Besides learning the proper use of the controls for normal energy management tasks, pilots should be equipped with the ability to identify, assess, and mitigate two major risks associated with mismanagement of energy: 1) unwanted deviations from the desired energy state; and 2) unintentional, irreversible deceleration and/or sink rate causing depletion of mechanical energy. The first risk involves unintended altitude-airspeed deviations (refer to Managing Energy Errors section). The second risk entails unforeseen, continuous airspeed and/or altitude loss coupled with little or no available excess power in a given flight condition (refer to Preventing Irreversible Deceleration and/or Sink Rate section).

Two Energy Management Scenarios Two flight scenarios illustrate the two major risks associated with failure to manage the airplane’s energy state and how a pilot can identify, assess, and mitigate those risks.

Scenario 1 Unintentionally descending below the desired glideslope on final approach to landing and failing to make the proper correction. [Figure 4-9] To bring the airplane back to the desired glideslope, should the pilot pitch up, throttle up, or both?

Scenario 2 Flying toward rising terrain and not being able to fly up and over it before impacting terrain. [Figure 4-10] Note the rising terrain all along the departure corridor. What can the pilot do to prevent an impending crash?

For both scenarios, this section will demonstrate how proper energy management can provide the pilot with the skill to manage the associated risks and avoid tragic results.

Managing Energy Errors In addition to learning effective techniques for maintaining stabilized path-speed profiles (e.g., tracking the glideslope) and transitioning from one profile to another during flight (e.g., leveling off from a descent), pilots should develop skills for managing unwanted deviations in vertical flight path and airspeed—returning the airplane to its target energy state. Since many inflight “energy crises” start as undetected, ignored or poorly managed path-speed deviations, pilots need the skills to recognize, correct and prevent these deviations.

Although the intention is to correct altitude and airspeed deviations, the pilot is always acting on the airplane’s energy state. Thus, it is important to translate altitude-speed deviations into energy errors. [Figure 4-11] Because the airplane’s total energy is distributed over altitude and airspeed, there are two types of energy errors: 1) total energy errors and 2) energy distribution errors.

state (5).

Monitoring the altimeter (or other flight path reference) and airspeed indicator allows the pilot to distinguish these two types of energy errors. In total energy errors, the airplane has too much energy (blue boxes) or too little energy (red boxes). The pilot will notice that altitude and speed deviate in the same direction (“lower-and-slower” or “higher-and-faster”). On the other hand, in energy distribution errors the airplane may have the correct amount of total energy (green boxes) but its distribution over altitude and speed is incorrect. Here, altitude and speed deviate in opposite directions (“higher-and-slower” or “lower-and-faster”). In this case, the pilot deals with relative deviations—not absolute altitude and speed.

Following energy management principles, total energy errors are corrected by increasing or decreasing energy using the throttle, while energy distribution errors are corrected by exchanging energy between altitude and speed using the elevator. To correct a combination of total energy and distribution errors, both controls need to be used simultaneously. Figure 4-12 summarizes the control skills needed to correct total energy and energy distribution errors.

Scenario 1 [Figure 4-9] is a good example to illustrate energy errors and the skills needed to correct and avoid them. Figure 4-13 actually depicts three possible scenarios (B, C, and D) where an airplane on final approach to land has descended below its intended flight path. Should the pilot pitch up, throttle up, or both? It depends. The airplane is lower than desired, but the pilot should check the airspeed as well. Relative to the target airspeed, the actual speed may be slower (B), faster (D), or on target (C). In all three cases, the goal is to return the airplane to its correct energy state (A), following a deviation in altitude and/or airspeed.

Lower-and-slower (B) is fundamentally different from lower-and-faster (D). The former requires advancing the throttle forward to regain total energy (3 in Figure 4-12), while the latter requires pulling back on the yoke/stick to null the energy distribution error (9 in Figure 4-12).

additional column giving caution to the “very slow” condition where careful AOA management is needed in addition to energy management.

Note that in the scenario depicted in B in Figure 4-13, advancing the throttle forward to increase energy would only succeed if excess thrust is available (PS > 0). This may not be the case if the pilot has badly mismanaged energy and slowed down to a speed where induced drag is so high that even applying full throttle would result in no surplus energy (see column “Cautions When Very Slow” in Figure 4-12). Depending on the flight condition, available excess power at full throttle may be negative (PS < 0). In this case, the only recourse is to first trade altitude for speed by pushing forward on the yoke/stick, reducing AOA and induced drag, and only then advancing the throttle forward to regain total energy. But if the airplane is too close to the ground, there may not be enough room to reverse the negative energy rate and prevent the airplane from striking the ground.

Now consider the scenario depicted in C in Figure 4-13, where the airplane has descended below the desired flight path but is flying at the correct speed. Here, even though there is no speed deviation, the pilot is faced with a combination of total energy and distribution errors. Regaining altitude without changing speed requires advancing the throttle forward while easing aft on the yoke/ stick (6 in Figure 4-12). In other words, decoupling altitude and airspeed (i.e. changing one without changing the other) demands the use of both controls simultaneously.

In all cases, path and speed should be monitored carefully as they are corrected, adjusting pitch attitude and throttle setting as appropriate. Once short-term deviations are corrected, the airplane will need to be trimmed for long-term control to maintain the desired path-speed profile (5 in Figure 4-12).

The above approach-to-landing scenario is just one example illustrating the risk of mismanaging altitude-speed deviations. Pilots need to be able to identify, assess, and mitigate altitude and/or airspeed deviations during any phase of flight, including traffic pattern operations, take-offs and climbs, cruise flight, descending flight, and any procedure or maneuver involving turns.

Clearly, skills for promptly correcting path-speed deviations can enhance flight safety but the pilot should also be aware of the risk of unrecoverable depletion of the airplane’s mechanical energy, especially as the airplane approaches the edges of its flight envelope where available excess power is zero.

Preventing Irreversible Deceleration and/or Sink Rate #

During normal flight, the airplane experiences many instances of negative energy rates (negative specific excess power or PS < 0) while decelerating at a constant altitude or descending at a constant airspeed; these are intended energy bleed rates. However, one of the greatest dangers from mismanaging the airplane’s energy state is encountering unintended, excessive deceleration and/or sink rate coupled with little or no positive excess power available under a given flight condition. Failure to recover above a certain critical altitude results in depletion of mechanical energy. Regardless of what the pilot does past that point, the airplane will hit the ground.

To help pilots understand the risk of unintended energy depletion, let’s take a closer look at Scenario 2 [Figure 4-10]. This flight scenario illustrates a situation that is all too common in general aviation: flying toward rising terrain and not being able to fly up and over it before impacting terrain.

As shown in Figure 4-10, there is rising terrain all along the departure corridor. The scenario is as follows:

1. A pilot of a normally-aspirated, twin-engine airplane departs out of Rocky Mountain Metropolitan airport (KBJC) in the morning on a nice summer day and flies into Aspen/Pitkin County airport (KASE).

2. The pilot enjoys the scenery around Aspen, eats lunch, and decides to return home in the early hot afternoon.

3. The pilot departs KASE off of runway 33. At full throttle/power the airplane takes longer to accelerate but rotates at the normal speed.

4. The pilot pitches to the normal pitch target, retracts the gear, and initiates a climb.

5. The pilot notices the airplane isn’t performing as desired. The pilot checks to see if the gear is up and

adjusts the mixtures to try and get a little more power.

6. The terrain is rising, the pilot gradually pitches up, and the airplane starts losing airspeed.

7. The airplane quits climbing.

8. The stall horn begins to sound.

The above scenario is hypothetical, but there have been very similar situations that have ended tragically.

The airplane in the above scenario has encountered an unintended deceleration and impending sink rate that could rapidly become irreversible. This can be shown in two ways, using the traditional power curve [Figure 4-14] and the energy map [Figure 4-15]:

curve depicted in Figure 4-4, note the lower power available curve at this high elevation (7,820 feet at the departure airport) and higher density altitude than standard during a hot afternoon.

As illustrated in the airplane’s power required and available curves [Figure 4-14], the airplane slows down, going from speed 1 where it is climbing (A: power available greater than power required), to speed 2, where it stops climbing (B: power available equal to power required), and continuing to speed 3 where the stall horn sounds (C: power available less than power required). The energy map [Figure 4-15] tells the same story from a total mechanical energy standpoint: the airplane has positive PS at point 1 and climbs to point 2 where it stops climbing since PS = 0, then continues to point 3, where the PS < 0 and the stall horn sounds.

per minute.

The question then is: what does the pilot do to recover from this predicament? The answer is proper energy management. The airplane needs to move to a different place on the energy map that will allow the airplane to begin climbing. So, what does that mean?

• As can be seen in Figure 4-12, the pilot is in a scenario akin to that at the desired altitude, but with cautions when very slow.
• The pilot then has to do something that is not intuitive; consider gaining speed at the expense of some

altitude initially to improve climbing performance with full throttle.

• Once the airplane accelerates to an airspeed in which the PS > 0, it can begin to climb again.

The above recovery scenario is shown in the energy map Figure 4-16, which illustrates the important role of the elevator in assisting the pilot to recover from unintentional and dangerous deceleration and/or sink rate (refer to Additional Role for the Elevator section).

The airplane needs to gain speed at the expense of some altitude, moving from point 3 where the PS < 0 to point 4 where the PS > 0. The airplane can then initiate a constant airspeed climb to point 5, at the desired target altitude and airspeed [Figure 4-16]. Note that the desired target climb airspeed in the presence of rising terrain may be VX, the speed for best angle of climb. VX is slightly slower than VY, the speed for best rate of climb, and will result in a lower climb rate but steepest climb angle. Once the airplane has recovered from the unintentional airspeed loss and begins climbing at VX, the pilot should assess the situation and make an important decision to mitigate further risk—either continue climbing or do something else. Should the airplane not have the needed performance to safely clear the rising terrain on its intended course, the pilot has at least another available option: make a 180 degree turn and return to land at the departure airport until temperature and density altitude conditions improve.

feet per minute.

The above rising terrain scenario is just one example illustrating the risk of irreversible deceleration and/or sink rate. Pilots need to be aware that unintentional depletion of mechanical energy can happen in various instances, especially as the airplane approaches the slow edge of its energy envelope at low altitude, where available specific excess power (PS) is zero. Examples include unstable/ slow approaches to landing; high-drag go-arounds where the pilot neglects to raise the gear and/or flaps; and steeper-than-normal turns in the traffic pattern. Note that irreversible sink rates do not necessarily involve exceeding the critical AOA resulting in a stall and spin. The airplane can be unstalled and still experience unrecoverable sink rates near the high-speed edge of its energy envelope, where available specific excess power (PS) is also zero. Two examples are high-speed steep spirals following botched steep level turns, and high-speed dives too close to the ground.

The bottom line? Should the airplane ever experience unintended excessive negative energy rates with little or no excess power available under a given flight condition, the pilot needs to use proper energy management allowing a prompt recovery and a suitable follow-up action.