Flight Operations Briefing Notes Takeoff and Departure Operations Understanding Takeoff Speeds

Flight Operations Briefing Notes
Understanding Takeoff Speeds

Flight Operations Briefing Notes Takeoff and Departure Operations Understanding Takeoff Speeds 
I  Introduction 
Pilots are used to calculating takeoff speeds and, therefore, understand the operational significance of V1, VR, and V2. However, they are slightly less familiar with the definitions of VMU, VMCG, and VMCA.. Takeoff speeds are a safety key element for takeoff, and enable pilot situational awareness and decision-making in this very dynamic situation. The use of erroneous takeoff speeds can lead to tail strikes, high-speed rejected takeoffs or initial climb with degraded performance. The objective of the following Flight Operations Briefing Notes is to provide, from an operational perspective, an overall review of takeoff speeds, and of the factors that affect the calculation and use of V speeds. 
II  Background Information This section is provided as a takeoff speeds refresher. However, additional information is also available in the Airbus “Getting to Grips with Aircraft Performance” brochure. 
II.1  Control Speeds and associated Takeoff Speeds The efficiency of such aerodynamic surfaces as the wings (for lift), the rudder, the ailerons, and the elevators, depends on adequate airflow speed. This airflow speed determines the minimum takeoff speeds. 

Flight Operations Briefing Notes
Understanding Takeoff Speeds
VMCG (Velocity of Minimum Control on Ground)
During the takeoff roll, it is of utmost importance to know the minimum speed at which the aircraft will remain controllable, in the event of an engine failure on ground. This is because, in such a case, and if the takeoff is continued, only the rudder will be able to counteract the yaw moment that is generated by asymmetric engine(s) thrust.
Per regulations, the minimum speed at which an aircraft is defined to be “controllable” (lateral excursion lower than 30 feet) after an engine failure on ground, is referred to as VMCG (Velocity of Minimum Control on Ground).
VMCG mainly depends on:
. Engine(s) thrust
. Pressure altitude.
If a failure occurs before reaching VMCG, the takeoff must be interrupted to maintain control of the aircraft.
Note: Steering is not used during certification flight tests. However, in real life operations, steering would be helpful in controlling the aircraft.

Figure 1
Ground Control after Engine Failure

V1: Decision Speed

V1 is the maximum speed at which a rejected takeoff can be initiated, in the event of an emergency. Additional information on this “Go/No-Go” decision can be found in the Flight Operations Briefing Note entitled: “Revisiting the Stop or Go Decision”.
V1 is also the minimum speed at which a pilot can continue a takeoff after an engine failure.
If an engine failure is detected after V1, the takeoff must be continued. This implies that the aircraft must be controllable on ground. Therefore, V1 is always greater than VMCG.
　
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