• Poor acceleration response in a jet engine from low  rpm. This characteristic requires that the approach be  flown in a high drag/high power configuration so that  sufficient power is available quickly if needed. • The increased momentum of the jet airplane making  sudden changes in the flightpath impossible. Jet  airplanes are consistently heavier than comparable  sized propeller airplanes. The jet airplane, therefore,  requires more indicated airspeed during the final  approach due to a wing design that is optimized for  higher speeds. These two factors combine to produce  higher momentum for the jet airplane. Since force is  required to overcome momentum for speed changes  or course corrections, the jet is far less responsive than  the propeller airplane and requires careful planning  and stable conditions throughout the approach. • The lack of good speed stability being an inducement  to a low-speed condition. The drag curve for many jet  airplanes is much flatter than for propeller airplanes,  so speed changes do not produce nearly as much drag  change. Further, jet thrust remains nearly constant  with small speed changes. The result is far less speed  stability. When the speed does increase or decrease,  there is little tendency for the jet airplane to re-acquire  the original speed. The pilot, therefore, must remain  alert to the necessity of making speed adjustments,  and then make them aggressively in order to remain  on speed. • Drag increasing faster than lift producing a high sink  rate at low speeds. Jet airplane wings typically have a  large increase in drag in the approach configuration.  When a sink rate does develop, the only immediate  remedy is to increase pitch attitude (AOA). Because  drag increases faster than lift, that pitch change  rapidly contributes to an even greater sink rate unless  a significant amount of power is aggressively applied. • The engine speed should be at an rpm that allows best  response when and if a rapid power increase is needed. • The optimum descent rate should be 500 to 700 fpm.  The descent rate should not be allowed to exceed 1,000  fpm at any time during the approach. • Indicated airspeed should be within 10 knots of the  target airspeed. There are strong relationships between  trim, speed, and power in most jet airplanes, and it is  important to stabilize the speed in order to minimize  those other variables. • The airplane should be on profile before descending  below 1,000 feet. Configuration, trim, speed, and  glidepath should be at or near the optimum parameters  early in the approach to avoid distractions and  conflicts as the airplane nears the threshold window.  An optimum glidepath angle of 2.5° to 3° should be  established and maintained. • The airplane should be in the landing configuration  early in the approach. The landing gear should be  down, landing flaps selected, trim set, and fuel  balanced. Ensuring that these tasks are completed  helps keep the number of variables to a minimum  during the final approach. The five basic elements to the stabilized approach are listed  below. Every approach should be evaluated at 500 feet. In a typical  jet airplane, this is approximately 1 minute from touchdown.  If the approach is not stabilized at that height, a go-around  should be initiated.  [Figure 15-24] The performance charts and the limitations contained in the  FAA-approved AFM are predicated on momentum values  that result from programmed speeds and weights. Runway  length limitations assume an exact 50-foot threshold height  at an exact speed of 1.3 times V$_{SO}$. That “window” is critical  and is a prime reason for the stabilized approach. Performance  figures also assume that once through the target threshold  window, the airplane touches down in a target touchdown  zone approximately 1,000 feet down the runway, after which  maximum stopping capability is used. These flying characteristics of jet airplanes make a stabilized  approach an absolute necessity. On final approach, the airspeed is controlled with power. Any  speed diversion from V$_{REF}$ on final approach must be detected  immediately and corrected. With experience, the pilot is able  to detect the very first tendency of an increasing or decreasing  airspeed trend, which normally can be corrected with a small  adjustment in thrust. It is imperative the pilot does not allow  the airspeed to decrease below the target approach speed  or a high sink rate can develop. Remember that with an  increasing sink rate, an apparently normal pitch attitude is no  guarantee of a normal AOA value. If an increasing sink rate  is detected, it must be countered by increasing the AOA and  simultaneously increasing thrust to counter the extra drag.  The degree of correction required depends on how much the  sink rate needs to be reduced. For small amounts, smooth and  gentle, almost anticipatory corrections is sufficient. For large  sink rates, drastic corrective measures may be required that,  even if successful, would destabilize the approach. Approach Speed Stabilized Approach 15-27