triangle at the top of the instrument dial. The VOR receiver  drives the solid pointer to indicate the magnetic direction TO  a tuned VOR station. When the ADF is tuned to an NDB,  the double, or hollow pointer, indicates the magnetic bearing  to the NDB. Since the flux gate compass continuously adjusts the  azimuth card so that the aircraft heading is at the top of the  instrument, pilot workload is reduced. The pointers indicate  where the VOR and ADF transmission stations are located  in relationship to where the aircraft is currently positioned.  Push buttons allow conversion of either pointer to either ADF  or VOR for navigation involving two of one type of station  and none of the other. An ILS is used to land an aircraft when visibility is poor. This  radio navigation system guides the aircraft down a slope to the  touch down area on the runway. Multiple radio transmissions  are used that enable an exact approach to landing with an  ILS. A localizer is one of the radio transmissions. It is used to  provide horizontal guidance to the center line of the runway.  A separate glideslope broadcast provides vertical guidance of  the aircraft down the proper slope to the touch down point.  Compass locator transmissions for outer and middle approach  marker beacons aid the pilot in intercepting the approach  navigational aid system. Marker beacons provide distance- from-the-runway information. Together, all of these radio  signals make an ILS a very accurate and reliable means for  landing aircraft.  [Figure 11-110] The localizer broadcast is a VHF broadcast in the lower  range of the VOR frequencies (108 MHz–111.95 MHz) on  odd frequencies only. Two modulated signals are produced  from a horizontally polarized antenna complex beyond the  far end of the approach runway. They create an expanding  field that is 2 1 ⁄ 2° wide (about 1,500 feet) 5 miles from the  runway. The field tapers to runway width near the landing  threshold. The left side of the approach area is filled with a  VHF carrier wave modulated with a 90 Hz signal. The right  side of the approach contains a 150 MHz modulated signal.  The aircraft’s VOR receiver is tuned to the localizer VHF  frequency that can be found on published approach plates  and aeronautical charts.  To save space in the instrument panel and to consolidate related  information into one easy to use location, the radio magnetic  indicator (RMI) has been developed. It is widely used. The  RMI combines indications from a magnetic compass, VOR,  and ADF into one instrument.  [Figure 11-109] The azimuth card of the RMI is rotated by a remotely located  flux gate compass. Thus, the magnetic heading of the aircraft  is always indicated. The lubber line is usually a marker or  The circuitry specific to standard VOR reception is inactive  while the receiver uses localizer circuitry and components  common to both. The signals received are passed through  filters and rectified into DC to drive the course deviation  indicator. If the aircraft receives a 150 Hz signal, the CDI of  the VOR/ILS display deflects to the left. This indicates that  the runway is to the left. The pilot must correct course with  11-49 Figure 11-109.  A radio magnetic indicator (RMI) combines a  magnetic compass, VOR, and ADF indications.  Figure 11-108.  In modern ADF, a rotor in a goniometer replaces a  the rotating loop antenna used in earlier models.  Instrument Landing Systems (ILS) Radio Magnetic Indicator (RMI) Localizer 33 30 24 21 15 12 6 3 W S E N HDG Motor ADF indicator From loop-drive amplifier To loop input of  the ADF  receiver Fixed loop Goniometer 33 30 24 2I I5 I2 6 3 N S W E