ATC uses an IFR release time2 in conjunction with
traffic management procedures to separate departing
aircraft from other traffic. For example, when controlling
departures from an airport without a tower, the
controller limits the departure release to one aircraft at
any given time. Once that aircraft is airborne and radar
identified, then the following aircraft may be released
for departure, provided they meet the approved radar
separation (3 miles laterally or 1,000 feet vertically)
when the second aircraft comes airborne. Controllers
must take aircraft performances into account when
releasing successive departures, so that a B-747 HEAVY
aircraft is not released immediately after a departing
Cessna 172. Besides releasing fast aircraft before slow
ones, another technique commonly used for successive
departures is to have the first aircraft turn 30 to 40
degrees from runway heading after departure, and then
have the second aircraft depart on a SID or runway heading.
Use of these techniques is common practice when
maximizing airport traffic capacity.
EXPECT DEPARTURE CLEARANCE TIME
Another tool that the FAA is implementing to increase
efficiency is the reduction of the standard expect departure
clearance time3 (EDCT) requirement. The FAA has
drafted changes to augment and modify procedures contained
in Ground Delay Programs (GDPs). Airlines may
now update their departure times by arranging their
flights’ priorities to meet the controlled time of arrival.
In order to evaluate the effectiveness of the new software
and the airline-supplied data, the actual departure
time parameter in relation to the EDCT has been
reduced. This change impacts all flights (commercial
and GA) operating to the nation’s busiest airports.
Instead of the previous 25-minute EDCT window (5
minutes prior and 20 minutes after the EDCT), the new
requirement for GDP implementation is a 10-minute
window, and aircraft are required to depart within 5 minutes
before or after their assigned EDCT. Using reduced
EDCT and other measures included in GDPs, ATC aims
at reducing the number of arrival slots issued to accommodate
degraded arrival capacity at an airport affected
by weather. The creation of departure or ground delays is less costly and safer than airborne holding delays in
the airspace at the arrival airport.
MANAGING SAFETY AND CAPACITY SYSTEM DESIGN
The CAASD is aiding in the evolution towards free flight
with its work in developing new procedures necessary
for changing traffic patterns and aircraft with enhanced
capabilities, and also in identifying traffic flow constraints
that can be eliminated. This work supports the
FAA’s Operational Evolution Plan in the near-term.
Rapid changes in technology in the area of navigation
performance, including the change from ground-based
area navigation systems, provide the foundation for aviation’s
global evolution. This progress will be marked by
combining all elements of communication, navigation,
and surveillance (CNS) with air traffic management
(ATM) into tomorrow’s CNS/ATM based systems. The
future CNS/ATM operating environment will be based
on navigation defined by geographic waypoints
expressed in latitude and longitude since instrument
procedures and flight routes will not require aircraft to
overfly ground-based navigation aids defining specific
APPLICATION OF AREA NAVIGATION
RNAV airways provide more direct routings than the
current VOR-based airway system, giving pilots easier
access through terminal areas, while avoiding the circuitous
routings now common in many busy Class B
areas. RNAV airways are a critical component to the
transition from ground-based navigation systems to GPS
navigation. RNAV routes help maintain the aircraft flow
through busy terminals by segregating arrival or departure
traffic away from possibly interfering traffic flows.
Further, RNAV provides the potential for increasing airspace
capacity both en route and in the terminal area in
several important ways.
Strategic use of RNAV airways nationwide is reducing
the cost of flying and providing aircraft owners more
benefits from their IFR-certified GPS receivers. Several
scenarios have been identified where RNAV routes provide
a substantial benefit to users.
- Controllers are assigning routes that do not require overflying ground-based NAVAIDs such as VORs.
- The lateral separation between aircraft tracks is being reduced.
- RNAV routes lower altitude minimums on existing Victor airways where ground-based NAVAID performance minimum reception altitude) required higher minimums.
- RNAV routes may allow continued use of existing airways where the ground-based NAVAID has been decommissioned or where the signal is no longer suitable for en route navigation.
- The route structure can be modified quickly and easily to meet the changing requirements of the user community.
- Shorter, simpler routes can be designed to minimize environmental impact.
Dozens of new RNAV routes have been designated, and
new ones are being added continuously. In order to designate
RNAV airways, the FAA developed criteria, en
route procedures, procedures for airway flight checks,
and created new charting specifications. Some of the
- Navigation infrastructure (i.e., the ground-based and space-based navigation positioning systems) provides adequate coverage for the proposed route/procedure.
- Navigation coordinate data meets International Civil Aviation Organization (ICAO) accuracy and integrity requirements. This means that all of the coordinates published in the Aeronautical Information Publication (AIP) and used in the aircraft navigation databases must be referenced to WGS 84, and the user must have the necessary assurance that this data has not been corrupted or inadvertently modified.
- Airborne systems meet airworthiness performance for use on the RNAV routes and procedures.
- Flight crews have the necessary approval to operate on the RNAV routes and procedures.
In the future, as aircraft achieve higher levels of navigation
accuracy and integrity, closely spaced parallel
routes may be introduced, effectively multiplying the
number of available routes between terminal areas.
RNAV can be used in all phases of flight and, when
implemented correctly, results in:
- Improved situational awareness for the pilot.
- Reduced workloads for both controller and pilot.
- Reduced environmental impact from improved
route and procedure designs.
- Reduced fuel consumption from shorter, more
For example, take the situation at Philadelphia
International Airport, located in the middle of some
highly popular north-south traffic lanes carrying New
York and Boston traffic to or from Washington, Atlanta,
and Miami. Philadelphia’s position is right underneath these flows. Chokepoints resulted from traffic departing
Philadelphia, needing to wait for a “hole” in the traffic
above into which they could merge. The CAASD helped
US Airways and Philadelphia airport officials establish a
set of RNAV departure routes that do not interfere with
the prevailing established traffic. Traffic heading north
or south can join the established flows at a point further
ahead when higher altitudes and speeds have been
attained. Aircraft properly equipped to execute RNAV
procedural routes can exit the terminal area faster — a
powerful inducement for aircraft operators to upgrade
their navigation equipment.
Another example of an RNAV departure is the PRYME
TWO DEPARTURE from Washington Dulles
International. Notice in Figure 1-10 the RNAV waypoints
not associated with VORs help free up the flow of
IFR traffic out of the airport by not funneling them to
one point through a common NAVAID.