tacx, the radio has a far greater max range than 90 feet (probably 900-3000+ feet depending on the transmitter). However, it would be impractical to carry the plane that far away every time to check the range. Most transmitters have a way of going into a reduced power mode for range testing (holding the trainer switch in your case). If in this reduced power state you can still have full control at 90 feet, then by the manufacturer's calculations you should have good range at full power.

If you do the test without holding the switch (or whatever the manual says with other radios) the test doesn't really help you much. Say for instance the radio's max range is 1000 feet (I don't know what your radio is rated, but 1000 is an easy number for an example). If there is a problem and the range is reduced by half, you could only get 500 feet away before going out of range. If you range test without holding the switch the radio will work fine at 90 feet, but in flight you might go beyond 500 feet and lose signal. However, if you do hold the switch during the test, you would lose control at 45 feet, due to the radio's half range issue. This would tell you there is a problem so you can look for the cause and correct it before flying.

I hope this helps you and any others who may have the same question about range checking their radio.

Note: I make assumptions and use examples here to explain the basics, but as the theme of this thread stresses, you must always check the manual for your radio to find out how to range check your system. Many radios have a different procedure for how to reduce the power, as well as how far to take the model to safely determine acceptable range.

Good luck. Have fun flying!