Stall and autoslat

[davierosoft 13]

Hi!I tried to stall some times the aircraft, with and without GW on FMC.I have some doubts. Autoslat is correctly working with GW set.It won't work without it. As far as I know autoslat MUST work before stall, the GW is not determinant for that.Also, there is no advice of stick shaker BEFORE the stall without GW and no band on the speed tape, only the red limit on the AOA indication (if used).Need pilot feedback about this, I'm pretty sure that shaker must run before stall also if the SWS doesn't know the weights, but I've not found exact info about this.

[ajacied551 1]

Hi Andrea, I try to explain how the stall warning system should function, You're right that the stall warning system don't need GW info, It look's to the TE flap position and AOA (Angle Of Attack) sensor position. A normal stall warning is set at a AOA trip point for each TE flap position. If the AOA is more than the trip point for a TE flap position the stall warning signal goes to the Control column stick shaker. To know the trigger point there is on the PFD a Pitch limit symbol (eyebrows) visible at each TE flap postion except when the flaps are up. (see FCOM 2 page 10.11.13). There is also a speed floor stall warning this uses the TE Flap position data and the airspeed data, if the airspeed gets to low for a specific TE flap position the stall warning signal goes to the stick shaker. AOA is not used for the speed floor stall warning. The Autoslat operation occurs when all of these condition occur:- Flap lever at 1, 2 or 5,- Airplane gets near a stall condition - Altenate operation is not active.

[davierosoft 13]

Is exactly what I know, but seems that some functions in NGX are disabled without GW setting. I was unable to have autoslat (while with GW they works)I was unable to have the warning band on speed tape without GW (I know that GW is used for flaps manouvering and performance data calculation but AOA is always the master, floor stall excepted).I toke these pictures about stall condition on NGX, the first w/o GW, the second with it. In that condition I've not tested the autoslat system that were tested previously:

[Spin737 102]

Why are you flying the plane without the GW? Before you takeoff, all boxed entries in the FMC should be filled in. With the FMC inop, you would be setting them by the manual controls.

[ajacied551 1]

I have look it up in the training manual and I quote Enter the Gross weight in the FMC Then the FMC sends this data to the Stall management computer This computer calculates the airplane performance data such as Vmin, Vmax and the PLI (Pitch Limit Indicator). Then the Stall management sends this Data to the DEU (Display Electronic unit) to show it on the CDS system. If I look to the pictures, it seams to be in working order. So you need to enter the Gross Weight in the FMC.

[davierosoft 13]

Manuals says that GW is mainly used to show the info on the PFDs, stall warning must do its job also without it.The autoslat system will not need this input, it looks for air/ground logic, TE flap position (1,2,5) and AOA.The stall warning must work if, in air, the FMC fails with loss of data. For human factor, a pilot input on a delicate system as it is the sws must not be the most important one.A wrong data cannot cause such kind of possible danger.Generally speaking, AOA info with air composition data, with aircraft ID and aircraft configuration (es. flaps) can let the computer calculate the weight of the plane using AOA. More weight in the same condition will result in much pitch up to increase lift at the same speed.AOA on the NGs are used also for performance data computation (from maintenance manual), so, the GW is an help, is a good thing, but never, I think, basic data that disable the SWS shaker before a stall or for autoslat.So, I need, possibly, a test on simulator (real) or info from manual.