The means of an instrument approach in most of the low rent world is a NDB approach which is essentially an AM radio station that the airplane uses a fix from along with a stopwatch to determine it's position relative to a runway and the timed descent which if done exactly as published, is a pretty reliable non-precision approach.
All one needs to do to slam a plane into a mountain is to operate a transmitter at the same frequency and place it a mile left or right of course and cut the transmission from the full time transmitter. We are talking very low wattage output. Such a setup could easily be fitted to a jeep, SUV, or anything else.
The flight path of Browns plane flew the approach precisely as published, only it brought them straight into a moutain instead of keeping a mile clear. The 600' Ceiling that day explains the attitude of the plane's impact and low speed. The pilots just never saw what they hit. There wasn't supposed to be anything there.
After the accident, pack up and take the bogus transmitter with you and turn the real one back on. Nobody's the wiser.