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Does the FAA give a regulatory definition of the term "Touchdown Zone" for use within the context of landing operations?


In 14 CFR 91.175 the FAA requires—in certain cases—that pilots must be in a position to land within the "Touchdown Zone":

(c) Operation below DA/DH or MDA. Except as provided in §91.176 of this chapter, where a DA/DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, below the authorized MDA or continue an approach below the authorized DA/DH unless—

(1) The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers, and for operations conducted under part 121 or part 135 unless that descent rate will allow touchdown to occur within the touchdown zone of the runway of intended landing;

Is this zone explicitly defined? If so, where is the applicable definition found?


No definition is offered in 14 CFR 1.1. However, several uses or definitions of this term do exist in various FAA advisory documents. These uses or definitions are generally similar, but include variances. A few of these include:

AC 91-79A (referencing an obsolete document):

the TDZ is referred to as a point 500-3,000 ft beyond the runway threshold not to exceed the first one-third of the runway

AIM 2–1–5:

3,000 ft beyond the landing threshold or to the midpoint of the runway, whichever is less.

The Pilot Controller Glossary:

The first 3,000 ft of the runway beginning at the threshold.

Also of note, the runway touchdown zone markings on long precision runways generally extend to 3,000 ft beyond the threshold.

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    $\begingroup$ Within your question you provided three answers from legitimate referenced sources that all say pretty much the same thing. What do you find lacking in these definitions, and kind of an answer would satisfy you? $\endgroup$ Sep 16 '19 at 15:37
  • $\begingroup$ … BTW, the differences are not lost on me, but will they really affect your decision to continue or not? E.g. if the approach is into a 5000' runway will you decide that you are OK to land past the midpoint since you choose to honor the Pilot Controller Glossary definition? (because while being past both the first third and the halfway point, you are still legally within the first 3000') $\endgroup$ Sep 16 '19 at 16:45
  • $\begingroup$ @MichaelHall Note that my question is specifically in search of regulatory definitions. Those that I offered above as part of my findings to this point are all advisory at best. Other FAA guidance that was not accepted data included even greater variance, some of which may have been misquotations. Note also that the cases where this definition might be important are relatively narrow. $\endgroup$
    – J Walters
    Sep 17 '19 at 1:41
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    $\begingroup$ @MichaelHall My interest as a pilot is not on how to determine when a go-around is necessary: landing within an appropriate zone is not difficult. The proper definition of the term becomes especially important in the case of instructing or training. For example, I have heard assertions that pilots are required, in everyday operations, to land within a certain narrow margin near the aiming point marker; I believe these assertions are in error. I believe that the answer to my question is that there is no single, regulatory definition. $\endgroup$
    – J Walters
    Sep 17 '19 at 1:45
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    $\begingroup$ I follow you. In these matters I always try to put the burden of proof on those making assertions to back them up. And I agree with your last sentence, I doubt there is a regulatory definition. And I don't think we want one either. Opens pilots up to risk of a flight violation for nothing more than poor technique. (or for an intentional long landing by a small plane on a big runway that doesn't want a long taxi...) $\endgroup$ Sep 17 '19 at 20:21
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Part 91 operation only requires "The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers". The touchdown zone referenced in 91.175c applies to 135 and 121 operations and they will have clarification in their op specs.(Which are also legally binding FAA approved documents.)

The interpretations I gather indicate that the touchdown zone means different things in different contexts. I would need to search a bit more but touchdown zone elevation as given on approach plates is measured at a specific point, which if I recall is at the aiming point.(1000ft)

For the airport operator, touchdown zone markings are required only for runways with precision approaches. It is 3000 feet, but there must be a minimum length blank space in the middle so the TDZ can be less than 3000ft for shorter runways or runways with displaced thresholds. The specifics use these documents.

AC 150/5340-1m section 2.7

https://www.ecfr.gov/current/title-14/chapter-I/subchapter-G/part-139

https://www.ecfr.gov/current/title-14/chapter-I/subchapter-G/part-139/subpart-D/section-139.311

And 14CFR 152 incorporates a list of Advisory Circulars by reference(Making those ACs regulatory)

Now these provide some nice bureaucratic circular references to each other. But the key part is that an airport requires a set of approved documents that cover the details of the airport. Those operational documents are binding,(explicitly stated in 14 CFR 139) and it is strongly implied that those operational documents must follow the guidelines of the referenced AC on Standards for Airport Markings.

AH HAA! More applicable to flight operations than airport operations: ([IFR]Procedure design standards) FAA Order 8260.3E appendix B-11

  1. Touchdown zone. The first 3000 feet of runway beginning at the threshold. For helicopter procedures it is identical to the landing area.
  2. Touchdown zone elevation. The highest runway centerline elevation in the first 3000 feet of the landing surface (touchdown zone).
  3. Visual descent point. The VDP is a defined point on the final approach course of a nonprecision straight-in approach procedure from which normal descent from the MDA to the runway touchdown point may be commenced, provided visual reference is established.
  4. Vertical guidance surface. The VGS is a narrow inclined plane centered on the runway centerline that is evaluated for obstructions between the DA/VDP and LTP[landing threshold point] for all straight-in aligned approach procedures.
  5. Visual glide slope indicator. The VGSI is an airport lighting aid that provides the pilot with a visual indication of the aircraft position relative to a specified glidepath to a touchdown point on the runway. PAPI and VASI are examples of VGSI systems.

And so the touchdown zone is indeed the first 3000 feet and touchdown point is essentially the aiming point used for calculating the glide slope of an approach and position of a vasi/papi. I find it interesting that the procedure design guidelines use the touchdown point as the assumption even for visual approaches. Considering there are runways of only 3000 feet there is still some ambiguity regarding "touchdown zone" in the context of 91.175c and 121.651, but both also state "made at a normal rate of descent using normal maneuvers" implying that the touchdown zone is dependent on the individual operation.(ie. If you would normally land before 2000ft then you your the TDZ for your operation is from threshold to 2000ft and you must be able to hit that same goal without getting fancy.)

In addition, the flight planning portion of a part 119 operation (which is what this whole mess is about) will follow explicit touchdown assumptions required in the company op specs. (ie Runway meets required landing length when calculated from the normal glide slope and aiming point with normal flare) And op specs are legally binding.

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  • $\begingroup$ If you read through most of order 8260.3 you will find the intent of 91.175c. A missed approach executed either beyond the missed approach point or below the minimum approach altitude(decision height) is not assured of obstacle clearance during the missed approach procedure in IMC. As such there should be minimal chance of executing a go around once committed to that final piece of the approach. This climb during missed approach is the reason many procedures have high minimums, obstacles on the approach side are not usually the issue. $\endgroup$
    – Max Power
    Jan 20 at 3:48
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Found this definition on an FAA website today:

The runway touchdown zone is usually defined as 1000 feet from the runway threshold or 1/3 the total available landing distance. This provides runway “underrun” in case the pilot comes up short of his/her aim point, as well as increased obstacle clearance while on final approach.

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    $\begingroup$ Quoting from the document linked: "FLYING LESSONS is an independent product of MASTERY FLIGHT TRAINING, INC." This is an independent product, is not FAA approved or accepted, and is therefor not an authoritative source in answering this question. $\endgroup$
    – J Walters
    Mar 29 '21 at 11:06

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