25.143—General.
(b)
It must be possible to make a smooth transition from one flight condition to any other flight condition without exceptional piloting skill, alertness, or strength, and without danger of exceeding the airplane limit-load factor under any probable operating conditions, including—
(2)
For airplanes with three or more engines, the sudden failure of the second critical engine when the airplane is in the en route, approach, or landing configuration and is trimmed with the critical engine inoperative; and
(c)
The airplane must be shown to be safely controllable and maneuverable with the critical ice accretion appropriate to the phase of flight defined in appendix C, and with the critical engine inoperative and its propeller (if applicable) in the minimum drag position:
(d)
The following table prescribes, for conventional wheel type controls, the maximum control forces permitted during the testing required by paragraph (a) through (c) of this section:
| Force, in pounds, applied to the control wheel or rudder pedals | Pitch | Roll | Yaw |
|---|---|---|---|
| For short term application for pitch and roll control—two hands available for control | 75 | 50 | |
| For short term application for pitch and roll control—one hand available for control | 50 | 25 | |
| For short term application for yaw control | 150 | ||
| For long term application | 10 | 5 | 20 |
(e)
Approved operating procedures or conventional operating practices must be followed when demonstrating compliance with the control force limitations for short term application that are prescribed in paragraph (d) of this section. The airplane must be in trim, or as near to being in trim as practical, in the preceding steady flight condition. For the takeoff condition, the airplane must be trimmed according to the approved operating procedures.
(f)
When demonstrating compliance with the control force limitations for long term application that are prescribed in paragraph (d) of this section, the airplane must be in trim, or as near to being in trim as practical.
(g)
When maneuvering at a constant airspeed or Mach number (up to VFC /MFC ), the stick forces and the gradient of the stick force versus maneuvering load factor must lie within satisfactory limits. The stick forces must not be so great as to make excessive demands on the pilot's strength when maneuvering the airplane, and must not be so low that the airplane can easily be overstressed inadvertently. Changes of gradient that occur with changes of load factor must not cause undue difficulty in maintaining control of the airplane, and local gradients must not be so low as to result in a danger of overcontrolling.
(h)
The maneuvering capabilities in a constant speed coordinated turn at forward center of gravity, as specified in the following table, must be free of stall warning or other characteristics that might interfere with normal maneuvering:
| Configuration | Speed | Maneuvering bank angle in a coordinated turn | Thrust/power setting |
|---|---|---|---|
| Takeoff | V2 | 30° | Asymmetric WAT-Limited. 1 |
| Takeoff | 2V2 XX | 40° | All-engines-operating climb. 3 |
| En route | VFTO | 40° | Asymmetric WAT-Limited. 1 |
| Landing | VREF | 40° | Symmetric for −3° flight path angle. |
| 1 A combination of weight, altitude, and temperature (WAT) such that the thrust or power setting produces the minimum climb gradient specified in § 25.121 for the flight condition. | |||
| 2 Airspeed approved for all-engines-operating initial climb. | |||
| 3 That thrust or power setting which, in the event of failure of the critical engine and without any crew action to adjust the thrust or power of the remaining engines, would result in the thrust or power specified for the takeoff condition at V2, or any lesser thrust or power setting that is used for all-engines-operating initial climb procedures. | |||
(1)
Controllability must be demonstrated with the ice accretion defined in appendix C that is most critical for the particular flight phase;
(2)
It must be shown that a push force is required throughout a pushover maneuver down to a zero g load factor, or the lowest load factor obtainable if limited by elevator power or other design characteristic of the flight control system. It must be possible to promptly recover from the maneuver without exceeding a pull control force of 50 pounds; and
(3)
Any changes in force that the pilot must apply to the pitch control to maintain speed with increasing sideslip angle must be steadily increasing with no force reversals, unless the change in control force is gradual and easily controllable by the pilot without using exceptional piloting skill, alertness, or strength.
(j)
For flight in icing conditions before the ice protection system has been activated and is performing its intended function, it must be demonstrated in flight with the ice accretion defined in appendix C, part II(e) of this part that: