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felixthecat
29th Jul 2011, 02:44
My understanding that TOGA during the takeoff and below 400ft disarms the LNAV/VNAV but gets rid of any derate. So it is thus useful in that the flight directors now command a straight ahead . In case of an engine out with no emergency turn very useful since it prevents the LNAV engaging at 50ft and telling you rubbish on the flight directors if there is a turn in the SID below 400ft

Now am I correct in that by NOT selecting TOGA the HDG select and TRK select are not available until 400ft? This making an emergency turn below 400ft difficult since the flight directors will still command the LNAV profile after 50ft which could be at odds with an emergency turn?

falconeasydriver
29th Jul 2011, 16:18
Now am I correct in that by NOT selecting TOGA the HDG select and TRK select are not available until 400ft? This making an emergency turn below 400ft difficult since the flight directors will still command the LNAV profile after 50ft which could be at odds with an emergency turn?

Err no? unless TRK and HDG SEL are normally inhibited below 400ft, find that out and you'll have your answer.

oz in dxb
29th Jul 2011, 20:07
Selecting TOGA below 400ft AGL will inhibit TR/HDG SEL. If extra thrust is needed below 400ft AGL, push the thrust levers up, then you can use TR/HDG.

Oz

safelife
29th Jul 2011, 20:15
Bring on more of this stuff. Reading that really makes me enjoy my Airbus.

felixthecat
30th Jul 2011, 01:56
Cool :) So I understood correctly even if I didn't write it very well :)

So briefly

1) No engine out i.e. straight ahead….can select TOGA…AP available above 200ft

2) Engine out with emergency turn above 400ft AGL…can select TOGA since HDG/TRK will be available again after 400ft... AP available above 200ft

3) Engine out with emergency turn below 400ft AGL….Don't select TOGA just advance thrust if needed and use HDG/TRK as required….AP available if the SID LNAV turn is AFTER the emergency turn point, since you can use HDG/TRK. If SID LNAV turn is BEFORE the emergency turn and still all below 400ft AP not available until HDG/TRK selected since it will follow the SID LNAV turn.

Think that makes sense?!?!? :ugh: ….and that was brief!

8che
30th Jul 2011, 14:55
Not quite that simple.

If you have TO-1 or TO-2 selected for take off you must not select TOGA as you will exceed these thrust settings and so bust your VMCA calc. Also the same if you manually advance thrust levers beyond the assumed temp limit and as this is not indicated its easy to do.

Why would you want to go for TOGA with single engine as you have adequate performance without as per the legal requirements ?

We have a nice feature where the EOsids (emergency turns) are all in the FMC and auto pop up on the map when an eng fail is detected. All you do is execute and continue with LNAV at 50ft.

5420N
30th Jul 2011, 15:50
If you have TO-1 or TO-2 selected for take off you must not select TOGA as you will exceed these thrust settings and so bust your VMCA calc. Also the same if you manually advance thrust levers beyond the assumed temp limit and as this is not indicated its easy to do.

Not according to the FCTM.

When using ATM, the takeoff thrust setting is not considered a takeoff operating limit since minimum control speeds (VMCG and VMCA) are based on the full rated takeoff thrust. At any time during takeoff, thrust levers may be advanced to the full rated takeoff thrust. (FCTM 3.15)

So a clear difference between using FIXED derate and ATM.

8che
30th Jul 2011, 16:25
I hope we agree If you see TO-1 or TO-2 on your EICAS you are using fixed derates and those should not be exceeded

I believe I did say you can move the thrust levers forward for Assumed temperature however with the combination of fixed derate and ATM reduction its not recommended as there is no indication of when you have passed the fixed derate limit. Thats what I meant by "beyond assumed temp limit"

Yes full power with ATM only then move as you wish

5420N
30th Jul 2011, 17:06
Indeed all agreed 8che,

Felixthecat,

Pressing TOGA after takeoff also disarms VNAV, so there will be no acceleration without your intervention.

Seems a lot to think about in a HIGH workload situation, I'd say keep it as simple as you can. I have not seen a situation that required more thrust as yet,
but you never know.

Our Ops manuals state that we disconnect the A/T and push the THR levers forward (EEC protected). Then again we only do the ATM for takeoff. This will also retain your ability to turn below 400.

Non Zero
30th Jul 2011, 20:25
Let try to clear a little bit here ... read carefully and do not interpret ... Boeing folks are lawyers but not stupid


With speed less than 50 KIAS, pushing a TO/GA switch activates the autothrottle in the thrust reference (THR REF) mode. The thrust levers advance to the selected thrust limit. If the autothrottle is not active by 50 knots, it cannot be activated until above 400 feet.
At 80 knots, the autothrottle mode annunciation changes to HOLD (and will stay in HOLD until 400 ft AGL when it'll change to THR REF).
With speed greater than 80 knots, pushing a TO/GA switch disarms LNAV and VNAV.

After lift-off


if a TO/GA switch is puched:

removes takeoff and climb derates and assumed temperature thrust reduction
A/T in HOLD, the A/T activates in THR REF.



Now ...

The autothrottle is in HOLD between 80 knots and 400 feet AGL. Take-off thrust (THR REF) must be reached before 80 knots and ...
.. in a normal take-off after takeoff thrust has been set, you shouldn't touch the thrust levers until or as early as 400 ft AGL (minimum altitude at which by regulation you are allowed to apply the first thrust reduction).
Engine Failure during an ATM, if more thrust is needed, thrust on the operating engine may be increased to full thrust by manually advancing the thrust levers while still on the runway, or by pushing the TO/GA switch when airborne. This is because the takeoff speeds consider VMCG and VMCA at the full rated takeoff thrust.
Engine Failure during a Fixed Derate, increase beyond the fixed derate limit could result in loss of directional control and should NOT be accomplished unless, in the option of the captain, terrain contact is imminent.
Engine Failure during a Combined, behave like a Fixed Derate.

And for the records , 400 ft AGL is also the minimum altitude at which you are allowed to iniziate a turn in case of a partial loss of thrust (for obstacle clearance) (so called Special EO SIDs). Airbus or Boeing ... you will not be able to obtain you minimum certified obstacle separation in the first and second segment climb if a turn is initiated before 400 ft AGL. :ok:

Now am I correct in that by NOT selecting TOGA the HDG select and TRK select are not available until 400ft? This making an emergency turn below 400ft difficult since the flight directors will still command the LNAV profile after 50ft which could be at odds with an emergency turn? Autothrottle system is different from AFDS and yes you cannot select any roll mode (including HDG/TRK) as low as 400ft AGL, but you shouldn't because you loose lift in a turn. In the Takeoff Logic the airplane will maintain rwy heading or extended rwy track if the two defers of more than 0.7 deg.
You shouldn't perform any emergency turn below 400 ft AGL unless you are following VFR which you and you only are responsible for your obstacle separation.

felixthecat
31st Jul 2011, 09:33
If you look at the emergency turn off 30R in Dubai depending on what aircraft you are flying you could well be below 400ft when you are required to turn, especially on a hot day in the height of summer full load and on a 300 RR.

I am sure there are other places with a similar problem.

I am lucky I don't have to deal with derate only ATM…..so I can push the thrust levers fully forward :)

Non Zero
31st Jul 2011, 11:57
depending on what aircraft you are flying
Well the thread title said 777

If you look at the emergency turn off 30R ... you could well be below 400ft when you are required to turn
Don't wanna sound sarcastic ... but are you sure? Post the EO SID for DXB so we can see!

I am lucky I don't have to deal with derate only ATM…..so I can push the thrust levers fully forward
Sure from one point of view ... but one day you might need to use Fixed Derate to increase your maximum allowable takeoff gross weight (not possible with ATM) ...

Capt Krunch
31st Jul 2011, 12:27
good show Non Zero:ok:

felixthecat
31st Jul 2011, 14:05
I Don't wanna sound sarcastic but

Well the thread title said 777

That it does and I started the thread, the company I work for flys the 777-200, 777-300, 777-200ER, 777-200LR, 777-300ER, 777-300ULR, 777-F with both the Rolls and the GE engines,

so as I said depending on what aircraft you are flying

Using a derate increases the weight?? As I said we just use ATM so I am familiar with that not derating, but seems counter intuitive that derate increases the weight, unless its something to do with VMCG/A ??

The engine out on 30R DXB is DXB 3.4 left 292 (off the top of my head since I don't have reference handy) so in an old 300 with the Rolls when its 40C+ and heavy you are pushing the 400ft for the turn.

Non Zero
31st Jul 2011, 15:22
@felixthecat really sorry if it sounds like a show, didn't mean to.
110% correct saying there different 777 ... correct!
So ... for the pourpose of the exercise lets use the most penalty situation ... old 300ULR with RR at MTOGW for an OAT +40C ... my question is ... how is it possible that in 4.3 miles a twin engine jet aircraft isn't capable of reach 400 ft AGL?
It is possible only if the takeoff is performed above the MTOGW for that day (rwy condition and elevation, OAT).
To be certified as a twin eng you need to meet a minimum required climb gradient. The airplane has to perform this minimum required climb gradient between 35ft and 400ft...

... but it would be interesting to see the EO SID for DXB 30R ...

felixthecat
31st Jul 2011, 15:46
No problem NonZ :ouch:

The DXB beacon is some 1000m prior to the threshold of 30R so you have already eaten up a whole chunk of the 3.4nm before the wheels even leave the ground….and then the engine fails :sad:

8che
1st Aug 2011, 06:11
Non Zero, can you clarify/expand on this ?

" Sure from one point of view ... but one day you might need to use Fixed Derate to increase your maximum allowable takeoff gross weight (not possible with ATM) ... "

Capt Krunch
1st Aug 2011, 06:54
Nice discussion.

8che tis might clear the air for you.

Derated take off Thrust (Fixed Derate) permits a higher takeoff weight when performance is limited by VMCG. This is because derated takeoff thrust allows a lower VMCG. (particularly sensitive when operating a 200LR with 115's hanging on the wing)

furthermore, derated takeoff thrust may also permit a lower takeoff weight when the takeoff weight is limited by the Minimum takeoff weight requirement.

sounds as clear as mud right :E

catpinsan
1st Aug 2011, 10:57
Typical examples where derates can benefit can be short runways and (on some aircraft) - take off with reduced braking due to antiskid not avail, brake deactivation, contaminated RW etc.

catpinsan
1st Aug 2011, 17:18
Dear Kijangnim,
We are talking here of situations requiring the lowest possible V1 due to various reasons such as the short RW, or lower brake effectivity for reasons such as contaminated RW or MEL (eg. antiskid, some brks deactivated). When the reduction of this V1 is limited by Vmc considerations the derate (TO1 TO2) option may allow take-off in such a situation because of the lower Vmc figure as compared to full TO or full TO with ATM and the smaller minimum RW length requirement.

As an example, take a DRY 5000ft RW with a brake deactivated - for the T7 that we fly, the V1MCG (at 30degC and 0 PrAlt) and minimum RW length requirements are:
TO=137kts, and a 5900ft RW (ASDA)
TO1=130kts and a 5300ft RW
TO2=122kts and a 4800ft RW.

If a V1 decrement of 15kts is to be applied to a V1 of137kts resulting in 122kts, this would have to be increased to 137 for the TO case , and increased to 130 in the TO1 case thus requiring a minimum RW of 5300ft or 5900ft respectively. On the other hand, TO2 would allow a take-off because 122kts = V1MCG and the RW is longer than the minimum 4800ft required for a TO2 accel-stop at V1MCG.

(the figure of 15kts decrement used above is for illustrative purposes only, and so also, the discussion does not comprehensively cover various scenarios.)

Upshot is - the case is one that arises due to low TOW/TO spds at VMCG and a short RW (ASDA) and controllability is the underlying issue.

Increased climb perf on the other hand depends on utilising the extra margin of available RW when NOT field length limited. It results in an increased V2 providing better CLB limited perf and TOW.

Salaams.

catpinsan

Non Zero
2nd Aug 2011, 15:38
Krunch always on spot ... 2 GEs how can you live without!

catpinsan excellent example!

I posted about ICP (which is just running faster to jump higher) as another contributing factor to a TOW increase, that all

And it is actually a very good contributing factor! The aim is to get the bird safe off the ground and away from obstacles!

stormyweathers
6th Aug 2011, 15:18
A higher V1 (engine failure speed) means a higher Accelerate-stop distance. V1 has to be above Vmcg. If you have a higher Vmcg, you need to mandatorily increase that V1 which means a higher Accelerate stop distance on a very short and slippery runway. A lower TO thrust means a lower Vmcg, means a lower V1, means more runway to stop, means a higher Take Off weight. Cheers.