The L Word[s]
Today marked the end of an air traffic control phraseological era: the clearance instruction “position and hold,” used when controllers want a plane to enter the runway environment but hold for the takeoff clearance, is to be used no longer.
Most people probably wonder what the big deal about a few changed words is.
It’s important because when pilots and controllers talk to each other, they’re often not actually listening to specific words.
 Particularly skilled use of holding instructions at KSFO. |
When most non-pilots listen to their first snippets of air traffic control, they tell me they have trouble understanding what is being said. Aviation radios use amplitude modulation, so the tonal quality of the human voice is often reduced.
Because of this, pilots and controllers learn early in training to communicate through a set of known set of words and phrases. Often times, what with the workload of flying the plane and a noisy cockpit, a pilot may only hear part of what was said, but can still decipher what was meant by listening for those key phrases, much like the human brain really only needs the right letters at the beginning and end of words to figure the word out.
That’s why changing phrases is a big deal.
What’s it being replaced with, you ask?
“Line up and wait,” which is the ICAO-standard phrase for that particular clearance instruction.
The reasoning behind changing it was to make the National Airspace System more “compatible” with the rest of the world1, and since being cleared onto and active runway is, y’know, one of the more important instructions, standardization is relevant.
(There was also an argument floated that it was easy to confuse “position and hold” with “position and roll,” but I don’t know that I buy this argument; a clearance of “position and roll” makes little operational sense, either for a pilot or a controller.)
It’s interesting to note that while the phrase is changing, the phrase notifying pilots approaching a runway that traffic is on it remains “traffic holding in position,” not “traffic lined up and waiting,” which seems an odd inconsistency.
It’s also been interesting to watch this change be announced, debated, and implemented. Some controllers have made the argument that the change in policy around the use of “position and hold,” in addition to the phraseology changes actually reduces safety3, contrary to the main reason cited for the change.
And, of course, phraseology is near and dear to many pilots’ and controllers’ hearts, and some people will always be stubborn4.
No matter which phrase feels more correct6, observing this change’s roll out presents some interesting questions for those who make configuration management7 their business.
There were some real tradeoffs to be made in terms of trying to get all of the users of the National Airspace System to change on a timetable that’s useful.
The consistency benefits of using ICAO-standard phrases must be weighed against the inconsistencies created by the fact that we continue to use older, “hold”-based phrases to describe aircraft in a state of what used to be “position and hold.”
And making these sorts of “human changes” always becomes an exercise in human factors analysis, but of all of the operational phrases to toy with, the one guarding planes off of active runways when they shouldn’t be there is a… pricey one to tinker with.
Despite all of that, until we’ve had a few months of lining up to wait, we’ll all just have to take a position on it, and hold… for now.
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1 And thus more familiar to foreign pilots2 operating in our airspace
2 Many of whom speak English as a second language already
3 The argument mainly centers around the fact that not being able to clear an aircraft onto the runway to hold before takeoff reduces an air traffic controller’s ability to predict the operational context in which they’re working
4 Although, given the gravity of the “line up and wait” clearance, it’s required to be read back, the interaction above may be common to the point until it’s drilled out of pilots5
5 You do NOT want to get into this type of argument with a controller on the frequency…
6 Or seems cooler
7 Which, at its core, is a guiding principle of the National Airspace System as well
I actually see a future* safety benefit to having different phrases for “move onto the runway and wait for a takeoff clearance” given to aircraft on the ground versus telling airborne aircraft about what’s happening, despite the inconsistency. Here’s why:
As you note, pilots listen for specific words and phrases. Under the old system, it was possible for a controller’s instruction “Flight 123, you’re cleared to land, Runway 28, traffic holding in position” to be mis-heard (or incompletely heard) as “position and hold” by an aircraft on the ground. By compartmentalizing the usage of “hold” and “position” entirely within the context of “things controllers say to airborne aircraft that do not directly affect those aircraft still on the ground”, it eliminates one possible source of confusion. A pilot trained entirely within the context of “line up and wait” may well know what “position and hold” means — witness the interaction you linked — but is much less likely to interpret a close juxtaposition of the words “Runway NN”, “position”, and “hold” as a clearance to taxi onto that runway.
A rare mistake? Yes, of course. Runway incursions in general are fairly rare, and “serious” runway incursions are even rarer. The flying public, however, seems to be particularly risk-averse when it comes to commercial aviation, to the point that _any_ risk is unacceptable in retrospect. That is, if a system is engineered so as to be “safe” to a certain probability of failure, the public will conflate the mathematical usage of “safe” with the colloquial usage of “safe” and assume the system is error-proof and error-free. When it turns out not to be, hysterics ensue. (A persuasive argument can be made that we have effectively removed mechanical and design flaws from the accident equation in Western commercial aviation — and very nearly so even in general aviation — and that everything left is human error. This directive partially addresses at least one possible source of human error.)
*Future, as opposed to right now, because American pilots are still in “position and hold” mode and may still be confused either by what “line up and wait” means or by mis-hearing another airplane being told about “traffic holding in position” as a “position and hold” clearance. Give this about a year or two to work its way out of our minds.
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