B737 classic level change

[framer]

Scenario;
After departure and after the PM has pushed the N1 button and bugged either 210, 220, or 230 kts, many pilots request from the PM ..."level change 250 kts"... or words to that effect.
Question;
Why do they do that?

I am not sure if it's a sign that they know the a/c systems better than I do or if it's a complete waste of time.
From what I can see pressing level change does nothing to the actual N1 settings as the TOGA mode is setting climb thrust anyway.

I have read the books and am still unsure.

I originally thought that these pilots were mistakenly thinking that the thrust is at take-off power while TOGA is being displayed and they wanted to set climb thrust to avoid being at the higher setting for more than five minutes. I now wonder because some of the pilots doing it are pretty switched on and I've asked them but the answers don't quite add up to me. Any opinions would be appreciated.
Framer.

[ab33t]

250 below fl100

[David Horn]

I assume it's to get the correct pitch commands from the flight directors, but don't know the Classic well enough to say for certain. So I could be completely wrong. :-)

[BOAC]

I would guess as ab33t says, having reduced to CLB power with "N1 - 210/20/30" for accel, when clean at the bugged 210/20/30, the next call is 250 for the climb speed limit?

"Press the N1 button (or VNAV if appropriate), verify that N1 Limit
annunciates CLB and that climb thrust is set........
~~~~~~~~~~~~
Complete the flap retraction and, maintaining a constant pitch attitude,
accelerate to appropriate climb speed. Do not exceed 220 kts until the
leading edge devices are retracted."

and

"If the Flight Director is used, at Aa the Handling Pilot should call for:
"VNAV", which will automatically provide Climb N1, or "Climb Power,
xxxKts" and follow the pitch commands which will give the correct
acceleration during flap retraction."

"Climb Power," is most easily achieved by pushing 'N1', LVLCHG being initially inhibited.

mistakenly thinking that the thrust is at take-off power while TOGA is being displayed??? - what is it at then?

[endofeng]

Also, if you are cleared above the SID alt constraint many will ask/apply level change 250 (once clean) to avoid ac levelling in vnav. Once the hard alt is deleted vnav is available again!!

[Sciolistes]

BOAC, TOGA is a pitch mode not an A/T one.

[BOAC]

Yup, of course, but I assumed he actually meant GA and I was indeed a trifle confused by the words TOGA mode is setting climb thrust anyway since 'TOGA mode' is 'setting' GA until N1 is pressed, is it not? (It's a while since I used non-VNAV.....)

[framer]

I think there is some confusion possibly caused by my initial post as to what I'm asking.
It has nothing to do with 250 below ten.
Nothing to do with levelling in VNAV
( I can see why you thought that though.)

??? - what is it at then?
when you push N1 it selects climb thrust.
BOAC I appologise for the confusion, i am talking about after N1 has be asked for at 1000ft , they ask for "level change ...knots"
It does not change the thrust setting, has nothing to do with Vnav, so why ask for level change .....knots, why not just ask for the speed?

[framer]

I've got a feeling David Horn is onto something.

[RobinR200]

Indeed, he is.
When only requesting speed xxx, the pitch would command the new speed but your FMA will still display TOGA as pitch command. Very confusing. Try it sometime!
By requesting the LVLCHG the FMA will display the SPD mode. Very appropriate at that stage.

VNAV what the hell is VNAV :E

(I fly the classics 300/500)

BUT why do u guys hit the N1 button at 1000´? No acceleration at 1500´ for u guys down under?

[Kirks gusset]

More than likely to climb above a VNAV constaint as one contributor has suggested.

[Checkboard]

ask for "level change ...knots"
It does not change the thrust setting, has nothing to do with Vnav, so why ask for level change .....knots, why not just ask for the speed?
Isn't it commanding "Bug Speed plus 20" which is usually V2 + 20? If you place the autopilot on, the bug jumps to the present speed, and the mode changes to LVL CHG anyway.

If you don't select a mode change, either by placing the autopilot in command or selecting LVL CHG, but just increase the bug - will it not command Bug+20 as it is supposed to? I haven't tried it.

[Sciolistes]

No it wont. Level change and toga behave identically after N1 has been selected.

[Jolly1]

Hi framer

A couple of questions first. What model of the 737 do you mean when you say you are flying a Classic? Are you flying in a mixed fleet with 200s? Are you flying with pilots that previously flew the 200 or early generation 300s minus glass?

There are some procedures that may be carryovers from the Boeing FCTM or from fleet standardization decisions in the past at your company

[Capt Chambo]

I believe the answer lies in how the Automatic Flight system will behave in the event of an engine failure. It's all in your FCOM (Tech. manual) in section 4.20. system description. There it will tell you that whilst pitch is in the TOGA mode, if you should lose an engine, pitch will command somewhere between V2 and V2+20. If you have remained in TOGA after the flaps have retracted and lose an engine, then if the TOGA logic still applies it may try to command a pitch attitude to bring the speed back to V2+20 (assuming it has electronically remembered what V2 was!). By selecting another pitch mode when the aeroplane is "clean" either VNAV,LV CHG or V/S you come out of TOGA mode and the above scenario can no longer happen.
It's the same in the single engine go-around scenario, once clean you select LVL CHG, and select max continuous thrust on the N1 page of the FMC.

The reason you need to either manually press the N1 on the MCP (or wait for N1 to be automatically selected via the FMC at thrust reduction altitude) is because your previous A/T mode was ARM, after THR HLD (which is a mode that allows manual thrust adjustment without interference from the A/T computer). By selecting N1 your thrust is now set via the FMC and A/T computer, and gives you the required thrust for the phase of flight that you are in (climb, cruise or descent).

[arba]

@RobinR200

I concure with your post, but I "hit" the "N1" at 800ft mostly.

[framer]

I'm flying EFIS -300's and 400's.
Many of the other pilots would have flown 200's years ago.

More than likely to climb above a VNAV constaint as one contributor has suggested.
Nope.

Isn't it commanding "Bug Speed plus 20" which is usually V2 + 20?
Nope. After N1 has been selected it will pitch for whatever speed is in the window while the A/T maintains climb thrust.

If you have remained in TOGA after the flaps have retracted and lose an engine, then if the TOGA logic still applies it may try to command a pitch attitude to bring the speed back to V2+20 (assuming it has electronically remembered what V2 was!).
I really doubt that. If its true then it needs serious condideration. I am pretty sure though that even if it did command the +20 after an engine failure it would be "bugged speed +20" not V2 +20.
BUT why do u guys hit the N1 button at 1000´? No acceleration at 1500´ for u guys down under?
Rarely. In sydney sometimes. You do it at 1500ft for noise abatement yeah?
Thanks for your comments....I'm still not sure if it's a good idea or a waste of time though.
More reading and thinking ahead. Ta

[Jolly1]

Based on that information there are several reasons why those you are flying with might use LVL CHG. On the 200 with the SP-177 AFDS system that was the preferred mode to use. Also on the Classic selecting LVL CHG automatically puts you in the N1 mode and is the recommended mode during engine out acceleration and climb up to software U10.7 even on the NG (U10.8 and later it is LVL CHG or VNAV).

By using LVL CHG as a standard you are using a procedure that stays the same during both 2 engine and engine out climbs. From a Human Factors point of view when you can harmonize a procedure for non normals with what you do everyday you decrease the chances for error.

Does your Company use the Boeing FCTM or a tailored FCOM Volume 1? What do the procedures in there call for? If it is not specified those you are flying with may have learned it as one of those dreaded undocumented techniques so many of us use cling to because they work even if we don't remember why!

[Kirks gusset]

Framer, I am curious as to why you would ask opinions and then discount them. Here's a scenario, you depart. select VNAV and then are told to "Climb Now" fl XXX or ALT XX, how are you going to do this.?. ATC expect the climb to start pronto, and getting the PNF to dig in the FMC and remove the altitude constraints and then remain in VNAV is not a good idea. I dont want to get into a debate about thrust modes etc or FMAs.. just an opinion on how you would achieve this without using LVL Change or VS,

[Sciolistes]

BUT why do u guys hit the N1 button at 1000´? No acceleration at 1500´ for u guys down under?
1,000' for our outfit too.

Also on the Classic selecting LVL CHG automatically puts you in the N1 mode
Do you have a reference. My reading of FCOM2 says that LVL CHG does not automatically select N1 mode. VNAV does though. Do you have reference.

Also on the Classic selecting LVL CHG...and is the recommended mode during engine out acceleration and climb up to software U10.7 even on the NG (U10.8 and later it is LVL CHG or VNAV).
My FCTM says that LVL CHG is not not used for single engine acceleration, which makes sense to me. The normal non-normal procedure we use is to bug up at acceleration height (i.e. TOGA FMA pitch mode) and then set A/T off, LVL CHG and MCT when flaps up and clean speed.

U10.8 and later it is LVL CHG or VNAVIn my FCTM the diff for U10.8 and later is to do with VNAV. LVL CHG has nothing to do with the FMC.

By using LVL CHG as a standard you are using a procedure that stays the same during both 2 engine and engine out climbs.
Harminisation? Oh you mean as in single engine go around harminisation :\

[framer]

Framer, I am curious as to why you would ask opinions and then discount them
Hi Kirk. Sorry if my simple "Nope" seemed a little dismissive. Earlier in the thread endofeng said that it may be something to do with avoiding levelling in VNAV, I responded to that with
Nothing to do with levelling in VNAV
( I can see why you thought that though.) so when the idea was put up a second time my response was simply "Nope" because I felt like I had been clear about that. Again, I apologise if it seemed rude or dismissive.
Here's a scenario, you depart. select VNAV and then are told to "Climb Now" fl XXX or ALT XX, how are you going to do this.?. ATC expect the climb to start pronto, and getting the PNF to dig in the FMC and remove the altitude constraints and then remain in VNAV is not a good idea. I dont want to get into a debate about thrust modes etc or FMAs.. just an opinion on how you would achieve this without using LVL Change or VS,
If I was in that exact scenario I would say something along the lines of "Level Change .......kts " and continue to follow the flight directors. I'm not sure why you think I wouldn't use Level change.... I wouldn't use V/s going uphill but thats just my preference (unless of course there was likelyhood of a TA)....anyway, this thread is not about that..........
Jolly,Also on the Classic selecting LVL CHG automatically puts you in the N1 mode
See this is where I start to come unstuck....it is already in N1 mode from the moment you pushed N1 at acceleration altitude. The A/T is commanding climb thrust in N1 mode . If you then go and push Level change it will still say N1 and it will still command climb thrust. The only thing that will change is that the pitch mode will go from TOGA to MCP speed.....now my problem with that is that they behave in an identical manner as far as I can see, if you bug up to 250 or 280 while pitch mode is in TOGA it pitches for that speed, it will stay in it and pitch for whatever speed you want until you select another mode (ie VNAV or MCP speed by putting the a/p in or selecting Level Change. So maybe my question should be "what is the difference between TOGA and mcp speed pitch modes when clean and above acceleration height?.
Anyway, thanks agaiin for your replies, still not sure if there is a benefit to doing it :).....more thinking required.

[InSoMnIaC]

Farmer - I think I get the jist of what you are asking. You want to know why someone would call for LVL change after having selected N1 during the climb out because according to your understanding of the AFDS, You can simply just wind up the speed and it will follow the speed anyway (without pressing LVL change).

according the this FCOM VOL 2 - in auto flt section, it says

that after the aircraft is airborne the FD commands 15deg pitch until a predetermined ROC is reached then it commands MCP plus 20kts (ie V2 plus 20)


So by just winding the speed selector up at your acceleration altittude and not selecting LVL CHG the aircraft will accelerate to the new MCP SPD PLUS 20kts (ie the pitch mode of the FD will still remain in TO MODE).

This is overcome by selecting a new pitch mode. eg. LVL CHG which will force it to follow the actual MCP speed. VNAV is not selected until flap retraction due to possibility of flap overspeed issues.

btw by selecting LVL CHG at 1000 and not N1 the aircraft will fly V2 speed and if there is less than 2.5 mins since takeoff then engine will remain at TO thrust.

[Sciolistes]

Pressing n1 ends t/o mode so toga does not command bug+20.

[InSoMnIaC]

Sciolistes Pressing n1 ends t/o mode so toga does not command bug+20.

pressing N1 just reduces engine thrust. It does nothing to the FD TO mode

[Jolly1]

Quote:
Also on the Classic selecting LVL CHG automatically puts you in the N1 mode
Do you have a reference. My reading of FCOM2 says that LVL CHG does not automatically select N1 mode. VNAV does though. Do you have reference.

Yes I do. Chapter 4 Section 20 with the exception that there is a 2 1/2 minute inhibit during initial takeoff.

Quote:
Also on the Classic selecting LVL CHG...and is the recommended mode during engine out acceleration and climb up to software U10.7 even on the NG (U10.8 and later it is LVL CHG or VNAV).
My FCTM says that LVL CHG is not not used for single engine acceleration, which makes sense to me. The normal non-normal procedure we use is to bug up at acceleration height (i.e. TOGA FMA pitch mode) and then set A/T off, LVL CHG and MCT when flaps up and clean speed.

I was speaking of what happens at flaps up. See Flaps Up - One Engine Inoperative in Chapter 3 of the FCTM. We are referring to "after departure" which I believe is what the initial question in this thread was. Also the Boeing FCTM only says "Ensure autothrottle is disconnected prior to reaching level off altitude so what you describe is a Company procedure.

Quote:
U10.8 and later it is LVL CHG or VNAV
In my FCTM the diff for U10.8 and later is to do with VNAV. LVL CHG has nothing to do with the FMC.

LVL CHG or VNAV are MCP Selections I never said they were FMC choices. However if you select VNAV one of the differences in U10.7 & U10.8 is in "Engine Out Logic" so you will have different results from selecting VNAV at that point U10.3 only changed the label of the ENG OUT CLB page.

Quote:
By using LVL CHG as a standard you are using a procedure that stays the same during both 2 engine and engine out climbs.
Harminisation? Oh you mean as in single engine go around harminisation http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/wibble.gif

There are many different reasons companies adopt certain SOPs grasshopper.

[framer]

Farmer - I think I get the jist of what you are asking. You want to know why someone would call for LVL change after having selected N1 during the climb out because according to your understanding of the AFDS, You can simply just wind up the speed and it will follow the speed anyway (without pressing LVL change).

Exactly.....why didn't I just say that?

But I am still wondering because

So by just winding the speed selector up at your acceleration altittude and not selecting LVL CHG the aircraft will accelerate to the new MCP SPD PLUS 20kts (ie the pitch mode of the FD will still remain in TO MODE).
is not correct, at least not in the a/c I fly, they happily pitch to the speed selected in the window.....all the way up into flight levels if you don't select anything else, and the whole time the FMA displays N1 in the a/t box and TOGA in the pitch box.
So.....why do they do it? There will be a reason I'm sure. I am not doubting it's the normal or maybe even best thing to do.......I just can't see the point in it and I wouldn't mind knowing.
thanks again for the answers.

[RAT 5]

This question was asked to our HOT years ago. The reply followed the lines of: you are asking the a/c to climb and accelerate. There is a ratio between the 2 parameters. TOGA gives 60/40 to climb/accel & LVLCH give 60/40 to accel/climb. True or not I have no idea. It could have been B.S. or true Boeing stuff. Either way, in his opinion, TOGA should remain until the takeoff is completed (it is a takeoff FMA) and then an en-route FMA should be displayed. Neater. You could stay TOGA & N1 to CRZ if you wanted, but it is untidy.

[Sciolistes]

Insomniac,
Yes, that was a fairly rash statement. But the fact is that that TOGA does not command bug+20 if you increase the speed on the MCP.

Jolly,
I don't think it says that LVL CHG automatically selects N1, it just says that it inhibits automatic selection for a period of time. That doesn't mean to say it doesn't, just that it doesn't say it does (at least not unambiguously).

Rat 5,
I don't think so, the acceleration pitch seems roughly the same for MCP SPD and TOGA FMAs accordingly. There is a mention of acceleration bounds in the FCTM for OEI with the advice to leave it in TOGA until flaps up clean speed.