Having spent all of my 50 year working life in aviation (both military and civilian), I can only register utter amazement that Uplinker's explanation for the 77 squawk is the first to appear!! That so-called 'professional' aviators should be so woefully unaware of the operation of the ATC environment which mediates and mandates their daily operation is both mind-boggling and deeply worrying, Lift your weary backsides from your self-satisfied isolation and go visit a working ATC Centre. If you can manage to loosen the mental constraints of 'Captain's Complex', there is a distinct possibility of gaining useful new knowledge!!. Thank Heavens I've retired!