For what reasons might a taxiway be mistaken for a runway?

Question

In this article, an airliner landed on a taxiway instead of a runway. What might be the reasons that a pilot can mistake a taxiway for a runway?

(I mostly know the answer for this question, but I want to see what you guys can find out too as well as making a reference point for others.)

Answer 1

Essentially, some taxiways look very like runways and they might even be more visible to pilots in certain conditions. That leads the pilots to focus on the taxiway rather than the runway.

In 2007 the FAA commissioned a study into ways to avoid pilots landing on taxiways, with special emphasis on KSEA (Seattle-Tacoma). One of their goals was to address exactly the scenario in the article you linked to:

Find a solution for the Seattle-Tacoma International Airport (SEA-TAC) problem by identifying possible visual aid enhancements to prevent pilots from mistakenly identifying taxiway Tango as the adjacent runway 16R as a landing surface.

The study mentions several reasons why pilots mistake taxiways for runways:

• A pilot will generally associate an air traffic control (ATC) instruction such as “cleared to land runway 16R,” with their visual presentation of the runway configuration. In other words, pilots see a taxiway where they expect to see a runway: this was a particular problem at KSEA because until the third runway was built, it had 16L and 16R, with taxiway T located to the right of 16R. Therefore a pilot landing on 16R would see three 'strips' with taxiway T as the rightmost one and might assume it was 16R. KSEA now has 3 runways with taxiway T between 16R and 16C.
• Some taxiways look physically very like runways, i.e width, surface material, square edges etc.
• Some taxiways stand out more clearly in low light conditions because their surface is lighter than the runways
• Sun glare can hide runway and taxiway markings so that pilots can't tell the difference visually

There's also an FAA engineering brief that explains how to identify potential problem taxiways, it gives essentially the same information as the study.

Both documents say that the most important point is to alert pilots in advance about the potential problem by giving warnings via ATIS, charts and so on. That's especially true for pilots who aren't familiar with the airport, and GA pilots make more mistakes than airline pilots so presumably training and general currency/professionalism as well as having at least 2 pilots in the cockpit makes a difference too.

Answer 2

Here's a shot of a more or less correct approach to Liverpool Airport (lined up a little outside):

Image Source

This is in clear daylight VFR conditions. Notice the taxiway to the right; long, straight, flat, and very runway-like. If the conditions weren't as clear and you were in a pattern where you crossed by the taxiway first, you might mistake it for the runway.

Here's a circling shot of DFW International from the southeast, almost in line with 31R to the right of the picture:

Source: Wikipedia

Each runway has a full-length or near-full-length taxiway, and because of the heat, movement count and weight considerations of the planes it regularly sees, all surfaces at the airport are concrete to minimize maintenance and resurfacing needs. Even on the normal north-south approaches, it can be difficult in some VFR conditions (with no approach lighting) to distinguish the runways from adjacent taxiways. The outlying diagonal 13/31 runways are worse in some regards as their taxiways are full-length and nearly as wide as the runway itself, and they have, in some circumstances, been used as runway surfaces, so the taxiway has a few tire scuffs and jet blast marks at the expected places for a runway. If you can't clearly see the threshold marker due to glare, it's not hard to at least line up for the taxiway and have to go around once you realize your mistake closer in.

In general, landing on a taxiway is more likely to happen:

• When the pilot is unfamiliar with airport layout, including student flights, diversions and recent renovations
• When the taxiway looks similar to the runway, i.e. same surface material and similar length/width
• In IMC at smaller D/E airports with poor/grandfathered lighting
• When the taxiway and runway layout or materials are opposite pilot expectations (e.g. taxiway outside the runway relative to primary terminal/hangar facilities)
• When the taxiway is the runway, or has been recently or regularly (during maintenance of the usual runway surface, or when abnormal aircraft movement counts require additional runways, like Oshkosh during EAA AirVenture)
• When a low-altitude, shallow glide slope approach is required which reduces the aspect angle and thus the ability to identify critical runway markings on long finals

Mistaken identity is generally less likely:

• In clear nighttime conditions when approach lighting is clearly visible (the runway will be unmistakably bordered in white with standard approach lighting including strobe arrays and green end lights, while most taxiways will be bordered in blue with minimal additional lighting and not easily visible from the air)
• When taxiways are clearly differentiable from their adjacent runways in length, width, material and pathway (other answers mentioned deliberate "chicanes" added to taxiways so it's obvious from the air that's not a landing surface; taxiways intentionally running at an angle to offer a different compass heading on approach are another option, but rare as this requires increased land area)
• When the pilot is well-educated on, and/or personally familiar with, the airport's runway/taxiway layout
• When a normal and/or steep glide slope is recommended, thus giving the pilot a high-aspect look at the complex.

Answer 3

As Air Traffic Controller, I can say that there are many reasons, but mostly:

• Unfamiliar airports.
• Poor visibility during taxi in and taxi out.
• Low situational awareness.
• Poor signage on airside.
• Bad judgement from the crew.

Answer 4

Taxiway "A" at the approach end of runway 29R has the words TAXI on the taxiway. Many A-10 and F-16 pilots over the years have mistaken the parallel taxiway with the runway. The primary is the approach is a LOC BC and as such is a little more difficult than standard for training pilots. They look up at MDA, right of center-line and see a long "runway" and not the taxiway.

KTUS Aerial map runway 29R

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I've personally trained pilots who have lined up on a taxiway. Two things were apparent, they were both visual approaches with no instrument backup to reference and they both looked up assuming the runway was right in front... like it always is.

One pilot commented he can't imagine a pilot mistaking a taxiway for a runway till he was circling one day and lined up on the parallel taxiway to the circling runway. We talked about it afterwards, he said. "Wow. I swore that was the runway. I identified the runway and my perception made it so... even though it wasn't. I need to take more time to confirm what my perceptions are telling me."

Answer 5

Pondlife has an excellent answer. I just wanted to add that at some (very few) airports, the taxiways are specifically constructed as an alternate landing surface, for emergency use in case the main runway is shut down. In this case, the taxiway could look very similar to the main runway, just without the appropriate markings.

Additionally, in theory an airport could be expanded, and old runways could be transitioned to be used as taxiways. This would make them look physically similar, again without the normal markings.

My own technique is to always have the ILS tuned up for the runway I am landing on (if there is one at that runway), even when doing a visual approach to prevent just this (or prevent landing on the wrong runway if there are multiple parallels). Lining up on the wrong piece of concrete should show up pretty clearly on the ILS, especially when very close in.