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elevation and range data and the other whose beam scans through a horizontal plane to provide azimuth and range data. Information obtained from this system is presented through the Azimuth Indicators and the Elevation Indicators each of which includes two cathodo ray tube presentations. One CRT presentation has a 10 mile range while the other has a 3 mile range. The 10 mile tube information is used during the initial stages of the approach, when the incoming plane is being lined up with the approach path, and the three mile tube information is utilized during the latter stages when extreme accuracy is required.

Present GCA is entirely mobile. It is located on the approaching pilots' left about half-way down the runway about 100 feet in from the edge of the runway.

In order to familiarize pilots with the communication procedure used in connection with GCA, Floyd Bennet which is equipped with this system will be used in this example. The procedure with the exception of call sign would be practically the same at any other installation.

Floyd Bennet GCA call is: "FLOYD BENNET GCA"

Available Communication at Floyd Bennet GCA unit.

(a) Transmitters

(1) MHF - 3 units (10 channels each)
(2) VHF - 3 units ( 4 channels each)

(b) Receivers

(1) MHF - 3 units (1500-9000 kc)
(2) VHF - 3 units (4 channels each)

From the above it will be seen that there is a wide coverage of frequencies possible but unfortunately, those assigned to airlines may only be had upon request. This is under a prearranged basis. In an emergency, the procedure is to call the company,who will, in turn, call the GCA unit. The frequencies which concern Colonial Airlines at the present writing for the GCA unit are:

MHF Communications           VHF Communications
    3117.5 kc                      118.3 mc
                                   118.5 mc
                                   140.58mc

In the event of communication trouble, the plane will report to last station contacted on last successful frequency for re-assignment of radio frequency or further instructions:

(a) At any time the pilot, while making a GCA, believes "FLOYD BENNET, GCA" is not transmitting, or has been blocked out, he will immediately climb to 1500 feet and return to the Rockaway Marker. He will hold over this point flying two minutes outbound and back to the marker until communications have been re-established.