Interference will either lengthen or shorten the pulse. If it lengthens it, the pulse merges with the immediately following pulse making one double length pulse which is outside the limit reagrdless of whether the first pulse would have been inside the limit. To shorten it will require a wave that is 180 degrees out of phase or thereabouts, switched on at just the right time in the pulse and switched off at just the right time later in the pulse. It's possible but of very low probability. Remember that PCM is not 100% foolproof, it has some very low probability of reading errors as a correct signal. In both cases the probabilities are low enough not to worry about them. The reality is, at my airfield where we have two known areas of trouble where every model without PCM or PPM failsafe glitches as regular as clockwork, my model never glitches, occasionally it has gone into failsafe for less than a second and then come back in control.

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