You know I was trying to help I spent 10 mins going thought the FCOMs to find info.

 

Just loved the tone of your reply with all the ?????

 

Good bye

 

 

Kyle -- I'm not sure Vernon's questioning the accuracy of the simulation, just trying to understand why the speeds on the APP REF page are different to the speeds on the speedtape.

 

Not so sure about that. From the pictures, the speeds match the tape exactly.

 

Still doesn't resolve the issue that the chart, that's being referenced in this discussion, is of dubious origin.

 

 

Not so sure about that. From the pictures, the speeds match the tape exactly.

 

No, he's not asking why the speedtape doesn't match the tables, he's asking why Vref15 (as displayed in the APP REF page at 148kts) doesn't equal 153 kts (which is displayed as Flap 15 speed on the speedtape and on the tables quoted).

 

The reason (as I'm sure you know) is because Vref15 =/= Vref40+20. The speedtape is correct (he'd selected Vref40 as his approach reference speed, so the speedtape builds the speed schedule from Vref40), and the table (which shows the flap speed schedule from Vref40) is also correct (regardless of its provenance).

 

The FMC APP REF page is also correct to display 148kts next to Flap 15, because it's a different calculation (1.3 x Vs1g(Flap15) rather than Vref40+20).

That table is showing maneuver speeds, not ref speeds.

Thanks simon and matt !

 

So Vref is target approach speed, MS allows for 25 degrees of bank (with 15 degree overshoot, I think) and 1.3g - figures from memory - and has very little to do directly with Vref!

Isn't my command speed not set at Flap maneuvering speed and not MS for flaps 15 ? And MS is the amber band for flaps down?

interesting stuff , Approach Speeds (FMC) versus  maneuvering speeds (Speedtape and table)

 

 

Angle of attack (LIFT) contributes to VREF (FMC-Approach) speeds also right ?

 

I have search the net to find a explanation of the Boeing 737 "AoA Visual indicator on the PFD" as i find it hard to understand . Is it showing the fuselage frome the side or ?

 

Lots of videos regarding AOA though.

 

Bank and overshoot ? what does Overshoot meens ?

 

Michael Moe

 

 

I have search the net to find a explanation of the Boeing 737 "AoA Visual indicator on the PFD" as i find it hard to understand . Is it showing the fuselage frome the side or ?

 

It shows body angle of attack (AoA). So, it's not necessarily showing your pitch angle, as much as it's showing the body pitch related to the AoA. Remember that AoA does not equal pitch. AoA is the angle between the flow direction of the air, and a reference line (usually the wing chord).

 

So, it's not really showing the fuselage, or anything like that - it's showing the angle between the actual airflow and the chord of the wing, essentially. Remember, though, that the chord changes with flap deployment.

Angle of attack (LIFT) contributes to VREF (FMC-Approach) speeds also right ?

 

Vref is defined as 1.23 x the 1g stall speed in the landing configuration at the stated aircraft weight. In other words, gear down, speedbrake in, flaps at the landing setting.

 

There are three permitted landing configurations for the 737: Flap 40, Flap 30 and Flap 15. I am reasonably (though not 100%) confident that when you enter your planned landing weight on the APP REF page, the FMC simply looks through a table and returns the appropriate values for Vref for each configuration. When you select a configuration & speed and enter it in to the FLAP/SPD line, this speed is displayed on the speedtape and the flap speed schedule built from it.

 

This is important because it implies that if you enter the planned landing weight incorrectly, Vref on the speedtape and all your flap manoeuvring speeds will also be wrong.

 

Again, I'm slightly hazy because I'm not an expert on the 737NG systems, but I believe I am correct in saying that the 'dynamically' generated data -- i.e. based on the actual sensed weight & conditions (derived in part from AOA) is the 'red army' on the speedtape. This will always be correct (assuming the relevant air data probes and computers are operating correctly).

 

Now, on to flap manoeuvring speeds...

 

 

 

Bank and overshoot ? what does Overshoot meens ?

 

Boeing gives you a speed schedule on which to extend/retract flaps. As long as you are at or above these speeds for each flap setting, you will have 'full manoeuvrability' -- which Boeing defines as 25 degrees of bank, plus a safety factor of 15 degrees (so that a ham-fisted pilot won't stall the aircraft by accidentally slightly exceeding 25 degrees) -- a total of 40 degrees of bank (though you're only ever going to use 25). Below the manoeuvring speed for each flap setting, the aircraft will still fly all the way down to the red band on the speed tape where the stick shaker activates, but you only have 'limited manoeuvrability' -- again, defined by Boeing as 15 degrees of bank, plus the 15 degree safety allowance.

 

The flap manoeuvring speeds are based on additives to Vref (generally in 20-knot increments). This is where it starts getting a little complicated, because which Vref depends on the aircraft type you're flying and I don't know the 737NG well enough to speak with absolute confidence. However, it would appear from the documentation posted that the 737 is a Vref40 aircraft -- in other words, the flap speed schedule is always based off Vref40, regardless of the actual landing configuration you will use. I stand to be corrected on this, however.

 

If I'm right, this is similar to the 767 but different to the 747-400, which uses manoeuvring speeds based on the actual selected Vref (to maintain commonality with the 747 classic). So in the 747, if you select Flap 30 for landing instead of Flap 25, all your flap speeds will change accordingly.

Do you meen that selecting forinstance Flaps 30 app speed in the FMC App page wil give you VREF40 maneuvering speeds on the speedtape?

 

I need somebody who knows the 737 better than I do to answer that definitively, but it's absolutely possible.

 

Remember, all the flap manoeuvring speeds have to do is give you a minimum of 1.3g to the stick shaker (which equates to 40 degrees of bank -- 25 degrees, plus the 15 degrees of overshoot that we mentioned before) at each flap setting. To make the flap speeds easier to remember (in the days before speedtapes with the flap speeds displayed on them!), Boeing decided to set the speeds as easy-to-remember additives from Vref that meet that requirement.

 

Let's take the example that Vernon is using: at 59 tonnes, Vref40 is 134kts. Using the table, the minimum clean manoeuvre speed at that weight is Vref40+70 = 204kts. So at any speed down to 204kts, you can bank up to 25 degrees.

 

Before reducing speed below 204kts, you select Flap 1. The Flap 1 manouevre speed is Vref40+50 = 184kts, so now you can slow to 184kts and retain full manouevrability. This goes on through Flap 5 (Vref40+30 = 164kts) and Flap 15 (Vref40+20 = 154kts) before selecting Flap 40 and Vref+5 (139kts) for landing.

 

But if you were using Flap 30 for landing, for instance, assuming the aircraft is designed for Vref40 operation, you still have full manoeuvre capability at the above-mentioned speeds. What's changed compared to your flap 40 landing when you select Flap 1 at 203kts? Nothing -- you're still at 59 tonnes. The only difference is that instead of selecting Flap 40 for landing you'll be selecting Flap 30 (with the accompanying higher Vref of 141kts making your final approach speed a minimum of Vref+5 = 146kts).

 

As I say, that assumes that the 737 flap speed schedule is designed in this manner: looking at the way in which the manoeuvre speeds are displayed on the speedtape in Vernon's image (clearly based off Vref40 even though he has selected Vref30 in the FLAP/SPD line) it would appear so, but I couldn't tell you with absolute certainty. I know that's how the 767 works, but I also know that the 747 is different: to illustrate, at 240 tonnes in the 747 Vref30 is 140kts and Vref25 is 146kts. Because the flap manoeuvring speeds are based off the selected Vref and not just Vref30, this means that if you're conducting a Flap 25 landing, your minimum clean speed at 240 tonnes will be Vref25+80 = 226kts instead of Vref30+80=220kts (and all the other flap speeds will differ accordingly)

 

One of the reasons why it's important to know your type and be careful when it comes to transferring knowledge and techniques from one type to another!

The NG flap speeds are based on Vref40, regardless of landing flaps.

 

 

Some planes define Vref30 from Vref40, and some have their own Vref30, but that is really not important and is

Looking at my topic and charts from the start, will i loose my 40* bank going below 153 kts (flap 15) my Flap MS ? 25* bank with 15* overshoot? and why does it reduce from my MS 153 kts to vref 15 148 kts ?

Looking at my topic and charts from the start, will i loose my 40* bank going below 153 kts (flap 15) my Flap MS ? 25* bank with 15* overshoot? and why does it reduce from my MS 153 kts to vref 15 148 kts ?

The flap manoeuvre speeds give you much more g margin than the minimum in most circumstances. You are not in danger of exceeding bank limits and you have not lost anything by the apparent 5 knot difference. See Matt's comments above. The difference is not something to worry about.

 

Think about it Vernon. Would Boeing provide flap manoeuvre speeds on take off that were inherently dangerous? They are different to the Vref presented for landing but the reason why has been explained.

Vernon -

 

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

 

If you fly the approach at 153 (148+5 wind), you'll have full maneuver capability.

 

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.