Stop Rollout Touchdown Check for stablized approach Stabilized  approach on  course on speed 2.5° – 3° glidepath 500 – 700 FPM decent 50' V$_{REF}$ 1,000' Flare Threshold window 500' window 1,000' window Figure 15-24.  Stabilized approach. A common error in the performance of approaches in jet  airplanes is excess approach speed. Excess approach speed  carried through the threshold window and onto the runway  increases the minimum stopping distance required by 20–30  feet per knot of excess speed for a dry runway and 40–50 feet  for a wet runway. Worse yet, the excess speed increases the  chances of an extended flare, which increases the distance  to touchdown by approximately 250 feet for each excess  knot in speed. beyond the normal aiming point. An extra 50 feet of height  over the threshold adds approximately 1,000 feet to the  landing distance. It is essential that the airplane arrive at  the approach threshold window exactly on altitude (50 feet  above the runway). The flare reduces the approach rate of descent to a more  acceptable rate for touchdown. Unlike light airplanes, a  jet airplane should be flown onto the runway rather than  “held off” the surface as speed dissipates. A jet airplane is  aerodynamically clean even in the landing configuration, and  its engines still produce residual thrust at idle rpm. Holding  it off during the flare in an attempt to make a smooth landing  greatly increases landing distance. A firm landing is normal  and desirable. A firm landing does not mean a hard landing,  but rather a deliberate or positive landing. Proper speed control on final approach is of primary  importance. The pilot must anticipate the need for speed  adjustment so that only small adjustments are required. It is  essential that the airplane arrive at the approach threshold  window exactly on speed. On final approach at a constant airspeed, the glidepath angle  and rate of descent is controlled with pitch attitude and  elevator. The optimum glidepath angle is 2.5° to 3° whether  or not an electronic glidepath reference is being used. On  visual approaches, pilots may have a tendency to make flat  approaches. A flat approach, however, increases landing  distance and should be avoided. For example, an approach  angle of 2° instead of a recommended 3° adds 500 feet to  landing distance. For most airports, the airplane passes over the end of the  runway with the landing gear 30–45 feet above the surface,  depending on the landing flap setting and the location of  the touchdown zone. It takes 5–7 seconds from the time the  airplane passes the end of the runway until touchdown. The  flare is initiated by increasing the pitch attitude just enough  to reduce the sink rate to 100–200 fpm when the landing  gear is approximately 15 feet above the runway surface. In  most jet airplanes, this requires a pitch attitude increase of  only 1° to 3°. The thrust is smoothly reduced to idle as the  flare progresses. A more common error is excessive height over the threshold.  This could be the result of an unstable approach or a stable  but high approach. It also may occur during an instrument  approach where the missed approach point is close to or at  the runway threshold. Regardless of the cause, excessive  height over the threshold most likely results in a touchdown  The normal speed bleed off during the time between passing  the end of the runway and touchdown is 5 knots. Most of  the decrease occurs during the flare when thrust is reduced.  15-28 Glidepath Control The Flare