Modern design, engineering, and manufacturing technology have produced outstanding multiengine airplanes. Their utility and acceptance have more than fulfilled the expectations of their builders. As a result of this rapid development and increasing use, many pilots have found it necessary to make the transition from single engine airplanes to those with two or more engines and complex equipment. Good basic flying habits formed during earlier training, and carried forward to these new sophisticated airplanes, will make this transition relatively easy, but only if the transition is properly directed.
The following paragraphs discuss several important operational differences which must be considered in progressing from the simpler single engine airplanes to the more complex multiengine airplanes.
1. Preflight Preparation. The increased complexity of multiengine airplanes demands the conduct of a more systematic inspection of the airplane before entering the cockpit, and the use of a more complete and appropriate checklist for each ground and flight operation.
Preflight visual inspections of the exterior of the airplane should be conducted in accordance with the manufacturer's operating manual. The procedures set up in these manuals usually provide for a comprehensive inspection, item by item in an orderly sequence, to be covered on a complete check of the airplane. The transitioning pilot should have a thorough briefing in this inspection procedure, and should understand the reason for checking each item.
2. Checklists. Essentially, all modern multiengine airplanes are provided with checklists, which may be very brief or extremely comprehensive. A pilot who desires to operate a modern multiengine airplane safely has no alternative but to use the checklist pertinent to that particular airplane. Such a checklist normally is divided under separate headings for common operations, such as before starting, takeoff, cruise, in range, landing, system malfunctions, and engine out operation.
The transitioning pilot must realize that multiengine airplanes characteristically have many more controls, switches, instruments, and indicators. Failure to position or check any of these items may have much more serious results than would a similar error in a single engine airplane. Only definite procedures, systematically planned and executed can ensure safe and efficient operation. The cockpit checklist provided by the manufacturer in the operations manual must be used, with only those modifications made necessary by subsequent alterations or additions to the airplane and its equipment.
In airplanes which require a copilot, or in which a second pilot is available, it is good practice for the second pilot to read the checklist, and the pilot in command to check each item by actually touching the control or device and repeating the instrument reading or prescribed control position in question, under the careful observation of the pilot calling out the items on the checklist (Fig. 16-2).
Even when no copilot is present, the pilot should form the habit of touching, pointing to, or operating each item as it is read from the checklist.
In the event of an in-flight emergency, the pilot should be sufficiently familiar with emergency procedures to take immediate action instinctively to prevent more serious situations. However, as soon as circumstances permit, the emergency checklist should be reviewed to ensure that all required items have been checked.
3. Taxiing. The basic principles of taxiing which apply to single engine airplanes are generally applicable to multiengine airplanes. Although ground operation of multiengine airplanes may differ in some respects from the operation of single engine airplanes, the taxiing procedures also vary somewhat between those airplanes with a nosewheel and those with a tailwheel type landing gear. With either of these landing gear arrangements, the difference in taxiing multiengine airplanes that is most obvious to a transitioning pilot is the capability of using power differential between individual engines to assist in directional control.
Tailwheel type multiengine airplanes are usually equipped with tailwheel locks which can be used to advantage for taxiing in a straight line especially in a crosswind. The tendency to weathervane can also be neutralized to a great extent in these airplanes by using more power on the upwind engine, with the tailwheel lock engaged and the brakes used as necessary.
On nosewheel type multiengine airplanes, the brakes and throttles are used mainly to control the momentum, and steering is done principally with the steerable nosewheel. The steerable nosewheel is usually actuated by the rudder pedals, or in some airplanes by a separate hand operated steering mechanism.
No airplane should be pivoted on one wheel when making sharp turns, as this can damage the landing gear, tires, and even the airport pavement. All turns should be made with the inside wheel rolling, even if only slightly.
Brakes may be used, as with any airplane, to start and stop turns while taxiing. When initiating a turn though, they should be used cautiously to prevent overcontrolling of the turn. Brakes should be used as lightly as practicable while taxiing to prevent undue wear and heating of the brakes and wheels, and possible loss of ground control. When brakes are used repeatedly or constantly they tend to heat to the point that they may either lock or fail completely. Also, tires may be weakened or blown out by extremely hot brakes. Abrupt use of brakes in multiengine as well as single engine airplanes, is evidence of poor pilot technique; it not only abuses the airplane, but may even result in loss of control.
Due to the greater weight of multiengine airplanes, effective braking is particularly essential. Therefore, as the airplane begins to move forward when taxiing is started, the brakes should be tested immediately by depressing each brake pedal. If the brakes are weak, taxiing should be discontinued and the engines shut down.
Looking outside the cockpit while taxiing becomes even more important in multiengine airplanes. Since these airplanes are usually somewhat heavier, larger, and more powerful than single engine airplanes they often require more time and distance to accelerate or stop, and provide a different perspective for the pilot. While it usually is not necessary to make S-turns to observe the taxiing path, additional vigilance is necessary to avoid obstacles, other aircraft, or bystanders.
4. Use of Trim Tabs. The trim tabs in a multiengine airplane serve the same purpose as in a single engine airplane, but their function is usually more important to safe and efficient flight. This is because of the greater control forces, weight, power, asymmetrical thrust with one engine inoperative, range of operating speeds, and range of center of gravity location. In some multiengine airplanes it taxes the pilot's strength to overpower an improperly set elevator trim tab on takeoff or go-around. Many fatal accidents have occurred when pilots took off or attempted a go-around with the airplane trimmed "full nose up" for the landing configuration. Therefore, prompt retrimming of the elevator trim tab in the event of an emergency go-around from a landing approach is essential to the success of the flight.
Multiengine airplanes should be retrimmed in flight for each change of attitude, airspeed, power setting, and loading. Without such changes, constant application of firm forces on the flight controls is necessary to maintain any desired flight attitude.
5. Normal Takeoffs. There is virtually little difference between a takeoff in a multiengine airplane and one in a single engine airplane. The controls of each class of airplane are operated the same; the multiple throttles of the multiengine airplane normally are treated as one compact power control and can be operated simultaneously with one hand.
In the interest of safety it is important that the flight crew have a plan of action to cope with engine failure during takeoff. It is recommended that just prior to takeoff the pilot in command review, or brief the copilot on takeoff procedures. This briefing should consist of at least the engine out minimum control speed, best all engine rate of climb speed, best single engine rate of climb speed, and what procedures will be followed if an engine fails prior to reaching minimum control speed. This latter speed is the minimum airspeed at which safe directional control can be maintained with one engine inoperative and one engine operating at full power.
The multiengine (light twin) pilot's primary concern on all takeoffs is the attainment of the engine out minimum control speed prior to liftoff. Until this speed is achieved, directional control of the airplane in flight will be impossible after the failure of an engine, unless power is reduced immediately on the operating engine. If an engine fails before the engine out minimum control speed is attained, THE PILOT HAS NO CHOICE BUT TO CLOSE BOTH THROTTLES, ABANDON THE TAKEOFF, AND DIRECT COMPLETE ATTENTION TO BRINGING THE AIRPLANE TO A SAFE STOP ON THE GROUND.
The multiengine (light twin) pilot's second concern on takeoff is the attainment of the single engine best rate of climb speed in the least amount of time. This is the airspeed which will provide the greatest rate of climb when operating with one engine out and feathered (if possible), or the slowest rate of descent. In the event of an engine failure, the single engine best rate of climb speed must be held until a safe maneuvering altitude is reached, or until a landing approach is initiated. When takeoff is made over obstructions the best angle of climb speed should be maintained until the obstacles are passed, then the best rate of climb maintained.
The engine out minimum control speed and the single engine best rate of climb speed are published in the airplane's FAA approved flight manual, or the Pilot's Operating Handbook. These speeds should be considered by the pilot on every takeoff, and ar discussed in later sections of this chapter.
6. Crosswind Takeoffs. Crosswind takeoffs are performed in multiengine airplanes in basically the same manner as those in single engine airplanes. Less power may be used on the downwind engine to overcome the tendency of the airplane to weathervane at the beginning of the takeoff, and then full power applied to both engines as the airplane accelerates to a speed where better rudder control is attained.
7. Stalls and Flight Maneuvers at Critically Slow Speeds. As with single engine airplanes, the pilot should be familiar with the stall and minimum controllability characteristics of the multiengine airplane being flown. The larger and heavier airplanes have slower responses in stall recoveries and in maneuvering at critically slow speeds due to their greater weight. The practice of stalls in multiengine airplanes, therefore, should be performed at altitudes sufficiently high to allow recoveries to be completed at least 3,000 feet above the ground.
It usually is inadvisable to execute full stalls in multiengine airplanes because of their relatively high wing loading; therefore, practice should be limited to approaches to stalls (imminent), with recoveries initiated at the first physical indication of the stall. As a general rule, however, full stalls in multiengine airplanes are not necessarily violent or hazardous.
The pilot should become familiar with imminent stalls entered with various flap settings, power settings, and landing gear positions. It should be noted that the extension of the landing gear will cause little difference in the stalling speed, but it will cause a more rapid loss of speed in a stall approach.
Power on stalls should be entered with both engines set at approximately 65 percent power. Takeoff power may be used provided the entry speed is not greater than the normal liftoff speed. Stalls in airplanes with relative low power loading using maximum climb power usually result in an excessive nose high attitude and make the recovery more difficult.
Because of possible loss of control, stalls with one engine inoperative or at idle power and the other developing effective power are not to be performed during multiengine flight tests nor should they be practiced by applicants for multiengine class ratings.
The same techniques used in recognition and avoidance of stalls of single engine airplanes apply to stalls in multiengine airplanes. The transitioning pilot must become familiar with the characteristics which announce an approaching or imminent stall, the indicated airspeed at which it occurs, and the proper technique for recovery.
The increase in pitch attitude for stall entries should be gradual to prevent momentum from carrying the airplane into an abnormally high nose up attitude with a resulting deceptively low indicated airspeed at the time the stall occurs. It is recommended that the rate of pitch change result in a 1 knot per second decrease in airspeed. In all stall recoveries the controls should be used very smoothly, avoiding abrupt pitch changes. Because of high gyroscopic stresses, this is particularly true in airplanes with extensions between the engines and propellers.
Smooth control manipulation is particularly a requisite of flight at minimum or critically slow airspeeds. As with all piloting operations, a smooth technique permits the development of a more sensitive feel of the controls with a keener sense of stall anticipation. Flight at minimum or critically slow airspeeds gives the pilot an understanding of the relationship between the attitude of an airplane, the feel of its control reactions and the approach to an actual stall.
Generally, the technique of flight at minimum airspeeds is the same in a multiengine airplane as it is in a single engine airplane. Because of the additional equipment in the multiengine airplane, the transitioning pilot has more to do and observe, and the usually slower control reaction requires better anticipation. Care must be taken to observe engine temperature indications for possible overheating, and to make necessary power adjustments smoothly on both engines at the same time.
8. Approaches and Landings. Multiengine airplanes characteristically have steeper gliding angles because of their relatively high wing loading, and greater drag of wing flaps and landing gear when extended. For this reason, power is normally used throughout the approach to shallow the approach angle and prevent a high rate of sink.
The accepted technique for making stabilized landing approaches is to reduce the power to a predetermined setting during the arrival descent so the appropriate landing gear extension speed will be attained in level flight as the downwind leg of the approach pattern is entered (Fig. 16-3). With this power setting, the extension of the landing gear (when the airplane is on the downwind leg opposite the intended point of touchdown) will further reduce the airspeed to the desired traffic pattern airspeed. The manufacturer's recommended speed should be used throughout the pattern. When practicable, however, the speed should be compatible with other air traffic in the traffic pattern. When within the maximum speed for flap extension, the flaps may be partially lowered if desired, to aid in reducing the airspeed to traffic pattern speed. The angle of bank normally should not exceed 30 degrees while turning onto the legs of the traffic pattern.
The prelanding checklist should be completed by the time the airplane is on base leg so that the pilot may direct full attention to the approach and landing. In a power approach, the airplane should descend at a stabilized rate, allowing the pilot to plan and control the approach path to the point of touchdown. Further extension of the flaps and slight adjustment of power and pitch should be accomplished as necessary to establish and maintain a stabilized approach path. Power and pitch changes during approaches should in all cases be smooth and gradual.
The airspeed of the final approach should be as recommended by the manufacturer; if a recommended speed is not furnished, the airspeed should be not less than the engine out best rate of climb speed (Vyse) until the landing is assured, because that is the minimum speed at which a single engine go-around can be made if necessary. IN NO CASE SHOULD THE APPROACH SPEED BE LESS THAN THE CRITICAL ENGINE OUT MINIMUM CONTROL SPEED. If an engine should fail suddenly and it is necessary to make a go-around from a final approach at less than that speed, a catastrophic loss of control could occur. As a rule of thumb, after the wing flaps are extended the final approach speed should be gradually reduced to 1.3 times the power off stalling speed (1.3 Vs0).
The roundout or flare should be started at sufficient altitude to allow a smooth transition from the approach to the landing attitude. The touchdown should be smooth, with the airplane touching down on the main wheels and the airplane in a tail low attitude, with or without power as desired. The actual attitude at touchdown is very little different in nosewheel and tailwheel type airplanes. Although airplanes with nosewheels should touch down in a tail low attitude, it should not be so low as to drag the tail on the runway. On the other hand, since the nosewheel is not designed to absorb the impact of the full weight of the airplane, level or nose low attitudes must be avoided.
Directional control on the rollout should be accomplished primarily with the rudder and the steerable nosewheel, with discrete use of the brakes applied only as necessary from crosswinds or other factors.
9. Crosswind Landings. Crosswind landing technique in multiengine airplanes is very little different from that required in single engine airplanes. The only significant difference lies in the fact that because of the greater weight, more positive drift correction must be maintained before the touchdown.
It should be remembered that FAA requires that most airplanes have satisfactory control capabilities when landing in a direct crosswind of not more than 20 percent of the stall speed (0.2 Vs0). Thus, an airplane with a power off stalling speed of 60 knots has been designed for a maximum direct crosswind of 12 knots (0.2 x 60) on landings. Though skillful pilots may successfully land in much stronger winds, poor pilot technique is apt to cause serious damage in even more gentle winds. Some light and medium multiengine airplanes have demonstrated satisfactory control with crosswind components greater than 0.2 Vs0. If this has been done it will be noted in the Pilot's Operating Handbook under operations limitations.
The two basic methods of making crosswind landings, the slipping approach (wing low) and the crabbing approach may be combined. These are discussed in the chapter on Approaches and Landings.
The essential factor in all crosswind landing procedures is touching down without drift, with the heading of the airplane parallel to its direction of motion. This will result in minimum side loads on the landing gear.
10. Go-Around Procedure. The complexity of modern multiengine airplanes makes a knowledge of and proficiency in emergency go-around procedures particularly essential for safe piloting. The emergency go-around during a landing approach is inherently critical because it is usually initiated at a very low altitude and airspeed with the airplane's configuration and trim adjustments set for landing.
Unless absolutely necessary, the decision to go around should not be delayed to the point where the airplane is ready to touch down (Fig. 16-4). The more altitude and time available to apply power, establish a climb, retrim, and set up a go-around configuration, the easier and safer the maneuver becomes. When the pilot has decided to go around, immediate action should be taken without hesitation, while maintaining positive control and accurately following the manufacturer's recommended procedures.
Go-around procedures vary with different airplanes, depending on their weight, flight characteristics, flap and retractable gear systems, and flight performance. Specific procedures must be learned by the transitioning pilot from the Pilot's Operating Handbook, which should always be available in the cockpit.
There are several general go-around procedures which apply to most airplanes, and are worth pointing out:
a. When the decision to go around is reached, takeoff power should be applied immediately and the descent stopped by adjusting the pitch attitude to avoid further loss of altitude.
b. The flaps should be retracted only in accordance with the procedure prescribed in the airplane's operating manual. Usually this will require the flaps to be positioned as for takeoff.
c. After a positive rate of climb is established the landing gear should be retracted, best rate of climb airspeed obtained and maintained, and the airplane trimmed for this climb. The procedure for a normal takeoff climb should then be followed.
The basic requirements of a successful go-around, then, are the prompt arrest of the descent, and the attainment and maintenance of the best rate of climb airspeed.
At any time the airspeed is faster than the flaps up stalling speed, the flaps may be retracted completely without losing altitude if simultaneously the angle of attack is increased sufficiently. At critically slow airspeeds, however, retracting the flaps prematurely or suddenly can cause a stall or an unanticipated loss of altitude. Rapid or premature retraction of the flaps should be avoided on go-arounds, especially when close to the ground, because of the careful attention and exercise of precise pilot technique necessary to prevent a sudden loss of altitude. It generally will be found that retracting the flaps only halfway or to the specified approach setting decreases the drag a relatively greater amount than it decreases the lift.
The FAA approved Airplane Flight Manual or Pilot's Operating Handbook should be consulted regarding landing gear and flap retraction procedures because in some installations simultaneous retraction of the gear and flaps may increase the flap retraction time, and full flaps create more drag than the extended landing gear.