CS 25.149 Minimum control speed

• ED Decision 2003/2/RM found in: CS-25 Amdt 27 - Large Aeroplanes (Jan 2023)

CS 25.149 Minimum control speed ED Decision 2003/2/RM (See [AMC 25.149](#_DxCrossRefBm1709820832)) (a) In establishing the minimum control speeds required by this paragraph, the method used to simulate critical engine failure must represent the most critical mode of powerplant failure with respect to controllability expected in service. (b) VMC is the calibrated airspeed, at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the aeroplane with that engine still inoperative, and maintain straight flight with an angle of bank of not more than 5°. (c) VMC may not exceed 1·13 VSR with – (1) Maximum available take-off power or thrust on the engines; (2) The most unfavourable centre of gravity; (3) The aeroplane trimmed for take-off; (4) The maximum sea-level take-off weight (or any lesser weight necessary to show VMC); (5) The aeroplane in the most critical take-off configuration existing along the flight path after the aeroplane becomes airborne, except with the landing gear retracted; (6) The aeroplane airborne and the ground effect negligible; and (7) If applicable, the propeller of the inoperative engine – (i) Windmilling; (ii) In the most probable position for the specific design of the propeller control; or (iii) Feathered, if the aeroplane has an automatic feathering device acceptable for showing compliance with the climb requirements of [CS 25.121](#_DxCrossRefBm1709820672). (d) The rudder forces required to maintain control at VMC may not exceed 667 N (150 lbf) nor may it be necessary to reduce power or thrust of the operative engines. During recovery, the aeroplane may not assume any dangerous attitude or require exceptional piloting skill, alertness, or strength to prevent a heading change of more than 20°. (e) VMCG, the minimum control speed on the ground, is the calibrated airspeed during the take-off run at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the aeroplane using the rudder control alone (without the use of nose-wheel steering), as limited by 667 N of force (150 lbf), and the lateral control to the extent of keeping the wings level to enable the take-off to be safely continued using normal piloting skill. In the determination of VMCG, assuming that the path of the aeroplane accelerating with all engines operating is along the centreline of the runway, its path from the point at which the critical engine is made inoperative to the point at which recovery to a direction parallel to the centreline is completed, may not deviate more than 9.1 m (30 ft) laterally from the centreline at any point. VMCG must be established, with – (1) The aeroplane in each take-off configuration or, at the option of the applicant, in the most critical take-off configuration; (2) Maximum available take-off power or thrust on the operating engines; (3) The most unfavourable centre of gravity; (4) The aeroplane trimmed for take-off; and (5) The most unfavourable weight in the range of take-off weights. (See [AMC 25.149(e)](#_DxCrossRefBm1709820835).) (f) (See [AMC 25.149(f)](#_DxCrossRefBm1709820832)) VMCL, the minimum control speed during approach and landing with all engines operating, is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the aeroplane with that engine still inoperative, and maintain straight flight with an angle of bank of not more than 5°. VMCL must be established with – (1) The aeroplane in the most critical configuration (or, at the option of the applicant, each configuration) for approach and landing with all engines operating; (2) The most unfavourable centre of gravity; (3) The aeroplane trimmed for approach with all engines operating; (4) The most unfavourable weight, or, at the option of the applicant, as a function of weight; (5) For propeller aeroplanes, the propeller of the inoperative engine in the position it achieves without pilot action, assuming the engine fails while at the power or thrust necessary to maintain a 3 degree approach path angle; and (6) Go-around power or thrust setting on the operating engine(s). (g) (See [AMC 25.149(g)](#_DxCrossRefBm1709820834)) For aeroplanes with three or more engines, VMCL-2, the minimum control speed during approach and landing with one critical engine inoperative, is the calibrated airspeed at which, when a second critical engine is suddenly made inoperative, it is possible to maintain control of the aeroplane with both engines still inoperative, and maintain straight flight with an angle of bank of not more than 5°. VMCL-2 must be established with – (1) The aeroplane in the most critical configuration (or, at the option of the applicant, each configuration) for approach and landing with one critical engine inoperative; (2) The most unfavourable centre of gravity; (3) The aeroplane trimmed for approach with one critical engine inoperative; (4) The most unfavourable weight, or, at the option of the applicant, as a function of weight; (5) For propeller aeroplanes, the propeller of the more critical engine in the position it achieves without pilot action, assuming the engine fails while at the power or thrust necessary to maintain a 3 degree approach path angle, and the propeller of the other inoperative engine feathered; (6) The power or thrust on the operating engine(s) necessary to maintain an approach path angle of 3o when one critical engine is inoperative; and (7) The power or thrust on the operating engine(s) rapidly changed, immediately after the second critical engine is made inoperative, from the power or thrust prescribed in sub-paragraph (g)(6) of this paragraph to – (i) Minimum power or thrust; and (ii) Go-around power or thrust setting. (h) In demonstrations of VMCL and VMCL-2 – (1) The rudder force may not exceed 667 N (150 lbf); (2) The aeroplane may not exhibit hazardous flight characteristics or require exceptional piloting skill, alertness or strength; (3) Lateral control must be sufficient to roll the aeroplane, from an initial condition of steady straight flight, through an angle of 20° in the direction necessary to initiate a turn away from the inoperative engine(s), in not more than 5 seconds (see [AMC 25.149(h)(3)](#_DxCrossRefBm1709820833)); and (4) For propeller aeroplanes, hazardous flight characteristics must not be exhibited due to any propeller position achieved when the engine fails or during any likely subsequent movements of the engine or propeller controls (see [AMC 25.149(h)(4)](#_DxCrossRefBm1709820832)).