Mount Erebus disaster

Information
The Mount Erebus disaster occurred on 28 November 1979 when Air New Zealand Flight 901 flew into Mount Erebus on Ross Island, Antarctica, killing all 237 passengers and 20 crew on board. Air New Zealand had been operating scheduled Antarctic sightseeing flights between 1977 and 1979. This flight was supposed to leave Auckland Airport in the morning and spend a few hours flying over the Antarctic continent, before returning to Auckland in the evening via Christchurch.

Pilots
The pilots consisted of Captain Jim Collins, first-officer Greg Cassin, and flight engineer Gordon Brooks.

Background
Jim Collins and Greg Cassin had never flown to Antarctica before (while flight engineer Gordon Brooks had flown to Antarctica only once previously), but they were experienced pilots and were qualified for the flight. On 9 November 1979, 19 days before departure, the two pilots attended a briefing in which they were given a copy of the previous flight's flight plan.

The flight plan that had been approved in 1977 by the Civil Aviation Division of the New Zealand Department of Transport was along a track directly from Cape Hallett to the McMurdo non-directional beacon (NDB), which, coincidentally, entailed flying almost directly over the 12,448-foot (3,794 m) peak of Mount Erebus. However, because of a typing error in the coordinates when the route was computerised, the printout from Air New Zealand's ground computer system presented at the 9 November briefing corresponded to a southerly flight path down the middle of the wide McMurdo Sound, approximately 27 miles (43 km) to the west of Mount Erebus. The majority of the previous 13 flights had also entered this flight plan's coordinates into their aircraft navigational systems and flown the McMurdo Sound route, unaware that the route flown did not correspond with the approved route.

Captain Leslie Simpson, the pilot of a flight on 14 November and also present at the 9 November briefing, compared the coordinates of the McMurdo TACAN navigation beacon (approximately 5 kilometres (3.1 mi) east of McMurdo NDB), and the McMurdo waypoint that his flight crew had entered into the INS (Inertial Navigation System), and was surprised to find a large distance between the two. After his flight, Captain Simpson advised Air New Zealand's Navigation section of the difference in positions. For reasons that were disputed, this triggered Air New Zealand's Navigation section to resolve to update the McMurdo waypoint coordinates stored in the ground computer to correspond with the coordinates of the McMurdo TACAN beacon, despite this also not corresponding with the approved route.

The Navigation section changed the McMurdo waypoint co-ordinate stored in the ground computer system at approximately 1:40 am on the morning of the flight. Crucially, the flight crew of Flight 901 was not notified of the change. The flight plan printout given to the crew on the morning of the flight, which was subsequently entered by them into the aircraft's INS, differed from the flight plan presented at the 9 November briefing and from Captain Collins' map mark-ups which he had prepared the night before the fatal flight. The key difference was that the flight plan presented at the briefing corresponded to a track down McMurdo Sound, giving Mount Erebus a wide berth to the east, whereas the flight plan printed on the morning of the flight corresponded to a track that coincided with Mount Erebus, which would result in a collision with Mount Erebus if this leg was flown at an altitude of less than 13,000 feet (4,000 m).

The computer program was altered such that the standard telex forwarded to US Air Traffic Controllers at the United States Antarctic science facility at McMurdo Station displayed the word "McMurdo", rather than the coordinates of latitude and longitude, for the final waypoint. During the subsequent inquiry Justice Mahon concluded that this was a deliberate attempt to conceal from the United States authorities that the flight plan had been changed, and probably because it was known that US Air Traffic Control would lodge an objection to the new flight path.

The flight had earlier paused during the approach to McMurdo Sound to carry out a descent, via a figure-eight manoeuvre, through a gap in the low cloud base (later estimated to be at approximately 2,000 to 3,000 feet (610 to 910 m)) while over water to establish visual contact with surface landmarks and give the passengers a better view. It was established that the flight crew either was unaware of or ignored the approved route's minimum safe altitude (MSA) of 16,000 feet (4,900 m) for the approach to Mount Erebus, and 6,000 feet (1,800 m) in the sector south of Mount Erebus (and then only when the cloud base was at 7,000 feet (2,100 m) or better). Photographs and news stories from previous flights showed that many of these had also been flown at levels substantially below the route's MSA. In addition, pre-flight briefings for previous flights had approved descents to any altitude authorised by the US Air Traffic Controller (ATC) at McMurdo Station. As the US ATC expected Flight 901 to follow the same route as previous flights down McMurdo Sound, and in accordance with the route waypoints previously advised by Air New Zealand to them, the ATC advised Flight 901 that it had a radar that could let them down to 1,500 feet (460 m). However, the radar equipment did not pick up the aircraft, and the crew also experienced difficulty establishing VHF communications. The distance measuring equipment (DME) did not lock onto the McMurdo Tactical Air Navigation System (TACAN) for any useful period.

Cockpit voice recorder transcripts from the last minutes of the flight before impact with Mount Erebus indicated that the flight crew believed they were flying over McMurdo Sound, well to the west of Mount Erebus and with the Ross Ice Shelf visible on the horizon, when in reality they were flying directly toward the mountain. Despite most of the crew being engaged in identifying visual landmarks at the time, they never perceived the mountain directly in front of them. Approximately six minutes after completing a descent in Visual Meteorological Conditions, Flight 901 collided with the mountain at an altitude of approximately 1,500 feet (460 m), on the lower slopes of the 12,448-foot (3,794 m) tall mountain. Passenger photographs taken seconds before the collision removed all doubt of a "flying in cloud" theory, showing perfectly clear visibility well beneath the cloud base, with landmarks 13 miles (21 km) to the left and 10 miles (16 km) to the right of the aircraft visible.

The crew input the coordinates into the plane's computer before they departed at 7:21 am from Auckland International Airport. Unknown to them, the coordinates had been modified earlier that morning to correct the error introduced previously and undetected until then. The crew evidently did not check the destination waypoint against a topographical map (as did Captain Simpson on the flight of 14 November) or they would have noticed the change. Charts for the Antarctic were not available to the pilot for planning purposes, being withheld until the flight was about to depart. The charts eventually provided, which were carried on the aircraft, were neither comprehensive enough nor large enough in scale to support detailed plotting. Such cross checks (and more crucially, real-time monitoring of the aircraft's actual position over the ground) was neither supported nor required, nor even encouraged, by the Navigation Section of Air New Zealand.

These new coordinates changed the flight plan to track 27 miles (43 km) east of their understanding. The coordinates programmed the plane to overfly Mount Erebus, a 12,448-foot-high (3,794 m) volcano, instead of down McMurdo Sound.

About four hours after a smooth take-off, the flight was 42 miles (68 km) away from McMurdo Station. The radio communications centre there allowed the pilots to descend to 10,000 ft (3,000 m) and to continue "visually." Air safety regulations at the time did not allow flights to descend to lower than 6,000 ft (1,800 m), even in good weather, although Air New Zealand's own travel magazine showed photographs of previous flights clearly operating below 6,000 ft (1,800 m). Collins believed the plane was over open water.

Collins told McMurdo Station that he would be dropping to 2,000 feet (610 m), at which point he switched control of the aircraft to the automated computer system. Outside there was a layer of clouds that blended with the white of the snow-covered volcano, forming a sector whiteout – there was no contrast between the two to warn the pilots. The effect deceived everyone on the flight deck, making them believe that the white mountainside was the Ross Ice Shelf, a huge expanse of floating ice derived from the great ice sheets of Antarctica, which was in fact now behind the mountain. As it was little understood, even by experienced polar pilots, Air New Zealand had provided no training for the flight crew on the sector whiteout phenomenon. Consequently, the crew thought they were flying along McMurdo Sound, when they were actually flying over Lewis Bay in front of Mt. Erebus.

At 12:49 pm, the ground proximity warning system (GPWS) began sounding a series of "whoop whoop pull up" alarms, warning that the plane was dangerously close to terrain.

The go-around power was immediately applied, but it was too late. There was no time to divert the aircraft, and six seconds later the plane crashed into the side of Mount Erebus and exploded, instantly killing everyone on board. The accident occurred at 12:50 pm at a position of 77°25′30″S 167°27′30″E and an elevation of 1,467 feet (447 m) AMSL.

McMurdo Station attempted to contact the flight after the crash, and informed Air New Zealand headquarters in Auckland that communication with the aircraft had been lost. United States search and rescue personnel were placed on standby.