This excerpt taken from the PCG 10-K filed Feb 18, 2005.
Accumulated Forced Outage(IMS) Duration:
The accumulated Forced Outage(IMS) duration in minutes shall be calculated as follows for each of the Transmission Line Circuits having a Forced Outage(IMS) frequency (fik) greater than zero for the calendar year k:
The durations of extended Forced Outages(IMS) shall be capped as described in Section 4.2.2. "Capping of Forced Outage(IMS) Duration" for the purposes of calculating the Availability Measures . In addition, certain types of events/Outages shall be excluded from the calculations of the Availability Measures as described in Section 4.2.3 "Excluded Events".
If a PTO makes changes to its Transmission Line Circuit identification, configuration, or Outage(IMS) data reporting schemes, the PTO shall notify the ISO at the time of the change. In its annual report to the ISO the PTO shall provide recommendations regarding how the Availability Measures and Availability Measure Targets should be modified to ensure they remain consistent with the modified Transmission Line Circuit identification or Outage(IMS) data reporting scheme, and that they provide an appropriate gauge of performance.