Competent pilots of light twins will plan the takeoff in sufficient detail to be able to take immediate action if and when one engine fails during the takeoff process. They will be thoroughly familiar with the airplane's performance capabilities and limitations, including accelerate/stop distance, as well as the distance available for takeoff, and will include such factors in their plan of action. For example, if it has been determined that the airplane cannot maintain altitude with one engine inoperative (considering the gross weight and density altitude), the seasoned pilot will be well aware that should an engine fail right after liftoff, an immediate landing may have to be made in the most suitable area available. The competent pilot will make no attempt to maintain altitude at the expense of a safe airspeed.
Consideration will also be given to surrounding terrain, obstructions, and nearby landing areas so that a definite direction of flight can be established immediately if an engine fails at a critical point during the climb after takeoff. It is imperative then, that the takeoff and climb path be planned so that all obstacles between the point of takeoff and the available areas of landing can be cleared if one engine suddenly becomes inoperative.
In addition, a competent light twin pilot knows that the twin engine airplane must be flown with precision if maximum takeoff performance and safety are to be obtained. For example, the airplane must lift off at a specific airspeed, accelerate to a definite climbing airspeed, and climb with maximum permissible power on both engines to a safe single engine maneuvering altitude. In the meantime, if an engine fails, a different airspeed must be attained immediately. This airspeed must be held precisely because only at this airspeed will the pilot be able to obtain maximum performance from the airplane. To understand the factors involved in proper takeoff planning, a further explanation of this critical speed follows, beginning with the liftoff.
The light twin can be controlled satisfactorily while firmly on the ground when one engine fails prior to reaching Vmc during the takeoff roll. This is possible by closing both throttles, by proper use of rudder and brakes, and with many airplanes, by use of nosewheel steering. If the airplane is airborne at less than Vmc, however, and suddenly loses all power on one engine, it cannot be controlled satisfactorily. Thus, on normal takeoffs, liftoff should never take place until the airspeed reaches and exceeds Vmc. The FAA recommends a minimum speed of Vme plus 5 knots before liftoff. From this point, an efficient climb procedure should be followed (Fig. 16-12).
An efficient climb procedure is one in which the airplane leaves the ground slightly above Vmc, accelerates quickly to Vy (best rate of climb speed) and climbs at Vy. The climb at Vy should be made with both engines set to maximum takeoff power until reaching a safe single engine maneuvering altitude (minimum of approximately 500 feet above field elevation or as dictated by airplane performance capability and/or local obstacles). At this point, power may be reduced to the allowable maximum continuous power setting (METO - maximum except takeoff) or less, and any desired enroute climb speed then may be established. The following discussion explains why Vy is recommended for the initial climb.
To improperly trained pilots, the extremes in takeoff technique may suggest "hold it down" to accelerate the airplane to near cruise speed before climbing, or "pull it off" below Vmc and climb as steeply as possible. If one considers the possibility of an engine failure somewhere during the takeoff, neither of these procedures makes much sense for the following reasons: Remember, drag increases as the square of the speed; so for any increase in speed over and above the best rate of climb speed, Vy, the greater the drag and the less climb performance the airplane will have. At 123 knots the drag is approximately one and one-half times greater than it is at 100 knots. At 141 knots the drag is doubled, and at 200 knots the drag is approximately four times as great as at 100 knots. While the drag is increasing as the square of the velocity (V x V), the power required to maintain a velocity increases as the cube of that velocity (V x V x V).
In the event of engine failure, a pilot who uses excessive speed on takeoff will discover suddenly that all energy produced by the engines has been converted into speed. Improperly trained pilots often believe that the excess speed can always be converted to altitude, but this theory is not valid. Available power is only wasted in accelerating the airplane to an unnecessary speed. Also, experience has shown that an unexpected engine failure so surprises the unseasoned pilot that proper reactions are extremely lagging. By the time the initial shock wears off and the pilot is ready to take control of the situation, the excess speed has dissipated and the airplane is still barely off the ground. From this low altitude, the pilot would still have to climb, with an engine inoperative, to whatever height is needed to clear all obstacles and get back to the approach end of the runway. Excess speed cannot be converted readily to the altitude or distance necessary to reach a landing area safely.
In contrast, however, an airplane will fly in level flight much easier than it will climb. Therefore, if the total energy of both engines is initially converted to enough height above the ground to permit clearance of all obstacles while in level flight (safe maneuvering altitude), the problem is much simpler in the event an engine fails. If some extra height is available, it usually can be traded for velocity or gliding distance when needed.
Simply stated then, altitude is more essential to safety after takeoff than is excess airspeed. On the other hand, trying to gain height too fast in the takeoff also can be very dangerous because of control problems. If the airplane has just become airborne and the airspeed is at or below Vmc when an engine fails, the pilot could avoid a serious accident by retarding both throttles immediately. If this action is not taken immediately, the pilot will be unable to control the airplane.
Consequently, the pilot always should keep one hand on the control wheel (when not operating hand controlled nose steering) and the other hand on the throttles throughout the takeoff roll. The airplane should remain on the ground until adequate speed is reached so that a smooth transition to the proper climb speed can be made. THE AIRPLANE SHOULD NEVER LEAVE THE GROUND BEFORE Vmc IS REACHED. Preferably, Vmc + 5 knots should be attained.
If an engine fails before leaving the ground it is advisable to discontinue the takeoff and STOP. If an engine fails after liftoff, the pilot will have to decide immediately whether to continue flight, or to close both throttles and land. However, waiting until the engine failure occurs is not the time for the pilot to plan the correct action. The action must be planned before the airplane is taxied onto the runway. The plan of action must consider the density altitude, length of the runway, weight of the airplane, and the airplane's accelerate/stop distance, and accelerate/go distance under these conditions. Only on the basis of these factors can the pilot decide intelligently what course to follow if an engine should fail. When the flight crew consists of two pilots, it is recommended that the pilot in command brief the second pilot on what course of action will be taken should the need arise.
To reach a safe single engine maneuvering altitude as safely and quickly as possible, the climb with all engines operating must be made at the proper airspeed. That speed should provide for:
1. Good control of the airplane in case an engine fails.
2. Quick and easy transition to the single engine best rate of climb speed if one engine fails.
3. A fast rate of climb to attain an altitude which permits adequate time for analyzing the situation and making decisions.
To make a quick and easy transition to the single engine best rate of climb speed in case an engine fails, the pilot should climb at some speed greater than Vyse. If an engine fails at less than Vyse, it would be necessary for the pilot to lower the nose to increase the speed to Vyse in order to obtain the best climb performance. If the airspeed is considerably less than this speed, it might be necessary to lose valuable altitude to increase the speed to Vyse. Another factor to consider is the loss of airspeed that may occur because of erratic pilot technique after a sudden, unexpected power loss. Consequently, the normal initial two engine climb speed should not be less than Vy.
In summary then, the initial climb speed for a normal takeoff with both engines operating should permit the attainment of a safe single engine maneuvering altitude as quickly as possible; it should provide for good control capabilities in the event of a sudden power loss on one engine; and it should be a speed sufficiently above Vyse to permit attainment of that speed quickly and easily in the event power is suddenly lost on one engine. The only speed that meets all of these requirements for a normal takeoff is the best rate of climb speed with both engines operating (Vy).