Black-hole approach after a long day
Situation. 21:30. The moon has set and there is no cultural lighting anywhere after the last waypoint. You are a PPL with 95 hours total time, of which 12 are at night, flying a C172 on the fourth leg of a long day. You woke at 05:30, flew three legs with short turnarounds, and drank little water to avoid in-flight discomfort in the heat; the cabin is at 32 °C.
Your destination is a desert aerodrome with no approach lighting, no PAPI or VASI, three unlit taxiways and a single row of green edge lights along one side of the runway. The surrounding terrain is flat, featureless desert. The nearest alternate is 45 minutes away and has no fuel. You have the planned 45-minute reserve plus a little.
On a five-mile straight-in final, the runway lights sit high in the windscreen and the picture tells you that you are too high, so you lower the nose and reduce power to 1,400 RPM. At about 300 ft you feel that you are arriving fast and flat, and the runway lights seem to be coming up at you.
1. What illusion is operating, and what is the visual mechanism that produces it?
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This is the black-hole approach illusion, and the picture in the windscreen is lying to you.
- With no approach lights, no visual approach slope indicator and a featureless dark area before the runway threshold, the normal cues that tell you how far you are from the threshold disappear. The runway lights become the only reference and they appear to 'float' in the darkness.
- Because the ground between you and the runway is unlit, there is nothing to fill the visual frame. The brain interprets the runway as being closer and lower than it is, so the pilot perceives being too high.
- The natural correction is to descend - exactly what you did at 1,400 RPM with the nose lowered. The result is an approach that is too low, too flat and undershooting, and the 'arriving fast and flat' sensation at 300 ft is the warning that the aiming point is short of the threshold.
- The risk is not discomfort: a black-hole approach ends in a low approach, a hard or long landing, or controlled flight into terrain short of the runway. The airport has only a single row of green edge lights, so there is no contrast on one side to correct the perception.
- Aggravating factors here: a moonless night, an unfamiliar aerodrome, no approach aids, and a tired pilot who is much less able to notice that the picture feels wrong.
2. You recognise the sensation at 300 ft. What do you do now, and what instruments and references do you use for the rest of the approach?
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Go around. Recognising the illusion is not the same as being able to correct it by feel - the picture is still lying.
- Power to full, carburettor heat cold, climb straight ahead on the centreline, flaps to take-off setting only when climbing, then rejoin the circuit for a deliberate approach.
- On the next approach, do not fly the picture. Fly numbers:
- Fly a defined profile: a 3° path is roughly 300 ft per nautical mile, so at 5 NM you should be about 1,500 ft, at 3 NM about 900 ft.
- Use the altimeter and the vertical speed indicator as primary - about 500–600 ft/min at a normal approach groundspeed - and the aiming point, not the threshold, as the target.
- Keep a constant airspeed and a constant attitude on final; if you must change power, change it in small steps and give the aircraft time to settle.
- Use the runway lighting geometry: keep the runway symmetrical in the windscreen and use the green edge lights on one side to judge drift, not height.
- If the aerodrome has any other aid - a remote altimeter setting, an RNAV approach that an equipped aircraft could fly, a lit nearby field - or if another aircraft is ahead, follow its reported height and path rather than your own perception.
- If the illusion persists, divert. A night landing at an unlit desert strip with no approach aids is not compulsory.
3. What is the human-factors chain that brought you to this point, and how would you break it in planning and in flight?
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The illusion is the last link, not the only one.
- Fatigue: 16 hours awake, four legs, short turnarounds and the early circadian low around 21:30. Fatigue degrades visual scanning, slows the recognition of an anomalous picture, and increases the tendency to persist with a plan already started - plan-continuation bias, the 'we are nearly there' pressure that also came from having a 45-minute alternate with no fuel.
- Dehydration: deliberately drinking little in 32 °C cabin heat reduces blood volume, worsens the effects of fatigue, and reduces tolerance to the heat and to any positive-G manoeuvring. It is a self-inflicted stressor.
- Inexperience with night visual references: 12 night hours are not enough to have a reliable internal model of what a correct night approach looks like at a dark airfield.
- Prevention begins before the flight: fewer legs, water on board, a rest break, and a realistic look at the destination's lack of approach aids - the decision to arrive at an unlit desert strip at night with no alternate fuel should be made on the ground, not at 300 ft.
- In flight: brief the illusion before the approach, set a minimum height at which you will go around if not stabilised, and insist on the go-around when the picture and the instruments disagree. Treat 'it feels fast and flat' as a mandatory go-around trigger rather than a prompt to fiddle with power.