However, equipment in general is much more complex
than it was even fifteen years ago. This has led to startling
changes in the patterns of equipment failure, as shown in
Figure 3. The graphs show conditional probability of failure against operating age for a wide variety of electrical
and mechanical items.
Pattern A is the well-known bathtub curve, and pattern
B is the same as Figure 2. Pattern C shows slowly increasing probability of failure with no specific wear-out age.
Pattern D shows low failure probability to begin with then
a rapid increase to a constant level, while pattern E shows