Tuesday, April 26, 2011

What's wrong with this picture, decoded

Okay, so yes. Despite the poor quality of the photo, many of you noted that this appears to be what we call a "Golden Towbar" in progress. For those unfamiliar with the term, a golden towbar is what we call it when a controller gets himself (well, his planes actually) into a situation that can only be solved through the use of a towbar (and presumably a tug with it). It is a moment celebrated by all of one's coworkers, mainly because they're ecstatic that it wasn't their faux pas.

As several of you noted in the comments, this is a face-off between the Southwest B737 exiting on Taxiway Yankee and the Emirates B777 taxiing westbound on Taxiway Echo.

Southwest has just landed on Runway 24 Right (as the United Airbus is doing in the background) and made the mid-field exit. As one of you mentioned, this is a common practice for Southwest, as they park at Terminal One. Missing this exit adds about a mile to their taxi back to the terminal. (Refer to Airport Diagram) The mid-field exit on Runway 24 Right can be Taxiway Zulu (aka "the forward highspeed") or Taxiway Yankee (aka "the reverse"). Taking the reverse is a bit more work for the pilots, as it's much more than a ninety-degree turn and requires coming nearly to a stop on the runway to make the turn. It also requires us to have enough space for them to have time to negotiate the turn and exit the runway before the next arrival reaches the threshhold. For whatever reason, many more Boeings make this intersection than do Airbuses. I've seen Air France B777s make the turn and exit at Yankee, although the usual perpetrators are Southwest and, to a much lesser extent, Alaska and Westjet. Back when Taxiway Sierra was still open, the Skywest E120s, CRJ7s, and Eagle Flight E140s would make this exit as well. Nowadays we direct them off onto Taxiway Zulu instead, as that puts them in position to use Taxiway Romeo to the south side of the Terminal complex. For some reason the Skywest CRJ2s hardly ever could make this intersection even though the larger CRJ7s would.

Meanwhile, Emirates is westbound on Echo because they require Runway 25 Right for their departure, as at least one of you postulated. This is another common practice at LAX; many of the long-haul departures require Runway 25 Right, which, at more than two miles from end to end, is the longest of our departure runways*. As a result, we frequently have to take large airplanes from the north side terminals around to the south side runways. In another Brand A versus Brand B conundrum, many more big Boeings seem to require Runway 25 Right than do big Airbuses. In fact, it's common for us to do just the opposite with the Airbus 380: It'll be parked on Gate 101, at the south end of the International Terminal, and taxi around to depart off of Runway 24 Left.

So now, with all of that out of the way, it's True confessions time.

Yours truly is Controller B in this scenario. "Controller B" is another term that we use amongst ourselves, and refers to the second controller involved in some sort of occurrence. "Controller A" is the primary controller involved, and would in this case be the north side Ground Controller. One of the Ground Controller's main responsibilities at LAX is to keep the runway exits clear, so that aircraft coming off the runways can do so without impediment.

Since Taxiway Echo is currently the only way to get from the north side terminal complex to Taxiway Romeo, the ground controller has to sequence his west-bound aircraft at the Delta Ten intersection. Until the next phase of the Taxiway Delta construction project (visible beyond the A380 and the TBIT) is completed, Delta Ten is the furthest point west that one plane can wait for another before blocking the exit at Yankee; once the upstream airplane passes D-10, you're committed. We call the process of taking an aircraft westbound on Echo "going upstream" since traffic normally flows eastward on Echo. It happens regularly, and is normally coordinated between the ground and local (tower) controllers. The exchange would usually be as simple as this:

GC: "After Southwest, I'll be upstream with Emirates."

LC: "Roger"

No, it's not quite by-the-book phraseology, but it normally gets the job done. As you might have guessed by now, said coordination didn't happen this time around. I was working the north side Local Control position (what most non-controllers think of as "tower") at the time, and gave Southwest instructions to cross Runway 24 Left and contact ground. My Assist (another controller whose function is to act as another set of eyes and ears for the Local Controller) and I then idly wondered if Emirates was going to the south side as we watched Southwest make the turn onto Yankee and head across the Left while Emirates began to taxi out of the D-10 alley. Since the ground controller hadn't said a thing and there was no traffic for the inboard runway, we weren't terribly concerned either way. This was shortly followed by my assist saying something along the lines of "Golly gee, he is!"

Okay, so I paraphrased that first bit just a little.

To understand how we dealt with the situation, take a look at this shot:

It looks like the same picture, but note the positions of Emirates and the United Airbus arriving on 24 Right: This shot was actually taken a second or so before the first one. While the positions of United and Emirates are different, Southwest can be seen to be stationary: We stopped Southwest short of Taxiway Echo to allow Emirates to go by, a maneuver were able to get away with because there was nothing happening on Runway 24 Left at the time. Alternatively, if we had really needed Southwest to clear the runway, he could have been told to make the hard right turn onto Echo westbound. Not an easy turn, and not in the direction he wants to go, but still a viable option.

So despite the ugly opening picture, there really is a happy ending. And that's the moral of this tale: As a controller, you constantly have to know what your options are. Pretty much everything we do can be done in more than one way; there's hardly ever only one solution to a given situation. The choice you make this time may not be what you did last time nor what you'll do next time. It all depends on what else is happening, be that airport conditions, other aircraft movements, or just a gut feeling. We're constantly playing a game of "What If": What if Southwest misses the exit; What if United doesn't slow down (and What if he does); What if Delta doesn't have a gate; What if Cactus isn't ready; What if Fedex doesn't see that guy; What if American goes around; What if Speedbird aborts; What if, What if, what if . . .

* - Fun Fact: While 25 Right is our longest runway for departures, Runway 7 Left is the longest for arrivals. This is thanks to the displaced threshhold on 25 Right, and is a favorite "trick question" for one of our instructors. It seems sort of trivial, but I needed to know that for real, early one morning a few years back. Thanks, Mark.


  1. Great post. I followed along with the airport diagram. Your blog has given this new pilot insight into the sometimes mysterious workings of the Tower. Thanks!

  2. I still think Qantas is missing part of a wing.

    I had assumed one plane was stationary but not the one you described, so that part looked okay to me.

    The wing however...