Is that not due to SIA internal requirements for an FO to have a number of PF sectors before being upgraded.
Many FOs chose the route of higher pay on long haul aircraft getting few sectors resulting in a long drawn out time before being eligible fir a command upgrade.
My understanding one of factors to be eligible they ask for is 500 PF sectors, which many would say is even insufficient to handle a transport category aircraft to its limits.
Where did the 500PF come from? I think you better get your facts right before such a post..it can cause heart attack for many!
