Takeoffs are optional, landings are mandatory

Takeoffs are Optional, Landings are Mandatory By Jim Sparks February 1998 Imagine flying to a distant destination and finding out that the pilot cannot find a runway for landing. Back in the time of Orville and Wilbur, this was not a...


Distance information is obtained from existing distance measuring equipment (DME). This is then provided to the flight crew on conventional flight deck displays. Equipment on board the aircraft for MLS operation includes a receiver, control panel, and external antenna.

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Localizer antenna
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Glideslope antenna
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MLS antennas installed on a Hawker

Global positioning systems (GPS) hold the key to the future of precision instrument landings. In fact, the 1994 Federal Radio Navigation Plan calls for the implementation of GPS for Category 1 approaches this year and Category 2 /3 is scheduled for 2001. This plan also includes the phase out of the ILS and MLS we currently use by the year 2010. GPS approaches can be used as overlays for present ILS or can even stand alone. This type of approach is made by following predetermined waypoints. Differential GPS (DGPS), in addition to providing a latitude, longitude position accuracy of .01 minutes, will also exceed the current height veracity.

Several components in the flight deck will enable the pilot to observe ILS data. In general aviation, a course deviation indicator will include two cross hair pointers; one reflecting the glideslope and the other displaying the localizer. When the two pointers are aligned over the aircraft symbol the aircraft is "ON the Beam."

Another common display is the attitude directional indicator (ADI). On more complex aircraft this instrument can be fitted with a glideslope pointer and a runway symbol (usually at the bottom of the display). The glideslope pointer will move above or below the fixed aircraft symbol alerting the pilot to the position of the center of the glide path. If the pointer is above the aircraft symbol, the pilot would have to pull up to get on the center of the beam. The runway icon moves left and right of the aircraft symbol advising the pilot of position relative to runway centerline. This information is provided by the navigation receiver.

Anytime an ILS frequency is dialed in the Nav receiver commands, the ILS symbols to appear. These selected frequencies are 108 to 111.95 MHz and only odd numbered ones. Frequencies other than odd numbers will cause the ILS symbols to bias out of view (BOV). In many installations, the left and right moving runway symbol may also have the ability to rise. The "rising runway" is controlled by the radio altimeter.

As the aircraft gets within about 100 feet above ground level (AGL), the runway symbol will begin moving toward the fixed aircraft symbol. At the point where the aircraft wheels touch the runway, the runway symbol contacts the fixed aircraft symbol on the cockpit display. Dual radio altimeters are among the numerous requirements for CAT 3 landings. Many aircraft today have the ability to couple the ILS components to the aircraft auto flight system and when coupled with auto throttles, auto brakes, and auto spoilers, the flight crew is just along for the ride.

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