Night VFR Part II — The Dark Side of Night Flying

by John Heiler, Regional Aviation Safety Officer, Pacific Region; and Dale Wilson, Assistant Professor, Central Washington University. This article is a follow-up to " Night VFR Part 1 — Do You See The Hazard? " published in ASL 4/2000.

Visual flight rules (VFR) flight is inherently more risky at night than it is during the day. Not only are certain types of accidents more likely at night, but there are also some accidents that occur only after dark. In Part I (ASL 4/2000), we discussed the importance of pre-flight planning and the hazards associated with ground operations at night. This article introduces the major hazards of night VFR (NVFR) operations during the take-off and climb phases of flight, while en route, and during the approach and landing phases of flight.

Takeoff and Climb — A critical hazard after takeoff at night occurs when climbing into black-hole conditions where there are no surface lights and the sky is overcast and/or moonless. Over three-quarters of night takeoff accidents occur during these dark-night conditions. A contributing factor in these accidents is the somatogravic or false climb illusion. When our body is accelerated after takeoff (or during an overshoot), the brain perceives acceleration and gravity as a single force acting both downward and backward. Pilots who experience this pitch-up illusion often respond by pitching the nose down. For example, the pilot of a Cessna T210 Centurion died after his airplane crashed into a frozen lake one and a half miles from the end of the runway after an NVFR departure from Flin Flon, Man. In a similar accident, three people on board a Piper PA-31 Chieftain were fatally injured when their MEDEVAC flight struck the dark waters of Lake Erie shortly after departing Pelee Island, Ontario. VFR and dark-night conditions prevailed, and the Transportation Safety Board of Canada (TSB) cited the somatogravic illusion as a causal factor in these accidents. Therefore, to ensure a positive rate of climb and safe terrain clearance during the initial climb phase at night, it is important to use your flight instruments until adequate outside visual references are established — do not rely solely on outside visual references.

En route — Reduced ability to see at night also creates hazards during the en route portion of flight. If you are not using radio navigation, it will be more difficult to navigate at night, especially on a dark night. There is simply not enough light to visually confirm your position, especially in sparsely settled areas. Therefore, you need to use other sources of navigation information, such as VORs, NDBs, and GPS.

It is also difficult to detect terrain at night, even in good weather conditions. Transport Canada recently studied several dark-night accidents that actually occurred in conditions of good visibility, but they happened over sparsely settled areas where there is literally nothing to see! Since it is difficult to visually detect terrain at night, you should plan for a safe obstacle clearance altitude of at least 2000 ft above the appropriate maximum elevation figure (MEF) indicated on your VFR Navigation Chart (VNC). If you are flying on an airway, you should plan for the minimum en route altitude (MEA) indicated on your IFR Navigation Chart. Also, when selecting an altitude, keep in mind that the retina of the eye is the first organ to experience hypoxia. To ensure adequate night vision, it is recommended that supplemental oxygen be used above 5000 ft MSL.

Finally, there is an increased risk of inadvertent flight into instrument meteorological conditions (IMC) at night. Even though an estimated 10% of VFR flight activity occurs at night, a full 30% of VFR-into-IMC accidents occur during the hours of darkness. It is more difficult to visually detect inclement weather when flying at night. Over a ten-year period, a TSB study found that VFR flight into IMC accounted for only 6% of all aircraft accidents yet was responsible for 26% of fatalities, making this the number one killer in aviation. Why are these accidents so deadly? Once VFR pilots enter cloud, either they fly into terrain while in controlled flight or they experience spatial disorientation and lose control of their aircraft. The latter was presumably the case for the non-instrument-rated pilot of a Cessna 150 who was killed when he struck terrain en route from Spirit River to St. Paul, Alberta. The TSB report indicates the pilot "continued flight into deteriorating weather conditions, probably became disorientated . . . lost control of the aircraft . . . [and] entered a spiral dive from which [he] could not recover." Since he was flying over a sparsely populated area at night, he would have had difficulty seeing the inclement weather, let alone the ground or horizon.

To avoid flying into IMC, not only should you obtain a thorough pre-flight weather briefing, you should also carefully monitor any weather changes while en route. Also, you can often detect the formation of low cloud or fog if you see a halo or glow around surface lights.

Approach and Landing — As you near your destination, it is important to understand the risk that darkness brings to the approach and landing phase of flight. It increases significantly when you conduct an approach in black-hole conditions. A black hole exists on dark nights when there are no surface lights between the aircraft and the runway environment. In these conditions, pilots have a strong tendency to fly too low and could crash short of the runway.

Comparision of the approach path flown by pilots during a night visual approach with the desired altitudes. Altitude is in the thousands of feet; distance from the runway is in miles. (After Kraft, 1978.) Illustration reproduced from Human Factors in Aviation by Earl Wiener and David Nagel, Academic Press Inc., 1988, with permission.

Ever since Dr. Conrad Kraft at Boeing verified this problem in a series of simulator studies in the late 1960s, the hazards of black-hole illusions have been widely publicized in the aviation community. Unfortunately, pilots still fall prey to this visual illusion. For example, while the crew of a C99 Airliner was conducting a visual approach to Moosonee, Ontario, they struck the trees and crashed seven miles short of the runway, killing one crew member and seriously injuring the others on board. In 1991, a Canadian Forces C-130 Hercules struck the terrain several miles short of the airport on a clear night while conducting a visual approach to Canadian Forces Station Alert. The black-hole illusion was cited by the TSB as a causal factor in these accidents.

An upsloping runway increases the black-hole illusion. Recently, the crew of a Boeing 767 was fooled by this illusion while on final approach for an upsloping runway at Halifax International Airport. In spite of proper guidance provided by the precision approach path indicator (PAPI), the crew responded with an unwarranted power reduction, causing the airplane to land short, damaging the tail skid and rear fuselage.

To avoid these illusions, you should supplement your outside visual reference to the runway with airport approach slope indicators (VASI, PAPI, etc.) or glide path information from your navigation instruments (ILS or GPS). Using distance measuring equipment (DME), you can also fly a three-degree approach angle by remaining 300 ft AGL per nautical mile flown. Also, consider overflying an unfamiliar airport before beginning your approach descent.

Summary — NVFR flight can be a pleasant experience, but the risks are clearly greater. A pilot who died in a typical "dark-night takeoff accident," had claimed earlier that flying at night was no different than flying during the day. Well there is one difference — you can’t see anything at night! Awareness of the hazards associated with each phase of NVFR flight will help you avoid becoming another statistic. Remember that an illusion, by definition, deceives us, so don’t completely trust your senses — use other aids to vision. If you are not instrument-rated, obtain some instrument training and maintain a minimum level of instrument proficiency. If you have an instrument rating, use it; it is your best defense against the hazards of night flying.

Contact your regional System Safety office for the latest on our NVFR safety promotion campaign.

This article is based in part on Dale Wilson’s article, "Darkness Increases Risks of Flight," published in the Flight Safety Foundation’s (FSF) Nov.-Dec. issue of Human Factors and Aviation Medicine, which can be accessed on the FSF Web site at http://www.flightsafety.org.