The first indication that an engine has quit will be a yaw and roll toward the failed engine. When flying in IMC, this rolling and yawing motion toward the dead engine will be displayed on the Attitude Indicator and Heading Indicator. The Ball on the Turn Coordinator will deflect toward the operating engine. 

Loss of the left engine on a conventional twin will have more adverse aerodynamic effects than the loss of the right engine or the loss of either engine on a twin-engine aircraft with counter-rotating props. For this reason the left engine is considered the critical engine.

Pitch

The partial loss of accelerated slipstream over the tailplane results in less negative lift on the tail, causing the aircraft to pitch down. T-tail aircraft will be less affected.

Roll

The lack of induced airflow over the wing reduces its lift, causing it to drop. Further loss of lift occurs due to the drag created by the windmilling propeller. The resulting imbalance in lift causes the aircraft to roll toward the inoperative engine. When the left engine fails in a conventional twin, this rolling tendency is exacerbated due to torque from the right engine. When the right engine fails, torque from the left engine helps to mitigate the right rolling tendency. 

Yaw

Asymmetrical thrust combined with the drag of the windmilling prop produces a yaw toward the dead engine. This yawing motion also results in a loss of lift since the flight path is no longer parallel to the longitudinal axis and the fuselage blocks some of the airflow over the wing. In a conventional twin, the right engine exerts more of a yawing tendency than the left engine because it's P-Factor works farther from the centerline of the aircraft, creating a longer lever arm. Therefore, failure of the left (critical) engine would produce a greater yawing tendency than a failure of the right engine. The rudder will also be less effective in counteracting the yawing tendency when the critical engine fails since it will no longer benefit from the spiraling slipstream. Spiraling slipstream produced by the left engine moves inward toward the longitudinal axis, creating additional airflow past the rudder. Spiraling slipstream produced by the right engine does not enhance rudder effectiveness because the airflow moves out and away from the longitudinal axis.

The following acronym summarizes the aerodynamic effects with the critical engine inoperative:

P-factor — causes a greater yawing tendency toward the left since the right engine’s center of thrust is farther from the longitudinal axis and has a longer arm

A-ccelerated Slipstream — causes a greater rolling tendency toward the left because of the induced lift generated by the propwash. P-factor produces more thrust on the right side of each propeller, placing each wing’s center of lift to the right of the engine. The right wing’s center of lift is further from the longitudinal axis than the left wing’s center of lift, giving it a longer lever arm and a stronger left rolling tendency.

S-piraling Slipstream — causes more yaw toward the left due to decreased rudder effectiveness and greater pitch downward due to reduced negative lift on the tail—airflow from the left engine moves inward toward the longitudinal axis and increases rudder effectiveness and negative lift on the horizontal stabilizer; airflow from the right engine moves away from the longitudinal axis and does not significantly increase rudder effectiveness or negative lift on the horizontal stabilizer.

T-orque — causes a roll toward the left, or toward the dead engine—when the right engine fails, torque from the left engine helps raise the right wing.

Performance

The climb performance of any aircraft is determined by the thrust horsepower available beyond what is required to maintain level flight. An engine failure in a light twin will cut total thrust horsepower by 50%. However, climb performance will typically be reduced by 80-90% or more. For example, if the thrust horsepower required to maintain level flight for a twin engine aircraft with two 200 horsepower engines is 175, an additional 225 horsepower will normally be available for climb. But the loss of an engine will leave only 25 horsepower available for climb (200 - 175). This weak climb capability will be exacerbated by the increase in drag (and resulting loss of lift) from the dead engine and the deflection of the control surfaces needed to compensate for it. 

Accelerate-Stop Distance is the maximum distance required (from brake release) to accelerate to Vr (with both engines at full power), experience an engine failure, and then decelerate to a complete stop using maximum braking. This distance will depend upon the density altitude, wind, and aircraft weight. After making these calculations during the pre-flight planning, pilots will need to make sure that the runway length is at least equal to the Accelerate-Stop Distance.

Accelerate-Go Distance is the distance required (from brake release) to accelerate to Vr, experience an engine failure, then continue until reaching an altitude of 50 feet AGL. 

Continuing a single-engine takeoff and crashing at 70 knots will result in four times the impact G-forces as running off the runway and hitting an obstacle at 35 knots. If the landing gear has not been retracted at the point of engine failure, it is better to reject the takeoff—even if airborne. Trying to retract the landing gear and flaps while attempting a climb on one engine can result in altitude losses of as much as 500 feet.

Vmc—With one engine inoperative, this is the lowest airspeed at which directional control can be maintained (the red line on the airspeed indicator). It is the point at which the rudder can no longer counteract the yawing tendency toward the failed engine. Loss of airspeed below Vmc will cause the aircraft to roll toward the inoperative engine, resulting in a loss of control. This is called Vmc Roll. Stall speed remains unchanged as density altitude increases, but Vmc gradually decreases due to decreased engine performance and reduced propeller efficiency. Vmc may vary due to changes in weight and balance, density altitude, power settings and aircraft configuration. For every degree of bank less than 5 degrees, Vmc could increase up to 3 knots (banking more than 5 degrees will likely decrease Vmc, but performance will be adversely affected).

Vyse—This is the best single-engine rate of climb speed (the blue line on the airspeed indicator). It is also the slowest rate of descent if you can't maintain altitude.

The Single Engine Service Ceiling is the maximum density altitude at which Vyse will produce a 50'/min climb with the critical engine inoperative. 

The Single Engine Absolute Ceiling is the maximum density altitude the aircraft can attain or drift down to with the critical engine inoperative

Procedures

The pilot’s first indication that an engine has failed will be a roll and yaw toward the dead engine. The RPM and Manifold Pressure gauges may still read close to normal since the relative wind will drive the constant speed propeller at the set RPM which in turn will drive the engine. Firm rudder pressure will be needed to control the yawing tendency and this will indicate which engine is still operative. If rudder pressure is applied on the side of the failed engine there will be little or no resistance (Dead Foot = Dead Engine). The rolling tendency should be controlled by banking the airplane 3-5 degrees toward the good engine. This configuration produces a zero sideslip and requires less rudder pressure to maintain a streamlined flightpath. Compensating only with the rudder results in a small detriment to performance but a significant increase in Vmc; compensating only with the ailerons decreases Vmc, but performance will suffer due to increased drag and adverse yaw. Achieving zero sideslip by using the right combination of rudder and aileron will minimize Vmc and maximize performance. Instead of centering the ball on the inclinometer as in normal coordinated flight, the ball should be offset 1/2 ball width toward the operating engine while banking 3-5 degrees in the same direction (Raise the dead and split the ball).

While correcting for yaw and roll, pilots should simultaneously maximize power by pushing both throttles all the way forward. Once aircraft control has been established, the suspected inoperative engine can be verified by reducing the throttle on each engine independently while watching for changes in RPM and Manifold Pressure. The dead engine will not show any change as the throttle is reduced. At this point the POH should be consulted to implement the correct procedures for restarting the engine. If it cannot be restarted, then it should be feathered to minimize drag and shut down. Flight should be continued at Vyse to the nearest suitable landing area.