The FAA's push to enable future airport operations in practically zero visibility is spurring a great deal of technology work not only for the airborne segment but the ground portion of a flight as well. The concept is to use sensors and displays to give pilots a clear view of their path from the gate to the runway and vice versa. Ideally, that presentation will also include alerts for situations where there is threat of an incursion from another aircraft or vehicle.

NASA continues to investigate a small solution to the big problem in the form of a head-mounted miniature display (HMD) to be worn by airline and business aviation pilots. Moving with the head and tracked in the cockpit, the HMD removes the field-of-view limitations of a fixed head-up display. Also, the technology can display information in color rather than in monochromatically.

The agency sees HMDs as a potential tool for “better-than-visual” (BTV) capability in the next-generation air transportation system. “The BTV operational concept replicates the capacity of today's VFR [visual flight rules] operations and more importantly, meets and improves on the safety of today's VFR flight in all weather [conditions],” says NASA.

In the 1990s, NASA used head-up and head-down displays as part of its Taxiway-Navigation and Situation Awareness and Runway Incursion Prevention Systems, work meant to increase taxi times in poor weather to a rate approaching VFR capabilities while preventing typical taxi errors, including wrong turns and getting lost. “This research also noted that two of the major [head-up display] limitations during ground operations were their monochrome form and limited, fixed field-of-view,” says NASA.

An HMD moving with the pilot's head gets around those problems, but brings with it a new set of challenges.

NASA Langley Research Center is in the midst of a full-motion simulator study with airline pilots to test the maturity of HMDs compared to head-up displays, particularly in relation to head tracking. Results of the earlier study were promising but revealed areas where improvements are needed, including head-tracking accuracy, data latency and motion sickness. The new HMDs were built by Thales subsidiary, InterSense.

Langley's lead aerospace engineer, Randy Bailey, says subject pilots will fly identical scenarios with a head-up display and also with the HMD in the Langley simulator to compare “within-subjects” performance and safety. Scenarios include low-visibility approach and landings using a simulated, enhanced flight-vision system (head-up display with forward-looking infrared sensor) down to 1000-ft. runway visual range (RVR) landings, and 300-ft. RVR takeoffs with HUD-type guidance and symbology.