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Multiengine TrainingMultiengine Training

It's All About Single-Engine Flying

For a pilot intent on continually advancing skills, ratings, and certificates, the natural progression is to earn the private pilot certificate, followed by an instrument rating, and then the multiengine rating. Stepping up to a multiengine airplane typically means stepping up to greater climb, cruise, and payload performance than most singles, and to the perceived safety of two engines and two systems.

Multiengine training also provides new perspectives on planning and decision-making. But two engines can be a double-edged sword. If a pilot of a multiengine airplane is not trained and proficient in handling an engine failure, it can be even more dangerous than a failed engine in a single. That's why most of the training for a multiengine rating concentrates on single-engine emergencies.

Aerodynamics And Flight Characteristics

Multiengine aerodynamics are different from the aerodynamics of single-engine airplanes. Because the propellers are in front of the wings, prop blast increases the airflow over the wing to generate as much as 60 percent of the wing's lift. The prop-blast portion of the wings' lift is relatively independent of angle of attack because the props are in a fixed position. Among other things, this can result in high pitch angles for power-on stalls. It also means that gross or abrupt power changes cause significant changes in lift. Therefore, you should avoid such excessive throttle inputs.

When one engine loses power, the operating engine yaws the airplane substantially because the thrust lines for the two engines run parallel to, but on opposite sides of the aircraft centerline. This means if one engine loses power, the pilot must counteract the resulting yaw with strong pressure on the opposite rudder pedal to restore directional control. That's why the first step toward becoming a safe, competent, multiengine pilot is to learn and understand the aerodynamic and performance problems associated with engine-out flight.

Single-Engine Aerodynamics And Performance

At first thought, you might assume that losing half your total power results in a 50-percent decrease in climb capability. Think again. An airplane's climb capability is related to the power available in excess of that needed for straight and level cruise. In many light twins, which are typically used in multiengine flight training, an engine failure can reduce climb performance 80 percent or more. Depending on aircraft weight and flight conditions, some twins cannot maintain a positive rate of climb-or even maintain altitude-on one engine.

When an engine fails, the aircraft rolls and yaws toward the dead engine. Asymmetric lift-the wing with the failed engine produces less lift-causes most of the roll. Asymmetric thrust, coupled with the increased drag of the dead engine's windmilling prop, causes the yaw.

To recover, you must counter the roll with aileron, counter the yaw with rudder, and feather the windmilling propeller to reduce drag. If your airspeed is too low, you might not have enough aileron and rudder effectiveness (particularly rudder) to correct the problem.

Multiengine performance and control depend on two important airspeeds.

The first is the single-engine best rate of climb speed-VYSE. It's often called "blue line" because this speed is marked on the airspeed indicator with a blue radial line. Although the resulting best rate of climb when flying on one engine might be negative, VYSE gives you the best performance the aircraft can muster.

The second is the minimum control airspeed-VMC. Marked on the airspeed indicator with a red radial line, it is the slowest airspeed at which you can maintain directional control of the airplane if the "critical engine"-the engine whose failure most adversely affects performance or handling-suddenly fails while the other engine is producing takeoff power. Maintaining "directional control" means you won't exceed a 20-degree heading change or a five-degree bank into the operating engine.

In twins with propellers that both rotate clockwise when viewed from the cockpit, the left engine is critical. If this engine fails, the yaw created by the operating right engine is exacerbated by P-factor.

Regardless of how many propellers an airplane has, each one produces P-factor, especially at low airspeeds and high angles of attack. Because the descending blade, which is on the right side of the prop disk when viewed from the cockpit, has a greater angle of attack, it produces more thrust than the ascending blade. This means the thrust line for the left engine is closer to the aircraft centerline than the thrust line for the right engine. The turning tendency will be much greater if the left engine fails.

Light twins with counter-rotating propellers-propellers that turn in opposite directions to each other-don't have a critical engine. Because the left prop turns clockwise and the right prop turns counter-clockwise, the P-factor thrust line from either engine is the same distance from the aircraft centerline.

There are other factors that affect VMCM. The rudder must compensate for the turning tendencies (yaw) caused by the operating engine, the drag of the windmilling propeller, and the aileron drag caused from trying to hold the wings level. As airspeed decreases, the rudder becomes less effective. Below VMC, the rudder can no longer do the job and the aircraft yaws uncontrollably toward the dead engine.

The airplane's center of gravity (CG) also plays a part in single-engine performance. All airplanes rotate around their CG. When the CG is at its aft limit, the rudder's lever arm is short, and the turning moment it creates is reduced. The opposite is true when the CG is at its forward limit, which means VMC can be lower. The airspeed indicator's red radial line notes VMC for the worst-case scenario, an aft CG.

In an airplane with normally aspirated engines (non-turbocharged), VMC decreases as altitude increases because engine power decreases with altitude. If the operating engine does not produce its full rated power, it doesn't generate as much yaw in a single-engine situation. If the engine isn't making full power, then VMC may well be below stall speed.

Single-Engine Training

Multiengine training includes a number of drills, and each is designed to teach a valuable aspect of performance. Many are designed to explore single-engine flight characteristics. Feathering a propeller-turning the blades parallel to the flight path to reduce drag-is an example. Conducted at a high altitude for safety, this drill not only teaches the steps for feathering a propeller, it lets you measure the airplane's actual climb performance at a known density altitude and weight.

The feathering drill also enables you to determine the airplane's zero-thrust setting. For example, you may find that an engine throttled back to 10 inches of manifold pressure reduces windmilling drag essentially to zero, the same as a feathered prop. You'll use this zero-thrust power setting in subsequent training to simulate a feathered prop.

A drag demonstration is another important exercise at a safe altitude. After reducing the power on an engine (usually the critical engine) to zero thrust, you'll fly at VYSE with the landing gear and flaps up and note the climb performance as indicated by the vertical speed indicator (VSI). Next, while maintaining heading and airspeed-and a safe altitude-you'll reduce power from zero thrust to idle and a fully windmilling propeller. Then you'll extend the landing gear and add flaps one notch at a time. With each change, note how the VSI indicates the effect of each drag-producing factor.

This drill demonstrates how much effect each emergency checklist item has if an engine fails. Multiengine students learn that a windmilling propeller usually produces the greatest amount of drag, underscoring the importance of feathering the propeller if an engine fails at low altitude.

The V demonstration teaches you about loss of directional control. After setting the power on the critical engine to zero thrust, you fly at VYSE. Then you slow the airplane and note how its controllability changes. The rudder becomes less effective, and as the airspeed reaches VMC, airflow over the rudder decays to the point where the rudder can no longer counteract the asymmetric thrust.

At this point the nose begins to drift toward the dead engine, accompanied by a roll in the same direction. To recover from VMC loss of control, lower the nose to gain airspeed and reduce power on the operating engine to decrease the yaw. For obvious reasons, you should have plenty of altitude in reserve (3,000 feet AGL minimum) for all VMC demonstrations.

Emergency Procedures

While the exact sequence of emergency procedures varies depending on the aircraft and situation (the airplane's pilot operating handbook gives the specifics, including what to do with the fuel pumps, landing gear, and flaps), some basic rules apply.

If one engine loses power; first, fly the airplane-counteract the yaw and roll-then advance the mixture, props, and throttles to maximum-power. If necessary, pitch the nose down to achieve and maintain blue line airspeed-VYSE.

Your next task is to identify the dead engine. Note which rudder pedal must be pushed to maintain directional control (the pedal you are not pushing is on the same side as the failed engine). Then, verify your identification by retarding the throttle on the dead engine and checking the engine instruments.

Finally, depending on your conditions, phase of flight, and altitude, you must decide whether you can quickly correct whatever caused the engine to lose power, such as fuel starvation, and attempt a restart, or feather the propeller to maximize single-engine performance.

Practicing this procedure will instill how important prompt, yet careful, action is when an engine fails. The best place to practice is at altitude, using 3,000 feet AGL or higher as your simulated runway elevation. At a safe altitude, you configure the twin for takeoff and begin climbing. Your instructor will commence the engine-out drill at some point during your simulated takeoff. Then, you'll learn how quickly the airplane can lose altitude-and how critical proper procedures and airspeeds are.

The single-engine go-around is another training exercise best practiced at altitude. It teaches how much altitude a single-engine twin can lose when it transitions from its landing configuration to its departure configuration. Based on what you learn from this exercise, you probably will choose an altitude, perhaps 300 feet AGL, below which you commit yourself to landing regardless of what happens.

An off-airport landing is a big concern to any pilot, but especially so in a twin because a twin's approach speed is usually faster than that of a single-engine airplane. Although you must maintain VMC or faster to maintain control of the aircraft, remember that VMC decreases when you decrease power on the operating engine. Approaching the touchdown area, you can reduce power on the good engine and slow the aircraft to minimize impact forces at touchdown.

Decision Making And Performance

When the engine on a single-engine airplane fails, your course of action is obvious and uncomplicated. In a light twin, however, your decision-making process is more complex because you have more options. To make the right decisions in an emergency, you must know the airplane's single-engine performance capability and your available options for each phase of flight.

Before you take off in a multiengine airplane you compute a number of performance parameters. These include accelerate/stop distance, accelerate/go distance, and the single-engine climb gradient. Accelerate/stop is the distance it takes to accelerate to liftoff speed and then stop if an engine fails at that precise point. If the runway is long enough to meet the accelerate/stop figure (and it should be if you fly by the rules), then you have the option of aborting the takeoff safely if an engine fails before liftoff.

If the runway isn't long enough to accelerate and stop, the airplane's accelerate/go performance may offer another option. Accelerate/go is the distance it takes to accelerate to liftoff speed, lose an engine, and then continue the takeoff to clear a 50-foot obstacle.

Even if you can clear the obstacle, your ability to continue safely depends on the airplane's single-engine climb gradient. Also, you must compare this gradient to instrument departure procedures if you're flying IFR. Whether you're facing rising terrain or IFR departure requirements, if you have to climb 600 feet per nautical mile, and your airplane's single-engine climb gradient is only 400 feet per nautical mile, you should consider reducing takeoff weight by decreasing the fuel load, leaving passengers or baggage behind, or waiting for more favorable conditions.

With this firmly embedded in your mind, develop a plan of action and say it out loud before takeoff. Spell out what actions you'll take if an engine fails before liftoff, after liftoff, and below some critical altitude. For example, you may decide that if an engine fails after liftoff, beyond the end of the runway, or at any altitude below 300 feet AGL, you will land straight ahead. If the engine fails at an altitude above 300 feet AGL, your single-engine capability may allow you to return to the airport and land.

A thorough captain's briefing should also include a review of emergency procedures, the actions a second pilot (if there is one) will take such as running checklists and making radio calls, and the direction you will circle or depart to avoid obstacles and use of favorable terrain and winds.

You also need to consider a possible enroute engine failure. Again, you must know the aircraft's performance limitations and capabilities. What is its single-engine service ceiling-the highest altitude at which it can extract a 50-foot-per-minute climb on one operating engine? If the minimum enroute altitudes (MEAs) along your route are higher than your airplane's single-engine service ceiling, your prospects are grim if a problem occurs. Flying is about having an out. In this case the out might be taking a more favorable route in the first place.

You also must evaluate cloud heights and bases, as well as icing conditions in terms of the airplane's single-engine service ceiling. While you might be able to fly over ice-filled clouds on two engines, the thought of descending into icing conditions on a single engine may be reason enough to consider another route, a lesser load, or a different day to make the flight.

Single-engine performance plays an important role in your arrival plans. For example, you may be able to fly an instrument approach on one engine, but if conditions make it unlikely the airplane could handle a missed approach or a single-engine go around, you might consider diverting to another airport with higher ceilings, lower terrain, and longer runways.

Flying the pattern or a circling approach from an instrument procedure on a single engine also requires careful planning. A multiengine airplane's relatively high landing approach speed may put you in a higher IFR approach category-which means a higher circling minimum. If a serious performance loss occurs, the airplane may not be able to maintain that higher circling minimum altitude. If the airplane can handle the circle to land, you may want to plan to circle in a direction that gives you a headwind on base. This minimizes the bank angle required for the turn from base to final.

Flying a light twin demands more planning and judgment than flying a single-engine aircraft. The debate surrounding multiengine aircraft and safety continues, but no one argues about the value of good multiengine initial and proficiency training. If not regularly practiced, these fine-honed skills become dull, and your chances of dealing successfully with an emergency diminishes. With a firm understanding of multiengine performance, and recurrent training to keep those engine-out skills sharp, flying a twin is not only safe, but twice the fun.