A catastrophic failure is easy to design against, precisely because it is easy to see. It trips an alarm, ends a test, gets written up. The failures that actually cause the most damage over a platform’s life are quieter: a sensor that drifts a fraction of a degree per flight hour, a link that degrades gracefully enough that nobody flags it, a battery that ages faster under one specific duty cycle.
These modes rarely appear in a single test. They accumulate across a fleet, over months, and by the time the pattern is visible in the data it has usually already cost something — a mission, a component, or trust in the system.
Designing for drift, not just failure
The fix is not more alarms. It is treating slow drift as a first-class thing to monitor, with its own instrumentation and its own review cadence, separate from the binary pass/fail checks that dominate most test programmes.
In practice that means logging more than the system strictly needs to operate, and reviewing that data on a schedule even when nothing has gone wrong. The goal is to catch the trend while it is still boring, long before it becomes a finding.
