off the beam

off the beam  {adv.} or  {adj. phr.}

1. (Of an airplane) Not in the radio beam that marks the path to follow between airports; flying in the wrong direction.

A radio signal tells the pilot of an airplane when his plane is off the beam.

2.  {slang}

Wrong; mistaken.

Maud was off the beam when she said that the girls didn't like her.

Contrast: ON THE BEAM.