response. The SCAS improved flight path response somewhat by using washed out FPC lever position to drive the spoilers to compensate for engine delays. With this SCAS implementation, the time constant of the flight path response to FPC lever became about 2 seconds as shown (gamma) in Fig.9. This response is slow enough to make precise glide slope control difficult in the presence of gust disturbances.
To compensate for this delay in flight path response, we adopted the gamma prediction symbol that NASA Ames used in their QSRA program as described in ref.15. The gamma prediction signal is obtained from a washed out FPC lever position signal as shown in Fig.9. This gives an almost instantaneous prediction of what the long term gamma change will be but is not accurate in the short term. This helps avoid Pilot Induced Oscillations due to aircraft response lag for low-band-width tasks such as approach. For high-band-width tasks likes the landing flare though, the error may be more significant. Consequently, we display separately the flight-path symbol and the gamma prediction symbol as shown in Fig.8. This allows the pilot to use the gamma prediction symbol for low band-width tasks such as approach but gives him the true gamma information when needed.
Fig.9 FPC Step Response of Gamma and Gamma Prediction
The gamma prediction mode of this symbol isused if FPC lever is engaged in SCAS modes. Gamma prediction has some problems in that the heave lag is not constant, depending on aircraft configuration, power, airspeed and angle of attack. Also the gamma prediction does not predict correctly for gust input or attitude change.
Fig.10 Pseudo A Mode of HUD
HUD Pseudo/Radar Guidance Mode A - As indicated earlier, the difference among the A, B, and C modes was in the guidance information display format, Pseudo Approach and Landing A Mode (Pseudo A Mode) is shown in Fig.10. This mode uses conventional glide-slope and localizer error scales on the left side and bottom of the display. The perspective run-way symbol is shown in an "on center line", "low on glide-slope" (Flight Path Reference below touchdown point) situation.
Fig.10 is shown for the pseudo mode as indicated by the unique symbol used for the Altitude Indication and the Flight-Path symbol. The head character of altitude indication "S" shows a simulation altitude in Pseudo Approach and Landing modes. The Flight-Path symbol of Fig.11 indicates to be a Radar Guidance Mode using the inertial velocity updated by the radar position data.
HUD Pseudo/Radar Guidance B Mode - The Radar Guidance B Mode" is shown in Fig.11. The flight path error symbol is the most important symbol in the guidance B mode. It is a triangle on the nominal selected flight path with the apex of the triangle 400 meters ahead of the aircraft, and the base of the tri-
