Document ID: chunk:federal_register_of_legislation:F2024C01244:reg:5:p75
Version: federal_register_of_legislation:F2024C01244
Segment Type: reg
Provision Reference: reg 5 (pt 75/225)
Character Range: 508558–511275

distribution as follows:

(a) for vertical beam spread — a minimum of 3 degrees;

(b) at -1 degree elevation — a minimum of 50% of the lower tolerance value of the peak intensity;

(c) at 0 degrees elevation — a minimum of 100% of the lower tolerance value of the peak intensity.

       (3) For subsection (2), vertical beam spread means the angle between 2 directions in a plane for which the intensity is equal to 50% of the lower tolerance value of the peak intensity.

       (4) If, instead of obstacle marking, a flashing white light is used during the day to indicate temporary obstacles in the vicinity of an aerodrome, the peak effective intensity of the light must be increased to 20 000  25% cd when the background luminance is 50 cd/m² or greater.

9.34 Characteristics of high-intensity obstacle lights

       (1) High-intensity obstacle lights are flashing white lights.

       (2) The effective intensity of a high-intensity obstacle light located on an object or structure, other than a tower supporting overhead wires or cables, must vary depending on background luminance as follows:

(a) 200 000  25% cd effective intensity at a background luminance above 500 cd/m²;

(b) 20 000  25% cd effective intensity at a background luminance between 50‑500 cd/m²;

(c) 2 000  25% cd effective intensity at a background luminance below 50 cd/m².

       (3) The effective intensity of a high-intensity obstacle light located on a tower supporting overhead wires or cables must vary depending on background luminance as follows:

(a) 100 000  25% cd effective intensity at a background luminance above 500 cd/m²;

(b) 20 000  25% cd effective intensity at a background luminance between 50‑500 cd/m²;

(c) 2 000  25% cd effective intensity at a background luminance below 50 cd/m².

       (4) High-intensity obstacle lights located on an object or structure, other than a tower supporting overhead wires or cables, must flash simultaneously at a rate between 40‑60 flashes per minute.

       (5) High-intensity obstacle lights located on a tower supporting overhead wires or cables must flash:

(a) sequentially in a cycle as follows: first the middle light, next the top light, and last the bottom light; and

(b) with a cycle frequency of 40‑60 flashes per minute; and

(c) within a cycle — so that the interval between the flashes of each of the lights mentioned in a row of column 1 of Table 9.34 (5) is as close as possible to the proportion of the cycle time mentioned in the same row in column 2.

     Table 9.34 (5)   High-intensity obstacle light flash rates
Flash interval between   Proportion of cycle time
middle and top light     1/13
top and bottom light     2/13
bottom and middle