On Friday, July 7, 2017, an Air Canada flight had an incident at SFO. The A320 was flying from Toronto to San Francisco, and accidentally lined up with the taxiway instead of the runway. To make matters worse, there were four planes on the taxiway that were waiting to take off (a United 787 headed to Singapore, a Philippine Airlines A340 headed to Manila, a United 787 headed to Sydney, and a United 737 headed to Orlando), so you can imagine how much fuel they had.
The Air Canada pilots were clearly confused. On final approach they asked air traffic control to confirm that the runway was clear, because they saw lights on it. Air traffic control confirmed the runway was clear. The Air Canada plane only realized it was about to land on the taxiway when the pilots of one of the planes waiting for takeoff told ATC what was going on. Days after the event we found out that the planes were less than 50 feet apart.
As it turned out, the reason the pilots confused the taxiway for the runway was that one of the runways was closed that evening. SFO has two parallel runways, and the left runway wasn’t in use, and the lights were off. They were supposed to land on the right runway, and to the right of that was a taxiway. Since the left runway wasn’t visible, they accidentally mistook 28R for 28L, and the taxiway for 28R.
It goes without saying that this shouldn’t happen, and that the runway and taxiway lights are different colors to avoid issues like this.
However, the great thing about most aviation disasters (or near disasters, in this case) is that we learn from them and improvements are made. We’ve now learned what changes are being made at SFO as a result of AC759. Per SFGATE:
The Federal Aviation Administration will now require pilots landing at night to do an instrument landing, using the runway’s advanced guidance systems, when a parallel runway is closed. In addition, two air traffic controllers must be on duty through the late-night arrival rush, said Ian Gregor, an FAA spokesman.
What makes aviation so incredibly safe nowadays is the number of redundancies in place. Neither of these things should be necessary if everything is going as planned. However, now we know about the potential for confusion (even if this was still primarily pilot error), and this is even less likely to happen in the future.