THE HONG KONG GOVERNMENT GAZETTE, JULY 27, 1928.
19. To require an aircraft to land, the following signals shall be used: -
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(a) By day three projectiles discharged at intervals of 10 seconds each showing, on bursting,.
black or yellow smoke.
(b) By night three projectiles discharged at intervals of 10 seconds each showing, on burst-
ing, green lights or stars.
In addition, when necessary to prevent the landing of aircraft other than the one ordered, a searchlight which shall be flashed intermittently shall be directed towards the aircraft whose landing is required.
20.-(a) In the event of fog or mist rendering aerodromes invisible, their presence may be indicated by a balloon acting as an aerial buoy and/or other approved means.
(b) In fog, mist, falling snow or heavy rainstorm, whether by day or night, an aircraft on the water shall make the following sound signals :--
(1) If not anchored or moored, a sound at intervals of not more than two minutes, consisting of two blasts of about five seconds' duration with an interval of about one second be- tween them.
(2) If at anchor or moored, the rapid ringing of an efficient bell or gong for about five seconds-
at intervals of not more than one minute.
SECTION III.
General Rules for Air Traffic.
21. Subject to the provisions of paragraph 43 of this Schedule, flying machines shall always give way to balloons, fixed or free, and to airships, and airships shall always give way to balloons, whether fixed or free.
22. Au airship, when not under its own control, shall be classed as a free balloon.
23. Kisk of collision can, when circumstances permit, be ascertained by carefully watching the compass bearing and angle of elevation of an approaching aircraft. If neither the bearing nor the angle of elevation appreciably change, such risk shall be deemed to exist.
24. The term "risk of collision" shall include all risk of accident due to undue proximity of other aircraft. Every aircraft that is required by these rules to give way to another to avoid collision shall. keep a safe distance, having regard to the circumstances of the case.
25. While observing the rules regarding risk of collision contained in paragraph 24 of this Schedule, a motor-driven aircraft must always manoeuvre according to the rules contained in the following para- graphs as soon as it is apparent that, if it pursued its course, it would pass at a distance of less. than 200 yards from any part of another aircraft.
26. When two motor-driven aircraft are meeting end on, or nearly end on, each shall alter its course to the right.
27. When two motor-driven aircraft are on courses which cross, the aircraft which has the other on its own right side shall keep out of the way of the other.
28. An aircraft overtaking another shall keep out of the way of the overtaken aircraft by altering its own course to the right, and must not pass by diving.
Every aircraft coming up with another aircraft from any direction more than 110 degrees from ahead of the latter, i.c., in such a position with reference to the aircraft which it is overtaking that at night it would be unable to see either of that aircraft's side lights, shall be deemed to be an over- taking aircraft, and no subsequent alteration of the bearing between the two aircraft shall make the overtaking aircraft a crossing aircraft within the meaning of these rules, or relieve it of the duty of keeping clear of the overtaken aircraft until it is finally past and clear.
As by day the overtaking aircraft cannot always know with certainty whether it is forward or abaft the direction mentioned above from the other aircraft, it should, if in doubt, assume that it is an overtaking aircraft and keep out of the way.
29. Where by any of these rules one of the two aircraft is to keep out of the way, the other shall keep its course and speed. When, in consequence of thick weather or other causes, the aircraft having the right of way finds itself so close that collision cannot be avoided by the action of the giving-way aircraft alone, it shall take such action as will best aid to avert collision.
30. Every aircraft which is directed by these rules to keep out of the way of another aircraft shall, if the circumstances of the case adınit, avoid crossing ahead of the other.
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