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Chapter 5 - Electronic Navigation 5-33

Light Up My Life: The Approach Lighting System (ALS)

Finally, we arrive at the last part of the ILS, the approach lighting system (ALS). Sherlock Holmes apprentice that you
are, you’ve probably noticed that the ILS brings you to within approximately 3,500 feet of the runway threshold at a ver-
tical height of 200 feet (Figure 57). That’s an awfully thrilling place to leave a pilot hanging, especially when most of the
ILS approaches we fly (known as Category I ILSs) require only a half mile visibility and no minimum ceiling height for
landing. This is precisely why the approach lighting system was developed. Keep in mind that when all the fancy elec-
tronic stuff is done, you still have to
make the last bit of the approach visual- Decision Altitude and the Middle Marker
ly. From DA (Decision Altitude, some-
times still referred to as DH or Decision
Height), it’s “no see, no go.” The ALS is
there to help pilots flying on instruments
transition to visual flight for landing.
The folks who developed the ALS
should be named Einstein for their sheer
brilliance in designing such a system of
lights. Relatively speaking, of course.
When you are at or near DA on an ILS,
you don’t have a lot of time to identify
the ALS. That’s why there are two basic
light systems: precision and nonpreci-
sion instrument runway approach light-
ing (Figure 58). (See page 17-1 for a def-
inition of precision instrument runway.)
Two common precision instrument
runway ALSs are named ALSF-1 and
ALSF-2. The ALSF l and ll systems are
often 2,400 to 3,000 feet in length and Fig. 57

Common Varieties of Approach Lighting
Precision Instrument Runway Nonprecision Instrument
Approach Lighting Runway Approach Lighting

Fig. 58