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FAA Glossaries

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Landing Under IFR

14 CFR §91.175 Takeoff and landing under IFR.

(c) Operation below DA/ DH or MDA.
Except as provided in paragraph (l) of this section, 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;

(2) The flight visibility is not less than the visibility prescribed in the standard instrument approach being used; and

(3) Except for a Category II or Category III approach where any necessary visual reference requirements are specified by the Administrator, at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:

(i) The approach light system, except that the pilot may not descend below 100 feet above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or the red side row bars are also distinctly visible and identifiable.

(ii) The threshold.
(iii) The threshold markings.
(iv) The threshold lights.
(v) The runway end identifier lights.
(vi) The visual approach slope indicator.
(vii) The touchdown zone or touchdown zone markings.
(viii) The touchdown zone lights.
(ix) The runway or runway markings.
(x) The runway lights.

San Francisco International (KSFO)

Scroll the view to the approach end of the 28L and 28R runways and zoom in. You can see the approach lighting system (ALS) extending out into the bay. There is an overrun area indicated by the chevrons at the end of the runway. The chevrons indicate that it is not usable and in fact it is an Engineered materials arresting system (EMAS) that is designed to catch aircraft that would otherwise overrun the runway and end up in the bay.

The white arrows indicate the displaced threshold. It may be used for taxiing, takeoff, and landing rollout, but not for touchdown. The striped bars are the threshold markings. The number of stripes relate to the width. The designation markings are next. These are typically referred to as “the numbers” although in this case there are also letters. The runway centerline extends just past the numbers and continues down the runway. The touchdown zone markings are next, followed by the aiming point markings (solid white bars 1,000′ from the end of the runway). The first set of touchdown zone marking consist of two sets of three stripes located 500′ from the runway threshold. The runway aiming point is 1,000′ from the threshold. Additional touchdown zone markings after the aiming point are spaced at 500′ increments. There are two sets with two stripes followed by two sets with one stripe. Along the side of the runway are side stripes. The touchdown zone marking and the side stripes are only present on runways with a precision approach. Refer to AIM 2-3-3 for details.

If you drag the image to show the intersection runways, you can see that 19L has an approach lighting system extending into the bay for the precision approach and 19R does not. The markings on 19R indicate that it should have a precision approach, but there are currently no instrument approaches for it or either 1L or 1R.

This view you can see the following elements required to operate below MDA/DA.
(i) The approach light system. YES
(ii) The threshold. YES
(iii) The threshold markings. YES
(iv) The threshold lights. NO – but it isn’t dark.
(v) The runway end identifier lights. SORT OF – if you zoom in you can see where they are.
(vi) The visual approach slope indicator. NO – but they have a PAPI
(vii) The touchdown zone or touchdown zone markings. YES
(viii) The touchdown zone lights. NO – but it isn’t dark.
(ix) The runway or runway markings. YES – several things here
(x) The runway lights. NO – but it isn’t dark.

If you visualize the runway, it should help remember the 10 things required to land. You can also group the items in the following list. You actually get 12 things because my list has a place for runway markings and TDZ markings and the FAR combines them in one item.

  • Lighting—Approach lighting system (100′ above TDZE), REIL, or VASI
  • Threshold, markings, lights.
  • TDZ, markings, lights
  • Runway, markings, lights

Definitions from the Pilot/Controller Glossary

Threshold—The beginning of that portion of the runway usable for landing.
Displaced Threshold—A threshold that is located at a point on the runway other than the designated beginning of the runway.
Touchdown zone—The first three thousand feet of the runway, beginning at the threshold. Note: This is why there are three sets of stripes along the runway. The first set and the aiming point are in the first 1,000′. Two sets with two stipes are in the second 1,000′. Two sets with 1 stripe are in the final 1,000′ of the TDZ.
Airport Lighting—This section of the glossary is fairly long. Click on this link and look for “airport lighting”

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