B737 Break-away thrust?

[Manicured garden]

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.

[RAT 5]

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.

[stilton]

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

[FlyingStone]

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...

[B737900er]

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:

[Skyjob]

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...

[LNIDA]

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

[FlyingStone]

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

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

[latetonite]

Config warning? Not in the NG.

[No Fly Zone]

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.;)

[ImbracableCrunk]

Config warning? Not in the NG.

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

[ImbracableCrunk]

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...

Reminds me of KAL.

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

[de facto]

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.

[TypeIV]

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

[de facto]

Lets hope so:E

[misd-agin]

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.

[bingofuel]

I listen to the Engineers opinion!!

sn04jBhpKkw

[vapilot2004]

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


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.

[RAT 5]

"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.

[de facto]

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.

[OhNoCB]

De facto -

Our lot also gives no info, so "That looks about right" is what is used.

[Capt. Inop]

Break-away thrust?

I have recently seen them up in the mid 60's N1. B737, no chocks in place.

[TypeIV]

35 n1 won't get you very far on some rural Russian fields:8

[Groucho]

Ask Airbus about the level for the AB340?

http://www.pprune.org/rumours-news/300539-brand-new-etihad-a340-600-damaged-toulouse-several-wounded-26.html

[ACMS]

We had a 777 stuck in the Tarmac after pushback in Dubai 7 years ago. Had to give up and de-plane the pax......

Ever been to VTBS? The new aprons are notorious for needing TOGA thrust to move...:eek:

[Manicured garden]

Thanks for all your answers guys. But here I'd like to say that despite many ideas; still missing the correct amount. Some ppl says it depends on weight, temperature etc. Of course, but it's meaningless to say that as we are all airliners. I do not want to extend the question but you should get it that what I was gonna ask was for normal Standard conditions.

So the some ppl says 35%N1 is normal limit but any source for that amount of thrust?

And here comes the second question; what should be the minimum distance to get closer to another aircraft? Same problem we had; what I ve been told is that it should be 50 m. minimum. (could depend on the types but I ask for same types) And when I ask the source, he told me that's an Air Law rule but I checked for that on Jeppesen Air Law book, not found.

Any idea?

[TypeIV]

An instructor I've flown with uses half of the take off as a guideline maximum limit without obtaining a clearence from the tower. I haven't encountered this anywhere in the manuals.

[FlyingStone]

normal Standard conditions

Define "normal standard conditions". What I would suggest is that you show your captain the following excerpt from the FCTM - granted, it's not a precise value, but it comes from Boeing itself.

Idle thrust is adequate for taxiing under most conditions. A slightly higher thrust setting is required to begin taxiing.

An instructor I've flown with uses half of the take off as a guideline maximum limit without obtaining a clearence from the tower.

Half of what? N1 is not a linear indication and 50% N1 will not give you one half of thrust at 100% N2.

[TypeIV]

N1 of course, more convenient than calculating kilo newtons when taxying on the apron :8

I've yet to find where it's written if there is such a thing at all, apparently a small piston aircraft was damaged due to the jet blast a while ago and the company were hold nonresponsible since they could prove that less than half of the take off thrust N1 was used, according to him. While the subject is up for discussion, I would like to ask if anyone has heard anything similiar?

[RAT 5]

And here comes the second question; what should be the minimum distance to get closer to another aircraft? Same problem we had; what I ve been told is that it should be 50 m. minimum

And much depends on what you are and what they are. A PA-31 behind a B747 is >50m. You'd get airborne if they went 40% break away. I was very nervous when I was in front of a B747 and I felt his shadow cover me like a shark over a scuba diver. I doubt he could even see me, so I reminded him I was first and still there. I once heard (rumour) of some guys in a DC-9 type a/c, who were getting close to their hold-over time during a lengthy taxi in USA, and it started to snow again, that "maybe we should get it close to the B747 jet blast and clean the wings a bit?" An A319 or EMB135 behind an A380 might be shaken not stirred if too close.
It's not an exact science, more common sense.

[Skyjob]

what should be the minimum distance to get closer to another aircraft?

The answer is the distance should be at least the length of the preceding aircraft, except (in EU) in Germany when operating a less than Heavy behind a Heavy which is defined at 200m.

So 737 behind 737 need to be able to fit 737 between tail and nose, 737 behind 777 need be able to fit 777 between tail and nose... except Germany where 737 behind 777 requires 200m.

This distance (preceding aircraft length) prevents the trailing aircraft being damaged by engine jet blast from the preceding aircraft, which generally speaking would have more jet blast the bigger the aircraft...

[Qwerti]

More than 40% is not uncommon at all on a hot day with a bit of slope, just make sure is clear behind you or theres jet blast fence.

[framer]

I think a pilot got blown over while doing a walk around in Brisbane and broke a bone a year or two ago so injuries do happen.

[JeroenC]

Skyjob, can you please provide reference? Never g'heard of it. Based in Germany...

[Skyjob]

Used to be contained in Jeppesen supplement, ATC section - Germany variations.
Will need to look up where they got their reference from


Jeppesen Airway Manual
STATE RULES AND PROCEDURES - EUROPE
GERMANY
RULES AND PROCEDURES
AVOIDANCE OF WAKE TURBULENCE
f) When taxiing behind an aircraft of higher wake turbulence category a minimum distance of 200m should be kept whenever possible.

[Dynamite1]

ACMS ...needed a minimum of 50 on the 738 past two days; to break out after push back at BKK....just started going there...

[OverRun]

ACMS - I knew the DXB problem you refer to, and the asphalt rutting was fixed shortly afterwards. I also know the BKK/VTBS rutting problems but don't anticipate any early resolution.