CFR > Title 14 - Aeronautics and Space > CHAPTER I—FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION > SUBCHAPTER J—NAVIGATIONAL FACILITIES (parts 170 to 171) > PART 171—NON-FEDERAL NAVIGATION FACILITIES > SUBPART J—Microwave Landing System (MLS) (§171.301 to §171.327) > 171.313—Azimuth performance requirements.

171.313—Azimuth performance requirements.

This section prescribes the performance requirements for the azimuth equipment of the MLS as follows:
(a) Approach azimuth coverage requirements. The approach azimuth equipment must provide guidance information in at least the following volume of space (see Figure 9):
Table 8b—Auxiliary Data Word Address Codes
No. I13 I14 I15 I16 I17 I18 I19 I20
1. 0 0 0 0 0 1 1 1
2. 0 0 0 0 1 0 1 0
3. 0 0 0 0 1 1 0 1
4. 0 0 0 1 0 0 1 1
5. 0 0 0 1 0 1 0 0
6. 0 0 0 1 1 0 0 1
7. 0 0 0 1 1 1 1 0
8. 0 0 1 0 0 0 1 0
9. 0 0 1 0 0 1 0 1
Code of Federal Regulations 822
10. 0 0 1 0 1 0 0 0
11. 0 0 1 0 1 1 1 1
12. 0 0 1 1 0 0 0 1
13. 0 0 1 1 0 1 1 0
14. 0 0 1 1 1 0 1 1
15. 0 0 1 1 1 1 0 0
16. 0 1 0 0 0 0 1 1
17. 0 1 0 0 0 1 0 0
18. 0 1 0 0 1 0 0 1
19. 0 1 0 0 1 1 1 0
20. 0 1 0 1 0 0 0 0
21. 0 1 0 1 0 1 1 1
22. 0 1 0 1 1 0 1 0
23. 0 1 0 1 1 1 0 1
24. 0 1 1 0 0 0 0 1
25. 0 1 1 0 0 1 1 0
26. 0 1 1 0 1 0 1 1
27. 0 1 1 0 1 1 0 0
28. 0 1 1 1 0 0 1 0
29. 0 1 1 1 0 1 0 1
30. 0 1 1 1 1 0 0 0
31. 0 1 1 1 1 1 1 1
32. 1 0 0 0 0 0 1 0
33. 1 0 0 0 0 1 0 1
34. 1 0 0 0 1 0 0 0
35. 1 0 0 0 1 1 1 1
36. 1 0 0 1 0 0 0 1
37. 1 0 0 1 0 1 1 0
38. 1 0 0 1 1 0 1 1
39. 1 0 0 1 1 1 0 0
40. 1 0 1 0 0 0 0 0
41. 1 0 1 0 0 1 1 1
42. 1 0 1 0 1 0 1 0
43. 1 0 1 0 1 1 0 1
44. 1 0 1 1 0 0 1 1
45. 1 0 1 1 0 1 0 0
46. 1 0 1 1 1 0 0 1
47. 1 0 1 1 1 1 1 0
48. 1 1 0 0 0 0 0 1
49. 1 1 0 0 0 1 1 0
50. 1 1 0 0 1 0 1 1
51. 1 1 0 0 1 1 0 0
52. 1 1 0 1 0 0 1 0
53. 1 1 0 1 0 1 0 1
54. 1 1 0 1 1 0 0 0
55. 1 1 0 1 1 1 1 1
56. 1 1 1 0 0 0 1 1
57. 1 1 1 0 0 1 0 0
58. 1 1 1 0 1 0 0 1
59. 1 1 1 0 1 1 1 0
60. 1 1 1 1 0 0 0 0
61. 1 1 1 1 0 1 1 1
62. 1 1 1 1 1 0 1 0
63. 1 1 1 1 1 1 0 1
64. 0 0 0 0 0 0 0 0

Code of Federal Regulations

Note 1: Parity bits I19 and I20 are chosen to satisfy the equations: I13 I14 I15 I16 I17 I18 I19 = EVEN I14 I16 I18 I20 = EVEN
Table 8c—Auxiliary Data
Word (See note 6) Data content Type of data Maximun time between transmissions (Seconds) Bits used Range of values Least significant bit
A1 Preamble Digital 1.0 12
Address 8
Approach azimuth antenna offset 10 −511 m to 511 m (See note 3) 1 m
Approach azimuth to MLS datum point distance 13 0 m to 8 191 m 1 m
Approach azimuth antenna alignment with runway centerline 12 −20.47° to 20.47° (See note 3) 0.01°
Approach azimuth antenna coordinate system 1 (See note 2)
Spare 13
Parity 7 (See note 1)
A2 Preamble Digital 1.0 12
Address 8
Approach elevation antenna offset 10 −511 m to 511 m (See note 3) 1 m
MLS datum point to threshold distance 10 0 m to 1 023 m 1 m
Approach elevation antenna height 7 −6.3 m to 6.3 m (See note 3) 0.1 m
Spare 22
Parity 7 (See note 1)
A3 Preamble Digital (See note 4) 12
Address 8
DME offset 10 −511 m to 511 m 1 m
DME to MLS datum point distance 14 −8 191 m to 8 191 m (See note 3) 1 m
Spare 25
Parity 7 (See note 1)
A4 Preamble Digital (See note 5) 12
Code of Federal Regulations 823
Address 8
Back azimuth antenna 10 −511 m to 511 m (See note 3) 1 m
Back azimuth to MLS datum point distance 11 0 m to 2 047 m 1 m
Back azimuth antenna alignment with runway centerline 12 −20.47° to 20.47° (See note 3) 0.01°
Spare 16
Parity 7 (See note 1)

Code of Federal Regulations

Note 1: Parity bits I70 to I76 are chosen to satisfy the equations which follow: For BIT I70: Even = (I13 ... I18) I20 I22 I24 I25 I28 I29 I31 I32 I33 I35 I36 I38 I41 I44 I45 I46 I50 (I52 ... I55) I58 I60 I64 I65 I70 For BIT I71: Even = (I14 ... I19) I21 I23 I25 I26 I29 I30 I32 I33 I34 I36 I37 I39 I42 I45 I46 I47 I51 (I53 ... I56) I59 I61 I65 I66 I71 For BIT I72: Even = (I15 ... I20) I22 I24 I26 I27 I30 I31 I33 I34 I35 I37 I38 I40 I43 I46 I47 I48 I52 (I54 ... I57) I60 I62 I66 I67 I72 For BIT I73: Even = (I16 ... I21) I23 I25 I27 I28 I31 I32 I34 I35 I36 I38 I39 I41 I44 I47 I48 I49 I53 (I55 ... I58) I61 I63 I67 I68 I73 For BIT I74: Even = (I17 ... I22) I24 I26 I28 I29 I32 I33 I35 I36 I37 I39 I40 I42 I45 I48 I49 I50 I54 (I56 ... I59) I62 I64 I68 I69 I74 For BIT I75: Even = (I13 ... I17) I19 I21 I23 I24 I27 I28 I30 I31 I32 I34 I35 I37 I40 I43 I44 I45 I49 (I51 ... I54) I57 I59 I63 I64 I69 I75 For BIT I76: Even = I13 I14 ... I75 I76

Code of Federal Regulations

Note 2: Code for I56 is: 0 = conical; 1 = planar.

Code of Federal Regulations

Note 3: The convention for the coding of negative numbers is as follows: − MSB is the sign bit; 0 = ; 1 = −. —Other bits represent the absolute value. The convention for the antenna location is as follows: As viewed from the MLS approach reference datum looking toward the datum point, a positive number shall represent a location to the right of the runway centerline (lateral offset) or above the runway (vertical offset), or towards the stop end of the runway (longitudinal distance). The convention for the antenna alignment is as follows: As viewed from above, a positive number shall represent clockwise rotation from the runway centerline to the respective zero-degree guidance plane.

Code of Federal Regulations

Note 4: Data Word A3 is transmitted at intervals of 1.0 seconds or less throughout the approach Azimuth coverage sector, except when back Azimuth guidance is provided. Where back Azimuth is provided transmit at intervals of 1.33 seconds or less throughout the approach Azimuth sector and 4.0 seconds or less throughout the back Azimuth coverage sector.

Code of Federal Regulations

Note 5: When back Azimuth guidance is provided, transmit at intervals of 1.33 seconds or less throughout the back Azimuth coverage sector and 4.0 seconds or less throughout the approach Azimuth coverage sector.

Code of Federal Regulations

Note 6: The designation “A1” represents the function identification code for “Auxiliary Data A” and address code number 1.

Code of Federal Regulations

Code of Federal Regulations 824
[Please see PDF for image: EC15SE91.014 ]
(1) Horizontally within a sector plus or minus 40 degrees about the runway centerline originating at the datum point and extending in the direction of the approach to 20 nautical miles from the runway threshold. The minimum proportional guidance sector must be plus or minus 10 degrees about the runway centerline. Clearance signals must be used to provide the balance of the required coverage, where the proportional sector is less than plus or minus 40 degrees. When intervening obstacles prevent full coverage, the ±40° guidance sector can be reduced as required. For systems providing ±60° lateral guidance the coverage requirement is reduced to 14 nm beyond ±40°.
(2) Vertically between:
(i) A conical surface originating 2.5 meters (8 feet) above the runway centerline at threshold inclined at 0.9 degree above the horizontal.
(ii) A conical surface originating at the azimuth ground equipment antenna inclined at 15 degrees above the horizontal to a height of 6,000 meters (20,000 feet).
(iii) Where intervening obstacles penetrate the lower surface, coverage need be provided only to the minimum line of sight.
(3) Runway region:
(i) Proportional guidance horizontally within a sector 45 meters (150 feet) each side of the runway centerline beginning at the stop end and extending parallel with the runway centerline in the direction of the approach to join the approach region. This requirement does not apply to offset azimuth installations.
(ii) Vertically between a horizontal surface which is 2.5 meters (8 feet) above the farthest point of runway centerline which is in line of sight of the azimuth antenna, and in a conical surface originating at the azimuth ground equipment antenna inclined at 20 degrees above the horizontal up to a height to 600 meters (2,000 feet). This requirement does not apply to offset azimuth installations.
(4) Within the approach azimuth coverage sector defined in paragraphs (a) (1), and (2) and (3) of this section, the power densities must not be less than those shown in Table 9 but the equipment design must also allow for:
(i) Transmitter power degradation from normal by −1.5 dB;
Table 9—Minimum Power Density Within Coverage Boundaries(dBW/m2)
Function Data signals Angle signals for various antenna beamwidths Clearance signals
1° 1.5° 2° 3°
Approach azimuth −89.5 −88 −85.5 −82 −88
High rate approach azimuth −89.5 −88 −88 −86.5 −88
Back azimuth −89.5 −88 −85.5 −82 −88
Approach elevation −89.5 −88 −88 −88
(ii) Rain loss of −2.2 dB at the longitudinal coverage extremes.
(b) Siting requirements. The approach azimuth antenna system must, except as allowed in paragraph (c) of this section:
(1) Be located on the extension of the centerline of the runway beyond the stop end;
(2) Be adjusted so that the zero degree azimuth plane will be a vertical plane which contains the centerline of the runway served;
(3) Have the minimum height necessary to comply with the coverage requirements prescribed in paragraph (a) of this section;
(4) Be located at a distance from the stop end of the runway that is consistent with safe obstruction clearance practices;
(5) Not obscure any light of an approach lighting system; and
(6) Be installed on frangible mounts or beyond the 300 meter (1,000 feet) light bar.
(c) On runways where limited terrain prevents the azimuth antenna from being positioned on the runway centerline extended, and the cost of the land fill or a tall tower antenna support is prohibitive, the azimuth antenna may be offset.
(d) Antenna coordinates. The scanning beams transmitted by the approach azimuth equipment within ±40° of the centerline may be either conical or planar.
(e) Approach azimuth accuracy. (1) The system and subsystem errors shall not exceed those listed in Table 10 at the approach reference datum.
At the approach reference datum, temporal sinusoidal noise components shall not exceed 0.025 degree peak in the frequency band 0.01 Hz to 1.6 Hz, and the CMN shall not exceed 0.10 degree. From the approach reference datum to the coverage limit, the PFE, PFN and CMN limits, expressed in angular terms, shall be allowed to linearly increase as follows:
(i) With distance along the runway centerline extended, by a factor of 1.2 for the PFE and PFN limits and to ±0.10 degree for the CMN limits.
(ii) With azimuth angle, by a factor of 1.5 at the ±40 degree and a factor of 2.0 at the ±60 degree azimuth angles for the PFE, PFN and CMN limits.
(iii) With elevation angle from 9 degrees to 15 degrees, by a factor of 1.5 for the PFE and PFN limits.
(iv) Maximum angular limits. The PFE limits shall not exceed ±0.25 degree in any coverage region below an elevation angle of 9 degrees nor exceed ±0.50 degree in any coverage region above that elevation angle. The CMN limits shall not exceed ±0.10 degree in any coverage region within ±10 degrees of runway centerline extended nor exceed ±0.20 degree in any other region within coverage.

Code of Federal Regulations

Note: It is desirable that the CMN not exceed ±0.10 degree throughout the coverage.
(f) Approach azimuth antenna characteristics are as follows:
(1) Drift. Any azimuth angle as encoded by the scanning beam at any point within the proportional coverage must not vary more than ±0.07 degree over the range of service conditions specified in § 171.309(d) without the use of internal environmental controls. Multipath effects are excluded from this requirement.
(2) Beam pointing errors. The azimuth angle as encoded by the scanning beam at any point within ±0.5 degree of the zero degree azimuth must not deviate from the true azimuth angle at that point by more than ±.05 degree. Multipath and drift effects are excluded from this requirement.
Table 10—Approach Azimuth Accuracies at the Approach Reference Datum
Error type System Angular error (degrees)
Ground subsystem Airborne subsystem
PFE ±20 ft. (6.1m) 1,2 ±0.118° 3 ±0.017°
CMN ±10.5 ft. (3.2m) 1,2,4 ±0.030° ±0.050°
Notes:
1 Includes errors due to ground and airborne equipment and propagation effects.