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When there is a relocated runway threshold, the PHAK says:

When the threshold is relocated, the closed portion of the runway is not available for use by aircraft for takeoff or landing, but it is available for taxi.

When does taxiing become become taking off? Can I apply takeoff power before reaching the relocated threshold so long as I don't rotate until past the threshold? If not, is there a maximum permissible speed and/or power I should maintain until that point?

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    $\begingroup$ Do you ever taxi under takeoff power? Not sure there is a reg for this, but I'd wait until I got there to apply full power. Because that's not how I taxi... ;) $\endgroup$
    – Michael Hall
    Jun 5 at 2:08
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    $\begingroup$ There’s no legal definition given for the word “takeoff”. I think what you’re talking about here is defined as a takeoff roll and when that’s delineated from high-speed taxiing. $\endgroup$
    – Carlo Felicione
    Jun 5 at 2:22
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    $\begingroup$ @Carlo: Brings to mind an anecdote from one of my instructors at the FAA Academy... the phraseology was something like "High-speed taxi on Runway 12 is approved, expect takeoff clearance before midfield." $\endgroup$
    – randomhead
    Jun 5 at 2:54
  • $\begingroup$ @CarloFelicione Yes, exactly. $\endgroup$
    – Chris
    Jun 5 at 3:52
  • $\begingroup$ @MichaelHall Depends how much I'm in a hurry I suppose. ;) $\endgroup$
    – Chris
    Jun 5 at 3:53

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From my comments above, I suppose the real difference is intent. If you’re moving forward at high speed with the intention of reaching decision/rotation speeds, thence raise the nose and lift off the runway, you’re performing a take off. If you’re simply moving the aircraft at high speed along the ground, that’s going to be a high speed taxi. Taxiing is generally considered the movement of an aircraft on the ground to and from parking or terminal areas and a runway for the purposes of flying. Near as I know, there is no other delineation beyond that.

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While it isn't directly applicable, the US Navy broadly categorizes mishaps into "flight" and "ground". A flight mishap may occur even if an aircraft never actually leaves the ground, for example an aborted takeoff that runs off the prepared surface and causes damage.

The way flight and ground mishaps are delineated is that flight starts "when takeoff power is applied, brakes are released, and the aircraft begins to move with the intent for flight."

Given this definition, (plus common sense) it seem obvious that going to full power before reaching the relocated threshold with the intent to takeoff would be a violation of the spirit and intent of this rule.

Ask yourself if you would be comfortable explaining your decision making process and actions to an NTSB mishap investigation team if something went wrong. ("Golly sir, I was just taxiing at full power and 50 knots when I crossed the line, I wasn't actually taking off yet...")

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  • $\begingroup$ Makes sense. Still, it makes me wonder what a reasonable line is. I wouldn't want to say "I wasn't at takeoff power, I was only at 90% power" to an NTSB Investigator either! ;) $\endgroup$
    – Chris
    Jun 5 at 20:53

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