Can I descend below DA?

4 Answers

1. 
   

   
   

   Lucas on Apr 24, 2014

   Yes you can descend below 100 feet above the TDZL with the red terminating bars in sight as long as the flight visibility is the one prescribed for the approach and the aircraft is in a position for a safe landing. Note that if you can see the red bars you are definitely able to see the approach light system as well, as it has a higher intensity. Refer to FAR 91.175

   (c) Operation below DH or MDA. Except as provided in paragraph (l) of this section, where a DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, at any airport below the authorized MDA or continue an approach below the authorized 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.

   Cheers
   Lucas

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2. 
   

   
   

   Boiler on Apr 25, 2014

   Lucas,
   Does this mean that you must have an ALSF1 or 2 to descend 100 feet below the DA without the runway environment in sight? If I recall, there are no “red terminating bars” on a MALSR for example. Thanks in advance

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3. 
   

   
   

   John D Collins on Apr 25, 2014

   You need an ALSF 1 or 2 to continue below the 100 foot above the TDZE unless you have one of the other cues available. In the case of a MALSR, if you have the approach lights, you can descend below the MDA/DA using them as the sole means of meeting the 91.175(c)(3) criteria, but if at 100 AGL, you don’t see one of the other cues, you must abandon the approach and initiate the missed approach.

   An observation, the FAA dropped using the TDZE on approach charts a few years ago and only printed THRE. This was done for ICAO harmonization. I pointed out at the ACF that this meant there was no way to comply with 91.175 regarding using the approach lights below the DA/MDA. They said Whoops. They have since published the missing TDZE values for the some 4000 approaches that they substituted THRE in a safety alert. It can be found at http://aeronav.faa.gov//d-tpp/1404/TDZE_rounded.pdf

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4. 
   

   
   

   Boiler on Apr 25, 2014

   Thanks for clearing that up for me, John

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