Besides, she's not really lying ... just delaying the truth. Not to mention, she will give you other indications that you're not going to make your profile... you just have to look for them.
Isn't that always the way... the signs are there, you just have to open your eyes?
The best indication that you will make your level off is the blue level-off arrow. But the level-off arrow doesn't instantaneously tell you when you'll level off, instead it continues to recalculate your level off based on your descent speed.
As you go above profile because ATC slowed you up, the blue arrow will continue to creep away. This should be your first indication that you'll be high. The second indication will be the Chinese glide slope. But then, these little green dots will only provide data that you're off your descent by more than 200 feet when they're pegged. Personally, I like the progress page the best.
Bottom line: We need drag to get her down. Interesting enough, the blue level-off arrow doesn't look at speed brakes. However, when you use the speed brakes to get her back on profile, the blue arrow will creep towards you because you're increasing your descent and putting yourself closer to the level off. Basically, you're actually taking her below her flight idle profile because you have to.
Once the blue arrow has moved to where you want the plane to level off, you can stow the speed brakes and she will continue to make that blue arrow level off point. Why? She wasn't counting on speed brakes to make it, therefore when you take them away... she doesn't care. She's on her profile based on your altitude and speed.
Morale of this story... learn how to read your Princess. You might have to babysit her. I'm still learning her ways, and using 3 to 1 for descent planning as a backup. Back to the back to the basics... 30 miles at 10,000 feet is a safe gouge.
Enjoy the Journey!
~ Karlene
The A320 is the same way. Not inserting your descent winds can also bite you on your descent. Most of our pilots also flew the MD-80 where the speed brakes were mostly a "poor planning handle," they had to learn that Fifi needs the speed brakes sometimes. And I still do 3 to 1 every day!
ReplyDeleteMikel... Yeah, on the Boeing if you used speedbrakes it meant "you" screwed up. But... the airbus is designed that way. Heck, you can use them with flaps. That's the most interesting shift for me converting. 3 to 1 is the best backup!
ReplyDeleteThanks for your comment!
When atc is giving radar vectors, do you have to use open descent and speedbrakes together or can you use it without the speedbrakes?
ReplyDeleteHey Ralph, Vectors and descending don't necessarily go together... but actually, "how" you descend with vectors does. You're right... only open descent on a vector (vs managed). And yes, you can do open descent without speedbrakes.
ReplyDeleteSpeedbrakes only come into play when the thrust is at idle (open descent) and ATC held you up too high, too long. Or... you didn't plan well, and you're behind profile. Speedbrakes will help you expedite that descent. They work anytime and with any flap and gear configuration. Vectors, or not.
Thanks for a great question!
If you were flying level and were in the descent or approach phase, would you use speedbrakes to slow down if you were too fast for using the flaps?
ReplyDeleteRalph, I'm assuming if we are "level" and in the "approach phase... ATC is not allowing us to descend. But, technically, we can't be in the descent phase until we descend. Maybe we started down and then they leveled us off?
ReplyDeleteBut... For what you are asking... Do we use Speedbrakes to slow? No. First step is to reduce the airspeed by reducing the power.