Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Boeing 737ng Primary Flight Display  
User currently offlineNovice From United Kingdom, joined Aug 2012, 90 posts, RR: 0
Posted (1 year 8 months 1 week 4 days 9 hours ago) and read 5662 times:

On the flight mode indicator there are three modes displayed 'N1' 'LNAV' and 'VNAV PTH'

I would like to understand these mode a bit better, i presume when 'N1' engaged alone will hold speed and the pilot flying will control lateral and vertical navigation manually? 'LNAV' and 'VNAV PTH' control lateral and vertical navigation modes? also is there any particular reason why the 'PTH' come after 'VNAV' and not after 'LNAV'?

Thanks

20 replies: All unread, jump to last
 
User currently offlineAAR90 From United States of America, joined Jan 2000, 3474 posts, RR: 46
Reply 1, posted (1 year 8 months 1 week 4 days 3 hours ago) and read 5566 times:

N1 Mode – A/T maintains thrust at N1 limit selected from FMC CDU. N1 mode engaged manually by pressing N1 Switch if N1 mode is compatible with existing AFDS modes.

(Normally used for climbs... Thrust limited to max n1 climb limit. )


LNAV Mode – In LNAV mode, the FMC controls AFDS roll to intercept and track active FMC route. Active route is entered and modified through FMC CDUs and can include SIDs, STARs, and instrument approaches.


VNAV Mode – The FMC commands AFDS pitch and autothrottle to fly vertical profile selected on FMC CDUs. Profile includes climb, cruise, descent, speeds, and can also include waypoint altitude constraints.



*NO CARRIER* -- A Naval Aviator's worst nightmare!
User currently offlineNovice From United Kingdom, joined Aug 2012, 90 posts, RR: 0
Reply 2, posted (1 year 8 months 1 week 4 days 2 hours ago) and read 5525 times:

Thanks for the reply AAR90, though i still can't really distinguish between 'N1' mode and 'VNAV' mode as they both seem to be controlling auto throttle?

User currently offlineStarlionblue From Greenland, joined Feb 2004, 17040 posts, RR: 66
Reply 3, posted (1 year 8 months 1 week 4 days 1 hour ago) and read 5518 times:

Quoting Novice (Reply 2):
i still can't really distinguish between 'N1' mode and 'VNAV' mode as they both seem to be controlling auto throttle?

N1 mode just maintains a certain thrust on the engines. VNAV follows an altitude profile, for example on a step down descent.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineNovice From United Kingdom, joined Aug 2012, 90 posts, RR: 0
Reply 4, posted (1 year 8 months 1 week 4 days 1 hour ago) and read 5505 times:

Would autothrottle not maintain a certain thrust on the engines, what would be the difference between autothrottle and N1 mode?

Thanks


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 5, posted (1 year 8 months 1 week 4 days ago) and read 5493 times:

Quoting Novice (Reply 2):
Thanks for the reply AAR90, though i still can't really distinguish between 'N1' mode and 'VNAV' mode as they both seem to be controlling auto throttle?
Quoting Novice (Reply 4):
Would autothrottle not maintain a certain thrust on the engines, what would be the difference between autothrottle and N1 mode?

I think you're mixing up how to read the PFD. Across the top is the Flight Mode Annunciator (FMA), which has three zones. In order, they are: Speed Mode | Lateral Mode | Vertical Mode

The Speed Mode determines how the autothrottles are controlled. The Lateral Mode determines the source for the airplane's path over the ground. The Vertical Mode determines the source for the altitude.

VNAV is a vertical mode and can't control the autothrottle. N1 is a speed mode where the autothrottle targets a particular fan speed (N1).

For example:
http://aviafilms.com/photos/737ng-pfd.jpg
This aircraft is running MCP SPD speed mode, LNAV lateral mode, and V/S vertical mode.

That means the autothrottes are tracking the speed dialed into the Mode Control Panel (MCP) by the pilot, the lateral mode is following the ground path defined by the flight plan in the FMC (LNAV), and the vertical mode is controlling the vertical speed (V/S) based off what speed the pilots dialed into the MCP.

Tom.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17040 posts, RR: 66
Reply 6, posted (1 year 8 months 1 week 4 days ago) and read 5488 times:

Quoting Novice (Reply 4):
Would autothrottle not maintain a certain thrust on the engines, what would be the difference between autothrottle and N1 mode?

The autothrottle is not a self-contained thing. It is a system that gets commands from the autoflight system and it sets the engines according to the commands. There is no autothrottle "mode". The autothrottle is an output of the autoflight system, like the servos that control the ailerons and elevator.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineNovice From United Kingdom, joined Aug 2012, 90 posts, RR: 0
Reply 7, posted (1 year 8 months 1 week 3 days 23 hours ago) and read 5463 times:

Thanks guys for clarifying that

User currently offlineAAR90 From United States of America, joined Jan 2000, 3474 posts, RR: 46
Reply 8, posted (1 year 8 months 1 week 3 days 12 hours ago) and read 5307 times:

Quoting Novice (Reply 2):
Thanks for the reply AAR90, though i still can't really distinguish between 'N1' mode and 'VNAV' mode as they both seem to be controlling auto throttle?

N1 mode sets thrust at a maximum N1 RPM (climb limit, cruise limit or usually AUTO) and is used for climbs. N1 mode will automatically engage (be displayed) when using LVL CHG or VNAV in a climb. The thrust goes to the maximum limit and stays there while speed is maintained by acft pitch attitude.

VNAV is a vertical flight profile. Think about it as an imaginary magenta line depicting the plane's altitude at various points along the ground. LNAV's magenta line depicts the plane's horizontal position across the ground; VNAV does the same thing only we can't see the magenta line (we use our imagination).   



*NO CARRIER* -- A Naval Aviator's worst nightmare!
User currently offlineSpeedbird128 From Pitcairn Islands, joined Oct 2003, 1648 posts, RR: 2
Reply 9, posted (1 year 8 months 1 week 3 days 11 hours ago) and read 5281 times:

Quoting AAR90 (Reply 8):
VNAV does the same thing only we can't see the magenta line (we use our imagination).



A306, A313, A319, A320, A321, A332, A343, A345, A346 A388, AC90, B06, B722, B732, B733, B735, B738, B744, B762, B772, B7
User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 10, posted (1 year 8 months 1 week 3 days 1 hour ago) and read 5174 times:

Thing to add regarding VNAV:

You refer to mode VNAV PTH. This means that there is a specific pre-computed path to follow. The other mode is VNAV SPD, which means the airplane will hold the speed commanded by the FMC.

I am a bit confused about N1 and VNAV PTH shown together. With N1 I would expect VNAV SPD, holding precomputed climb speed and taking what it could.

VNAV PTH I would expect on descend with idle mode or FMS SPD, in this case airplane follows the path and either adds a little throttle if needed to maintain speed, or asks for drag. I could see VNAV PTH used in climb, (i.e. geometric VNAV with multiple climb restrictions in procedure) but not with N1 regime.



The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 11, posted (1 year 8 months 1 week 3 days ago) and read 5156 times:

Quoting tdscanuck (Reply 5):
VNAV is a vertical mode and can't control the autothrottle.

The vertical mode switches autothrottle from speed mode to thrust mode (N1 in this case). I'd say that was control.

Quoting tdscanuck (Reply 5):
N1 is a speed mode where the autothrottle targets a particular fan speed (N1).

It's less confusing to refer to it, as the FCOM does, as an autothrottle mode, because on other aircraft types it might well say EPR (with a PW or RR engine), THR or THR REF, which are certainly not speeds.

Quoting Starlionblue (Reply 6):
There is no autothrottle "mode".

There is, it's what the FMA annunciates on the left of the display. When the A/T is controlling speed it's behaving rather differently to when it's controlling thrust, or at idle, so it's in a different control mode.

Quoting Fabo (Reply 10):
VNAV PTH I would expect on descend with idle mode or FMS SPD, in this case airplane follows the path and either adds a little throttle if needed to maintain speed, or asks for drag. I could see VNAV PTH used in climb, (i.e. geometric VNAV with multiple climb restrictions in procedure) but not with N1 regime.

VNAV PTH can also be annunciated in level flight, the path being horizontal.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17040 posts, RR: 66
Reply 12, posted (1 year 8 months 1 week 3 days ago) and read 5152 times:

Quoting Jetlagged (Reply 11):
Quoting Starlionblue (Reply 6):
There is no autothrottle "mode".

There is, it's what the FMA annunciates on the left of the display. When the A/T is controlling speed it's behaving rather differently to when it's controlling thrust, or at idle, so it's in a different control mode.

Sorry that was sloppy terminology on my part. What I meant was that the autothrottles control the engines depending on an autoflight mode. So in VNAV they control the engines in a certain way, in N1 another way.

Or am I confused?



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 13, posted (1 year 8 months 1 week 2 days 23 hours ago) and read 5139 times:

Quoting Jetlagged (Reply 11):
Quoting tdscanuck (Reply 5):
VNAV is a vertical mode and can't control the autothrottle.

The vertical mode switches autothrottle from speed mode to thrust mode (N1 in this case). I'd say that was control.

Good clarification; VNAV can command what mode the autothrottle is in, but VNAV can't directly command the autothrottle. It's the autothrottle that figures out where to actually put the throttle (the method the autothrottle will use depends on what VNAV wants with respect to vertical path).

Quoting Jetlagged (Reply 11):
It's less confusing to refer to it, as the FCOM does, as an autothrottle mode, because on other aircraft types it might well say EPR (with a PW or RR engine), THR or THR REF, which are certainly not speeds.

True.

Quoting Starlionblue (Reply 12):
So in VNAV they control the engines in a certain way, in N1 another way.

Or am I confused?

I'd say it's confusing to contrast VNAV and N1 that way because they're two different things...VNAV is a veritcal path control, N1 is a throttle control. The autothrottle can control the engine based on the target speed of the engine (N1/EPR/TPR/IDLE) or on the speed of the aircraft (SPD). VNAV is a vertical path mode...for some parts of a VNAV path, like climbs or descents, you want to autothrottle to control on engine speed. For others, you want it to control on aircraft speed. VNAV can tell the autothrottle what type of control it wants, the autothrottle will select the appropriate autothrottle mode to actually execute that.

Tom.


User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 14, posted (1 year 8 months 1 week 2 days 18 hours ago) and read 5093 times:

Quoting Jetlagged (Reply 11):
VNAV PTH can also be annunciated in level flight, the path being horizontal.

Of course. But then you wouldnt have N1 in level flight anyway, would you?

Maybe in an acceleration segment I suppose it could be....



The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 15, posted (1 year 8 months 1 week 2 days 15 hours ago) and read 5061 times:

Quoting Fabo (Reply 14):
Of course. But then you wouldnt have N1 in level flight anyway, would you?

Not for very long.   But then again I never said you would.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 16, posted (1 year 8 months 1 week 2 days 13 hours ago) and read 5041 times:

Quoting Jetlagged (Reply 15):
But then again I never said you would.

Yep  

Would probably help if Novice told us what specific situation is he refering to with FMA in this configuration.

Also I have not been in the NG cockpit for a while. Would benefit from a refresher...  



The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
User currently offlinemandala499 From Indonesia, joined Aug 2001, 6864 posts, RR: 75
Reply 17, posted (1 year 8 months 1 week 2 days 9 hours ago) and read 4981 times:

Autothrottle Modes:
N1 - the autothrottle maintains thrust at the selected N1 limit displayed on the thrust mode display, including full go-around N1 limit.
GA - the autothrottle maintains thrust at reduced go-around setting.
RETARD - displayed while autothrottle moves thrust levers to the aft stop. RETARD mode is followed by ARM mode.
FMC SPD - the autothrottle maintains speed commanded by the FMC. The autothrottle is limited to the N1 value shown on the thrust mode display.
MCP SPD - the autothrottle maintains speed set in the MCP IAS/MACH display. The autothrottle is limited to the N1 value shown on the thrust mode display.
THR HLD - the thrust lever autothrottle servos are inhibited; the pilot can set the thrust levers manually.
ARM - no autothrottle mode engaged. The thrust level autothrottle servos are inhibited; the pilot can set thrust levers manually. Minimum speed protection is provided.

Note: engaging LVL CHG or VNAV climb automatically engages A/T N1 mode.
On T/O, when pressing TO/GA switch, thrust mode changes from ARM to N1, until 84kts, where A/T mode changes to THR HLD. After 800ft, at THR HLD changes to ARM. Pressing the N1 button will then reduce the thrust automatically when reaching the thrust reduction altitude.

So, N1, doesn't care about your speed... it'll give you all it can give... the Autopilot or the pilot does everything else but thrust.

Speed control under automation is done with the autothrottle and the autopilot.
Autopilot does the pitch and roll... autothrottle just simply does the thrust.

Climb and descents are done in 2 ways...
Speed + V/S: V/S is set, and the autothrottle adjusts to maintain the selected speed.
LVL CHG + N1/RETARD: A/T goes to full available thrust, or to idle, the autopilot will adjust pitch to keep the selected speed. (LVL CHG is also known as FL CH on some Boeings).

(I wouldn't climb a lot on SPD + V/S...    )

In Airbus, LVL CHG + N1/RETARD is called OP CLB and OP DES... Open Climb and Open Descent... it'll show OP CLB or OP DES on the pitch control on the FMA... and the Thrust Mode Announciator part of the FMA does... *now where the hell are my books?*

Quoting Fabo (Reply 16):
Would probably help if Novice told us what specific situation is he refering to with FMA in this configuration.

VNAV PTH with N1?
Remove the SPD REStriction below 10,000 on the FMC and get a level acceleration segment... preferably with a heavy TOW, you'll get VNAV PTH and N1.    Eg: Take off with low initial climb (say, 3000 or 4000, to keep under the arrivals as part of a long SID, and ATC wants to 'get rid of you ASAP' but still keep you on the SID profile, you can get a cancel speed restriction on your take off clearance... and you're damn heavy... you might just get that VNAV PTH and N1.   

Mandala499



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 18, posted (1 year 8 months 1 week 2 days 8 hours ago) and read 4959 times:

Quoting mandala499 (Reply 17):
you might just get that VNAV PTH and N1.   

Isnt it VNAV ALT if level? But as I said, I have been out the loop for a while, might be mixing stuff up  
Quoting mandala499 (Reply 17):
.. it'll show OP CLB or OP DES on the pitch control on the FMA... and the Thrust Mode Announciator part of the FMA does... *now where the hell are my books?*

THR CLB or THR IDLE.... I am trying to embrace FiFi now, see...

by the way, do you know how to tell a new airbus pilot from seasoned airbus pilot?
The new one asks "What is it doing now?"
The seasoned one says "Its doing it again!"
 



The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
User currently offlinemandala499 From Indonesia, joined Aug 2001, 6864 posts, RR: 75
Reply 19, posted (1 year 8 months 1 week 2 days 7 hours ago) and read 4956 times:

Quoting Fabo (Reply 18):
Isnt it VNAV ALT if level? But as I said, I have been out the loop for a while, might be mixing stuff up

Dun ask me!    am just regurgitating the FCOM here!

Quoting Fabo (Reply 18):
THR CLB or THR IDLE.... I am trying to embrace FiFi now, see...

Yeah... those!... Fifi???? *LOL! that's a new one*

Quoting Fabo (Reply 18):
by the way, do you know how to tell a new airbus pilot from seasoned airbus pilot?
The new one asks "What is it doing now?"
The seasoned one says "Its doing it again!"

And how do you tell a seasoned one from an instructor?
Instructor says, "you're doing it again!" (that's an actual one!    )



When losing situational awareness, pray Cumulus Granitus isn't nearby !
User currently offlineFabo From Slovakia, joined Aug 2005, 1219 posts, RR: 1
Reply 20, posted (1 year 8 months 1 week 2 days 7 hours ago) and read 4945 times:

Quoting mandala499 (Reply 19):
Fifi???? *LOL! that's a new one*

Used to go by "playstation", but that would not reflect well on me now try to actually make sense of Airbus logic   Cpt. Dave used to go by that new one... Wish he will bring the blog back.

[Edited 2013-01-14 11:17:50]


The light at the end of tunnel turn out to be a lighted sing saying NO EXIT
Top Of Page
Forum Index

Reply To This Topic Boeing 737ng Primary Flight Display
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
Primary Flight Display posted Wed Jul 25 2001 17:26:12 by Corsair2
Boeing 737ng Flap Settings? posted Thu Dec 6 2012 15:18:46 by Novice
Boeing 737NG Maintenance Training posted Wed Mar 30 2005 21:47:28 by Troubleshooter
Boeing 737NG Development Cost posted Wed Sep 22 2004 02:02:54 by N328KF
Boeing 737NG - Which Tank Gets Filled First? posted Wed Jul 7 2004 00:40:07 by Mozart
Primary Flight Controls posted Tue Mar 2 2004 22:43:32 by Airways45
The Boeing 737, And Flight Time posted Sat Sep 20 2003 00:03:45 by Cancidas
737NG Flight Deck Display Configurations posted Thu Sep 15 2011 16:05:15 by WestJetForLife
737NG Flight Deck Display Formats posted Wed Sep 14 2005 12:52:16 by ZSOFN
Source For Boeing Flight Control Description. posted Fri Jul 6 2012 15:37:27 by airtechy

Sponsor Message:
Printer friendly format