Chapter 3
Introduction
Preparation for the arrival and approach begins long
before the descent from the en route phase of flight.
Planning early, while there are fewer demands on the
pilot’s attention, leaves the pilot free to concentrate on
precise control of the aircraft and better equipped to deal
with problems that might arise during the last segment
of the flight.
Arrivals
This chapter focuses on the current procedures pilots and
air traffic control (ATC) use for instrument flight rule (IFR)
arrivals in the National Airspace System (NAS). The objective
is to provide pilots with an understanding of ATC arrival
procedures and pilot responsibilities as they relate to the
transition between the en route and approach phases of
flight. This chapter emphasizes standard terminal arrival
routes (STARs), descent clearances, descent planning, and
ATC procedures, while the scope of coverage focuses on
transitioning from the en route phase of flight, typically
the origination point of a STAR to the STAR termination fix.
Optimum IFR arrival options include flying directly from the
en route structure to an approach gate or initial approach
fix (IAF), a visual arrival, STARs, and radar vectors. Within
controlled airspace, ATC routinely uses radar vectors for
separation purposes, noise abatement considerations
when it is an operational advantage, or when requested by
pilots. Vectors outside of controlled airspace are provided
only on pilot request. The controller tells the pilot the
purpose of the vector when the vector is controller-initiated
and takes the aircraft off a previously assigned non-radar
route. Typically, when operating on area navigation
(RNAV) routes, pilots are allowed to remain on their own
navigation.
Navigation in the Arrival Environment
The most significant and demanding navigational
requirement is the need to safely separate aircraft. In a
non-radar environment, ATC does not have an independent
means to separate air traffic and must depend entirely on
information relayed from flight crews to determine the
actual geographic position and altitude. In this situation,
precise navigation is critical to ATC’s ability to provide
separation.
Even in a radar environment, precise navigation and
position reports, when required, are still a primary means
of providing separation. In most situations, ATC does not
have the capability or the responsibility for navigating
an aircraft. Because they rely on precise navigation by
the flight crew, flight safety in all IFR operations depends
directly on the pilot’s ability to achieve and maintain
certain levels of navigational performance. ATC uses radar
to monitor navigational performance, detect possible
navigational errors, and expedite traffic flow. In a non-
radar environment, ATC has no independent knowledge
of the actual position of the aircraft or its relationship to
other aircraft in adjacent airspace. Therefore, ATC’s ability
to detect a navigational error and resolve collision hazards
is seriously degraded when a deviation from a clearance
occurs.
The concept of navigation performance, previously
discussed in this book, involves the precision that must
be maintained for both the assigned route and altitude.
Required levels of navigation performance vary from area
to area depending on traffic density and complexity of
the routes flown. The level of navigation performance
must be more precise in domestic airspace than in oceanic
and remote land areas since air traffic density in domestic
airspace is much greater. For example, there are three
million flight operations conducted within Chicago Center’s
airspace each year. The minimum lateral distance permitted
between co-altitude aircraft in Chicago Center’s airspace
is eight nautical miles (NM) (3 NM when radar is used).
The route ATC assigns an aircraft has protected airspace
on both sides of the centerline, equal to one-half of the
lateral separation minimum standard. For example, the
overall level of lateral navigation performance necessary for
flight safety must be better than 4 NM in Center airspace.
When STARs are reviewed subsequently in this chapter, it is
demonstrated how the navigational requirements become
more restrictive in the arrival phase of flight where air traffic
density increases and procedural design and obstacle
clearance become more limiting.
The concept of navigational performance is fundamental to
the code of federal regulations and is best defined in Title
14 of the Code of Federal Regulations (14 CFR) Part 121, §
121.103 and 121.121, which state that each aircraft must
be navigated to the degree of accuracy required for ATC.
The requirements of 14 CFR Part 91, § 91.123 related to
compliance with ATC clearances and instructions also
reflect this fundamental concept. Commercial operators
must comply with their Operations Specifications
(OpSpecs) and understand the categories of navigational
operations and be able to navigate to the degree of
accuracy required for the control of air traffic.
In the broad concept of air navigation, there are two major
categories of navigational operations consisting of Class
I navigation and Class II navigation. Class I navigation is
any en route flight operation conducted in controlled or
uncontrolled airspace that is entirely within operational
service volumes of International Civil Aviation Organization
(ICAO) standard navigational aids (NAVAIDs) (very high
frequency (VHF) omnidirectional radio range (VOR), VOR/
distance measuring equipment (DME), non-directional
beacon (NDB), etc.).
Class II navigation is any en route operation that is not
categorized as Class I navigation and includes any operation
or portion of an operation that takes place outside the
operational service volumes of ICAO standard NAVAIDs.
For example, aircraft equipped only with VORs conducts
Class II navigation when the flight operates in an area
outside the operational service volumes of federal VORs.
Class II navigation does not automatically require the
use of long-range, specialized navigational systems if
special navigational techniques are used to supplement
conventional NAVAIDs. Class II navigation includes
transoceanic operations and operations in desolate and
remote land areas, such as the Arctic. The primary types
of specialized navigational systems approved for Class II
operations include inertial navigation system (INS), Doppler,
and global positioning system (GPS). Figure 3-1 provides
several examples of Class I and II navigation.
Descent Planning
Planning the descent from cruise is important because of
the need to dissipate altitude and airspeed in order to arrive
at the approach gate properly configured. Descending early
results in more flight at low altitudes with increased fuel
consumption, and starting down late results in problems
controlling both airspeed and descent rates on the
approach. Prior to flight, pilots need to calculate the fuel,
time, and distance required to descend from the cruising
altitude to the approach gate altitude for the specific
instrument approach at the destination airport. While
in flight prior to the descent, it is important for pilots to
verify landing weather to include winds at their intended
destination. Inclimate weather at the destination airport can
cause slower descents and missed approaches that require
a sufficient amount of fuel that should be calculated prior to
starting the descent. In order to plan the descent, the pilot
needs to know the cruise altitude, approach gate altitude
or initial approach fix altitude, descent groundspeed, and
CLASS I
CLASS I
CLASS I
CLASS I
CLASS I
CLASS I
VORTAC A VORTAC B
Route 1
Route 2
CLASS II
1 hour or less
CLASS II
more than 1 hour
Route 3
The area encompassed by the cylinders represents the volume of airspace within the operational service volume
(OSV) of ICAO standard NAVAIDs. The altitude of your aircraft with respect to the location of the NAVAID is a
primary factor in determining OSV range.”
Your aircraft navigating from A to B is conducting Class I navigation because you remain within the OSV of
ICAO standard NAVAIDs during your entire flight.
Your aircraft navigating from A to B is conducting Class I navigation while within the OSV of the NAVAIDs.
You are conducting Class II navigation during the portion of your route outside the OSV of the NAVAIDs.
Because the duration of the Class II navigation is 1 hour or less, long-range navigation equipment or a flight
navigator may not be required.
Your aircraft navigating from A to B is conducting Class I navigation while within the OSV of the NAVAIDs.
You are conducting Class II navigation when outside the OSV of the NAVAIDs. The duration of the Class II
navigation is more than 1 hour. Therefore, long-range navigation equipment or a flight navigator is required.
NOTE:
Route 1
Route 2
Route 3
Figure 3-1. Example of Class I and II navigation.
descent rate. This information must be updated while
in flight for changes in altitude, weather, and wind. The
approach gate is an imaginary point used by ATC to vector
aircraft to the final approach course. The approach gate
is established along the final approach course 1 NM from
the final approach fix (FAF) on the side away from the
airport and is located no closer than 5 NM from the landing
threshold. Flight manuals or operating handbooks may also
contain a fuel, time, and distance to descend chart that
contains the same information.
One technique that is often used is the descent rule of
thumb, which is used to determine when you need to
descend in terms of the number of miles prior to the point
at which you desire to arrive at your new altitude. First,
divide the altitude needed to be lost by 300. For example,
if cruising altitude is 7,000 feet and you want to get down
to a pattern altitude of 1,000 feet. The altitude you want to
lose is 6,000 feet, which when divided by 300 results in 20.
Therefore, you need to start your descent 20 NM out and
leave some extra room so that you are at pattern altitude
prior to the proper entry. It is also necessary to know what
rate-of-descent (ROD) to use.
To determine ROD for a three-degree path, simply multiply
your groundspeed by 5. If you are going 120 knots, your
ROD to fly the desired path would be 600 fpm (120 × 5
= 600). It was determined in the previous example that a
descent should be initiated at 20 NM to lose 6,000 feet. If
the groundspeed is 120 knots, that means the aircraft is
moving along at 2 NM per minute. So to go 20 NM, it takes
10 minutes. Ten minutes at 600 fpm means you will lose
6,000 feet.
The calculations should be made before the flight and rules
of thumb updates should be applied in flight. For example,
from the charted STAR pilots might plan a descent based on
an expected clearance to “cross 40 DME West of Brown VOR
at 6,000” and then apply rules of thumb for slowing down
from 250 knots. These might include planning airspeed at 25
NM from the runway threshold to be 250 knots, 200 knots at
20 NM, and 150 knots at 15 NM until gear and flap speeds
are reached, never to fall below approach speed.
Vertical Navigation (VNAV) Planning
Vertical navigation (VNAV) is the vertical component of
the flight plan. This approach path is computed from the
top-of- descent (TOD) point down to the end-of-descent
waypoint (E/D), which is generally the runway or missed
approach point, which is slightly different than to the
approach gate for non-flight management system (FMS)
equipped aircraft. [Figure 3-2] The VNAV path is computed
based upon the aircraft performance, approach constraints,
weather data (winds, temperature, icing conditions, etc.)
and aircraft weight.
Figure 3-2. VNAV path construction.
Figure 3-3. VNAV performance path.
Figure 3-4. VNAV geometric path.
The two types of VNAV paths that the FMS use is either a
performance path or a geometric path. The performance
path is computed using at idle or near idle power from
the TOD to the first constrained waypoint. [Figure 3-3]
The geometric path is computed from point to point
between two constrained waypoints or when on an
assigned vertical angle. The geometric path is shallower
than the performance path and is typically a non-idle
path. [Figure 3-4]
LNAV/VNAV Equipment
Lateral navigation/vertical navigation (LNAV/VNAV)
equipment is similar to an instrument landing system (ILS)
in that it provides both lateral and vertical approach course
guidance. Since precise vertical position information is
beyond the current capabilities of the GPS, approaches with
LNAV/VNAV minimums make use of certified barometric
VNAV (baro-VNAV) systems for vertical guidance and/or
the wide area augmentation system (WAAS) to improve
GPS accuracy for this purpose.
GPS ENR
FLAGGED
119.000
121.600
114.10
116.00
--.- vor
MSG PROC FPL NAV
ETEGS
DIST BRG
120kt 04:52
9.74n m 332°TRK 332°
Lnav/Vnav
C345 SUNOL RW34Lm
DTK
346°
This GPS/RNAV provides lateral and vertical
guidance during an RNAV approach.
Figure 3-5. WAAS data provide lateral and vertical guidance.
Note: WAAS makes use of a collection of ground stations
that are used to detect and correct inaccuracies in the
position information derived from the GPS. Using WAAS,
the accuracy of vertical position information is increased
to within three meters.
To make use of WAAS; however, the aircraft must be
equipped with an IFR-approved GPS receiver with WAAS
signal reception that integrates WAAS error correction
signals into its position determining processing. The WAAS
enabled GPS receiver [Figure 3-5] allows the pilot to load an
RNAV approach and receive guidance along the lateral and
vertical profile shown on the approach chart. [Figure 3-6]
It is very important to know what kind of equipment is
installed in an aircraft, and what it is approved to do. It is
also important to understand that the VNAV function of
non-WAAS capable or non-WAAS equipped IFR-approved
GPS receivers does not make the aircraft capable of flying
approaches to LNAV/VNAV minimums.
FMS are the primary tool for most modern aircraft, air
carriers, and any operators requiring performance based
navigation. Most of the modern FMS are fully equipped
with LNAV/VNAV and WAAS. The FMS provides flight control
steering and thrust guidance along the VNAV path. Some
less integrated systems may only advise the flight crew
of the VNAV path but have no auto-throttle capability.
These less integrated systems require an increase in pilot
workload during the arrival/approach phase in order to
maintain the descent path.
Descent Planning for High Performance Aircraft
The need to plan the IFR descent into the approach gate
and airport environment during the preflight planning
stage of flight is particularly important for turbojets. TOD
from the en route phase of flight for high performance
aircraft is often used in this process and is calculated
manually or automatically through a FMS based upon the
altitude of the approach gate. A general rule of thumb for
initial IFR descent planning in jets is the 3 to 1 formula.
This means that it takes 3 NM to descend 1,000 feet. If
an airplane is at FL 310 and the approach gate or initial
approach fix is at 6,000 feet, the initial descent requirement
equals 25,000 feet (31,000–6,000). Multiplying 25 times
3 equals 75; therefore, begin descent 75 NM from the
approach gate, based on a normal jet airplane, idle thrust,
speed Mach 0.74 to 0.78, and vertical speed of 1,800–2,200
fpm. For a tailwind adjustment, add 2 NM for each 10 knots
of tailwind. For a headwind adjustment, subtract 2 NM for
each 10 knots of headwind. During the descent planning
stage, try to determine which runway is in use at the
destination airport, either by reading the latest aviation
routine weather report (METAR) or checking the automatic
terminal information service (ATIS) information. There can
be big differences in distances depending on the active
runway and STAR. The objective is to determine the most
economical point for descent.
An example of a typical jet descent-planning chart is
depicted in Figure 3-7. Item 1 is the pressure altitude from
which the descent begins; item 2 is the time required
for the descent in minutes; item 3 is the amount of fuel
consumed in pounds during descent to sea level; and item
4 is the distance covered in NM. Item 5 shows that the chart
is based on a Mach .80 airspeed until 280 knots indicated
airspeed (KIAS) is obtained. The 250 knot airspeed limitation
Figure 3-6. RNAV (GPS) approach.