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hold the nose up. If allowed to progress unchecked, Mach tuck may eventually occur. Although Mach tuck develops gradually, if it is allowed to progress significantly, the center of pressure can move so far rearward that there is no longer enough elevator authority available to counteract it, and the airplane could enter a steep, sometimes unrecoverable, dive. 

An alert pilot would have observed the high airspeed indications, experienced the onset of buffeting, and responded to aural warning devices long before encountering the extreme stick forces shown. However, in the event that corrective action is not taken and the nose is allowed to drop, increasing airspeed even further, the situation could rapidly become dangerous. As the Mach speed increases beyond the airplane’s M$_{MO}$, the effects of flow separation and turbulence behind the shock wave become more severe. Eventually, the most powerful forces causing Mach tuck are a result of the buffeting and lack of effective downwash on the horizontal stabilizer because of the disturbed airflow over the wing. This is the primary reason for the development of the T-tail configuration on some jet airplanes, which places the horizontal stabilizer as far as practical from the turbulence of the wings. Also, because of the critical aspects of high-altitude/high-Mach flight, most jet airplanes capable of operating in the Mach speed ranges are designed with some form of trim and autopilot Mach compensating device (stick puller) to alert the pilot to inadvertent excursions beyond its certificated M$_{MO}$. 

## Recovery From Overspeed Conditions 

A pilot must be aware of all the conditions that could lead to exceeding the airplane’s maximum operating speeds. 

Good attitude instrument flying skills and good power control are essential. 

The pilot should be aware of the symptoms that will be experienced in the particular airplane as the V$_{MO}$ or M$_{MO }$is being approached. These may include: 

• Nose-down tendency and need for back pressure or trim. 

• Mild buffeting as airflow separation begins to occur after critical Mach speed. 

• Activation of an overspeed warning or high speed envelope protection. 

The pilot’s response to an overspeed condition should be to immediately slow the airplane by reducing the power to flight idle. It will also help to smoothly and easily raise the pitch attitude to help dissipate speed. The use of speed brakes can also aid in slowing the airplane. If, however, the nose-down stick forces have progressed to the extent that they are excessive, some speed brakes will tend to further aggravate the nose-down tendency. Under most conditions, this additional pitch down force is easily controllable, and since speed brakes can normally be used at any speed, they are a very real asset. If the first two options are not successful in slowing the airplane, a last resort option would be to extend the landing gear, if possible. This creates enormous drag and possibly some nose up pitch. This would be considered an emergency maneuver. The pilot transitioning into jet airplanes must be familiar with the manufacturers’ recommended procedures for dealing with overspeed conditions contained in the FAA-approved Airplane Flight Manual for the particular make and model airplane. 

## Mach Buffet Boundaries 

Thus far, only the Mach buffet that results from excessive speed has been addressed. The transitioning pilot, however, should be aware that Mach buffet is a function of the speed of the airflow over the wing— not necessarily the airspeed of the airplane. Anytime that too great a lift demand is made on the wing, whether from too fast an airspeed or from too high an angle of attack (AOA) near the M$_{MO}$, the “high speed buffet” will occur. However, there are also occasions when the buffet can be experienced at much slower speeds known as “low speed Mach buffet.” 

The most likely situations that could cause the low speed buffet would be when an airplane is flown at too slow of a speed for its weight and altitude causing a high AOA. This very high AOA would have the same effect of increasing airflow over the upper surface of the wing to the point that all of the same effects of the shock waves and buffet would occur as in the high speed buffet situation. 

