Originally Posted by SR71
I've touched down in a light 737 at a GS of <90kts on a day when it was gusting 65kts. I didn't even think about GS. The only thing I seek to preserve on finals is IAS. If I fly through a shear, I need to regain IAS surely, not GS?
Been following the thread with interest, and I think this is the crux of it. Having a minimum GS serves to protect the IAS. BUT that's not the only way of doing it.
<disclaimer> I'm just an interested PPL, with aspirations to bigger tin..</disclaimer>
Starting assumption is that a large transport category aircraft has significant inertia (resistance to change), so if the 65kt headwind suddenly disappears, it's going to be a big issue accelerating the aeroplane. If it happens at just the wrong moment we might finish up with upset passengers, and possible landing gear protruding from places it shouldn't: We all know that IAS makes it fly, however, we have some need to protect the IAS.
If we implement a minimum GS <airbus>, we protect the IAS because even if the wind should spontaneously reduce to zero, we're still rocking along fast enough to fly - the IAS will take a dive, but it will take a dive from a higher point to a point at which the plane still flies.
In the event that there is no shear, and we fly through a continuously decreasing headwind, the IAS will slowly wind down to some target value, at which point the IAS will stop decreasing, and GS will start to increase (it's GS mini, not target GS). In the event the headwind remains, we will arrive at a higher IAS AND GS than might be necessary.. but it's still not an excessive GS (perhaps somewhere around a 0 headwind GS), so shouldn't be a problem.
If we don't reference GS <boeing> then given the reported conditions, and experience, then I presume we (the pilot) takes some action to protect the IAS by adding some knots for headwind/gust factor?
Which surely amounts to about the same thing (protecting the IAS), just by different routes?