any of the following imaginary surfaces will require special aeronautical study: (1) Approach surface. (2) Horizontal surface. (3) Conical surface.

(4) Transitional surface.

(e) Under most conditions, the limits prescribed in paragraphs (a), (b) and (c) of this section will be the determining factor. However, in the areas immediately adjacent to the runways and under certain conditions where the terrain rises rapidly in the airport area, the surfaces specified in paragraph (d) of this section become a more limiting factor from the absolute height of requirements.

§ 17.16 Shielded antenna structures.

In any special aeronautical study conducted under the provisions of this subpart, the circumstances that the antenna structure will be shielded by natural formations or existing man-made structures will be taken into account.

(a) Nothing in the criteria in this subpart concerning antenna structures or locations shall apply to those structures authorized prior to February 15, 1951, the effective date of these criteria.

(b) No change in any of these criteria or relocation of airports shall at any time impose a new restriction upon any then existing or authorized antenna structure or structures.

Subpart C-Specifications for Obstruction Marking and Lighting of Antenna Structures

§ 17.21 Painting and lighting, when required.

Antenna structures shall be painted and lighted when:

(a) They require special aeronautical study; or

(b) They exceed 170 feet in height above the ground.

(c) The Commission may modify the above requirement for painting and/or lighting of antenna structures, when it is shown by the applicant that the absence of such marking would not impair the safety of air navigation, or that a lesser marking requirement would insure the safety thereof.

§ 17.22 Particular specifications to be used.

(a) Where special aeronautical study is not required, the Commission will

assign painting and lighting specifications as set forth in this subpart.

(b) Where special aeronautical study is required, the Commission will, insofar as is consistent with the safety of life and property in the air, also assign painting and lighting specifications listed in this subpart.

(c) However, where antenna installations are of such a nature that their painting and lighting in accordance with these specifications are confusing or endanger rather than assist airmen or are otherwise inadequate, the Commission will specify the type of painting and lighting or other marking to be used in the individual situation.

§ 17.23

Specifications for the painting of antenna structures in accordance with § 17.21.

Antenna structures shall be painted throughout their height with alternate bands of aviation surface orange and white, terminating with aviation surface orange bands at both top and bottom. The width of the bands shall be equal and approximately one-seventh the height of the structure, provided however, that the bands shall not be more than 40 feet nor less than 11⁄2 feet in width.

§ 17.24 Specifications for the lighting of antenna structures up to and including 150 feet in height.

(a) Antenna structures up to and including 150 feet in height above the ground located in areas set forth in § 17.15 shall be lighted as follows:

(1) There shall be installed at the top of the tower at least two 100-, 107-, or 116-watt lamps (#100 A21/TS, #107 A21/TS or #116 A21/TS, respectively) enclosed in aviation red obstruction light globes. The two lights shall burn simultaneously from sunset to sunrise and shall be positioned so as to insure unobstructed visibility of at least one of the lights from aircraft at any angle of approach. A light sensitive control device or an astronomic dial clock and time switch may be used to control the obstruction lighting in lieu of manual control. When a light sensitive device is used, it should be adjusted so that the lights will be turned on at a north sky light intensity level of about 35 foot candles and turned off at a north sky light intensity level of about 58 foot candles.

$17.25 Specifications for the lighting of antenna structures over 150 feet up to and including 300 feet in height. (a) Antenna structures over 150 feet up to and including 300 feet in height above the ground shall be lighted as follows:

(1) There shall be installed at the top of the structure one 300 m/m electric code beacon equipped with two 500- or 620-watt lamps (PS-40, Code Beacon type), both lamps to burn simultaneously, and equipped with aviation red color filters. Where a rod or other construction of not more than 20 feet in height and incapable of supporting this beacon is mounted on top of the structure and it is determined that this additional construction does not permit unobstructed visibility of the code beacon from aircraft at any angle of approach, there shall be installed two such beacons positioned so as to insure unobstructed visibility of at least one of the beacons from aircraft at any angle of approach. The beacon shall be equipped with a flashing mechanism producing not more than 40 flashes per minute nor less than 12 flashes per minute with a period of darkness equal to one-half of the luminous period.

(2) At the approximate mid point of the over-all height of the tower there shall be installed at least two 100-, 107-, or 116-watt lamps (#100 A21/TS, #107 A21 TS or #116 A21/TS, respectively) enclosed in aviation red obstruction light globes. Each light shall be mounted so as to insure unobstructed visibility of at least one light at each level from aircraft at any angle of approach.

(3) All lights shall burn continuously or shall be controlled by a light sensitive device adjusted so that the lights will be turned on at a north sky light intensity level of about 35 foot candles and turned off at a north sky light intensity level of about 58 foot candles.

$17.26 Specifications for the lighting of

antenna structures over 300 feet up to and including 450 feet in height. (a) Antenna structures over 300 feet up to and including 450 feet in height above the ground shall be lighted as follows:

(1) There shall be installed at the top of the structure one 300 m m electric code beacon equipped with two 500- or 620-watt lamps (PS-40, Code Beacon type), both lamps to burn simultaneous

ly, and equipped with aviation red color filters. Where a rod or other construction of not more than 20 feet in height and incapable of supporting this beacon is mounted on top of the structure and it is determined that this additional construction does not permit unobstructed visibility of the code beacon from aircraft at any angle of approach, there shall be installed two such beacons positioned so as to insure unobstructed visibility of at least one of the beacons from aircraft at any angle of approach. The beacons shall be equipped with a flashing mechanism producing not more than 40 flashes per minute nor less than 12 flashes per minute with a period of darkness equal to one-half of the luminous period.

(2) On levels at approximately twothirds and one-third of the over-all height of the tower, there shall be installed at least two 100-, 107-, or 116watt lamps (#100 A21/TS, #107 A21/TS or #116 A21/TS, respectively) enclosed in aviation red obstruction light globes. Each light shall be mounted so as to insure unobstructed visibility of at least one light at each level from aircraft at any angle of approach.

(3) All lights shall burn continuously or shall be controlled by a light sensitive device adjusted so that the lights will be turned on at a north sky light intensity level of about 35 foot candles and turned off at a north sky light intensity level of about 58 foot candles. § 17.27 Specifications for the lighting of antenna structures over 450 feet up to and including 600 feet in height. (a) Antenna structures over 450 feet up to and including 600 feet in height above the ground shall be lighted as follows:

(1) There shall be installed at the top of the structure one 300 m/m electre code beacon equipped with two 500- or 620-watt lamps (PS-40, Code Besora type, both lamps to burn simultaneously, and equipped with artation red color filters. Where a rod or other e struction of not more than 20 feet height and incapable of supporting tha beacon is mounted on top of toe structure and it is determined that the wowot construction does not perms costructed viability of the code beacon from aircraft at any angle di approach.. there shall be trutalled two much teacons positioned so as to the ZORICUsen Vinolity of at least one of the seast sa

from aircraft at any angle of approach. The beacons shall be equipped with a flashing mechanism producing not more than 40 flashes per minute nor less than 12 flashes per minute with a period of darkness equal to one-half of the luminous period.

(2) At approximately one-half of the over-all height of the tower one similar flashing 300 m/m electric code beacon shall be installed in such position within the tower proper that the structural members will not impair the visibility of this beacon from aircraft at any angle of approach. In the event this beacon cannot be installed in a manner to insure unobstructed visibility of it from aircraft at any angle of approach, there shall be installed two such beacons. Each beacon shall be mounted on the outside of diagonally opposite corners or opposite sides of the tower at the prescribed height.

(3) On levels at approximately threefourths and one-fourth of the over-all height of the tower, at least one 100-, 107-, or 116-watt lamp (#100 A21/TS, #107 A21/TS or #116 A21/TS, respectively) enclosed in an aviation red obstruction light globe shall be installed on each outside corner of the tower at each level.

(4) All lights shall burn continuously or shall be controlled by a light sensitive device adjusted so that the lights will be turned on at a north sky light intensity level of about 35 foot candles and turned off at a north sky light intensity level of about 58 foot candles.

§ 17.28

Specifications for the lighting of antenna structures over 600 feet up to and including 750 feet in height. (a) Antenna structures over 600 feet up to and including 750 feet in height above the ground shall be lighted as follows:

(1) There shall be installed at the top of the structure one 300 m/m electric code beacon equipped with two 500- or 620-watt lamps (PS-40, Code Beacon type), both lamps to burn simultaneously, and equipped with aviation red color filters. Where a rod or other construction of not more than 20 feet in height and incapable of supporting this beacon is mounted on top of the structure and it is determined that this additional construction does not permit unobstructed visibility of the code beacon

from aircraft at any angle of approach, there shall be installed two such beacons positioned so as to insure unobstructed visibility of at least one of the beacons from aircraft at any angle of approach. The beacon shall be equipped with a flashing mechanism producing not more than 40 flashes per minute nor less than 12 flashes per minute with a period of darkness equal to one-half of the luminous period.

(2) At approximately two-fifths of the over-all height of the tower one similar flashing 300 m/m electric code beacon shall be installed in such position within the tower proper that the structural members will not impair the visibility of this beacon from aircraft at any angle of approach. In the event this beacon cannot be installed in a manner to insure unobstructed visibility of it from aircraft at any angle of approach, there shall be installed two such beacons. Each beacon shall be mounted on the outside of diagonally opposite corners or opposite sides of the tower at the prescribed height.

(3) On levels at approximately fourfifths, three-fifths and one-fifth of the over-all height of the tower, at least one 100-, 107-, or 116-watt lamp (#100 A21/ TS, #107 A21/TS or #116 A21/TS, respectively) enclosed in an aviation red obstruction light globe shall be installed on each outside corner of the tower at each level.

(4) All lights shall burn continuously or shall be controlled by a light sensitive device adjusted so that the lights will be turned on at a north sky light intensity level of about 35 foot candles and turned off at a north sky light intensity level of about 58 foot candles.

§ 17.29

Specifications for the lighting of antenna structures over 750 feet up to and including 900 feet in height. (a) Antenna structures over 750 feet up to and including 900 feet in height above the ground shall be lighted as follows:

(1) There shall be installed at the top of the structure one 300 m/m electric code beacon equipped with two 500- or 620-watt lamps (PS-40, Code Beacon type), both lamps to burn simultaneously, and equipped with aviation red color filters. Where a rod or other construction of not more than 20 feet in height and incapable of supporting this

beacon is mounted on top of the structure and it is determined that this additional construction does not permit unobstructed visibility of the code beacon from aircraft at any angle of approach, there shall be installed two such beacons positioned so as to insure unobstructed visibility of at least one of the beacons from aircraft at any angle of approach. The beacons shall be equipped with a flashing mechanism producing not more than 40 flashes per minute nor less than 12 flashes per minute with a period of darkness equal to one-half of the luminous period.

(2) On levels at approximately twothirds and one-third of the over-all height of the tower one similar flashing 300 m/m electric code beacon shall be installed in such position within the tower proper that the structural members will not impair the visibility of this beacon from aircraft at any angle of approach. In the event these beacons can not be installed in a manner to insure unobstructed visibility of the beacons from aircraft at any angle of approach, there shall be installed two such beacons at each level. Each beacon shall be mounted on the outside of diagonally opposite corners or opposite sides of the tower at the prescribed height.

(3) On levels at approximately fivesxths, one-half, and one-sixth of the over-all height of the tower, at least one 100-, 107-, or 116-watt lamp (#100 A21/ TS. #107 A21/TS or #116 A21/TS, respectively) enclosed in an aviation red obstruction light globe shall be installed on each outside corner of the tower at each level.

(4) All lights shall burn continuously or shall be controlled by a light sensitive device adjusted so that the lights will be turned on at a north sky light intensity level of about 35 foot candles and turned off at a north sky light intensity level of about 58 foot candles.

17.30 Specifications for the lighting of antenna structures over 900 feet up to and including 1,050 feet in height. (a) Antenna structures over 900 feet up to and including 1,050 feet in height above the ground shall be lighted as follows:

620-watt lamps PS-41. Code Beacon type) both lamps to burn simultaneously, and equipped with aviation red color filters. Where a rod or ciber construction of less than 20 feet in height and incapable of supporting this beacon is mounted on top of the structure and it is determined that this additional construction does not permit unobstructed visibility of the code beacon from aircraft at any angle of approach, there shall be installed two such beacons positioned so as to insure unobstructed visibility of at least one of the beacons from aircraft at any angle of approach The beacons shall be equipped with a flashing mechanism producing not more than 40 flashes per minute nor less than 12 flashes per minute, with a period of darkness equal to one-half of the luminous period.

(2) On levels at approximately foursevenths and two-sevenths of the overall height of the tower one similar flashing 300 m/m electric code beacon shall be installed in such position within the tower proper that the structural members will not impair the visibility of this beacon from aircraft at any angle of approach. In the event these beacons cannot be installed in a manner to insure unobstructed visibility of the beacons from aircraft at any angle of approach, there shall be installed two such beacons, at each level. Each beacon shall be mounted on the outside of diagonally opposite corners or opposite sides of the tower at the prescribed height.

(3) On levels at approximately sixsevenths, five-sevenths, three-sevenths and one-seventh of the over-all height of the tower at least one 100-, 107-, or 116-watt lamp (#100 A21/TS, #107 A21/ TS or #116 A21/TS, respectively) enclosed in an aviation red obstruction light globe shall be installed on each outside corner of the structure.

(4) All lights shall burn continuously or shall be controlled by a light sensitive device adjusted so that the lights will be turned on at a north sky light intensity level of about 35 foot candles and turned off at a north sky light intensity level of about 58 foot candles. § 17.31 Specifications for the lighting of antenna structures over 1,050 feet up to and including 1,200 feet in height. (a) Antenna structures over 1,050 feet up to and including 1,200 feet in height

1 There shall be installed at the top of the structure one 300 m/m electric code beacon equipped with two 500- or