When a plane takes off "normally" it starts, by definition, on the ground. There will be weight on wheels, so TOGA should, it would seem, be inhibited?? Clearly a nonsense - I must be misunderstanding something. So why is TOGA not inhibited for a "normal" takeoff - or what is it the PF does to override the inhibition? Or does the operation of the button change from TO to GA such that in TO mode the WOW is not relevant, only in GA? If the function changes, what tells the TOGA function that this is not a take off, but is a go around - or vice versa?
The autoothrottle is part of the auto pilot system. The autopilot has multiple modes such as takeoff, cruise, and approach. When in takeoff mode the TOGA switch activates the Take Off function. When in Approach mode the TOGA switch activates the Go Around function. When in Approach mode weight on wheels (or a very low radar altitude) will inhibit TOGA.
In another question - surely the thing the RAAS system should be "concerned" about is how much usable runway is ahead - not how much lies behind the plane - but again I may be miusnderstanding.
That depends on how the RAAS system is set up. For example on a dry runway, 4000 ft remaining may be plenty to stop the aircraft. But that may be insufficient for a wet or snowy runway. So the RAAS may be set up to give an alert whenever a certain amount of runway has been used to account for "a worst case scenario" that RAAS cannot detect. Normally the flight crew would know what the braking action is on a runway and take appropriate action when RAAS provides an alert. On a dry runway the appropriate action would probably be to land the aircraft. If there is poor braking action, the appropriate action may be to do a Go Around. In this case the airline's operating manual apparently required the flight crew to do a Go Around with
any RAAS alert. That sounds prudent on paper, but under the right set of circumstances it may be imprudent. In this case the circumstances all lined up to result in an unnecessary disaster. RAAS also provides alerts during ground taxi to alert the pilot they are about to cross a runway. If the pilots have received clearance to cross the runway, the pilots ignore the alert and proceed, but if not, they should stop. It also provides an alert in the event they line up for takeoff on a taxiway instead of a runway.