As for HOLDS, it occurs to me that new aircraft cause holds.
When I joined the various forces were well established and the different sqns were building up. The training system however had had to start the recruitment and training 2 years earlier.
EFA is to come in to servive in 2000. The current jets will retire from 2001-2 as the EFA force builds up but until this happens the system needs more pilots for EFA. They get them from the front line. The front line back fills from the training system. The training system started in 1997 in order to provide the numbers of into service pilots for the back fill.
In 2003 the number of Jags and GR1s going out of service is rising rapidly and there are plenty of spare P & N. The navs are either wasted or transfered to the F3 and the pilots move on to EFA. The training system thus started to reduce the nav intake in 2000 and the pilot intake a year later.
By 2004 the system was reaching equilibrium, the EFA in to service was matched nicely by the Jag and Tornado out of service so the training system was scalled back in 2002 to ensure that it could replace natural wastage.
There was a sudden influx of pink elephants and the training system could not cope.