Failure Effects Evaluation for ATC Automation System

Table 3

Scoring method of occurrence degree.

Score	The possibility of failure		Reference value of failure probability
1	Rare	Low possibility of failure mode	1/106
2	Low	Possibility of failure mode is relatively low	1/20000
			1/4000
3
4	Middle	Middle possibility of failure mode	1/1000
5			1/400
6			1/80
7	High	High possibility of failure mode	1/40
8			1/20
9	Extremely; high	Extremely high possibility of failure mode	1/2
			1/8
10