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50,000 Feet Previous
1,400 Feet Current
1,000 Feet Previous
12,152 Feet Current
16,000 Feet Previous
Figure 5-37. ILS Final Approach Segment Design Criteria.
200
100
0 150 700 1,200 1,800 2,400
CAT II
CAT I
CAT III c
CAT III b
CAT IIIa
Runway Visual Range (feet)
Decision Height (feet AGL)
Photo Courtesy of Cessna
The lowest authorized ILS minimums, with all required ground and airborne systems components operative, are
• CAT I — Decision Height (DH) 200 feet and Runway Visual Range (RVR) 2,400 feet (with touchdown
zone and centerline lighting, RVR 1800 feet),
• CAT II — DH 100 feet and RVR 1,200 feet,
• CAT IIIa — No DH or DH below 100 feet and RVR not less than 700 feet,
• CAT IIIb — No DH or DH below 50 feet and RVR less than 700 feet but not less than 150 feet, and
• CAT IIIc — No DH and no RVR limitation.
NOTE: Special authorization and equipment are required for CAT II and III.
Figure 5-38. ILS Approach Categories.
5-52
The weather conditions encountered in CAT III operations range from an area where visual references are
adequate for manual rollout in CAT IIIa, to an area
where visual references are inadequate even for taxi
operations in CAT IIIc. To date, no U.S. operator has
received approval for CAT IIIc in OpsSpecs.
Depending on the auto-flight systems, some airplanes
require a DH to ensure that the airplane is going to land
in the touchdown zone and some require an Alert
Height as a final crosscheck of the performance of the
auto-flight systems. These heights are based on radio
altitude (RA) and can be found in the specific aircraft’s
AFM. [Figure 5-39]
Both CAT II and III approaches require special ground
and airborne equipment to be installed and operational,
as well as special aircrew training and authorization.
The OpsSpecs of individual air carriers detail the
requirements of these types of approaches as well as
their performance criteria. Lists of locations where
each operator is approved to conduct CAT II and III
approaches can also be found in the OpsSpecs.
ILS APPROACHES TO PARALLEL RUNWAYS
Airports that have two or three parallel runways may
be authorized to use parallel approaches to maximize
the capacity of the airport. There are three classifications of parallel ILS approaches, depending on the
runway centerline separation and ATC procedures.
PARALLEL
Parallel (dependent) ILS approaches are allowed at
airports with parallel runways that have centerlines
separated by at least 2,500 feet. Aircraft are allowed
to fly ILS approaches to parallel runways; however,
the aircraft must be staggered by a minimum of 1 1/2
NM diagonally. Aircraft are staggered by 2 NM
diagonally for runway centerlines that are separated
by more than 4,300 feet and up to but not including
9,000 feet, and that do not have final monitor air
traffic controllers. Separation for this type of
approach is provided by radar. [Figure 5-40]
Though this type of approach procedure is approved
for several airports, it is not required that the approach
chart contain information notifying flight crews of the
use of parallel approaches. Therefore, a pilot may not
know that parallel approaches are approved or used at a
specific airport based on the information contained on
the chart. ATC normally communicates an advisory
over ATIS that parallel approach procedures are in
effect. For example, pilots flying into Sacramento,
California may encounter parallel approach procedures. [Figure 5-41]
SIMULTANEOUS
Simultaneous parallel ILS approaches are used at
authorized airports that have between 4,300 feet and
9,000 feet separation between runway centerlines. A
dedicated final monitor controller is required to
monitor separation for this type of approach, which
Figure 5-39. Category III Approach Procedure.
Dependent Parallel
ILS Approaches
2,500'
or
Greater
Staggered
Separation
1
1
/ 2 Miles
Minimum
Separation
Figure 5-40. Parallel (Dependent) ILS Approach Separation
Criteria.
5-53
eliminates the need for staggered approaches. Final
monitor controllers track aircraft positions and issue
instructions to pilots of aircraft observed deviating
from the LOC course. [Figure 5-42]
Triple simultaneous approaches are authorized
provided the runway centerlines are separated by
at least 5,000 feet and are below 1,000 feet MSL
airport elevation. Additionally, for triple parallel
approaches above airport elevations of 1,000 feet
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