Federal Aviation Administration, DOT Section 171.311 Note 3: Characters are encoded using the International Alphabet Number 5, (IA-5): Note 4: Coding for status bit: 0 = Function not radiated, or radiated in test mode (not reliable for navigation). 1 = Function radiated in normal mode (for Back Azimuth, this also indicates that a Back Azimuth transmission follows). Note 5: Date items which are not applicable to a particular ground equipment shall be transmitted as all zeros. Note 6: Coding for status bits: I21 I22 0 0 DME transponder inoperative or not available. 1 0 Only IA mode or DME/N available. 0 0 FA mode, Standard 1, available. 1 1 FA mode, Standard 2, available. Note 7: The value coded shall be the actual beamwidth (as defined in Section 171.311 (j)(9) rounded to the nearest 0.5 degree. Note 8: When back Azimuth guidance is provided, Data Words 4 and 6 shall be transmitted at intervals of 1.33 seconds or less throughout the Approach Azimuth coverage and 4 seconds or less throughout the Back Azimuth coverage. Note 9: When Back Azimuth guidance is provided, Data Word 5 shall be transmitted at an interval of 1.33 seconds or less throughout the Back Azimuth coverage sector and 4 seconds or less throughout the Approach Azimuth coverage sector. Note 10: Coding for status bit: 0 = Function not radiated, or radiated in test mode (not reliable for navigation). 1 = Function radiated in normal mode. (4) Minimum glidepath the lowest angle of descent along the zero degree azimuth that is consistent with published approach procedures and obstacle clearance criteria. (5) Back azimuth status shall represent the operational status of the Back Azimuth equipment. (6) DME status shall represent the operational status of the DME equipment. (7) Approach azimuth status shall represent the operational status of the approach azimuth equipment. (8) Approach elevation status shall represent the operational status of the approach elevation equipment. (9) Beamwidth the width of the scanning beam main lobe measured at the Section3 dB points and defined in angular units on the antenna boresight, in the horizontal plane for the azimuth function and in the vertical plane for the elevation function. (10) DME distance shall represent the minimum distance between the DME antenna phase center and the vertical plane perpendicular to the runway centerline which contains the MLS datum point. (11) Approach azimuth magnetic orientation shall represent the angle measured in the horizontal plane clockwise from Magnetic North to the zero-degree angle guidance radial originating from the approach azimuth antenna phase center. The vertex of the meas- ured angle shall be at the approach azimuth antenna phase center. NOTE: For example, this data item would be encoded 090 for an approach azimuth antenna serving runway 27 (assuming the magnetic heading is 270 degrees) when sited such that the zero degree radial is parallel to centerline. (12) Back azimuth magnetic orientation shall represent the angle measured in the horizontal plane clockwise from Magnetic North to the zero-degree angle guidance radial originating from the Back Azimuth antenna. The vertex of the measured angle shall be at the Back Azimuth antenna phase center. NOTE: For example, this data item would be encoded 270 for a Back Azimuth Antenna serving runway 27 (assuming the magnetic heading is 270 degrees) when sited such that the zero degree radial is parallel to centerline. (13) Back azimuth proportional coverage limit shall represent the limit of the sector in which proportional back azimuth guidance is transmitted. (14) MLS ground equipment identification shall represent the last three characters of the system identification specified in Section 171.311(i)(2). The characters shall be encoded in accordance with International Alphabet No. 5 (IA- 5) using bits b1 through b6. NOTE: Bit b7 of this code may be reconstructed in the airborne receiver by taking the complement of bit b6. (k) Residual radiation. The residual radiation of a transmitter associated with an MLS function during time intervals when it should not be transmitting shall not adversely affect the reception of any other function. The residual radiation of an MLS function at times when another function is radiating shall be at least 70 dB below the level provided when transmitting. (l) Symmetrical scanning. The TO and FRO scan transmissions shall be symmetrically disposed about the mid-scan point listed in Tables 4a, 4b and 5. The mid-scan point and the center of the time interval between the TO and FRO scan shall coincide with a tolerance of plus or minus 10 microseconds. (m) Auxiliary data - (1) Addresses. Three function identification codes are reserved to indicate transmission of Auxiliary Data A, Auxiliary Data B, 863 VerDate Sep<11>2014 08:20 May 17, 2019 Jkt 247048 PO 00000 Frm 00873 Fmt 8010 Sfmt 8010 Y:\SGML\247048.XXX 247048