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CS 25.149
Minimum control speed
(See AMC 25.149)
(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.
(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 20º.
(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; The aeroplane trimmed for take-off; and
(5) The most unfavourable weight in the range of take-off weights. (See AMC 25.149(e).)
The only thing they have in common is some of the spelling!