My cockatiel is pulling out his feathers, not the little fluffy ones, but his long wing feathers.

I wouldn't normally be concerned about this because he did pull out some of his long ones last year coming into summer, and I assumed it was part of the moulting process.

What's different this year is that he's hurting himself in the process. He'll pull on a feather and cry out, then he'll keep pulling and keep crying until he gets the feather out. It's definitely a painful yelp, and not one of his usual noises.

Does anyone know if this is normal?