Paragraph 50 Warning Signals to aircraft in flight

In the United Kingdom, by day or by night, a series of projectiles discharged from the ground at intervals of 10 seconds, each showing, on bursting, red and green lights or stars, shall indicate to the commander of an aircraft that his aircraft is flying in or about to enter an active danger area or an area to which regulations made pursuant to article 74(1)(a)(iii) of the Order relate and that he is required to take such action as may be necessary to leave the area or change course to avoid the area.