AT and FD behaviour with the FD switches OFF

[Sylle]

Hello Hardy,

I wanted to practice some raw data flying and noticed the following that should be checked with one of the type-rated guys on the forum here.

- Load situ 01 Departure 001 - Sydney - Los Angeles
- Turn BOTH FD switches OFF
- Advance thrust levers and press TOGA
- FD appears on both PFDs with FMA; THR REF | TO/GA | TO/GA

I believe the FDs should NOT have appeared in this case.
Automatic display of FD with both switches in off (and AP off) will occur when the AT is armed for go-around (when thrust reference mode on primary EICAS switches back to G/A at flap extension).

I certainly could be wrong but I would expect the following to happen when pressing TOGA on the ground below 50kts with both FD off:
- Advance thrust levers and press TOGA
- FMA; THR REF |        |    
- @65 kts; FMA HOLD |        |    
Pressing THR on MCP above 400ft AGL;
- Thrust reference mode changes to CLB
- FMA THR REF |        |    

Don't know if you specifically checked the situation described above during the development so I would appreciate feedback from any of the 744 experts here.

Regards,
Syvain

[Hardy Heinlin]

Hi Sylle,

I think I checked this function 900 times during the development.

Sorry for my bad memory; are you the man with the 737 type rating? There are lots of differences to the 744.


Regards,

|-|ardy

[John H Watson]

My 747-400 manuals say that the airspeed must be more than 80kts for this auto-on function to work

Rgds
JHW

[Hardy Heinlin]

If the exact airspeed value is airline specific, I'll set an average value. Maybe 65.

Is 50 a 737 thing?


|-|

[John H Watson]

re 80kts... I'm just talking about the FD auto-on function.

Sylle mentioned 50kts because it's the max value for A/T engagement (only) when pushing the TOGA switch.

Having said that, would the FD's appear if you pushed the TOGA switches a second time above 80kts airspeed?

[Hardy Heinlin]

Having said that, would the FD's appear if you pushed the TOGA switches a second time above 80kts airspeed?

According to your 747-400 manuals, they appear when you push while the speed is above 80:

My 747-400 manuals say that the airspeed must be more than 80kts for this auto-on function to work

[John H Watson]

True. I was thinking pushing the TOGA switch a second time on the ground might have unwanted side effects like removing derates, but I see this only happens in the air.

[Sylle]

Sorry for my bad memory; are you the man with the 737 type rating? There are lots of differences to the 744.

Yes indeed  :oops:  but I promise I closely check the 744 FCOM I have here before posting possible issues on the forum now  :lol:
My expectations were based on how the 767 behaves in this case. The wording in the FCOM however was again quite different and rather vague unfortunately.
I have another 744 FCOM on my desktop at home... will see if there is something more mentioned in that one.

Is 50 a 737 thing?

No... JHW is right - I just found the mention of 50kts as max value for AT engagement. Couldn't find a reference to 80kts so I didn't dare including it  :mrgreen:

737 behaviour is quite different indeed.
Auto display of FD 737
When pressing TOGA above 80kts and below 2000ft or before 150 sec after liftoff

Auto display of FD 767
When pressing TOGA above 80kts and flaps not up.

Based on the info JHW found, I would expect the 744 to behave like the 767.

Thanks for looking into this issue. I appreciate it!

Cheers,
Sylvain

[Hardy Heinlin]

If the flaps-out condition is not documented, I won't include it.

On the 744 the flaps-out condition is often used as an approach config trigger, and that may often be given by a G/S-captured condition as well.


Regards,

|-|ardy

[Sylle]

Hi |-|ardy,

More info found in another FCOM

CHAPTER 4, SECTION 20
Flight Director Display
The flight director steering indications normally display any time the related Flight Director switch is ON.
Pushing a TO/GA switch when airspeed is greater than 80 knots and the flaps are out of up displays steering indications when the Flight Director switch(es) is OFF.
In this case, steering indications can be removed by cycling the flight director switch(es) ON and OFF.

Regards,
Sylvain

[Sylle]

JHW,

Would you have any info about what should happen when pressing THR on the MCP above 400ft AGL with both FD OFF??

In PSX only the Thrust Reference Mode switches from TO to CLB but the AT stays in HOLD.
I would expect it to re-engage in THR REF.

Regards,
Sylvain

[John H Watson]

Would you have any info about what should happen when pressing THR on the MCP above 400ft AGL with both FD OFF??

THR REF mode is engaged when:

A/T armed
Airplane above 400' (AGL)
Not "TO" THR LIM (Sylvain, wouldn't the aircraft still be in this thrust limit mode in your scenario?)
FLCH not active (F/D off?) By active, do they mean FD and A/P?
VNAV mode not active (F/D off?)
Not GA THR LIM
Select THR mode on MCP

If VNAV is not armed, will the TO (thrust limit) mode still change to CLB at thrust reduction height (or Flaps 5)?

[Hardy Heinlin]

Pushing a TO/GA switch when airspeed is greater than 80 knots and the flaps are out of up displays steering indications when the Flight Director switch(es) is OFF.

OK, just found this in my manuals too. I overlooked this note during the development.


Thanks,

|-|ardy

[Hardy Heinlin]

According to my notes, the THR switch will not engage the THR REF mode when no pitch mode is engaged.

All in all, it requires certain conditions when the thrust reference is G/A, and some other certain conditions when the thrust reference is not G/A.

I'll show you the PSX code (too lazy to translate it to prose):

Code Select Expand

static SwitchEvent sePushThr = new SwitchEvent() {
void switching( int i ) {
if ( Network.notClient() && FmcVnav.acftHeight > 400 ) {

if ( ( ( FmcThrustLim.selThrLimMode == FmcThrustLim.CLB
|| FmcThrustLim.selThrLimMode == FmcThrustLim.CLB1
|| FmcThrustLim.selThrLimMode == FmcThrustLim.CLB2
|| FmcThrustLim.selThrLimMode == FmcThrustLim.CRZ
|| FmcThrustLim.selThrLimMode == FmcThrustLim.CON )
&& ( pitchEngaged == ALT || pitchEngaged == V_S ) )
||
( FmcThrustLim.selThrLimMode == FmcThrustLim.GA
&& ( pitchEngaged == G_S || pitchEngaged == FLARE
|| ( ( pitchEngaged == ALT || pitchEngaged == V_S )
&& Flaps.eiuLever > 4 ) ) )
) {
setThrottleModes( THR_REF );
}
FmcThrustLim.setClbOrCon( false );
if ( FmcVnav.belowThrRed ) {
FmcVnav.belowThrRed = false;
FmcGlobal.mem1.trans( true, false, FmcGlobal.MEM_BLO_THR_RED );
if ( CduHub.anyCduHas( CduHub.pgThrustLim ) ) {
CduHub.pg[ CduHub.pgThrustLim ].processAll();
}
}
         }
}
};
(FmcVnav.acftHeight refers to the barometric elevation record stored at 100 KIAS.)


Regards,

|-|ardy


P.S.: The pitch mode conditions above could also be interpreted as not TO/GA, FLCH or VNAV, in which case "no-pitch-mode" would be a positive condition. I will recheck my notes for the exact wording ...

P.P.S.: Originally, the 400 ft condition was relevant for the takeoff phase only, hence the FLARE mode, which engages way below 400 ft during the glideslope ride, was relevant too. Now, in the above code, the FLARE mode check is actually obsolete.

[osss]

Pushing a TO/GA switch when airspeed is greater than 80 knots and the flaps are out of up displays steering indications when the Flight Director switch(es) is OFF.

OK, just found this in my manuals too. I overlooked this note during the development.

Hello!

I just practiced some visual patterns too and it seems that switching FD on with TO/GA works only in the air (v. 10.1.1-beta6). But it should be possible during take off roll too. Another several features I found are:

- AT mode does not change to HOLD at 65 kts with FD switches OFF. With FD ON everything OK.

- During approach thrust reference changes to G/A (with flaps extension, flaps in landing position or glideslope capture) only if cruise level was reached before. i.e. full cycle (Takeoff - climb - cruise - descent) is complete. I did not reach cruise level and I did not have GA thrust reference on final with flaps 30.

- Anyway pressing TO/GA should changes the reference thrust limit to GA. But it does not.

- The reference thrust limit should be locked in GA when flaps are in landing position or glideslope is captured. But is it possible to change it to any other.

Thank you
Stan

[Hardy Heinlin]

Hello Stan,

thank you for the hints. Are you referring to certain airline manuals or sims?

Just to be sure that I understand what you mean, let me recheck each point:

1. You mean, when both FD switches are off, and TOGA is pushed on the ground above 50 KIAS, the TO/GA roll and pitch modes should be displayed? -- In PSX, and on the real 744, as far as I know, the TO/GA switch is inoperative above 50 KIAS until after lift-off.

2. You mean, when both FD switches are off, and TOGA is pushed on the ground before reaching 50 KIAS, and roll and pitch modes are blank, the A/T mode should change from THR REF to HOLD when passing 65 KIAS, even though the TOGA modes are not armed? I don't know if this is correct, but you may be right.

3. In PSX, the FMC applies the G/A thrust reference logic only when the FMC is in ACT DES; this is to avoid unwanted thrust reference changes when a TO or CLB thrust reference is set (TO provides the same power as GA anyway, and CLB only activates when the initial departure phase is over; why would you request such a time limited, critical thrust setting higher than CLB or CON at high and safe altitudes?). -- But you may be right regarding landing flaps or G/S engagement resetting the GA reference, even when not in ACT DES. But I don't think this is possible while a TO reference is in use. Pushing the TO/GA switch will just remove TO derates, and will not change to GA; I think this has been proven in the BA sim a couple of weeks ago.

4. You wrote: "The reference thrust limit should be locked in GA when flaps are in landing position or glideslope is captured. But is it possible to change it to any other." -- I don't understand the last sentence. Can the pilot change the thrust reference, or is it locked in GA? You may be right; it may change to GA when changing to flap 25 or 30, or when changing to G/S pitch mode, but once GA is set, it can certainly be changed again by the pilot.


Regards,

|-|ardy

[Hardy Heinlin]

Hi all,

any opinions, doubts, confirmations ...? Obviously, these are rather unusual scenarios, and not clearly documented.

I could modify a few things in the next beta.


Regards,

|-|ardy

[Britjet]

Interesting - I could check some of these out in the sim this weekend..
Peter

[Hardy Heinlin]

If that would be possible ... Thank you, Peter!


|-|ardy

[Britjet]

I will have limited opportunity to check all if this today - but how does this sound?

Start of Take-off - FDs OFF. Derate entered.
Below 50kts - Press TOGA - observe FMAs
Above 80kt - Press TOGA again - observe FMAs
Below 400ft - Press THR - observe EICAS and FMAs.

On approach - (without reaching FMC cruise altitude)..select CLB as limit in FMC
Extend Flap - check GA appears. Try changing EPR limit in FMC. If it changes reselect CLB then...
Select flaps to landing position - check GA appears - try changing EPR limit in FMC

I think I'll film it ;-)

Peter