This just in from my club. Thought it was worthwhile posting here. I only edited names:

Greetings:

I wanted to pass this important information along just in case you didn't know. I didn't, but then no novice flyers want to fly mode 1 so I've been spared the experiencee! This situation almost caused a crash at the field on a recent Saturday. Submitted by xx with some edits by xx.

As a result of a near-crash experience at the field recently, I've run some tests on the use of a trainer (slave) transmitter on a buddy cable. As is usually the case with most buddy box set-ups, the slave transmitter was on a frequency different from that of the master unit. I running some tests "after the fact" I found that the slave transmitter will only work (as a slave) when the crystal and battery are installed, so removing the crystal or battery doesn't solve the potential problem. If the on/off switch on the slave transmitter is inadvertently turned on, even though it's attached to the master transmitter via the cable, the slave transmitter will still transmit RF on its frequency. If someone were by chance flying on the slave transmitter's frequency at that moment, oops! We were very lucky that a crash was avoided! Thank goodness it was xx, whose very agile thumbs saved the day ... and his plane.

As a result of this sitatuion I found that if the slave transmitter is on a frequency different from the master transmitter, a novice holding the slave transmitter can cause a potential problem for someone flying on the slave transmitter's frequency by turning on his slave transmitter. (Would make sense to the novice to turn it on so it works, right?) To avoid this problem in the future I now have put red tape over the on-off switch on the buddy box and will instruct new pilots using the slave not to turn that switch on under penalty of severe flagilation or death, whichever comes first! DX7 anyone?

I don't know if this is true with all slave/master transmitter connections, but it certainly was true in this case. I was there at the moment of epiphany. Our thanks to xx and, of course, to Quickie xx for "exposing" the problem.

xx.