Unfortunately, that is what happened to Chyloe. When she was a baby, she lost the flight feathers on her left wing. Each time she grows a new one on that side, she loses it when she flaps her wings so she cannot fly.
With normal moulting, the new feathers grow in as the old ones come out and, as Jane says, the bird can always fly.
Max, CAG (In my heart forever) Taz, Tiel (Rest in peace my sweet girl) Chyloe, CAG