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Instrument Flying Handbook
The Air Traffic Control System
Communication Procedures and Facilities

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Instrument Flying


Table of Contents

Chapter 1. Human Factors
Chapter 2. Aerodynamic Factors
Chapter 3. Flight Instruments
Chapter 4. Section I
Airplane Attitude Instrument
Using Analog Instrumentation
Chapter 4. Section II
Airplane Attitude Instrument
Using an Electronic Flight

Chapter 5. Section I
Airplane Basic
Flight Maneuvers
Using Analog Instrumentation
Chapter 5. Section II
Airplane Basic
Flight Maneuvers
Using an Electronic Flight

Chapter 6. Helicopter
Attitude Instrument Flying

Chapter 7. Navigation Systems
Chapter 8. The National
Airspace System

Chapter 9. The Air Traffic
Control System

Chapter 10. IFR Flight
Chapter 11. Emergency

Center Radar Displays.
Figure 9-11. Center Radar Displays.

A common clearance in these situations is "When able,
proceed direct to the Astoria VOR .." The words "when able'
mean to proceed to the waypoint, intersection, or NAVAID
when the pilot is able to navigate directly to that point using
onboard available systems providing proper guidance, usable
signal, etc. If provided such guidance while flying VFR, the
pilot remains responsible for terrain and obstacle clearance.
Using the standard climb gradient an aircraft is 2 miles
from the departure end of the runway before it is safe to
turn (400 feet above ground level (AOL)). When a Center
controller issues a heading, a direct route, or says "direct
when able," the controller becomes responsible for terrain
and obstruction clearance.

Another common Center clearance is "Leaving (altitude)
fly (heading) or proceed direct when able." This keeps the
terrain/obstruction clearance responsibility in the flight deck
until above the minimum IFR altitude. A controller cannot
issue an IFR clearance until an aircraft is above the minimum
IFR altitude unless it is able to climb in VFR conditions.

On a Center controller's scope, 1 NM is about 1/28 of an inch.
When a Center controller is providing Approach/Departure
control services at an airport many miles from the radar
antenna, estimating headings and distances is very difficult.
Controllers providing vectors to final must set the range on
their scopes to not more than 125 NM to provide the greatest
possible accuracy for intercept headings. Accordingly, at
locations more distant from a Center radar antenna, pilots
should expect a minimum of vectoring.

A Center controller’s Scope.
Figure 9-12. A Center controller's Scope.

Center Symbology.
Figure 9-12. A Center controller's Scope.