I must agree that all the posts here are sensible and logical. (with the exception of course of VMK's post
) I agree that you can either descend, slow down and configure in a certain number of track miles or you can't, and you shouldn't throw yourself into a situation where you're not entirely sure whether it will work or not and ultimately throw it all away at 5 miles when you're still struggling to get it below 200 knots, but....
I've been trying to think about a better way of explaining what I'm looking for...
Let's say you're at 250 knots (ATC speed restriction) passing 10,000 feet or so, on a heading of North. ATC have you on what is effectively a long left base leg for RWY 27. Your estimated track miles, based on maintaining the current heading until you get a final vector for the approach at about 15 miles out, leaves you with about 35 miles to run. Just lovely!
But there is the possibility that you could turned in earlier for a shorter final of say 7 or 8 miles...
If they turn you now, your track miles would reduce to say 27 or 28 miles. Still no problem with speedbrake!!
But if they turned me later would I still be OK?? Do I need to use speedbrake now to cover both possibilities? If I knew how much extra RoD or increase in descent angle I should get, I could work that out. If I will only get a few hundred feet per minute extra with speedbrake, then I should really use it now, because it will have a longer period of time to adjust my profile. But, if I could effectively double my descent gradient, then I can wait and see what they give me as I'll still be able to manage the situation later.
Now, I realise of course that I can pay attention to what happens when using speedbrake over the next few weeks/months and I will have my answer. But, with PPRuNe available to tap into the knowledge of so many, I just can't resist!!!
So, does that make it a little clearer?? Does anyone know, or has anyone ever thought about the effectiveness of speedbrake this way before?? Am I alone in planet ODD??
Hope that helps!!
Thanks everyone!