Approach Lights Good

While there are aircraft that are equipped to fly an instrument approach (Cat II or Cat II) and land with virtually no visibility, most of us mere mortals need to be able to see a fair distance down the runway at the end of an instrument approach in order to land legally. Approach charts will list minima or minimums (sic) as a Minimum Descent Altitude or Decision Height and a minimum visibility. In the U.S., flight visibility controls whether or not you can continue and land. This seems counterintuitive until you consider ... the approach lighting system!

Here's an example of straight-in approach minima for an ILS. The Decision Height is 421 MSL (200 feet Above Ground Level) and the minimum visibility (which controls whether or not you may land legally) is 1800 feet (3/8 statute miles).



If you are still flying in the clouds at the DH prescribed for this instrument approach and you can make out the approach lights, 14 CFR 175(c) "Operating Below the DH or MDA" allows you to descend to 100 feet above the touchdown zone. That might just get down you to where the visibility is good enough to land. And the rules say you can descend even lower if "... the red terminating bars or the red side row bars are also distinctly visible and identifiable." The regulations don't describe red terminating or red side row bars and since the AIM doesn't provide a color illustration of approach lighting in Chapter 2, this is where some pilots get confused.

When giving an instrument proficiency check, I make a point of asking the pilot to describe the red side row bars or red terminating bars. A common answer is "Oh, those are the red lights at the departure end of the runway." Now think about it: Runways served by an instrument approach procedure that also have approach lighting are probably at least a mile long. If you can see the departure end of the runway as you approach the threshold, that's some pretty good visibility and it's unlikely that you'd even need the approach lights unless the cloud ceiling is very low.

Below is the illustration from the AIM that I've modified to outline the location of the red lights. The approach lighting systems that have red terminating bars are ALSF-1 installations. ALSF-2 installations are the ones with red side row bars. When you consider all the airports in the U.S., large and small, the ALSF-1 and ALSF-2 installations are not all that common. In fact, these systems are usually installed only at larger airports where the specialized, very low visibility approaches are also allowed.



Here is a link to a photograph of ALSF-2 approach lighting which shows the "red side bars" on either side of the sequenced, flashing lights in the center row (sometimes referred to as "the rabbit"). I wasn't able to find a photograph of an ALSF-1 installation.

On many occasions, seeing approach lighting systems much less elaborate than ALSF-1 and ASLF-2 have allowed me to descend below the DH and find the visibility I needed to land. Approach lights good!