AIM CHG 2



assigned altitude until established on glide slope. These
approaches procedurally require utilization of the ILS
glide slope for wake turbulence mitigation. Pilots should
not confuse these simultaneous dependent operations with
(SOIA) simultaneous close parallel PRM approaches,
where PRM appears in the approach title.
c. Minimum Safe Altitudes (MSA) are published
for emergency use on IAP charts. MSAs provide
1,000 feet of clearance over all obstacles, but do not
necessarily assure acceptable navigation signal
coverage. The MSA depiction on the plan view of an
approach chart contains the identifier of the center
point of the MSA, the applicable radius of the MSA,
a depiction of the sector(s), and the minimum
altitudes above mean sea level which provide
obstacle clearance. For conventional navigation
systems, the MSA is normally based on the primary
omnidirectional facility on which the IAP is
predicated, but may be based on the airport reference
point (ARP) if no suitable facility is available. For
RNAV approaches, the MSA is based on an RNAV
waypoint. MSAs normally have a 25 NM radius;
however, for conventional navigation systems, this
radius may be expanded to 30 NM if necessary to
encompass the airport landing surfaces. A single
sector altitude is normally established, however when
the MSA is based on a facility and it is necessary to
obtain relief from obstacles, an MSA with up to four
sectors may be established.
d. Terminal Arrival Area (TAA)

1. The TAA provides a transition from the en

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route structure to the terminal environment with little
required pilot/air traffic control interface for aircraft
equipped with Area Navigation (RNAV) systems. A
TAA provides minimum altitudes with standard
obstacle clearance when operating within the TAA
boundaries. TAAs are primarily used on RNAV
approaches but may be used on an ILS approach when
RNAV is the sole means for navigation to the IF;
however, they are not normally used in areas of heavy
concentration of air traffic.
2. The basic design of the RNAV procedure
underlying the TAA is normally the "T" design (also
called the "Basic T"). The "T" design incorporates
two IAFs plus a dual purpose IF/IAF that functions as
both an intermediate fix and an initial approach fix.
The T configuration continues from the IF/IAF to the
final approach fix (FAF) and then to the missed
approach point (MAP). The two base leg IAFs are
typically aligned in a straight-line perpendicular to
the intermediate course connecting at the IF/IAF. A
Hold-in-Lieu-of Procedure Turn (HILPT) is
anchored at the IF/IAF and depicted on U.S.
Government publications using the "hold-in-lieu
-of-PT" holding pattern symbol. When the HILPT is
necessary for course alignment and/or descent, the
dual purpose IF/IAF serves as an IAF during the entry
into the pattern. Following entry into the HILPT
pattern and when flying a route or sector labeled
"NoPT," the dual-purpose fix serves as an IF, marking
the beginning of the Intermediate Segment. See
FIG 5-4-1 and FIG 5-4-2 for the Basic "T" TAA
configuration.