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INTRODUCTION (Ref I)

This leaflet was previously issued as Leaflet 601/3 of DEF STAN 00-970 Issue I and contains information related to 2.21.5.

Speed stability with flight path constrained is defined in terms of the change of flight path angle with airspeed when the airspeed is changed by the use of the pitch inceptor only, the power setting remaining unchanged by the crew.

When an aeroplane is constrained to follow a rectilinear flight path by use of the pitch inceptor, the conventional phugoid degenerates into a simple subsidence or divergence in airspeed. It is during the landing approach that this mode is most likely to have its greatest effect, since it may increase the pilot's workload to an unacceptable level if the airspeed divergence is too rapid. The stability of this mode can be simply expressed in terms of the rate of change of flight path angle with airspeed when the airspeed is stabilised at a series of steady values by use of the pitch control only.