ALSF-I, II

5 Answers

1. 
   

   
   

   John D Collins on Dec 06, 2016

   You are already below the DA and in the visual segment so If you spot the red terminating bars, you can continue the approach to touchdown. Of course you must also have the minimum flight visibility called for in the approach.

   +1 Votes 1 Votes  0 Votes

2. Best Answer
   
   

   
   

   Skyfox on Dec 07, 2016

   The approach lighting system (ALS) is the set of light bars and/or moving strobes out ahead of the runway. The regulation 91.175, which I take it you’re talking about, says that if you see those lights of the ALS you’re allowed to descend to 100′ above the TDZE “unless the red terminating bars or the red side row bars are also distinctly visible and identifiable”, in which case you’d be allowed to continue the descent to landing. This applies whether it’s ALSF 1 or 2 because those numbers only refer to different layouts of the lights. If you can’t see those terminating or side row bars you’d have to maintain that 100′ altitude above TDZE until or unless you can see any other part of the runway environment. That includes:

   visual glideslopes (VASI, PAPI, etc.)
   runway end identifier lights (REIL, the flashing strobes on either side of the threshold)
   the runway (itself, the markings, or lights)
   the touchdown zone (itself, the markings, or lights)
   the threshold (itself, the markings, or lights)

   If you see any of those parts, AND you’re in a position for normal approach and landing, AND the flight visibility is at or above approach minimums, then you can continue your approach and landing visually as long as you keep those things in sight. But if all you can see is the ALS and none of the red terminating or side row bars, you’re stuck at 100′ up until you see more of it.

   +1 Votes 2 Votes  1 Votes

3. 
   

   
   

   Mae on Dec 07, 2016

   Thanks Skyfox.

   so, upon seeing the ALS, I could descend down to 100 above TDZE on precision and nonprcision approaches, including LNAV, LOC, ILS RNAV.. etc if I am correct ?

   I am not sure why I was taught to level off at DA, MDA even when the ALS was visible.

   Mae

   0 Votes 0 Votes  0 Votes

4. 
   

   
   

   John D Collins on Dec 08, 2016

   Skyfox,

   You said: “But if all you can see is the ALS and none of the red terminating or side row bars, you’re stuck at 100′ up until you see more of it.”

   This is incorrect.

   If you descend below the DA, you are in the visual segment. If you don’t see the red terminating or side row bars or one of the other authorized visual runway cues, you are not stuck at 100 feet up, you must execute the missed approach because you don’t have the required visual cues.

   +2 Votes 2 Votes  0 Votes

5. 
   

   
   

   John D Collins on Dec 08, 2016

   Mae, you wrote: “I am not sure why I was taught to level off at DA, MDA even when the ALS was visible.”

   Level off at an MDA is acceptable until reaching the MAP, but never permitted when the approach has vertical guidance with a DA. The DA is the altitude where you decide to initiate the missed approach or have the required visual cues to continue the landing. The point 100 feet above the runway TDZE is not a new MDA for either a vertically guided approach or a non precision approach.

   The whole point of the approach light systems is to aid the pilot in getting to the runway in low visibility conditions. At the typical ILS Category 1 approach with minimums of 200 feet and a half mile, when the conditions are truly at minimums, geometry says it is impossible to see the runway threshold at the DA as it is 0.72 miles away. That is why when the ALS is OOS, visibility minimums go the 0.75 mile. So the approach lights guide the pilot to the point they must be able to see the other cues or abandon the approach. At 100 feet above the TDZE, the pilot is 0.36 miles from the threshold. If you can’t see one of the other runway cues, then the flight visibility is below minimums. When there is an ALSF-I system installed, the red terminating bars are within a hundred feet of the threshold and with an ALSF-II is installed, the red side row bars are located in 100 foot increments beginning 900 feet from the threshold and ending at 100 feet before the runway threshold. You must be able to see all of the side row bars. In effect either is a visual cue that indicates the runway end in the immediate vicinity.

   When there is an approach lighting system such as the MALSF/MALSR installed, there are no red side row or terminating bars. If you clearly have the approach lights at the DA/MDA, you may continue the descent, but by 100 feet above the TDZE, you must have one of the other visual cues to continue the descent as the red side row/threshold bars don’t exist.

   Here is a quote of the relevant portion of the regulation:

   91.175 (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.

   +3 Votes 3 Votes  0 Votes