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here for intercepting and maintaining such arcs are applicable
to any facility that provides DME information. Such a facility
may or may not be collocated with the facility that provides
final approach guidance.
As an example of flying a DME arc, refer to Figure 7-17 and
follow these steps:
1. Track inbound on the OKT 325° radial, frequently
checking the DME mileage readout.
2. A 0.5 NM lead is satisfactory for groundspeeds of 150
knots or less; start the turn to the arc at 10.5 miles. At
higher groundspeeds, use a proportionately greater
lead.
7-18
005° Radial
10°
10°
20°
20°
11 DME arc
9 DME arc
Desired arc
10 DME
OBS
N
E
S
W
3
33
24
21
15
12
306
NAV
GS
View is from the pilots
perspective, and the
movable card is reset
after each turn
33
30
24
21
15
12
6
3
S
W
E
N
HDG
33
30
24
21
15
12
6
3
S
W
E
N
HDG
33
30
24
21
15
12
6
3
W
S
E
N
HDG
Figure 7-17. Using DME and RMI Figure 7-18. Using DME and RMI To Maintain an Arc. to maintain arc.
3. Continue the turn for approximately 90°. The roll-out
heading will be 055° in a no wind condition.
4. During the last part of the intercepting turn, monitor
the DME closely. If the arc is being overshot (more
than 1.0 NM), continue through the originally planned
roll-out heading. If the arc is being undershot, roll-out
of the turn early.
The procedure for intercepting the 10 DME when outbound
is basically the same, the lead point being 10 NM minus 0.5
NM, or 9.5 NM.
When flying a DME arc with wind, it is important to keep a
continuous mental picture of the aircraft’s position relative to
the facility. Since the wind-drift correction angle is constantly
changing throughout the arc, wind orientation is important.
In some cases, wind can be used in returning to the desired
track. High airspeeds require more pilot attention because of
the higher rate of deviation and correction.
Maintaining the arc is simplified by keeping slightly inside
the curve; thus, the arc is turning toward the aircraft and
interception may be accomplished by holding a straight
course. When outside the curve, the arc is “turning away”
and a greater correction is required.
To fly the arc using the VOR CDI, center the CDI needle
upon completion of the 90° turn to intercept the arc. The
aircraft’s heading will be found very near the left or right
side (270° or 90° reference points) of the instrument. The
readings at that side location on the instrument will give
primary heading information while on the arc. Adjust the
aircraft heading to compensate for wind and to correct for
7-19
distance to maintain the correct arc distance. Recenter the
CDI and note the new primary heading indicated whenever
the CDI gets 2°–4° from center.
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 bearing pointer
is on the wingtip reference, turn the aircraft 20° toward
the facility to return to the arc.
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