Black-Hole Visual Approach to an Upsloping Runway
At 21:30 local, a twin-engine turboprop is on a visual approach to runway 27 at a remote airfield. The runway is 1,800 m long and slopes upward by 1.2% toward the threshold; there is no PAPI or VASI, and there are almost no lights between the final approach fix and the runway. Visibility is 10 km with a calm wind, and the crew is cleared for a visual approach. The first officer is flying; the captain has just completed line check and is encouraging a 'stable, continuous' descent. On short final the first officer says, 'We are high,' pushes the nose down, and the EGPWS gives a 'sink rate' caution at 500 ft AGL. The runway lights appear to rise in the windscreen. The captain can see the threshold and says, 'Keep it coming, we are nearly there.'
1. Explain the visual illusion affecting the approach and why the first officer's 'we are high' sensation is unreliable.
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This is a black-hole approach combined with an upsloping runway. With few lights between the aircraft and the runway, there is no reliable motion parallax or ground texture to show the true approach path; the runway appears higher and farther away than it is. An upslope makes the runway surface appear to rise toward the threshold, which also makes the aircraft seem too high. The first officer's sensation is therefore predictable: the crew responds by pushing down and flying a lower-than-normal path. The 'sink rate' caution at 500 ft AGL is an objective cue that the descent has become excessive. The runway lights appearing to rise in the windscreen is consistent with getting low, not high. Visual illusions are not corrected by staring harder; they are corrected by cross-checking the altimeter, vertical speed and approach path, and by using stabilized-approach criteria. If the airport has no vertical guidance, the crew should use a published visual approach path or a constant-angle descent and a minimum altitude check.
2. What should the captain do at the 'sink rate' caution, and what stabilized-approach criteria apply?
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At the 'sink rate' caution the captain should call 'go-around' or take control and initiate a go-around immediately; an EGPWS warning is a hard trigger, not a suggestion. Continuing because the threshold is visible is plan continuation bias. A go-around is cheap; a low, unstable approach at night with no vertical guidance is not. The captain should also stop encouraging a 'continuous' descent when the aircraft is already low and the runway is upsloping. Company criteria should require the aircraft to be on the correct lateral and vertical path, with sink rate not excessive, speed stable, landing checklist complete and power set by 500 ft in VMC or 1,000 ft in IMC. Here the aircraft is at 500 ft AGL with a sink-rate warning, so it is unstable and must go around. After the go-around, the crew should rebrief: instruments as primary, a minimum decision altitude for the visual approach, and a diversion or precision approach if still uncomfortable. Report the EGPWS event under the operator's safety reporting system.