There are many different mayfly emerger patterns that are designed to give the illusion of a mayfly dun trying to escape its nymphal shuck. Often these emerger patterns can be very effective when trout are feeding on the struggling duns as they emerge in the surface film. I don't take credit for originating this pheasant tail, PT Emerger pattern. I am sure others have tied it and maybe called it by different names, such as a Comparadun Emerger.
My PT Emerger is very close to Bob Wyatt's Deer Hair Emerger (DHE) pattern which is in his book titled: What Trout Want, The Educated Trout and Other Myths. Wyatt's DHE uses hare's underfur dubbing for the body and the thread is wrapped back over the dubbed body as ribbing. His thorax is spiky hare's mask dubbing.
The PT Emerger pattern is taking some of the best features I found on other emerger patterns that I have used or read about and incorporated them into the PT Emerger pattern. The idea of using pheasant tail fibers and copper ribbing for the body is to represent the shuck hanging just below the surface film. I don't add a tail (neither does Bob Wyatt) because I find that hinders the body from sinking below the surface film when the fly lands on the water. Adding floatant to the thorax section along with the comparadun style deer hair wing helps the front portion of the fly to rest on the surface while the pheasant tail body hangs below the surface film.
Hook: Curved Hook #14 - #!8
Thread: Uni-thread 8/0 Tan, Gray or Brown
Body: Pheasant Tail fibers wrapped way around the bend of the hook
Rib: Copper wire
Thorax: Hare's mask dubbing (spiky)
Wing: Fine deer hair (comparadun style wing)
Tie in the copper wire ribbing and pheasant tail fibers first and wrap forward to the flat part of the hook shank. After tying in the deer hair wing, clip the deer hair butt ends but don't hide them under the dubbing. Wrap a little bit of the dubbing behind the deer hair wing to cover the thread wraps. Then pull the deer hair wing back and wrap the thread and then dubbing in front of the wing to help support the upright wing.
I haven't tried it yet, but I am sure you could use CDC for the upright wing and the fly pattern would be just as effective, if not more so.