B737 Break-away thrust?
 

Hi guys,

Yesterday during flight, captain asked me if I know the break-away thrust of this plane (737) and as I didn't know, he told me 35% N1 is the published break-away thrust. He told me it's written in AML then we looked for it but it wasn't there. I am not satisfied with that that's why I'd like to ask you guys if any of you know whether it's true and/or where I can find that N1 value published?

Thanks in advance to all, safe flight.

It will depend on weight, gradient of the taxiway and any strong wind component. It is unlikely to be more than 40%, It is what is necessary and sometimes can be idle. To say there is a fixed figure sounds like someone trying to be a smarty-pants.

Your answer is 'the amount of thrust required to move the Aircraft'

Sounds like one of those guys whose explanation for everything is "But Boeing says [insert a value/phrase/procedure/system description/etc.]", yet when you ask them where it's written, it has always seemed to disappear with the latest revision of the manual in question...

Sounds like the same type of captain who tried convincing me that I couldn't select flaps 15 until l i can verify gear down and 3 greens, :{ Funny that his English was ELP 4, and English is my mother tongue :ugh:

Agreed with the other posters, it is a variable amount of thrust which is sufficient to start the aircraft moving from stationary.
Our OM-A refers to average of 30%, but no given for it. Rarely but occasionally have required in excess of 40%, especially when from stationary on an uphill slope being heavy...

All depends on mass and environment, a ferry flight, just release the brakes, 79T on frozen ruts might need 50%+ a lot more if the ramp rats have left the chocks in place

Maybe he just can't stand the configuration warning :E

Config warning? Not in the NG.

Your Chain Got Yanked!
 

In all seriousness, I think said captain was yanking your chain. All responses are ~reasonable, but I go with @Stilton, '...that necessary to move the aircraft...' That said, remember the 'breakaway' qualifier: Once the SOB is moving, back off; far less is necessary to Keep it Moving. And (got to love it!!) don't forget @LNIDA's note about Ramp Rats and Chocks. (From a standing start, can you taxi over chocks? YES! Can it be done at 30% N1? NFL.
Under Any circumstances, if not moving before reaching <40% N1, it is time to back-off and investigate. I pity the fellow or gal whose aircraft moves forward at 40%, yet leaves the nose and two (or more) main gears in their original position. That would cause a difficult conversation and some very creative Carpet Dancing.
"If you're not invited to sit, expect to dance." := (Unknown pilot meeting with chief pilot)
I think you got your chain yanked. Captain was simply establishing the pecking order, you flunked and s/he does not like CRM. Got a better idea? I'd like to hear it.;)

I fly with guys who still wait to go F15 even though I've called for it. Grrr.

Reminds me of KAL.

Oh, that is in a Korean-only memo. No English version.

If you cant move forward with 40% then what do you do? call a tug?:D
Your captain is an idiot and never was this number ever mentionned anywhere and certainly not an engine limitation.
I suggest you get more familiar with this oh forgotten but useful manual...FCTM and read the taxi section and all the others while you are at it.Always good to refresh your memory and avoid situations like this.

I guess he was pulling your plonker and had a good laugh afterwards

Lets hope so:E

Ops manual - 35% normal limit, up to 40% allowed.

But there are places where 40% will not be enough. There you do whatever is necessary. Mexico City - 757 wouldn't move with 50% N1. Called MX to a/c - "no problem." Eventually took about 70% to move from the rut in the taxiway. They disconnect the planes from the tug at the same spot and the ruts keep getting bigger and bigger.

I listen to the Engineers opinion!!

Stilton provides the best answer, however there are guidelines. Typically around 25-30% N1 will get you moving on a level surface and idle thrust keeps it going until after a brake and turn. It may take a few seconds at lower settings to get rolling. Somewhere I have seen the 35% limit number for taxi breakaway, but cannot recall the source - perhaps it comes from CFM maintenance data?

The only guidance I know from Boeing is a warning against >50% N1 during single-engine taxi - two primary reasons - FOD ingestion and jet blast concerns.

"If you cant move forward with 40% then what do you do? call a tug?"

Remove the chocks! It has happened, when in a rush, a B737 jumped the chocks at an extreme N1%. Pause & think.

We are talking about a smooth level surface here and sea level.,many times at 70T+,40 %is barely enough.
40% is not a limit but I see it as the beginning of a caution area.the vortex created with 40 % disappears with a 10 kts headwind..so always better to push in HW if heavy and poor ground surface.
If very light,especially the 700 s will move on with idle thrust but my airline is making money so quite rare:E

I would think confirming the chocks are off by voice or hand signal a given when no pushback.

Now what interests me is the minimum distance your Airline recommmends you to be behind another same size or larger airline based on their expect break away thrust..
I always use 60 Meters minimum but my current airline has no info on this.