Wheresthecoffee,
You are correct, but only for constant wind speeds. The discussion above relates to rapid changes to headwind component experienced during an approach.
The GS Mini function recognises the difference between the instantaneous wind and the wind reported on the ground and increases the target airspeed to maintain the groundspeed that the aircraft should have at the threshold. This means that if the wind does drop off dramatically, the aircraft will have enough energy to keep flying. So the 'bus most likely would handle large loss of airspeed if the wind at the surface was low (although 50 knots would be pushing it!) and would certainly handle it better than other aircraft. IAS keeps you airborne but GS is very important too!
I personally think GS mini is marvellous. It really comes into play during transient increases in headwind component during the approach. This is an example I was given:
VAPP=140Kts, Surface headwind 10Kts, GS mini=130Kts
Airbus
During approach aircraft experiences a sudden increase in headwind component to 30 knots, the bus sets a new VAPP target speed of 160Kts to maintain GS of 130Kts. This requires an increase in power. A few seconds later the wind shears to zero headwind component and the IAS drops to 130Kts, but since the engines are already at high power the recovery to the original VAPP of 140 Kts is well underway. GS was never below 130Kts at any stage.
Aircraft other than Airbus
Same speeds and conditions.
During approach aircraft experiences a sudden increase in headwind component to 30 knots, power is reduced (possibly to idle) to maintain VAPP of 140kts. GS now 110Kts. A few seconds later the wind shears to zero headwind component and the IAS drops to 110Kts also. If the aircraft doesn't stall immediately, the engines are now at idle and recovery to a safe airspeed may not be possible before the ground arrives. By allowing the GS to reduce on the approach the situation became critical.
Obviously, shears to a tailwind are going to cause problems for all aircraft...
CP