High Speed Protection

James Albright

Updated: 2020-07-15

What is it?

The airplane doesn't want you to exceed VMO / MMO and will pull the throttles back or pull the nose up to keep you within the speed envelope. See Auto-Throttle Speed Protection (ASP) for details about that. The following is paraphrased from [G500 Ground and Flight Operations, pp. 107-108] to enhance readability.

VMAX Mode (Flight Director Overspeed Protection)

The VMAX Mode generates flight director commands to prevent you or the autopilot from exceeding VMO/MMO when in the VS, FPA, VPATH, or ASEL-descent modes.

This mode will activate based on predicted overspeeds and will be annunciated with an amber VMAX in the FMA vertical window (furthest right). If the autopilot is engaged it will enter the VMAX vertical mode if the system predicts it will exceed VMO/MMO + 5 knots. If the autopilot is off, the pilot will be prompted with flight director commands.

The mode will deactivate when the aircraft is below VMO/MMO and the command generated by the in-use flight director will prevent further overspeed.

High-Speed Protection (HSP)

The High Speed Protection (HSP) function of the flight control computers is active under normal control law. It works with the autopilot off and the auto-throttles on or off, at or below 60° of bank. HSP activates when airspeed is above VMO/MMO, or earlier if the aircraft is accelerating). Activation is annunciated by a cyan CAS message.

When HSP is active, an increase in airspeed above the trim speed results in a pitch-up, and the pilot's maximum nose-down command is limited. The overall effect is to increase the pitch attitude of the aircraft to slow the rate of acceleration and reduce the aircraft's speed.

HSP will deactivate when airspeed is below VMO/MMO.