The reach mend buys a drag-free drift when the water between you and the fish runs faster than the water the fish sits in. He guides 250 to 300 people a year; a couple of dozen can do it.

What the instructor says

• Slow and level. A nice slow forward cast — at full speed it still looks slow — with a level trajectory, buying time to reach.
• Stop, reach, drop. Stop high, move sideways, then drop; do both at once and the fly drags.
• No drag, and nearly 90°. Once the fly hits it stays stopped; the form wants the final rod position nearly 90 degrees to the tape — 45 is the video’s older figure — and he finishes at 85 or 90.
• Aim at the target. He lands two inches, then a foot and a half from the cone; most examiners are happy within three feet.
• Not always upstream. Downstream reach mends have their uses.

Putting it to work

1. Stop high, move sideways, drop — the fly must not move after it lands.
2. Nearly 90 degrees is the standard; 85 or 90 removes all doubt.

Source

From the FFI CI walkthrough series by Dayle Mazzarella (Chapter 3 — FFI Casting Instructor Certification Tasks, Fly Fishing Coach International), lesson 5, 00:03:38. See the video library and the task pages for the exam wording; terms follow the FFI Fly Casting Definitions.