The terms and definitions specific to this chapter appear below.

Aircraft Energy Management #

The process of planning, monitoring and controlling altitude and airspeed targets in relation to the airplane’s energy state. Note that this definition is concerned with managing mechanical energy (altitude and airspeed) and addresses the safety (flight control) side of energy management. It does not address the efficiency (aircraft performance) side of energy management, which is concerned with how efficiently the engine generates mechanical energy from fuel and how efficiently the airframe spends that energy in flight.

Energy System #

A flying airplane is an open energy system. That means that the airplane can gain energy from some source (e.g., fuel) and lose energy to the environment (e.g., surrounding air). In addition, energy can be added to or removed from the airplane’s total mechanical energy stored as altitude and airspeed.

Total Mechanical Energy #

Sum of the energy in altitude (potential energy) and the energy in airspeed (kinetic energy).

Kinetic Energy #

Amount of energy due to the airspeed, expressed as ½mV², where m = airplane’s mass, and V = airspeed.

Potential Energy #

Amount of energy due to the altitude, expressed as mgh, where m = airplane’s mass, g = gravitational constant, and h = altitude.

Energy State #

The airplane’s total mechanical energy and its distribution between altitude and airspeed.

Energy Exchange #

Trading one form of energy (e.g., altitude) for another form (e.g., airspeed).

Energy Balance Equation #

According to this equation, the net transfer of mechanical energy into and out of the airplane (a function of thrust minus drag) is always equal to the change in its total mechanical energy (a function of altitude and airspeed). Note that this simplified definition does not account for long-term changes in total mechanical energy caused by the reduction in aircraft weight as fuel is gradually burned in flight.

Power Available #

The airplane’s rate of energy gain due to maximum available engine thrust at a given airspeed. Expressed as TV, where T = engine thrust and V = airspeed. Usually measured in horsepower, foot-pound per minute, or foot-pound per second.

Power Required #

The airplane’s rate of energy loss due to total drag at a given airspeed. Expressed as DV, where D = total drag and V = airspeed. Usually measured in horsepower, foot-pound per minute, or foot-pound per second.

Specific Excess Power (PS) Measured in feet per minute or feet per second, it represents rate of energy change—the ability of an airplane to climb or accelerate from a given flight condition. Available specific excess power is found by dividing the difference between power available and power required by the airplane’s weight.

Energy Height or Total Specific Energy (ES) Measured in units of height (e.g., feet), it represents the airplane’s total energy per unit weight. It is found by dividing the sum of potential energy and kinetic energy by the airplane’s weight. It also represents the maximum height that an airplane would reach from its current altitude, if it were to trade all its speed for altitude.

Energy Error An altitude and/or airspeed deviation from an intended target expressed in terms of energy. Depending on the airplane’s total amount of energy and its distribution between altitude and airspeed, energy errors are classified as total energy errors, energy distribution errors, or a combination of both errors.

Total Energy Error An energy error where the total amount of mechanical energy is not correct. The airplane has too much or too little total energy relative to the intended altitude-speed profile. When this error occurs, the pilot will observe that altitude and airspeed deviate in the same direction (e.g., higher and faster than desired; or lower and slower than desired). An example would be an airplane on final approach that is above the desired glide slope and at a faster airspeed than desired.

Energy Distribution Error An energy error where the total mechanical energy is correct, but the distribution between potential (altitude) and kinetic energy (airspeed) is not correct relative to the intended altitude-speed profile. When this error occurs, the pilot will observe that altitude and airspeed deviate in opposite directions (e.g., higher and slower than desired; or lower and faster than desired). An example would be an airplane on final approach that is above the desired glide slope and at a slower airspeed than desired.

Irreversible Deceleration and/or Sink Rate #

Unrecoverable depletion of mechanical energy as a result of continuous loss of airspeed and/or altitude coupled with insufficient excess power available under a given flight condition. Failure to recover above a certain critical AGL altitude results in the airplane hitting the ground regardless of what the pilot does.