How about a few words from the horses mouth on spares and availability.......
ON THE AVAILABILITY OF THE CH149 CORMORANT FLEET
4 CONCLUSIONS
Studying the performance measure of the fleet relating to Search and Rescue (SAR) standby aircraft availability in an ideal sparing situation provides an answer as to whether the fleet’s poor availability is a result of its maintenance programme (which includes its scheduled inspections and maintenance, corrective maintenance, and so on), and whether or not the problem of the fleet’s availability could possibly be solved by solving the logistical problem.
It was found that in order to meet the target range, at least 7 aircraft are required at MOB Comox, and at least 6 aircraft are required at all other MOBs assuming an ideal access to spares.
Hence at least 25 or 19 aircraft are required if four or three bases are desired, respectively. 
Additionally, it was shown that a 25% reduction in the durations of the major, minor, and out-of-sequence inspections of the aircraft had significant impacts on the number of aircraft required. It was found that with these reductions in place, only 5 aircraft would be required at each base in an ideal sparing situation, for a total of 20 aircraft if 4 MOBs are in operation, or a total of 15 aircraft if 3 MOBs are in operation. It should not be expected that the current fleet of 14 aircraft can operate indefinitely from 4, or even 3, MOBs without significant changes to the fleet’s maintenance program.
These results imply that the fleet’s availability problem (of not meeting the target range for the performance measure) cannot theoretically be solved simply by addressing the logistical problem of the spares – the maintenance demands of the fleet need to be reduced or the size of the fleet would have to be increased in order to meet the performance measure’s target range.
http://www.informs-sim.org/wsc08papers/142.pdf