In cases where an ILS is installed, a back course may
be available in conjunction with the localizer. Like
the localizer, the back course does not offer a glide
slope, but remember that the back course can project
a false glide slope signal and the glide slope should
be ignored. Reverse sensing will occur on the back
course using standard VOR equipment. With an
HSI (horizontal situation indicator) system,
reverse sensing is eliminated if it is set appropriately
to the front course. [Figure 5-57 on page 5-66]
Figure 5-57. Baton Rouge Metro/Ryan (KBTR), Baton Rouge, Louisiana, LOC BC RWY 4L.
LOCALIZER-TYPE DIRECTIONAL AID
An LDA is a NAVAID that provides nonprecision
approach capabilities. The LDA is essentially a localizer.
It is termed LDA because the course alignment
with the runway exceeds 3 degrees. Typically, an LDA installation does not incorporate a glide slope component.
However, the availability of a glide slope associated
with an LDA is noted on the approach chart. This
type of NAVAID provides an approach course between
3 and 6 degrees, making it similar in accuracy to a
localizer, but remember that the LDA is not as closely
aligned with the runway and it does not offer a navigable
back course. Currently there are less than 30 LDA
installations in the U.S., and as a result, most pilots are
not familiar with this type of instrument approach.