MD-11
Flight Crew Air Transport Pilot (ATP)
Human-Machine Interface
Aircraft Equipment Problem Less Severe
Aircraft; Human Factors
Twenty seven minutes after takeoff the Number 1 Autopilot kicked off due to a loss of quantity and pressure in the Number 2 Hyd System. We accomplished all QRH items and continued to scheduled landing. The only additional item of note with the incident was a firm landing. I used the HUD 'flare command' very accurately but the resulting landing was harder than expected. With the loss of some Elevator Authority due to the loss of the Number 2 Hyd I am concerned that the feedback loop for the HUD display is only a mirror of the output from the FCC and not an accurate depiction of what the flight controls are doing. In other words I think the Elevator may have been operating at some reduced rate and the flare command was presenting accurate info for a fully operational Hyd System and Elevator; which we didn't have today.
MD11 Captain experiences the failure of the number two hydraulic system due to fluid loss. Flight continues to destination where a firm landing occurs. Reporter followed flight director flare command precisely and believes the system did not take into account the hydraulic failure and the resulting reduced elevator rate.