boeing flight protections

[sudden Winds]

Hi Folks,

What´s the Boeing equivalent of all the Airbus flight envelope protections? I am assuming if they do exist, they´re only introduced in the newer models, the 777, the NGs, the 767-400 the new 747s and the 787.....
Thank you !
SW.

[Dream Land]

Here we go again...:}

[Dan Winterland]

They do have some. I think they're called skill, experience and airmanship.

[Tight Slot]

On the 75/76 there is the Alpha protection based on angle of attack. Gives you some protection via the auto thrust (throttle sorry, been a while) giving a bog load of power and an FMA of "ALPHA" on the ADI.

[c100driver]

A common misconception that non FBW Boeing has an "alpha protection" mode.

They don't but they have a "speed reversion mode" of which angle of attack is but one input. Speed reversion mode has some very large traps for the unwary and in no way can be considered an alpha protection.

I have not flown the 777 or 787 so cannot comment on FBW Boeings.

[A37575]

Speed reversion mode has some very large traps for the unwary and in no way can be considered an alpha protection.



Yet despite the above valid warning there are many Boeing operators who do not switch off the autothrottle when flying manually - preferring to leave it armed rather than off.

[alexban]

The 737 classic and NG has protection for avoiding exceedind Vmo/Mmo ,wing flap placard speed and landing gear placard speed. Also for not going bellow minimum speed (which some call alpha floor protection). Minimum speed is based on angle of attack and is aproximately 1.3Vs for the current flap configuration.
Those protection are available with at least one component of the AFS engaged or armed (ap or a/t).
when full manual you will only get warnings -stick shacker , overspeed clacker and MCP limiting symbols.
When ap pitch or autothrottle are on or armed ,they will engage and maintain speed in the protected area.
The reversion modes are used in case the selected control can not maintain any longer the speed in the safe area (for ex one select Vs of 6000'/min ,soon the speed will decrease approaching stall .When at 1.3Vs the modes will change and the ap will go to lvl chg ,reducing pitch so to achieve minimum speed + 5 kt.)
The same goes for the a/t .If armed,when sensing minimum speed it will kick in (very fast) and the speed will be maintained above minimum.
On the Bus , in the approach to stall regime, alpha protection limits the amount of pitch-up that can be commanded, thereby preventing too high an angle of attack (AOA). Should the situation deteriorate further in the approach to stall regime, the alpha floor protection also will apply take-off go-around thrust (TOGA).
On Boeing ,there is no limit of pitch (other than PLI on the EHSI ) ,but the AFS will compute max AOA and apply thrust if max AOA -,minimum speed is achieved.The a/t must be armed for this to happen.
I would like to know about the mode reversion traps you're talking about ,c100 driver.

[airbond]

Again this issue has been brought up!!

The Boeing flight crew training manual (B737) clearly states: the A/T ARM mode is not recommended. (CH 1.34)

On APP if A/P is off then A/T should also be completely off. Either all OFF or all ON.

No ifs and Buts. Airbus is a different kettle of fish, and should not be mixed with boeing.

Thats all.

[c100driver]

Thanks for the good summary Alexban.

As you mentioned the major trap with speed reversion is when in a V/S or VNAV mode the A/P will revert to LVL CHG and then head for the MCP altitude. For a VNAV (RNP) approach in CL aircraft will head for 00000 (you must have an altitude below airfield elevation in the CL for RNP/VNAV) and close the thrust levers. For a two engine or more importantly a single engine V/S NDB or VOR approach with the MCP altitude set at MDA the F/D will lead the PF to pitch down to follow the F/D which if they are not watching the FMA modes can be destabilising.

The second smaller gotcha is that the A/T will only return you to a speed higher than 1.3 VS then return to ARM. This can and has caused confusion on the Flight Deck as to what is happening.

If crews know what to look for it really is not a problem, but it can turn ugly with an underperforming PM.

I do agree with Boeing though All On or All Off, but my employer does not pay me to fly it that way.

[Jonty]

On the B757 Autothrottle use is recommended during take-off and climb in either automatic or manual flying (FCTM 1.31)
I would add to that, and leave it armed during an approach as if the GA switches are pushed then the autothrottle will respond. And even give the thrust for 2000fpm, while I can concentrate and yelling "centre command" ;)