B747.400 Manoeuvre margin display.
 

The PFD.The airspeed tape.The "red bricks" with the yellow caution range above it.
Who knows what software drives this data?Or is it driven by the AOA sensor(I dont think so). Our fleet is currently exprncg problems with this display.It is sitting too far up the tape.It is a little distracting.
Thankyou

"Min and Max speeds are an FMC computation integrated with Max speeds from the ADC and Min and Max speeds provided by the MAWEA stall warning function" - The foregoing is a paraphrase from the Boeing FMC training notes and the whole thing runs to several pages. I could try to scan and post the whole shooting match or, if you can point more directly at the query area, I'll try to extract the necessary detail.

both the red and black barber poles(on top and the bottom of the speed tape) are a positioned by the symbol generator based on data supplied to it by the Stall Warning Computer.

as for the yellow extensions from the barber poles...the lower one indicates a .3g margin to stick shaker(or min maneuver speed)...
the upper one indicates .3g margin to high speed buffet at high altitudes.

the source for these again is the Stall Warning Computer based on FMC gross weight calculations.


maybe u'd like to compare the indications of the min man. speed with the fixed speed schedule.. with or without the RPR ...

It's not clear to me what part of the display you are talking about, so I'll choose the yellow Manoeuvre Margin. This is set on the FMC MAINTenance pages under PERFormance Factors.
The monthly Nav Database updates can reset some of the parameters on the PERF FACTORS page. As the problem is fleetwide, I suspect this is your problem. BTW, what is your normal manoeuvre margin... 1.2? 1.3? Or something else?

Please let us know how you go.
Rgds.
Q.

Thanx to QUAVION SKYNET CORNISH JACK
My apologies for the lack of clarity of my submit.The low speed red barber pole and attendant yellow caution range is sitting too high up on the airspeed tape.eg on departure with the flap up tick postnd. at 255 kts the very top of the yellow is sitting at 255 kts with the a/c clean.On landing ,vref30 135 kts,the very top of the yellow is sitting at 135 kts.
For QUAVION our selected margin on the FMSCDU PERF page is 1.3g.

"For QAVION our selected margin on the FMSCDU PERF page is 1.3g."

Hmmm.... In which case, this sounds unlikely to be your problem. From memory, the FMC defaults to 1.2, which would mean the yellow band would go down, not up.

Unfortunately, this is a very complex system... too many variables/components to consider: AOA (vanes and associated heaters), airspeed(CADC's), flap position(FCU inputs), gear position(PSEU input) and speedbrake handle position (APFD?) are all inputs to the (two) MAWEA stall warning cards (SWMC's). Boeing have said in the past that AOA will tend to give the largest error. +1 degree can give a 5 to 10 kt error, but if only one vane is u/s, then the red brick values would be different on the Capt's and F/O's displays. Note however, that the manoeuvre margins would be the same... as the FMC's use the greater of the computed stall speeds (from the two SWMC's) to calculate manoeuvre margin.....at least this is the way it works with the flaps out of up.

I'm just wondering what effect the Fifth Pod and Gear Down dispatch switches in the MEC have on manoeuvre margins.... Would this also raise the flap markers as well as the stall speeds and manoeuvre margins?

The puzzling thing is the fact that you have this problem throughout the fleet. Sounds like a software thing... or someone's been fitting wrong dash number computers to your aircraft.
Methinks you need Boeing's expert help here.... ;-)

Good luck!
Rgds.
Q.

...if you have a default of 1.3 in the perf factors (ie CAA/JAR config/1.2 is FAA config)....just wondering what your default crz CG on perf init page would be??? Is it 20% or something different? This will definately change your maneuver margin (yellow band thingy) and also max alt calculations. But as per the raspberry blobs being too high ya got me stuffed. Look forward to the answer to this one when you find out.

Hey Carpe,

Taught a little GS on this. The material always presented the red squares as maneuvering limits, based-on numbers you put in the box compared to the Boeing perf manual (stored in the FMC's) and obviously info from ADC's, etc. But it can also be a placard speed limit if lower.

The top yellow line was presented as "max. manuever speed to buffet." And yes, I am sure these values will change depending on whether 1.2 or 1.3 G is your selected perf. as has already been mentioned.

Hope the terminology is correct...I haven't taught a GS class in a couple months...that stuff disappears fast.

Just to be sure, are we talking about a real metal B747-400 or a flightsim game?

If it is a real metal B747-400 and the speed tapes are indicating buffet margins incorrectly, surely a Tech Log entry is necessary?

Addditionally, get a company boffin to give the local Boeing rep a call, its what they are there for.

To be sure.We are talking about a real metal B747-400.A fleet of them precisely.
Boeing Corp have being contacted I understand.

"We are talking about a real metal B747-400. A fleet of them precisely. Boeing Corp have being contacted I understand."

Rumour has it that an airline in the Southern Hemisphere has thus very same problem....

Q.

P.S. Of course, there is a chance that you are this very same airline (grin).