744 TO-B

[Check_Airman 3]

Hi,During preflight, the Thrust Limit page displays "TO-B" below TO-2. This feature is unavaiable to us, but what does it do in the real plane?PS. Is there any way I can assign the G/A switch a keystroke? I can't find it in the key assignments menu.Paul

[markadeane 272]

Nothing shows up in the FMC manual, but I would hazard a guess that it allows you to have a secondary thrust limit configuration all set up in case it is required.I base this on nothing more than a wild guess, so the input of any of our resident experts would be appreciated.As for the G/A key command, I believe it is listed as 'Select TOGA' or something similar?

[Qavion 19]

TO-B is "Takeoff Bump"It is the reverse of derating. I forget the special circumstances in which you would use it, but obviously, it's going to increase the wear and tear on your engines. I've seen it on only a few 744's (On some of Air New Zealand's 744's, for example).http://forums.avsim.net/user_files/157549.jpgI remember playing with it once... If I remember correctly, it does really wierd things to your EPR displays.Cheers.Q>

[markadeane 272]

Ah so that's what it is! Thanks Q!Man, the boy-racer / turbocharged / Pimp-my-RB211's / speed freak in me likes the concept...Anyone able to elaborate on Qavions contribution in terms of when you'd use it and by how much it increases the available thrust?

[markadeane 272]

Too late to edit my original post but now that I'm home I see the G/A key command appears to actually be listed as "MCP Set TOGA"

[Check_Airman 3]

I'd LOVE to see if that could be modelled. imagine the FUN!!!

[cowpatz 243]

We have 3 aircraft with it but don't ask me what it does. I know that it arms CLB and sets a higher than max TO thrust and inhibits the V speeds on the FMC but that is a bout it. It is not a feature we use. Has got me curious though. A good potential question to have up my sleeve to ask a check captain on a route check. CheersSteve

[markadeane 272]

Would be interested to hear back on that Steve. Though by the sounds of it it's not something central to the ordinary ops of the aircraft.

[Check_Airman 3]

>Would be interested to hear back on that Steve. Though by the>sounds of it it's not something central to the ordinary ops of>the aircraft.I agree!!

[crvm 0]

>Would be interested to hear back on that Steve. Though by the>sounds of it it's not something central to the ordinary ops of>the aircraft. Boeing says this ...Increased thrust. This may allow increased revenue generation. Some examples are as follows: Increased thrust may allow more payload to be carried out of short runways where aircraft performance would otherwise be limited. Similarly, obstacle-limited runways may allow the increased thrust to carry more payload or fuel. Increased fuel may allow more range and hence the ability to service more destinations non-stop out of a given runway. Increased thrust may allow more payload or fuel to be carried from "hot and high" airports like Mexico City or Denver, where otherwise aircraft performance would be limited at lower thrusts. Increased thrust may take the form of blanket increase in thrust or one of limited duration, for example a ten-minute takeoff thrust rating. This rating allows takeoff thrust to be maintained for ten minutes after takeoff, enabling takeoff from a short runway and/or an obstacle-limited runway, with higher surrounding obstacles or terrain.Best,Randy J. Smith

[Check_Airman 3]

Thanks Randy,How is this increase achieved though? I'm sure the engines are not allowed to exceed AFM limits...or are they?Paul

[cowpatz 243]

Odd really as there is a 5 min limitation on the use of max TO thrust. Not sure how this would fit in operationally and what the downside of it is. How much above max is it? 10 min seems a very long time on what appears to be an overboost condition.CheersSteve

[crvm 0]

Here is something on the 737-700 with the bump option..http://www.boeing.com/commercial/aeromagaz...asetakeoff.html Best,Randy J. Smith

[crvm 0]

>Thanks Randy,>>How is this increase achieved though? I'm sure the engines are>not allowed to exceed AFM limits...or are they?>>Paul I think it is the other way - meaning, the max thrust on a particular engine type is increased to it's actual certified max limit allowing for higher takeoff weights. Without the bump option it appears a particular engine generates less >than true certified max output on non bump optioned engines.Best,Randy J. Smith