Not a US regulatory requirement. 91.309 says a lot about the tow hook and the tow line but nothing about mirrors.

However a mirror may be a local organizational requirement. The Civil Air Patrol seems to require it.

It is very hard for the tow pilot to see the spoilers hanging out at low altitude right after liftoff if you can't glance back at the glider. No radio will help you there to see it, unless someone on the ground sees and helps you. Turning your head to look out the back window (if even possible) while keeping the tow plane in a safe climb attitude in this situation is a bad idea.

Depending on the tow plane, this is a critical situation where it is very easy to loose control of the tow plane. In the few years I have been towing, being zapped by spoilers hanging out behind me has happened to me twice. It is like trying to tow around a ton of bricks a few MPH just above stall speed barely climbing if at all.

Common sense should put the mirror in any tow plane. And it should be used. Frequently.

Besides, think of all the other cool reasons you could tell the uninitiated what that thing is for.

On Wednesday, July 20, 2016 at 12:48:11 PM UTC-5, Charlie M. (UH & 002 owner/pilot) wrote:
While not a "US regs expert", I am not aware of a reg.
But, I consider it a cheap "second info referral" to help all involved.

From an, "ISO background", safety/quality is everyone's job......

Curious to see if a US reg shows up.