Definition
VMCG is the minimum speed on the ground at which, following the sudden failure of the critical engine during the takeoff roll, the pilot can maintain directional control of a multi-engine airplane using rudder alone, with the remaining engine(s) at takeoff power, and without the use of nosewheel steering. Below this speed, the rudder cannot generate enough yawing force to counter the asymmetric thrust of the operating engine(s).
Plain English
VMCG is the slowest ground speed at which, if one engine quits during the takeoff run, the rudder alone is strong enough to keep the airplane going straight down the runway. Below that speed, the rudder cannot do the job by itself.
Context Anchor
Seen in multiengine takeoff planning, especially when discussing engine failure during the takeoff roll.
Derivation
V stands for velocity (speed), MC for minimum control, and G for ground. So VMCG literally means the minimum control speed while still on the ground — distinguishing it from VMCA, which is the same idea but in the air.
Why Pilots Care
It tells the pilot the earliest safe speed to continue a takeoff after an engine failure without losing directional control on the runway.
Grounding Statement
Below VMCG, the airplane may not have enough airflow over its control surfaces to overcome the turning force from the operating engine.
Intuition Check
VMCG is not a normal rotation speed or a target speed. It is a lower control limit for an engine-failure case while the airplane is still on the ground.
Example Sentence 1
During the takeoff briefing, the captain noted that any engine failure below VMCG would result in an immediate rejected takeoff.
Example Sentence 2
After the right engine failed at 85 knots, the pilot immediately closed both throttles because the aircraft was below VMCG and directional control was being lost.