I use this transmitter for my flight simulators. I always miss the 5th channel for Gyro sensitivity or landing gear.

Finding the connection for the 5th channel was not so difficult. There was already a connection for it. I use it for an extra-switched channel but you can also use a potentiometer for a extra proportional channel.

With the transmitter in front of you, you will find under the antenna the chip. At the left hand side 3rd pen down you will find two soldering-pads. Here you can solder your switch like I did or a potentiometer. See pictures for explanation.

(Ed.- Frank kindly gave KAPER permission to reprint this article from his web site. Frank is not a KAPER, but I'm sure that this information will prove useful.)