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Part of approach lighting system inoperative

Asked by: 4020 views Instrument Rating

If an airport has NOTAM'd the approach lead-in strobe lights as OTS but the runway alignment lights and the rest of the approach lighting system is operational, must you use the lowest minimums available as if theĀ  approach lights were completely out (ie take the 1/4 viz penalty)?

2 Answers



  1. Cody Barringer on Jan 16, 2014

    The wording in the TPP page I1 says “A dot portrayed with approach lighting letter identifier indicates sequenced flashing lights installed WITH the approach lighting system..”

    The “with” makes me think that the dot is not considered part of the approach lighting, but an add-on. If this were the case then no, you shouldn’t have to change the minimums.

    On the other hand, the “F” in ALSF stands for “sequenced flashing lights” which makes me think it is an integral part of the system (since it is part of the name) and therefore you would have to change the minimums.

    If, for example, you had a MALSR with the dot, then you shouldn’t have to change anything, because a MALSR doesn’t have the strobes by default, you just wouldn’t have the option of descending to 100ft AGL since there would be no strobes.

    I’d be interested to see what others think.

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  2. John D Collins on Jan 16, 2014

    I would think that a NOTAM indicating the failure of any component of the approach light system would require that the 1/4 SM penalty would be applicable.

    A MALS system has 7 rows of 5 light bars separated by 200 feet, with two additional 5 light bars on either side of the 1000 foot bar segment with a total length of 1400 feet. The MALSF is the same layout and length as the MALS except that the last three 5 light bars also have sequenced flashing strobes. The MALSR, is the same as the MALS except it has the RAIL extending the system by 5 to 7 additional sequenced flashing lights each separated by 200 feet from the light(s) in front of them for a total length of at least 2400 feet.

    91.175 (c)(3)(i) states:”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.” Strobes are not mentioned and the 100 feet reference is above the TDZE and not AGL.

    As a side point, about 4000 approaches don’t have TDZE printed on the approach chart, but have THRE which is the Threshold Elevation. This was done for international harmonization and is now recognized as an error. Technically, TDZE is not known to the pilot if THRE is printed on the chart, so there is no way on these approaches to satisfy 91.175 (c)(3)(i). THRE can be up to 20 feet lower than the permitted TDZE value, so instead of 100 feet, using the THRE value would put the aircraft at 80 feet above the TDZE..

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