- This case study from the Avoidable Accidents Series - Visual flight at night accidents shows that even when undertaken by appropriately qualified pilots, night flight clearly presents an added level of complexity.
In August 2011, the pilot of a Twin Squirrel AS355F2 helicopter and two film crew were travelling to various locations in the Lake Eyre region of South Australia for a television documentary. On the second day, they arrived at an island in the Cooper Creek inlet at about 1715 to meet and interview a tour group.
The pilot and film crew departed the island at about 1900. It was after last light and, while there was no low cloud or rain, it was a dark night. The moon had not risen and there was no visible horizon. Apart from the tour group’s campfire on the island, there was no other source of terrestrial lighting, and there would have been very little ambient illumination from any sources other than stars. Witnesses reported that the helicopter initially climbed vertically while moving rearwards.
This was most likely to maintain a visual reference to the campfire, which was the only available ground light source. The witnesses then observed the helicopter depart in an easterly then north-easterly direction. This was contrary to what they expected as they understood that the crew were returning to their accommodation at Muloorina Station, which was to the south.
Even when undertaken by appropriately qualified pilots, night flight clearly presents an added level of complexity.
The helicopter levelled off at 1,500 ft AMSL and then commenced a turn to the right. As the helicopter had initially travelled in the wrong direction, it is probable that the pilot engaged in programming the helicopter's global positioning system (GPS) for their journey to their accommodation during this turn. Twelve seconds after beginning the turn, the helicopter started descending with the bank angle increasing. Based on the GPS data and flight path estimations, it was calculated that the helicopter impacted terrain at about 1902, about 38 seconds after it started descending. Wreckage examination indicated that the helicopter impacted terrain in a 90° right-side low attitude.
The pilot had been flying for over 30 years as a commercial pilot with over 16,000 hours experience, mostly in helicopters. He also had a night visual flight rules (VFR) rating and had 483 night flying hours in total, but only 3.4 hours in the last 12 months, and 30 hours in the past 4 years. Although he had some instrument flight time, this was more than 30 years before the accident. As such, he probably did not have enough recent night flying experience nor the level of instrument proficiency at the time of the accident needed for the very dark conditions.
The ATSB investigation concluded that the pilot probably became spatially disoriented after initiating the right turn and did not recognise the descent and increasing bank angle in sufficient time to recover.
Lessons learnt
In very dark conditions, visual meteorological conditions (VMC) essentially equates to instrument flight rules (IFR) in terms of available external visual information. Pilots need to reassess their night flying experience, recency and proficiency before every night flight, taking into account the level of instrument flying required based on the level of darkness.
Any pilot can become spatially disoriented given the right conditions. Distractions and high workload can inadvertently remove attention away from monitoring instruments, reducing the chance of recognising spatial disorientation.
Read the report: VFR flight into dark night involving Aérospatiale, AS355F2 (Twin Squirrel) helicopter, VH-NTV, 145 km north of Marree, South Australia, on 18 August 2011
The ATSB advises all operators and pilots considering night flights under the VFR to systematically assess the potential for the flight to encounter dark night conditions by reviewing weather conditions, celestial illumination and available terrain lighting. If there is a likelihood of dark night conditions, the flight should be conducted as an instrument flight rules (IFR) operation, or conducted by a pilot who has an IFR-equivalent level of instrument flying proficiency and in an aircraft that is equipped to a standard similar to that required under the IFR.
Conclusion
Data from accidents associated with the risks from night visual flight indicate that they can affect pilots at all stages of experience or qualification, in any type of aircraft. Pilots do not become immune from these risks as experience increases. The harsh outcomes of night accidents can be seen in the photos throughout this booklet. Three in four accidents involving visual flight at night have fatal outcomes.
The risks associated with night visual flying cannot be avoided—they must be understood, identified and managed. Control problems can be identified by cross-referencing information from flight instruments. They can be managed by focussing on aircraft control and using the most reliable information source. The risks from controlled flight into terrain can be managed by calculating LSALTs (lowest safe altitude), knowing terrain elevation during the cruise, and knowing where hills and obstacles are in the circuit area during take-off and landing. The knowledge can be obtained by thorough pre-flight preparation, by accurate horizontal navigation to know where you are, and accurate vertical navigation to know your distance from obstacles below. Everything is more difficult to see at night. Terrain and obstacles are often not illuminated, and it is more difficult to detect cloud. When it is time to fly low enough to land, a detailed plan of how to avoid all obstacles along the expected flightpath is necessary to maintain safety.
Visual night flying is sufficiently different from both day visual flight and (except in very dark conditions) instrument flight that it needs to be treated as a separate skill in its own right. It requires a disciplined integration of two very different skill sets of instrument flight and degraded visual flight to develop sufficient situational awareness to enable safe flight. To maintain these skills, a pilot needs to have enough recent experience and practice. When flying over land or oceans without light sources, on dark nights with no visible moon, visual flight at night is essentially the same as instrument flight.
Before every night flight, systematically assess the potential for the flight to encounter dark night conditions by considering weather conditions, celestial illumination and available terrestrial lighting. Only fly in environments that do not exceed your capabilities. In very dark conditions, consider following instrument procedures if you are rated or avoid areas with limited terrestrial lighting if you are not.
In night visual flight, there is more chance of any pilot becoming influenced by illusions. Have a coping strategy in place, and be prepared to revert to instrument flight to recover from any spatial disorientation.
Read more about Visual flight at night accidents: What you can’t see can still hurt you.