What kind of passage I may use this Key and What's the name of this Key?

Question

I'm a flute player and I bought this flute sometime ago and I'd like to know:

Flute Yamaha 371 Allegro version

What kind of passage I may use this Key and What's the name of this Key?

Please, I'd like the references or a comment of a recognized flute player or some article with the example.

Edited:

I found the name of the key the the manufacturer's website. They call it the Ice lever (A#).

Reference from Yamaha

Can you give me an example of how the Ice lever is used in practice?

I'm accustomed to using alternative keys depending the passages on the music sheet, but this key doesn't make sense because B flat is very near to this key.

The key:

The hole that key close:

Answer 1

That's an alternative B-flat key. It's particularly useful in chromatic combinations e.g. B B♭ A B♭, in chromatic scales, or for trills e.g. A♭ to B♭. Or for this kind of chromatic phrase

There are two advantages of using this key rather than than the F key ("long B♭"):

• There are two springs less to overcome pressing the key down, so it's faster and less noisy
• The key can be left down in passages that go down to A, A♭ or G and back

The Woodwind Fingering Guide calls this the "Bb trill key". Others call it the "B-flat lever". Yamaha calls it the "Ice lever" (possibly from the German word "Ais" for A#, pronounced "ice").

Blogger Jennifer Cluff has a series of articles on using the three different B-flat alternatives: part 1, part 2, more.