Vernon -
 
Your chart is talking about maneuver speeds. The FMC is showing Vref.

 

I would also like to mention that chart is right, whoever created it, its right. I have the same chart in my Ryanair FCOM.

 

 

In the flare, you'll go below 153. Why are you worried about that at 20 feet? I really hope you're not planning to bank 40, 30, or even 20 degrees in the flare. You'll drag a nacelle or flap faring before this becomes an issue.
 
I still don't see what the issue is.

 

Well thats what i mentioned in my last post matt. going below 153 you'll loose your full maneuvre capability. I was just unsure! 

 

So why does Boeing or the FMC allow a drop in speed to 148kts vref ?

So why does Boeing or the FMC allow a drop in speed to 148kts vref ?

 

Because Vref is not defined in the same way as the manoeuvring speeds. As Matt says, you don't need full manoeuvre capability in the flare: the greater design priority is to reduce the landing distance by reducing the speed of the aircraft at touchdown.

 

Again, the manoeuvre speeds guarantee you a minimum of 1.3g to the stick shaker, and in many cases quite a bit more because Boeing decided to make the schedule easy to remember with nice round numbers.

 

Vref is not required to guarantee you the same margin. It's as simple as that: different speeds based on different calculations.

 

 

So why does Boeing or the FMC allow a drop in speed to 148kts vref ?

 

The maneuvering speeds are those minimum speeds recommended for maneuvering the airplane after takeoff and before landing.

 

 

What drop?

A drop from 153 kts flaps 15 or Vref 40 + 20 at 69t to 148kts

 

But isn't the Maneuvre speed for flaps down the amber band ? And the green circles are the flaps maneuvering speed?

 

FCTM

 

 

Flaps Down Amber Band

For all flaps-down operations (any time the flaps are not full-up) the minimum maneuver speed is the slowest speed that provides full maneuver capability, 1.3g or 40° of bank (25° of bank and 15° overshoot) to stick shaker. The top of the amber band does not vary with g load.

As airspeed is decreased below the top of the amber band, maneuver capability decreases. In 1g flight, the speed in the middle of the amber band provides adequate maneuver capability or 30° of bank (15° of bank and 15° overshoot). The speed at the bottom of the amber band (top of the red and black tape) corresponds to stick shaker activation for the current g load. If the g load is increased during maneuvering, the stick shaker activation speed increases also.

 

 

 

Minimum maneuver speeds (displayed as the top of the lower amber band) should not be confused with flap maneuver speeds. Flap maneuver speeds are based on airplane weight, while the minimum maneuver speed is calculated using airplane angle of attack and current airspeed. These speeds provide independent means to ensure that the current airspeed provides at least full maneuver capability for terminal-area maneuvering.

 

Correct me if i'm wrong!

 

 

Correct me if i'm wrong!

 

The whole point of landing is to transition the wing from a flying, to a non-flying state. In order to do this, you're going to need to bleed airspeed off. A wing in a non-flying state being a stalled wing, essentially, this process is, by its very nature going to bring you closer to the amber band.

 

Of course, the reason all of this works is that you plan to bleed the speed off tactically in a manner that you hit the ground (hopefully on the wheels) at around the same point you'd otherwise stall. In theory. There's a lot more to it than that.

 

My point is, you seem to be clutching to all of these concepts of speeds and all of that when the basic issue here is:

When you land the plane, you want it to stop flying. A plane stops flying by slowing down (in an elementary sense).

Yeh thats very true and make sure to get those spoilers up to destroy that remaining lift

I have several Boeing books and they're throwing the terms around a bit, so yes, there might be some confusion.

 

There are:

Flap Maneuver Speeds (The number on the speed tape) Based on weight.

Minimum Maneuver Speeds (The top of the amber band) Based on AOA and airspeed.

 

Both will give you 25+15 = 40, at least, during normal ops.

 

1. Stay above the Flap Maneuver Speed during the configuration for the approach
2. Fly the approach at Vref+ADD.
3. Don't overthink this.

They don't tell you everything in the books, and you won't find out some reasons for this stuff unless you talk to the guys that were there when this stuff went down. I just flew with one of those guys. Pretty interesting trip.

 

 

I have several Boeing books and they're throwing the terms around a bit, so yes, there might be some confusion.
 
There are:
Flap Maneuver Speeds (The number on the speed tape) Based on weight.
Minimum Maneuver Speeds (The top of the amber band) Based on AOA and airspeed.
 
Both will give you 25+15 = 40, at least, during normal ops.
 
Stay above the Flap Maneuver Speed during the configuration for the approach
Fly the approach at Vref+ADD.
Don't overthink this.
They don't tell you everything in the books, and you won't find out some reasons for this stuff unless you talk to the guys that were there when this stuff went down. I just flew with one of those guys. Pretty interesting trip.

 

Thanks matt, now i can put this too bed lol

 

Happy contrails

Me to :-)

 

Thanks Michael Moe

Note: VREF speed provides adequate buffet margin for an inadvertent 15° overshoot beyond 15° bank.

 

So only 15* degree bank is allowed at vref

Note: VREF speed provides adequate buffet margin for an inadvertent 15° overshoot beyond 15° bank.

 

So only 15* degree bank is allowed at vref

???

 

Vref+5 gives you a 40 deg bank buffet margin, so 25 plus 15 for overshoot. Vref will give you 37 deg buffet margin, but you'll only be less than Vref+5 during flare.

Why are we getting into this discussion at all? If you're banking that much at or near VREF, you have other issues to worry about...

 

...like scraping a wing or a nacelle.

 

 

 

Again, I'm all for digging deep into knowledge, but sometimes you really need to step back and look at the big picture. You're really only that close to VREF when you're pretty close to the ground (if you're father away from the ground, you might want to review your procedures).

 

Step back.

See big picture.

I just found that in my FCOM and makes sense from what you are saying kyle at vref why would you bank 25* anyway!

I just found that in my FCOM and makes sense from what you are saying kyle at vref why would you bank 25* anyway!

I think you might be misinterpreting what your FCOM says. Vref as defined is not limited to 15 deg bank + 15 deg overshoot. If it was then all the flap manoeuvre speeds based on it would be equally limited.

Yeh i must be kevin! So what is it actually pointing too lol