MTTA sits before MTTR in the timeline — it's purely about how long a reported fault sits unclaimed, not how long the fix takes. A fault reported at 9:00 and picked up at 9:45 has a 45-minute MTTA, regardless of whether the repair itself takes five minutes or five hours.
It's a routing and staffing metric more than a technical one. A rising MTTA usually means faults aren't reaching the right person automatically — floor staff reporting to a form nobody monitors, or a queue with no escalation when nothing picks it up in a set window.