Groundspeed Mini Function
Does the 738 have an similar function to the Airbus GS Mini? For those unfamiliar, the airbus system is designed to ensure the aircraft maintains a minimum groundspeed during gusty approaches. Consider the following. You have a target approach speed of 145kts and autothrust/autothrottle is engaged. You encounter a positive shear of 15 kts so your IAS now increases to 160kts and your groundspeed reduces to 130kts. With a conventional system, because you're now above your target approach speed the thrust will be REDUCED to achieve target. The shear then ceases and your IAS and GS reduce accordingly - however , you've already lost an additional 5-10kts due to trying to reduce to your original target approach speed so you're now slow, with reduced/idle thrust AND reducing energy. Unless the thrust is applied appropriately a sink could develop very quickly.
On the Bus, when the gust is encountered your target approach speed actually INCREASES (to maintain GS) which requires thrust to be maintained or increased. As the gust recedes, and target speed slowly reduces, thrust is adjusted SLOWLY back to what's required. This is a dynamic function and results in the target approach speed sliding up and down the speed scale during the approach - but it maintains the aircraft energy and keeps the engines spooled to avoid a low energy/low thrust scenario.
So, with a rapid sink into the sea, there is a possibility of positive shear (gust front with the heavy rain encounter) with an associated thrust response as described above leading to an unrecoverable situation.
Can any Boeing drivers confirm the systems or procedures (increased approach speed?) required in such conditions.
A4