Threats, clearly visible during the day, are masked by darkness. In fact, controlled flight into terrain (CFIT) at night is a major problem for rotor-wing operations. CFIT is defined as colliding with the Earth or a man-made object under the command of a qualified flight crew with an airworthy aircraft.
During the 1970s, CFIT became a major problem for commercial aviation. In response the FAA mandated the installation of ground proximity warning systems (GPWS) in commercial airliners. Although this resulted in a drop in CFIT accidents, these earlier systems were plagued with false and late warnings. Improved versions, called enhanced ground proximity warning systems (EGPWS), were introduced. These systems have made a valuable contribution to the reduction of fixed-wing CFIT accidents.
CFIT at night during VMC has been especially troublesome for helicopters in the air medical industry. According to the Air Medical Physician Association, half of all EMS accidents happen at night. EGPWS have been discussed as a solution to reduce the air medical helicopter accident rate. However, because of the unique low-flying operation of helicopters the effectiveness of current EGPWS is unclear. This prompted Honeywell to introduce the Mark XXII EGPWS, specifically designed to address the needs of helicopters. Moreover, the company is developing a database of power lines to add to the system. As computer memory capability grows, databases will be able to contain more detailed maps.
However, by the time the EGPWS activates, the pilot has probably already lost situational awareness. A method to help with situational awareness is improving the pilot’s ability to see obstructions at night. That’s the technology behind night vision goggles (NVG). They work by detecting and amplifying existing visible light, so there must be at least some light available for them to work. Originally NVG were only for military use, but recently they have been allowed in the air medical industry, and more than half of the EMS helicopters are flying with them.
Another technology that holds promise is enhanced vision systems (EVS) which detects and displays thermal energy not visible to the naked eye. In this arrangement a camera is mounted in the nose and feeds the image to a monitor in the cockpit. Some glass cockpit systems will project the image behind the attitude indicator for better situational awareness. These systems are effective in smog, smoke, duststorms, and other limited visibility situations. Likewise, they can help in brownout and whiteout conditions. The U.S. military uses thermal imaging systems in combination with NVGs.
The air medical industry is expecting the FAA to possibly mandate additional equipment requirements like they did with earlier with commercial aviation. With the different technologies available it will be interesting to see what happens.