What this air crew saw ahead of them as the aircraft levelled out at 3000 feet and then later at 1500 feet was a long vista of flat snow-covered terrain, extending ahead for miles. Similarly, the roof of the solid overcast extended forward for miles. In the far distance the flat white terrain would either have appeared to have reached the horizon many miles away or, more probably, merged imperceptibly with the overhead cloud thus producing no horizon at all. What the crew could see, therefore, was what appeared to be the distant stretch of flat white ground representing the flat long corridor of McMurdo Sound. In reality the flat ground ahead proceeded for only about 6 miles before it intercepted the low ice cliff which marked the commencement of the icy slope leading upwards to the mountain, and at that point the uniform white surface of the mountain slope proceeded upwards, first at an angle of 13°, and then with a gradually increasing upward angle as it merged with the ceiling of the cloud overhead. The only feature of the forward terrain which was not totally white consisted of two small and shallow strips of black rock at the very bottom of the ice cliff, and these could probably not be seen from the flight deck seats owing to the nose-up attitude of 5° at which the aircraft was travelling, or they were mistaken for thin strips of sea previously observed by the crew as separating blocks of pack ice. The aircraft had thus encountered, at a fateful coincidence in time, the insidious and unidentifiable terrain deception of a classic whiteout situation. They had encountered that type of visual illusion which makes rising white plateaux appear perfectly flat. This freak of polar weather is known and feared by every polar flier. In some Arctic regions in the Canadian and in the north European winter, it is responsible for numbers of light aircraft crashes every year. Aircraft fly, in clear air, directly into hills and mountains. But neither Captain Collins nor First Officer Cassin had ever flown at low altitude in polar regions before. Even Mr Mulgrew [the commentator for the passengers], with his antarctic experience, was completely deceived. The fact that not one of the five persons on the flight deck ever identified the rising terrain confirms the totality of this weird and dangerous ocular illusion as it existed on the approach to Mt. Erebus at 12.50 p.m. on 28 November 1979.