What is the definition of VMCG?

VMCG is the minimum speed on the ground at which directional control can be maintained with the critical engine inoperative and take-off thrust on the remaining engines.

What does VMCA represent?

VMCA is the minimum speed in the air at which the aircraft can be controlled directionally with the critical engine failed and take-off power on the operative engine(s).

How do VMCG and VMCA differ?

VMCG applies to ground roll during take-off, while VMCA applies after lift-off in the air.

Why do both VMCG and VMCA decrease with higher pressure altitude?

Both decrease because reduced air density leads to less asymmetric thrust, making control easier at lower speeds.

Why is it important to know VMCG and VMCA for take-off planning?

Knowing these speeds ensures safe directional control during an engine failure, both on the ground and in the air.

VMCG and VMCA Explained

Medium4 min readPerformance Aeroplanes

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Why this matters

Knowing VMCG and VMCA allows pilots to maintain control during an engine failure at the most vulnerable stages of take-off, directly impacting safety and the ability to keep the aircraft on the runway or under control in the air.

VMCG and VMCA are minimum control speeds critical to safe take-off and climb in multi-engine aircraft. VMCG (minimum control speed on the ground) defines the lowest speed at which directional control can be maintained during the take-off roll with a critical engine failed, while VMCA (minimum control speed in the air) is the lowest speed at which the aircraft remains controllable in flight under similar conditions. Both speeds ensure the pilot can keep the aircraft straight and safe following an engine failure, but they apply to different phases of take-off.

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Explanation

VMCG Explained

VMCG stands for minimum control speed on the ground. It is the lowest speed, during the take-off run, at which the aircraft can be kept straight on the runway using only aerodynamic controls (rudder, ailerons, nosewheel steering not considered) after the failure of the critical engine. Below VMCG, the asymmetric thrust from the operating engine(s) cannot be countered, and the aircraft may veer off the runway. VMCG is determined with take-off power set, the most adverse weight and centre of gravity, and the aircraft in the take-off configuration.

VMCA Explained

VMCA is the minimum control speed in the air, just after lift-off, with the critical engine inoperative. It is the lowest speed at which the aircraft can be kept straight and level with a maximum of 5° bank towards the operating engine(s), using aerodynamic controls only. VMCA is established with take-off power on the operative engine(s), the most unfavourable centre of gravity, and the aircraft in the take-off configuration. If speed falls below VMCA after engine failure, the aircraft may become uncontrollable in yaw and roll.

Difference Between VMCG and VMCA

VMCG applies during the ground roll before lift-off; VMCA applies once airborne.
VMCG is usually lower than VMCA, but both are limiting speeds for take-off safety.
Both speeds decrease with increasing altitude and temperature, as engine thrust (and thus asymmetric force) reduces in thinner air.

Operational Relevance

V1 (take-off decision speed) must never be less than VMCG, ensuring that if an engine fails before V1, the aircraft can be controlled on the ground.
VR (rotation speed) must not be less than 1.05 × VMCA, ensuring control is maintained immediately after lift-off.

Understanding these speeds is crucial for safe take-off performance calculations and for handling engine failures during critical phases of flight.

The essentials

Key Points

VMCG is the minimum control speed on the ground after a critical engine failure.

VMCA is the minimum control speed in the air with a critical engine inoperative.

VMCG ensures directional control on the runway; VMCA ensures control after lift-off.

Both speeds are calculated with the most adverse weight and centre of gravity.

VMCG and VMCA decrease with higher altitude and temperature due to reduced thrust.

V1 must not be less than VMCG; VR must not be less than 1.05 × VMCA.

Exceeding these speeds is essential for safe take-off and climb performance.

Watch out

Exam Traps & Typical Mistakes

Confusing VMCG (ground) with VMCA (airborne) and applying the wrong speed to the wrong phase.

Assuming VMCG and VMCA are unaffected by altitude or temperature—both decrease as air density drops.

Believing nosewheel steering is included in VMCG determination—it's not; only aerodynamic controls count.

Thinking V1 can be less than VMCG—V1 must always be equal to or greater than VMCG.

Overlooking that VR must be at least 1.05 × VMCA, not simply equal to VMCA.

Test yourself

Example Exam Questions

Question 2Easy

How does an increase in pressure altitude affect VMCA?

Question 3Medium

What is the primary difference between VMCG and VMCA?

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