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AIM

10/12/17

5−4−9

Arrival Procedures

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

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 5−4−2 and FIG 5−4−3 for the Basic “T” TAA

configuration.