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Instrument Flying Handbook
Navigation Systems
Traditional Navigation Systems

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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

With an RMI, in a no wind condition, pilots should
theoretically be able to fly an exact circle around the facility
by maintaining an RB of 90° or 270°. In actual practice,
a series of short legs are flown. To maintain the arc in
Figure 7-18, proceed as follows:

1. With the RMI bearing pointer on the wingtip reference
(90° or 270° position) and the aircraft at the desired
DME range, maintain a constant heading and allow the
bearing pointer to move 5°-10° behind the wingtip.
This will cause the range to increase slightly.

2. Turn toward the facility to place the bearing pointer
5-10° ahead of the wingtip reference, and then
maintain heading until the bearing pointer is again
behind the wingtip. Continue this procedure to
maintain the approximate arc.

3. If a crosswind causes the aircraft to drift away from
the facility, turn the aircraft until the bearing pointer is
ahead of the wingtip reference. If a crosswind causes
the aircraft to drift toward the facility, turn until the
bearing is behind the wingtip.

4. As a guide in making range corrections, change the RB
10°-20° for each half-mile deviation from the desired
arc. For example, in no-wind conditions, if the aircraft
is 1/2 to 1 mile outside the arc and the hearing pointer
is on the wingtip reference, turn the aircraft 20° toward
the facility to return to the arc.

Without an RMI, orientation is more difficult since there is
no direct azimuth reference. However, the procedure can be
flown using the OBS and CDI for azimuth information and
the DME. for are distance.

Intercepting Lead Radials
A lead radial is the radial at which the turn from the are to the
inbound course is started. When intercepting a radial from
a DME are, the lead will vary with are radius and ground
speed. For the average general aviation aircraft, flying arcs
such as those depicted on most approach charts at speeds
of 150 knots or less, the lead will be under 5°. There is no
difference between intercepting a radial from an are and
intercepting it from a straight course.

With an RMI, the rate of bearing movement should be
monitored closely while flying the arc. Set the course of the
radial to he intercepted as soon as possible and determine
the approximate lead. Upon reaching this point, start the
intercepting turn. Without an RMI, the technique for radial
interception is the same except for azimuth information,
which is available only from the OBS and CDI.

The technique for intercepting a localizer from a DME arc
is similar to intercepting a radial. At the depicted lead radial
(LR 223 or LR 212 in Figures 7-19, 7-20, and 7-21), a
pilot having a single VOR/LOC receiver should set it to the
localizer frequency. If the pilot has dual VOR'LOC receivers,
one unit may be used to provide azimuth information and the
other set to the localizer frequency. Since these lead radials
provide 7° of lead, a half standard rate turn should be used
until the LOC needle starts to move toward center.

DME Errors
A DME/DME fix (a location based on two DME lines of
position from two DME stations) provides a more accurate
aircraft location than using a VOR and a DME fix.

DME signals are line-of-sight; the mileage readout is the
straight-line distance from the aircraft to the DME ground
facility and is commonly referred to as slant range distance.
Slant range refers to the distance from the aircraft's antenna
to the ground station (A line at an angle to the ground
transmitter. GPS systems provide distance as the horizontal
measurement from the WP to the aircraft. Therefore, at 3,000
feet and 0.5 miles the DME (slant range) would read 0.6 NM
while the GPS distance would show the actual horizontal
distance of .5 DME. This error is smallest at low altitudes
and/or at long ranges. It is greatest when the aircraft is closer
to the facility, at which time the DME receiver will display
altitude (in NM) above the facility. Slant range error is
negligible if the aircraft is one mile or more from the ground
facility for each 1,000 feet of altitude above the elevation of
the facility.

Area Navigation (RNAV)
Area navigation (RNAV) equipment includes VOR/DME,
LORAN, GPS, and inertial navigation systems (INS). RNAV
equipment is capable of computing the aircraft position,
actual track, groundspeed, and then presenting meaningful
information to the pilot. This information may be in the form
of distance, cross-track error, and time estimates relative to
the selected track or WP. In addition, the RNAV equipment
installations must be approved for use under IFR. The Pilot's
Operating Handbook/Airplane Flight Manual (POH/AFM)
should always be consulted to determine what equipment is
installed, the operations that are approved, and the details of
equipment use. Some aircraft may have equipment that allows
input from more than one RNAV source, thereby providing
a very accurate and reliable navigation source.