From google: Multi engine aircraft usually have their engines off to either side of the fuselage. This means that if one engine fails, the other engine will produce what's called asymmetric thrust (one engine is stronger than the other). This in turn, because it's off to the side of the aircraft will cause it to yaw in the direction of the dead engine. Should the dead engine also have its prop windmilling, it'll cause more drag than if the prop blades were turned parallel to the wind and thus aggravate the situation by not only not producing thrust but actually acting as a speed brake. To counteract this and continue flying straight you'd have to apply the aircraft's rudder. The rudder is an airfoil sticking out into the wind in order to yaw the aircraft, thus if the amount of air flowing over it is reduced, the effectiveness of the rudder is reduced. This has the effect that there's a minimum airspeed (i.e. minimum amount of airflow over the rudder) that's enough to allow the rudder to counteract the asymmetric thrust as well as some other properties like engine torque. This speed is called 𝑣𝑚𝑐 v m c , or minimum controllable airspeed (there are actually two of these, one airborne and one on the ground). If speed drops below this airspeed, the plane will start to increase the yaw away from the live engine, to the point where eventually the outer wing produces more lift than the inner wing and the aircraft rolls over. That's the 𝑣𝑚𝑐 v m c roll. Avoiding it is a matter of keeping the airspeed up to maintain rudder authority, and/or reducing thrust to the live engine while regaining airspeed. Further steps, like identifying the failed engine and feathering its prop, as well as flying with a slight bank towards the live engine should be undertaken as well as part of the recovery. Furthermore it's advisable to never turn into the dead engine, as the live engine will make it harder to stop the turn. Turning into the live engine will make it harder to start the turn, but the engine will help you get out of it. Since the engines usually spin in the same direction, the effect of torque differs, the torque of one engine aggravates the situation, where the torque of the others alleviates it, thus 𝑣𝑚𝑐 v m c is specified as the minimum controllable speed if the latter (known as the critical engine) fails and the prop continues to windmill, i.e. the worst possible aerodynamic scenario in the case of a single engine failure barring an uncontained failure causing damage or otherwise changing the aerodynamic properties of the aircraft.