HUD, EVS, and SVS: Vision Technologies, Minima, and Limitations
Advanced display technologies are used to enhance pilot situational awareness and lower operational minimums.
Head-Up Display (HUD)
A transparent screen (Combiner) that projects critical flight data into the pilot's forward field of view.
- Content: Replicates PFD data (Attitude, Speed, Altitude, FMA, Flight Path Vector). It does not typically show Engine data or System synoptics.
- Benefits:
- Situational Awareness: Pilot keeps "eyes out" while monitoring instruments.
- Lower Minima: Allows for lower Take-off and Landing visibility minimums (e.g., manual CAT III approaches).
- Smoother Control: Improves flight path tracking.
- Crosswind Declutter: A mode that removes outer tapes (Speed/Alt) to prevent them from obscuring the runway view during high drift-angle landings.
Enhanced Vision System (EVS)
Uses real-time external sensors (Infrared/IR Cameras, Millimeter Wave Radar) to "see" through darkness or weather.
- Principle: Detects thermal differences (e.g., hot runway lights vs cold ground).
- Display: Projected on the PFD or Video-capable HUD.
- Benefit: Can lower landing minima because it provides a real visual reference of the runway environment when the naked eye cannot see it yet.
Synthetic Vision System (SVS)
Generates a Virtual 3D image of the outside world using an onboard Database (Terrain, Obstacles, Airports) and GPS position.
- Principle: "Flight Simulator" style view on the PFD background.
- Limitation: It is a Synthetic (Computer Generated) image, not a real-time sensor view. It depends entirely on the accuracy of the Navigation System and Database.
- Minima: Does NOT lower landing minima (unlike EVS) because it does not confirm the actual external visibility or runway blockage.
- Benefit: Excellent Terrain Awareness and Situational Awareness in IMC.