Old 744 Forum

Archived posts

Magenta thrust reference line on EICAS

Page: 1

Author Post
Moderator
Registered: May 2009
Posts: 5140
Hi experts,

I'm realizing that my thrust reference indication model on the EICAS is slightly incomplete. Interestingly, the missing effect must be very exotic: No PS1 or PSX user has ever complained about it in the past 18 years :-)

I've been thinking that the effect I've noticed on some real decks might have been certain irregularities of the real EICAS software, but now I saw it in several videos and it cannot be just coincidence: That magenta reference line goes to idle when VNAV descent phase is active. In PS the line has always been indicating the thrust reference limit, corresponding with the green digits at the top of the EICAS screen, no matter whether VNAV is engaged or not. The only noticeable effect in PSX being the line displayed in magenta whenever VNAV is engaged.


Boeing says:

"Reference EPR Indicator:
Indicates green, EPR limit for the thrust mode. Indicates in magenta, target EPR commanded by FMC when VNAV is engaged." (Same for N1 on GE engines.)


So I guess the magenta line should indicate ...

- THR REF LIMIT when the CLB phase is active (or when in CRZ CLB).
- Target EPR (FMC CRZ page 3L) when the CRZ phase is active (not in CRZ CLB).
- Idle EPR when the DES phase is active and when at or above planned path.

... AND all that only when the A/T is disengaged.

Example:
https://www.youtube.com/watch?feature=player_detailpage&v=7g0xL88ebXs#t=199

The Boeing quote is also a bit vague regarding "when VNAV is engaged". On the photo below, and on many other photos, the line is green even when VNAV is engaged.

I think in PSX it should stay green when the A/T is engaged.


Cheers,

|-|ardy


User posted image
Member
Registered: May 2009
Posts: 374
Location: LLBG
Hi,

I noticed something else in this video (didn't check against PSX yet).
When the aircraft is on taxiway parallel to the runway, the vertical FD line is still in the middle even though LOC was still engaged.
Latter this line was not displayed (the horizontal line did, best seen when the aircraft enters the parking position but notice that at this stage engines 2 and 3 already shutdown).

Cheers,

P.S. even though I was on a B744 50 hours ago, I wasn't in position to video the EICAS (or anything else for that matter). After last time I didn't even try. Didn't recover from that one yet 8).
_______________
Avi Adin
LLBG
Moderator
Registered: May 2009
Posts: 5140
Hi,

did you ride that simulator in England? :-)

Just watched the vertical FD bar in that video, and I think it moves to the left at ca. 10:10 during the turn. Remember the FD is a steering command, not a deviation indicator. If you're not on the LOC beam but on a good course towards the beam, the steering command is in the center.


Cheers,

|-|ardy
Member
Registered: May 2009
Posts: 374
Location: LLBG
Hardy Heinlin wrote
did you ride that simulator in England? :-)

Remember the FD is a steering command, not a deviation indicator. If you're not on the LOC beam but on a good course towards the beam, the steering command is in the center.

No, 737 doesn't do it for me :)

I know that but the aircraft is not "towards the beam", it is parallel to it and since the aircraft is very close to the LOC antenna, I expected "sharp" correction command. I wonder if it has something to do with speed or it is because the aircraft is so close to the antenna and the F/D (FCCs) thinks there is no way to get the aircraft back on course so it doesn't try (but then one could expect LOC).

Cheers,
_______________
Avi Adin
LLBG
Member
Registered: May 2011
Posts: 143
Hardy Heinlin wrote
The Boeing quote is also a bit vague regarding "when VNAV is engaged". On the photo below, and on many other photos, the line is green even when VNAV is engaged


My guess based on another B-oeing: if you disconnect the autothrottle in the situation in the picture, the green line becomes magenta.
Moderator
Registered: May 2009
Posts: 5140
I think so too. Being magenta, it's sort of a director. And that is only required when the A/T is inactive. When the A/T is active, the white command line would mostly agree with the "director" line anyway.

Also, I read somewhere that the target thrust indicated on FMC CRZ page 3L is mainly for use when the A/T servo is inoperative. So I think in CRZ the line turns magenta and moves down to the 3L value when the A/T is disengaged in CRZ.
Member
Registered: May 2010
Posts: 843
On the Boeing 767, the target thrust is magenta when the FMC is computing the target, and green when the Thrust Management Computer (Autothrottle computer) is computing the target. On the B744, the FMC and A/T are both modules of the FMC on the B744 which confuses the issue.
Member
Registered: May 2010
Posts: 843
Regarding the latest beta:

Quote
0.5.0005. EICAS thrust reference line now remains green when A/T is engaged.


In the KLM Engineering training notes:

Quote
Target Thrust
The target thrust cursor is calculated by the FMC. The target cursor shows magenta in climb when VNAV is engaged. The target thrust cursor changes to green during other phases of flight when VNAV is engaged. It shows magenta in descent when VNAV idle thrust mode is active and anti-ice is on. The magenta thrust target also shows then the autothrottle arm swith is off for pilots' response in manual thrust applications.


In other training notes, the cursor is said to change at thrust reduction in climb.

In PSX, I'm not seeing any change of colour in climb.

Rgds
JHW
« Last edit by John H Watson on Sun, 07 Jun 2015 04:02:30 +0000. »
Moderator
Registered: May 2009
Posts: 5140
Thanks. I'll add these conditions in one of the next betas.

Quote
In other training notes, the cursor is said to change at thrust reduction in climb.

You mean it's green for takeoff thrust limits, and changes to magenta when a CLB or CON limit activates?


|-|ardy
Member
Registered: May 2010
Posts: 843
Quote
You mean it's green for takeoff thrust limits, and changes to magenta when a CLB or CON limit activates?


Sorry, the notes don't expand on this.

I was trying to pick colours in this video:

https://www.youtube.com/watch?v=USh_zuH4J7s

They look magenta-ish in the latter stages of the video, but I couldn't see when they changed from green. Does KLM use Flaps 5 or an altitude for thrust reduction?

Rgds
JHW
Member
Registered: May 2010
Posts: 843
Quote
and changes to magenta when a CLB or CON limit activates?


I was trying to come up with a theory for magenta in climb and also thought about limits. Apart from A/T OFF....

VNAV active (A/P or FD) and
Thrust command equals thrust (mode) limit.

However, I'm not sure about CON or why it should turn magenta for Anti-Ice (NAI and WAI?)
Member
Registered: May 2010
Posts: 843
The engineering manuals do say the cursor turns green at CRZ... but do we have any real world videos of VNAV step climbs?
Moderator
Registered: May 2009
Posts: 5140
In this video it's green during takeoff, and changes to magenta when climb thrust activates (I checked the colors with some photo tools):
https://www.youtube.com/watch?v=USh_zuH4J7s

In that video it's magenta with the A/T disengaged, but -- and that disagrees with the KLM notes -- the A/T is still armed and anti-ice is off:
https://www.youtube.com/watch?feature=player_detailpage&v=7g0xL88ebXs#t=199


|-|
Member
Registered: May 2009
Posts: 374
Location: LLBG
Does anyone understand why in the takeoff video at the end we can see altitude window at 13000, aircraft around 15000 and flight director still commands pitch up (VNAV engaged)?

Cheers,
_______________
Avi Adin
LLBG
Member
Registered: May 2010
Posts: 843
..and why is the magenta selected altitude cursor on the PFD at the top of the altitude scale?
Member
Registered: May 2010
Posts: 843
Quote
In that video it's magenta with the A/T disengaged, but -- and that disagrees with the KLM notes -- the A/T is still armed and anti-ice is off:


Perhaps VNAV with speed intervention is not considered to be full VNAV?
Member
Registered: May 2009
Posts: 374
Location: LLBG
_______________
Avi Adin
LLBG
Moderator
Registered: May 2009
Posts: 5140
The color design is pretty bizzarre. By green and magenta they want to indicate something to the crew, but their manuals don't explain it. So why do they change the color anyway if nobody understands the meaning?

For example, why do they show TO thrust limits in green and all other thrust limits in magenta? Why do I need this color change? Is it a reminder that the TO thrust limit shouldn't last for more than 10 minutes? Or should that mean that TO thrust limits never change with the rising pressure altitude and TAT (keep refering to the recorded air data at TOGA push?) so that the limit line remains static, so that only the other limit modes are dynamic with changing pressures and temps? But then why is it green in CRZ while the cruise limits are dynamic as well? Very strange design, in my opinion.


|-|
Member
Registered: May 2009
Posts: 479
Location: EFTO
Hardy wrote
Why do I need this color change?


Didactic trick: just to keep people on their toes?
See this thread!
:D

Cheers,
Martin
Member
Registered: May 2011
Posts: 143
The way I always understood it:

Red are full (mechanical if you wish) hard limits.

Green N1 is a hard limit driven by certain selections. So you cannot change it (you cannot change derates for takeoff without recalculating everything).

Magenta N1 is a target value driven by the FMC. In VNAV CLB the autothrottle actively uses these targets so they are indicated magenta. The targets can always change, either by the FMC, or by you. You can go from CLB to CLB-1, to CLB-2 and back to CLB as much as you want. You can go to CON if you want to as well. The FMC will slowly remove CLB derates as well during the climb.

In CRZ there is no "engine target", the actual target is a speed. No magenta is used in standard cruise situation (VNAV PTH + A/T).

However, if you notice the autothrottle is chasing the target (speed) too much, you need to change the target from a speed to an N1 value. You do this by disconnecting the autothrottle. The engine instruments will now display the cruise target N1 which is used in turbulent conditions (calculated by the FMC). It is up to the pilots to set the N1 as close as possible to the target N1.

Hope this makes some sense...
Moderator
Registered: May 2009
Posts: 5140
Yes, it makes sense.

While we're at it: Would you say that the green takeoff thrust limits remain static all the way from the first TOGA push until changing to a climb thrust limit? I mean for all kinds of TO limits: TO, TO-1, TO-2 and assumed temp D-TO ...

Or does the indication vary with pressure altitude and TAT? The other limit modes vary for sure.


|-|ardy
Member
Registered: May 2011
Posts: 143
No idea, but I've always considered them as "real-time" since we only do rough checks on these values and they change over time with temperature/pressure rises/decreases on the ground. I don't think the "THR REF" mode "clicks" the limit to a certain value once TOGA is engaged.
Moderator
Registered: May 2009
Posts: 5140
My summary at the moment, based on photos, videos, and KLM notes ...


The target thrust cursor is magenta when:


VNAV SPD is engaged for climb
(indicates thrust reference)

or

VNAV ALT or PTH is engaged & ACT CRZ & A/T is disengaged
(indicates database target thrust for cruise level flight)

or

VNAV SPD or PTH is engaged for idle descent & A/T is disengaged
(indicates low idle)

or

VNAV SPD or PTH is engaged for idle descent & anti-ice is on
(indicates high idle)



|-|
« Last edit by Hardy Heinlin on Thu, 18 Jun 2015 00:50:28 +0000. »
Moderator
Registered: May 2009
Posts: 5140
Now in 10.0.5-beta7 (item 0.5.0038):

http://aerowinx.com/forum/topic.php?id=2939

Page: 1

Old 744 Forum is powered by UseBB 1 Forum Software