Method of amending navigation data of a global navigation system

A method for reducing the effect of clock frequency jumps on a position determination device in a global navigation system in which a plurality of space vehicles, each having at least one clock, transmit information to the position determination device;

• said method comprising:
• a) said position determination device receiving navigation signals from space vehicles of a first group of space vehicles that have clocks in which frequency jumps do not occur;
• b) checking
• b1) whether navigation signals received from a number of space vehicles of said first group of space vehicles that are available sufficient to calculate a global navigation solution;
• and
• b2) whether an integrity risk calculated with the navigation signals received from the space vehicles of said first group of space vehicles is less than or equal to a predetermined acceptable maximum integrity risk;
• c) continuing with calculating a navigation solution, or with a critical operation if the conditions of steps b1) and b2) are fulfilled;
• or otherwise, continuing with step d);
• d) said position determination device receiving navigation signals from space vehicles of a second group of space vehicles having clocks in which frequency jumps can occur;
• e) adding, with integrity and in a safe manner, said navigation signals received from a space vehicle of said second group to said navigation signals received from the space vehicles of said first group;
• f) checking whether an integrity risk calculated for all combinations of the navigation signals received from the space vehicles of said first group, together with a sub-set of space vehicles of said second group which have integrity, is less than or equal to a predetermined acceptable maximum integrity risk;
• g) continuing with calculating the navigation solution or the critical operation if the condition of step f) is fulfilled;
• or otherwise, adding navigation signals received from another space vehicle of said second group to the navigation signals used in step f), with integrity and in a safe manner and repeating with step f).