ENG FAILURES

[Hardy Heinlin]

This [E/O] detection is used as one of the inputs to the FMC during takeoff phase for the VNAV function...
VNAV ACTIVE (so in flight) and Engine failure sensed and below engine out acceleration height and below the thrust reduction point and airplane at Vref+98 = CON will set automatically

These conditions all together make no algorithmic sense to me. You can't be above VREF+98 when your acceleration height or thrust reduction height is low (e.g. 400 ft).

I just restricted my automatic CON selection logic. But in the criteria I didn't include the heights. Just the VREF+98 alone.

Also, I understand that once the post VREF+98 phase has started, CON will be autoselected by executing a change from the ALL ENG page to the E/O page. But what about the MCP's THR switch and FLCH switch? According to the manuals, pushing the switch should change the thrust reference to CLB (all engines) or CON (e/o). I assume I need not modify anything in this area.


Cheers,

|-|ardy

[tango4]

Thanks a lot Peter !
And Hardy, sorry for having hijacked the topic. Don't hesitate to move those messages to another topic if you want.

Charles

[Skybird]

Charles,

With FLCH, the autothrottle entered a HOLD mode because the pilot manually moved the thrust levers for more than 1.2sec, forcing them to be at idle. The system is then in a "sleep" situation, leaving the authority to the pilot.

This seems to apply to the 777. I have never heard you could do this on the 744. Maybe Peter will get more on that subject...

[tango4]

Thanks A LOT !!!!!!!!
I was not able to find this info anywhere ! Do you know if it is documented in the FCOM ? I desperately tried to find it (I have the FCOM provided by PMDG for info). If you know where it is that would be great. Or is it one of those things that is not documented properly ?

And we'll be waiting for Peter's dinner debrief !

Charles

[Skybird]

These conditions all together make no algorithmic sense to me. You can't be above VREF+98 when your acceleration height or thrust reduction height is low (e.g. 400 ft).

I just restricted my automatic CON selection logic. But in the criteria I didn't include the heights. Just the VREF+98 alone.

Hardy, my sentence looks confusing.
You reach the E/O acceleration height (inserted on the TO REF page), you accelerate and when passing Vref+98, CON is automatically set.
If an engine failure occurs above the thrust reduction point inserted in the FMC, which is in fact 1500ft or F5, the CLB thrust will remain. CON will activate upon EXEC of the 1E/O page.

If you disregard the 1500 and F5 values in your logic, and only keep the Vref+98 condition, loosing an engine between 1501 and 3000ft (NADP1 procedure) will lead to CON selecting automatically... which is wrong...
Correct?

[Skybird]

Also, I understand that once the post VREF+98 phase has started, CON will be autoselected by executing a change from the ALL ENG page to the E/O page. But what about the MCP's THR switch and FLCH switch? According to the manuals, pushing the switch should change the thrust reference to CLB (all engines) or CON (e/o). I assume I need not modify anything in this area.

I agree for the switches... Nothing changes.
Executing the E/O page will select CON if not previously set by the +98 take off conditions.

[Hardy Heinlin]

At VREF+40 I set flap 5, and this activates the thrust reduction (if "5" is entered in the FMC).

So, at VREF+40 I have passed the thrust reduction point.

Now how can I get the FMC to autoswitch to CON at VREF+98 if the thrust reduction point is already passed?


In an earlier version, when E/O detected, PSX switched to CON at the thrust reduction point. Then I learned from Peter that this won't happen before reaching VREF+98. So that's how the current version works. It won't switch to CON at the thrust reduction point already; it will wait untit VREF+98 is reached.

I just rechecked some Lufthansa data and this confirms that CON is autoselected above VREF+98 regardless of the flap acceleration or thrust reduction heights being passed or not. Passing VREF+98 after takeoff is the only CON trigger.

I think the purpose of this logic is simply to delay the thrust reduction. You reach VREF+98 when the flaps are up. With E/O, reduce your thrust from TO to CON only when the flaps are up, not earlier. No matter what heights are entered.

[Christo van der Loo]

Don't they mean the "thrust reduction" point to be where you change from TO to CON after an engine failure after take off?

That would make more sense to me. So you take off and after you accelerated past Vref+98 and you then get an engine failure it will stay in CLB. Because by the time you pass Vref+98 CLB would have been set already.

So to get CON after that point you need to EXC the ENG out page.

This is a quote from the 777 FCOM

"   5    Thrust Reduction

Condition: airplane has accelerated to VREF + 78 knots

Result: thrust is automatically reduced from selected takeoff to continuous (CON) thrust. If the engine failure occurs above the thrust reduction point, the current climb thrust is maintained."

I read the thrust reduction point to be VREF+78.

Chris

[Hardy Heinlin]

That's probably what Steve meant to say. We were talking about 2 different features:

(A) Changeover from TO to CON (automatic) when E/O has been detected before.

(B) Changeover from CLB to CON (manual) when E/O has been detected before.

Of course, (A) can be discussed only when E/O has been detected before reaching the thrust reduction point. Otherwise there would be no "TO" thrust limit.

Of course, (B) can be discussed only when E/O has been detected after reaching the thrust reduction point. Otherwise there would be no "CLB" thrust limit.

Once the E/O is detected before the FMC entered thrust reduction point, the FMC entered thrust reduction point is no longer valid. Not any height nor any flap 5 selection will trigger the thrust reduction. Only reaching VREF+98 will trigger the thrust reduction.

There is an editable flap acceleration height for all engines, and an editable flap acceleration height for E/O.

There is just one editable thrust reduction point, and that is for all engines.

The thrust reduction point for E/O is not on the TAKEOFF REF page. This is fixed at the VREF+98 point.

So, if Steve explicitly says the CON autoselection works only below the thrust reduction point, I can only assume he means the ALL ENG thrust reduction point. The E/O thrust reduction point is VREF+98: of course, that must be ahead of us when we're anticipating the CON autoselection, there is no need to mention this explicitly :-)


|-|ardy

[Hardy Heinlin]

Does anybody know which answer is correct?


(1) The thrust limit changes to CON when selecting and executing an E/O page while an E/O condition is detected.

(2) The thrust limit changes to CON when selecting and executing an E/O page, no matter wether an E/O condition is detected or not.


|-|

[Skybird]

Hardy, YES! I think you got it!!  

Chris, I am pretty sure the thrust reduction point is the one inserted in the FMC, not where it changes to CON after an eng failure on TO.

To summarize:

CON is AUTO selected at Vref+98 if an engine has failed at or below the thrust reduction point value inserted on the FMC TO REF page:
In other words:
- at or below 1500ft if following NADP 1
- at or below F5 speed if following NADP 2

Note: the thrust reduction point on the FMC TO REF page is always an ALL ENG thrust reduction point

[Hardy Heinlin]

That was the misunderstanding:

CON can be autoselected if ...

"... an engine has failed at or below"

versus

"... the aircraft is at or below"


These words in italic font were missing :-) There was just the words "when at or below", without a reference as to what has to be "at or below" -- the aircraft or the E/O bang.


:-)

[Skybird]

(1) The thrust limit changes to CON when selecting and executing an E/O page while an E/O condition is detected.

(2) The thrust limit changes to CON when selecting and executing an E/O page, no matter wether an E/O condition is detected or not.

From what I remember, (2) is correct...

[Britjet]

Two threads going on here. Re the FLCH hold - sorry - It cost me a very fine wine and I still don't know :-(

Peter

[Planedriver]

Hey together,

During Take Off, With VNAV active, an Engine failure, and flaps  fully retracted,the reference Trust Limit changes to con at Vref+98.the planned thrust reduction point is inhibited.
There are already newer FMC versions ( NG FMC BP3,0 and on) on 744 and -8. Here the change to con is under the same condition at flaps up maneuver Speed+18

[Hardy Heinlin]

There are already newer FMC versions ( NG FMC BP3,0 and on) on 744 and -8. Here the change to con is under the same condition at flaps up maneuver Speed+18

Hi,

you mean there is no change in the newer FMC?

Flap up speed = VREF + 80

VREF + 80 + 18 = VREF + 98


Cheers,

|-|ardy

[Planedriver]

That's right

[Planedriver]

But for the newer FMC and -8 the flap maneuver Speeds are computed by the flight Management Computer using weight and current airplane altitude.this allows better optimization of operating Speeds and maneuver cabability.

[tango4]

By now you should know that ATC's job is to make arlines (and pilots) lose money  
If one of your friends is still active, you should buy him another bottle and have him try that in the full flight sim.
And if you come by Paris, I'd be glad to offer you a drink !

Anyway, thanks for asking !

Charles

Two threads going on here. Re the FLCH hold - sorry - It cost me a very fine wine and I still don't know :-(

Peter

[Planedriver]

2 is correct😊