Like the VOR approach, an NDB approach can be
designed using facilities both on and off the airport,
with or without a FAF, and with or without DME availability.
At one time it was commonplace for an instrument
student to learn how to fly an NDB approach, but
with the growing use of GPS, many pilots no longer
use the NDB for instrument approaches. New RNAV
approaches are also rapidly being constructed into airports
that are served only by NDB. The long-term plan
includes the gradual phase out of NDB facilities, and
eventually, the NDB approach will become nonexistent.
Until that time, the NDB provides additional availability
for instrument pilots into many smaller, remotely located
The NDB Runway 9 approach at Charleston Executive
Airport, is an example of an NDB approach established with an on-airport NDB that does not incorporate a
FAF. [Figure 5-51] In this case, a procedure turn or
penetration turn is required to be a part of the approach
design. For the NDB to be considered an on-airport
facility, the facility must be located within one mile of
any portion of the landing runway for straight-in
approaches and within one mile of any portion of
usable landing surface for circling approaches. The
final approach segment of the approach is designed
with a final approach area that is 2.5 NM wide at the
facility, and increases to 8 NM wide at 10 NM from the
facility. Additionally, the final approach course and the
extended runway centerline angle of convergence cannot
exceed 30 degrees for straight-in approaches. This
type of NDB approach is afforded a minimum of 350
feet obstacle clearance.
When a FAF is established for an NDB approach, the
approach design criteria changes. It also takes into
account whether or not the NDB is located on or off the
airport. Additionally, this type of approach can be made
both moving toward or away from the NDB facility.
The St. Mary’s, Alaska, NDB DME RWY 16 [Figure
5-52 on page 5-62] is an approach with a FAF using an
on-airport NDB facility that also incorporates the use
of DME. In this case, the NDB has DME capabilities
from the LOC approach system installed on the airport.
While the alignment criteria and obstacle clearance
remain the same as an NDB approach without a FAF,
the final approach segment area criteria changes to an
area that is 2.5 NM wide at the facility and increases to
5 NM wide, 15 NM from the NDB.