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Instrument Flying Handbook
Navigation Systems
Instrument Approach Systems

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Instrument Flying
Handbook

Preface

Table of Contents

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

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

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
Operations

Precision and Nonprecision ALS Configuration.

ALSF— Approach light system with sequenced flashing lights
SSALR—Simplified short approach light system with runway alignment indicator lights
REIL—Runway and identification lights
MALSR—Medium intensity approach light system with sequenced flashing lights (and runway alignment)
ODALS— Omnidirectional approach light system

Figure 7-37. Precision and Nonprecision ALS Configuration.

The visual approach slope indicator (VASI) gives visual
descent guidance information during the approach to a
runway. The standard VASI consists of light bars that
project a visual glide path, which provides safe obstruction
clearance within the approach zone. The normal GS angle
is 3°; however, the angle may be as high as 4.5° for proper
obstacle clearance. On runways served by ILS, the VASI
angle normally coincides with the electronic GS angle.
Visual left/right course guidance is obtained by alignment
with the runway lights. The standard VASI installation
consists of either 2-, 3-, 4-, 6-, 12-, or 16-Light units arranged
in downwind and upwind light bars. Some airports serving
long-bodied aircraft have three-bar VASIs, which provide two
visual glide paths to the same runway. The first glide path
encountered is the same as provided by the standard VASI.
The second glide path is about 25 percent higher than the first
and is designed for the use of pilots of long-bodied aircraft.

The basic principle of VASI is that of color differentiation
between red and white. Each light projects a beam having
a white segment in the upper part and a red segment in the
lower part of the beam. From a position above the glide path
the pilot sees both bars as white. Lowering the aircraft with
respect to the glide path, the color of the upwind bars changes
from white to pink to red. When on the proper glide path,
the landing aircraft will overshoot the downwind bars and
undershoot the upwind bars. Thus the downwind (closer)
bars are seen as white and the upwind bars as red. From a
position below the glide path, both light bars are seen as
red. Moving up to the glide path, the color of the downwind
bars change from red to pink to white. When below the
glide path, as indicated by a distinct all-red signal, a safe
obstruction clearance might not exist. A standard two-bar
VASI is illustrated in Figure 7-38.

 
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