AFH 4-17

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. Figure 4-16. The energy loss scenario recovery viewed in the energy map. Specific excess power (PS) contours are labeled in units of 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.