Sid,
BALPA will not enter negotiations regarding NAPS unless the deal on offer to those on BARP is improved to one which is industry leading. Whether or not there's a chance of getting those guys onto NAPS is another issue. The BARP guys have an awful lot more to lose if they don't back the campaign. The pensionable pay increases (on which BARP is also based) will be restricted to inflation. That will cost an effective 56% of the pension at retirement in 30 years time. I'm on NAPS and that will be a significant hit. Those on BARPS will not even have a pot to p!ss in.
If they choose not to join us (it may yet be deemed illegal), the BARPS guys are all at least fifteen years from command so even if they turn up, they won't be going flying anyway.