30,000 pounds;
    - (ii) (6WT + 450,000)/70 for WT between 30,000 and 100,000 pounds; and
    - (iii) 0.15 WT for WT over 100,000 pounds.
- (b) For towing points not on the landing gear but near the plane of symmetry of the airplane, the drag and side tow load components specified for the auxiliary gear apply. For towing points located outboard of the main gear, the drag and side tow load components specified for the main gear apply. Where the specified angle of swivel cannot be reached, the maximum obtainable angle must be used.
- (c) The towing loads specified in [paragraph (d)](#d) of this section must be reacted as follows:
  - (1) The side component of the towing load at the main gear must be reacted by a side force at the static ground line of the wheel to which the load is applied.
  - (2) The towing loads at the auxiliary gear and the drag components of the towing loads at the main gear must be reacted as follows:
    - (i) A reaction with a maximum value equal to the vertical reaction must be applied at the axle of the wheel to which the load is applied. Enough airplane inertia to achieve equilibrium must be applied.
    - (ii) The loads must be reacted by airplane inertia.
- (d) **The prescribed towing loads are as follows—**