Why aircraft line up on the taxiway instead of the runway

A pilot on short final is looking for a long grey rectangle with a centre line down it. If you have built a parallel taxiway the same width as your runway, and lit it well, you have built two of those. Occasionally somebody lands on the wrong one.

This is not a training problem, nor is it a competence problem. It is a design problem that gets handed to the flight crew at the moment of their highest workload, and it is almost always inherited — nobody sets out to build a decoy runway. It happens when a taxiway is widened, or shoulders added for a larger code letter, or when a runway is narrowed on paper without the paint changing on the ground.

What actually distinguishes them

At 200 ft the crew has fewer discriminators than people assume. Runway markings are white and taxiway markings are yellow, which is no help at all in poor visibility or the wet. Runway edge lights are variable white — though they may be yellow over the last 600 m, or one third of the length. Taxiway edge lights are blue and taxiway centre line lights are green, except on an exit, where they alternate green and yellow out to the ILS critical area boundary. Two of those exceptions sit near the threshold, which is exactly where you least want the cue to be ambiguous.

Seven things that help

1. Confirm the runway markings are genuinely to standard — full width, correct designator, threshold markings present and visible, not worn to grey, and they have black edging if required on concrete or bleached asphalt.
2. Check the taxiway is not carrying anything that reads as runway furniture at a distance — no white transverse bars, no misread designator.
3. Verify the aeronautical ground lighting is unambiguous by night and at dusk, which is when most of these events happen.
4. Consider taxiway centre line lighting, switching, alignment, and cannot be confused with a threshold bar.
5. Look at the approach from where the flight crew looks at it — regularly fly it, by drone is fine.
6. Publish a warning in the AIP entry, not a NOTAM, where the geometry is genuinely confusing. It is not an admission of failure; it is information the crew can brief.
7. Ask your ATC unit whether they have seen line-ups to the wrong surface. They may have, and it may not have been reported.

None of these is expensive. What is expensive is the alternative.