SPEED!!
DESCENDING
Speed requirement by ATC is 250, indicated speed is 280 so a call of "SPEED" would be appropriate by PM
APPROACH
ATC require 180 due to traffic behind/ahead but ias is 200, so a PM call of "SPEED" would be appropriate
2000 feet aal (IMC).IAS is very close to the current flap setting limit speed and is say accelerating due to eg a tailwind, so a PM call of "SPEED" would be appropriate to avoid damaging the flap drives etc.
1000 feet aal (IMC).Landing flap is selected, Vref plus 15 (say 135) is our TARGET speed due to gusts at the runway surface but ias is 146 (more than target plus 10- a common industry-wide trigger for the "SPEED" call), PM should call "SPEED".
300 feet aal Due to a drop off in headwind, ias drops below Vref, say its now 118, requiring the PM to call out "SPEED"
Does this answer your question? Pete.