Salt Lake City LDA 35

Approaches with offsets between the final approach course and the runway are a unique threat that should be briefed ahead of time. If you typically expect to see a runway straight ahead, even a slight change on a diagonal will make it harder to pick it out, especially at night when there are other lights nearby:
  1. Edge lights will visually be further apart, so it will be harder to make out the runway.
  2. Approach light systems will slant off in a different direction.
  3. Other clutter or visual illusions may trick you, especially with crosswinds.
One especially tricky one is the LDA 35 into Salt Lake. The final approach course to all three runways is 344, probably designed that way to keep traffic in the valley between the mountains. Going into 35, you then need to make a 5-degree right turn on short final to line up.
The first time I flew this approach, the weather was advertised as overcast 2000 and winds out of the west at 10 knots. We initially planned 34R, but Approach gave us 35 on short notice. I quickly briefed the threat of misidentifying 34R as the target, but didn’t fully appreciate how strong the illusion was until we broke out. I saw all three runways far enough out (32 has dimmer lights), and verbally IDed them “34L, 34R, and 35 over there, that’s ours.”

The thresholds of 34R and 35 are .5 nm apart, and about 6 nm from the FAF. Applying the 60:1 rule, you get a 5-degree lateral displacement to the left for 34R from the 35 approach course. To get a 5-degree crab angle, we solve 5/60=XWC/135=11.25 knots. With that westerly wind, when you break out at KERNN you’re looking directly at 34R, and it’s 5 degrees offset. In other words, the crab angle will make 34R look exactly how 35 should in a no-wind scenario. 35, meanwhile, is 5 degrees off to the right, and a further 5 degrees offset course.

Mitigation strategies

Awareness of these issues is often half the battle. In the case of the LDA 35 at Salt Lake, here’s what I would plan:
  1. Determine when you’ll break out of the soup and do some napkin math on how many degrees you expect the runways to be separated by.
  2. Determine your crab angle using 60:1 or your nav display and plan to look in your ground track direction, not your heading. It’s probably a good idea to physically point that side during your briefing to really cement it in your head. Your biggest threat range is probably 3-7 miles and the corresponding wind strength to point you at the wrong runway.
  3. Plan to ID all three runways if you’re going to break out early.
  4. Plan a composite scan all the way down and be ready to go missed if you mess it up.

Related scenario: right crosswind 34R

All the same math applies if you’re on a straight in to 34R. If you get an 11-knot right crosswind (I have no idea how common this is in Salt Lake), you’ll be crabbed 5-degrees right and perfectly aligned with 35 if you break out right on 6-mile final (angles exaggerated to make it more visible). Your mitigation plan will be pretty similar in this case.