On July 24, 2000 in Sumner, Georgia, an AS350B Astar collided with the ground in a heavily wooded area during a clear dark night. According to the NTSB, no pre-existing airframe or engine malfunctions were identified during the post-crash examination. They determined the probable cause as the pilot experiencing spatial disorientation, which resulted in a loss of control of the helicopter. A contributing factor was the dark night.
Threats, clearly visible during the day, are masked by the darkness. In fact, Controlled Flight into Terrain (CFIT) at night is a major problem for fixed and 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. So much so that 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.
While EGPWS have made a valuable contribution to the reduction of CFIT accidents, by the time the EGPWS activates, the pilot has already lost situational awareness.
Due to the unique, low flying operation of helicopters the effectiveness of EGPWSs is less clear. CFIT at night during VMC has been especially troublesome for the aeromedical industry. According to the Air Medical Physician Association, half of all EMS accidents happen at night.
For example, on November 14, 2001 the pilot of a BO 105 LS reported that while performing a normal take-off from a non-airport shortly after midnight on a dark moonless night, he lost visual references outside the helicopter, became disoriented, and collided with terrain. He further stated that no mechanical malfunction or failure had occurred during the accident flight. The NTSB determined the probable cause was the pilot’s failure to maintain adequate separation from terrain during the initial climb. Factors include spatial disorientation and a dark moonless night.
In response to this type of accident Honeywell introduced the Mark XXII EGPWS, specifically designed to address the needs of helicopters. Moreover, the company is developing a database of powerlines to add to the system. As computer memory capability grows, databases will be able to contain more detailed maps. Synthetic vision systems will benefit from this and hold great promise for improving situational awareness. Yet, it is unlikely that these systems would prevent all night time accidents.
Obviously, the key to preventing these accidents is improving the pilot’s ability to see obstructions–the idea behind Night Vision Goggles (NVG). Regulations governing NVG are soon forthcoming and several companies have begun offering comprehensive training courses.
One such company is Bell Helicopter. Recently, I got to fly NVGs in a Bell 407 and talk with Scott Baxter, Bell’s Assistant Chief NVG instructor. Since I had never used NVGs, instructor Vance Duffy showed me how to adjust and calibrate them. I departed Bell’s well-lighted helipad and in about ten minutes was comfortable enough to fly tree top level along a river. In fact, the details in the tree leaves were clearly visible. A quick peek outside the goggles clearly demonstrated their ability to improve vision.
Bell’s course uses an advanced Litton M949 Infinity series goggle. The course is comprehensive; including all normal maneuvers, confined area operations, and autorotations. The most important aspect is the training in aeronautical decision-making and situational awareness. According to Baxter, students are taught that NVGs are not a panacea and their limitations must be respected. He added that the principle of, "thinking about what you are doing at all times," is stressed throughout the course.
The underlying cause in the vast majority of these accidents is loss of situational awareness. How do pilots become detached from their surroundings? This has been the subject of many studies. Weather plays a large role; however, inadequate planning, unfamiliar terrain, and distraction are also cited as possible reasons. The emphasis, therefore, must be teaching pilots how to maintain situational awareness at all times. A concept that is profound indeed, yet boils down to the simple premise of understanding where your aircraft is in relation to its surroundings.
You can send questions or comments to Tim McAdams at firstname.lastname@example.org.