B737 classic level change
Thread Starter
B737 classic level change
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.
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.
Join Date: May 2007
Location: Manchester, UK
Age: 38
Posts: 128
Likes: 0
Received 0 Likes
on
0 Posts
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. :-)
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes
on
0 Posts
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.
??? - what is it at then?
"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
Join Date: Jan 2003
Location: NW
Posts: 131
Likes: 0
Received 0 Likes
on
0 Posts
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!!
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes
on
0 Posts
Yup, of course, but I assumed he actually meant GA and I was indeed a trifle confused by the words
since 'TOGA mode' is 'setting' GA until N1 is pressed, is it not? (It's a while since I used non-VNAV.....)
TOGA mode is setting climb thrust anyway
Thread Starter
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.)
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?
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?
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?
Join Date: Apr 2000
Location: NL
Posts: 27
Likes: 0
Received 0 Likes
on
0 Posts
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
(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?
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
(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?
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?
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?
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.
Join Date: Feb 2006
Location: USA
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
B737classic level change
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
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
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).
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).
Last edited by Capt Chambo; 24th Jan 2010 at 21:11. Reason: Clarity & grammar
Thread Starter
I'm flying EFIS -300's and 400's.
Many of the other pilots would have flown 200's years ago.
Nope.
Nope. After N1 has been selected it will pitch for whatever speed is in the window while the A/T maintains climb thrust.
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.
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
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.
Isn't it commanding "Bug Speed plus 20" which is usually 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!).
BUT why do u guys hit the N1 button at 1000´? No acceleration at 1500´ for u guys down under?
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
Join Date: Feb 2006
Location: USA
Posts: 7
Likes: 0
Received 0 Likes
on
0 Posts
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!
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!
Join Date: Nov 2002
Location: Dublin
Posts: 652
Likes: 0
Received 0 Likes
on
0 Posts
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,
Join Date: Aug 2008
Location: Betwixt and between
Posts: 666
Likes: 0
Received 0 Likes
on
0 Posts
BUT why do u guys hit the N1 button at 1000´? No acceleration at 1500´ for u guys down under?
Also on the Classic selecting LVL CHG automatically puts you in the N1 mode
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).
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.
