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 30 6 NAV GS 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 Instrument view is from  the pilot’s perspective,  and the movable card is  reset after each turn Figure 9-18. Using DME and RMI to maintain an arc. 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 9-19, 9-20,  and 9-21 ), 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. 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 displays 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. 9-19 DME Errors