How sharp is your radio work? If it’s up to standards you know that “Line up and wait” is ATC phraseology “designed to position an aircraft onto the runway for an imminent departure,” as explained in Aeronautical Information Manual section 5-2-5.
Those instructions (shorthand: LUAW) are not a takeoff clearance, but you should expect one almost immediately. Pilots with long memories will recall that LUAW replaced “Taxi into position and hold” in September 2010.
Another thing LUAW isn’t is a phrase for a pilot who has taxied onto a nontowered airport runway for takeoff to announce over the common traffic advisory frequency, presumably to inform others that he will be sitting out there for a while before rolling for takeoff. But that’s what Attebury heard some pilots doing.
“Well, what should I say?’ the pilot asked him.
Attebury told him, “Don’t get on the runway until ready for takeoff.”
The practice irked Attebury enough that he reached out to AOPA for an assist in getting his safety message out.
“I don’t think we’ve explained that to the world,” he said by phone. “It’s a clearance given by the tower and should never be used by a pilot.”
If ill-advised phraseology is—well—ill advised, the more egregious practice of dawdling on the runway can distract other pilots, cause go-arounds, or worse. Note that the AIM uses the word “imminent” for the takeoff clearance to follow LUAW.
And even at towered airports where LUAW clearances are legitimately in play, pilots should maintain situational awareness: The FAA notes in the AIM that “analysis of accidents and incidents involving aircraft holding in position indicate that two minutes or more elapsed between the time the instruction was issued to line up and wait and the resulting event,” such as another aircraft going around or landing over the lined-up-and-waiting aircraft.
If a “reasonable amount of time” has elapsed since you were instructed to line up and wait, AIM guidance recommends querying ATC for further instructions.
And—yes—the AIM gives examples of correct terminology.