= perdido, perdido de rumbo, desviado de rumbo, sin rumbo, sin norte.
Ex: Russia has launched an investigation into why a manned space capsule returned to earth hundreds of miles off course.
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* be off course = desviarse del rumbo, perder el rumbo, perder el norte, estar fuera de rumbo.
* fly off + course = desviarse del rumbo, perder el rumbo, perder el norte.

The following video provides you with the correct English pronunciation of the word "off course", to help you become a better English speaker.