平视显示器（HUD） (Head-Up Display)

什么是平视显示器（HUD）？

A Head-Up Display (HUD) is an avionics system that projects essential flight data — airspeed, altitude, attitude, flightpath vector, approach guidance, and other symbology — onto a transparent combiner glass directly in the pilot's forward field of view. Unlike conventional instruments in the glass cockpit that require the pilot to look down into the cockpit, the HUD allows pilots to simultaneously monitor instrument data and the outside visual environment without shifting head position or focus.

工作原理

A HUD consists of three components: a projector unit (usually above the glareshield), a combiner glass (a partially reflective panel that folds down in front of the pilot's eyes), and a display processor. The projector uses a CRT or LED light source to project collimated (optically parallel) imagery onto the combiner. Because the image is collimated, it appears focused at infinity — the pilot's eye can simultaneously read the HUD symbols and focus on terrain or runway without refocusing.

• Primary flight symbology: Airspeed tape, altitude tape, vertical speed, heading, attitude horizon — mirroring the PFD
• Flightpath vector (FPV): A circle/cross showing where the aircraft is actually going (as opposed to where it's pointed) — invaluable for energy management and crosswind landings
• Approach guidance: Coupled to ILS localizer and glideslope, with conformal runway symbology for precision approaches
• Enhanced Vision System (EVS): Infrared camera imagery overlaid on the HUD, showing runway lights and terrain in fog

发展与现代系统

Fighter aircraft HUDs from the 1960s were adapted for civil aviation by the 1990s. Alaska Airlines pioneered commercial HUD use for low-visibility Cat III approaches. Today, HUDs are offered as standard or optional on the Airbus A220, A320neo, A350, Boeing 737 MAX, 777X, and 787. The Rockwell Collins (now Collins Aerospace) HGS-3500 and Thales TopHUD are the most common airliner systems. Combined Vision Systems (CVS) merge EVS infrared imagery with Synthetic Vision System (SVS) terrain databases, creating a seamless day-night all-weather outside view.

监管要求

FAA AC 120-28D and EASA AMC/GM to CS-AWO govern HUD use for low-visibility operations. A HUD is required for some operators seeking Cat IIIb approval with reduced decision height. EVS-equipped HUDs can receive credit allowing pilots to use natural visual references — including EVS imagery — to continue below Decision Altitude, effectively gaining approach credit for visibility. HUD systems must meet TSO-C159b and demonstrate luminance and contrast ratios sufficient for use in direct sunlight (typically 10,000+ foot-lamberts).