The airspeed increases which appear on all flight data recorders of aircraft which crashed in microburst wind shears are examined. Two reasons for these airspeed increases are suggested which contradict previous analysis. One reason is evident now from the recent studies on optimum trajectories.Another type of airspeed increase which occurs when aircraft escape a microburst is also examined. Several cases of both types of airspeed increases are discussed to show how some previous analysis has underestimated the severity of the wind shears which consequently has caused pilots to underestimate the risks involved.With reference to the study of optimum trajectories, recommendations to pilots are examined to discover if some pilots have been taught a recovery procedure which actually decreases their chance of successful penetration of a microburst. Other suggestions to pilots are compared to those based upon the optimum trajectory analysis.