Flex TO computation

[gman1986 14]

No worries

[3-2-1-Now 126]

@3-2-1-Now

 

First off, WHAT'S UP WITH THE CAPS?

 

Secondly on a B777 that's lightly loaded not using de-rated thrust/assumed temp is probably a higher safety risk then using as the aircraft is way overpowered in that scenario. Therefore a lot more difficult to control.

 

CAPS are/were for emphasis. I'm not shouting.

 

 

 

Secondly on a B777 that's lightly loaded not using de-rated thrust/assumed temp is probably a higher safety risk then using as the aircraft is way overpowered in that scenario. Therefore a lot more difficult to control.

Hence my original comment of "the risk is too damn high". In your scenario however, it could be argued there is greater risk (large asymmetric thrust together with low inertia = bad day), so you could use ATM to offset the risk of too much power against runway available (remembering that the effective runway is much longer now, as you're so much lighter).

 

There is another part to this equation: as the A340 demonstrated, even with the damaged tail, it is generally safer to take to the air than to try and stop. If they tried to stop.....you figure it out.

 

I'd like to clarify that I always held this view regarding Flex/ATM, and it is not the result of any particular accident.

 

Best regards,

Robin.

[E6BAV8R 88]

There is another part to this equation: as the A340 demonstrated, even with the damaged tail, it is generally safer to take to the air than to try and stop. If they tried to stop.....you figure it out.

 

That is every multi-engine airplane - it is called 'Accelerate Stop' and 'Accelerate Go Distance'.  In this case they hit their Accelerate Go speed.

[RudiJG1 172]

We can pray the once finished with PFPX they will make a TOPCAT 777 profile.

A couple of forum postings suggest that B777 (-232, -300 models) profiles will be included in PFPX.

[tombeckett2285 7]

[Fabo 213]

 

 

A couple of forum postings suggest that B777 (-232, -300 models) profiles will be included in PFPX.

 

PFPX yes, TOPCAT, well, my money is not this year anyway.

 

I am not going to go into yes derate or no derate debate (been there once... feel free to reference), but about the Sydney accident and the speed and weight difference - EK pilots are crossfleet on A330/340 types. Their weight appeared normal to them, because they were used to such figures from the A330.

[Noble. 142]

PFPX yes, TOPCAT, well, my money is not this year anyway.

 

I am not going to go into yes derate or no derate debate (been there once... feel free to reference), but about the Sydney accident and the speed and weight difference - EK pilots are crossfleet on A330/340 types. Their weight appeared normal to them, because they were used to such figures from the A330.

 

That gives some insight, doesn't make it any more acceptable though as I'm sure you'll agree.  :smile:

[Fabo 213]

Absolutely. These things should not happen...

[Circletoland 13]

My suggestion: don't use it. .... "The risk is too damn high!".

...

Best regards,

Robin.

 

 

That´s funny, ten thousands of flights are flexing and assuming every day but hey, yes maybe you are right!! It´s dangerous!!! We should all think about your words man! ;)

 

No serious, lots of certification tests have proven, a birdstrike for instance with an engine running in full rated setting for takeoff has a much higher percentage of leading to serious engine failure, broken fans, uncontained engine troubles etc.. besides that, if you have an engine failure with full thrust, the aircraft is a lot harder to control... so many more reasons to assume and derate... than "just" economic reasons... (millions of dollars a year!!) 

 

 

 

Secondly on a B777 that's lightly loaded not using de-rated thrust/assumed temp is probably a higher safety risk then using as the aircraft is way overpowered in that scenario. Therefore a lot more difficult to control.

 

 

Absolutely right, there are several serious incidents with short runway´s, light weight - full thrust and LOW INITIAL ALTITUDES on the T7... for instance level off at 800ft AGL, CM2 flying, A/P engaged at minimum altitude, due to running into ALT ACQ. the aircraft rapidly reached the flap speed, so CM1 disengaged the A/P retarded the thrust to idle while they got a continues climb clearance by ATC... The PF selected the higher ALT and continued climb with V/S (!) and both forgot about the disengaged A/T letting the speed drop into the shaker... pretty dangerous! 

 

Anyway, we use assumed and derated thrust in about 19 of 20 cases. Usually on long runway´s you still have plenty of runway left even in the stop case.. but if not, just shorten the runway in you calc tool and you´ll be fine! Of course a triple cross check of the takeoff data is important! But that´s our job! We have procedures, checklists and IT-solutions which check the correct performance setting to ensure safety for us and our passengers!

 

Cheers,

Berni

[Fabo 213]

Hello Berni, nice to see you come out of the woodwork. I recall we had some nice conversations after the NGX came out. Still in Yellowcub? How has SWG treated you?

 

Anyway, don't bother, some people are just against some things no matter arguments. I sense a similar case here.

 

 

On the topic of weights... I know we are in the 777 category, but here is a neat little 737-800 trick a friend tought me - take your V2, last two digits, add 20. You should about have your weight. This is almost exact for F5, needs a bit of adjustment for F1 or F10.

And second trick, crosscheck the weights from three sources (this is universal)

-You will usually get a preliminary weight estimate, based on bookings and such (in commercial ops)

-Check this with the loadsheet. Does it fit? If there is a difference, why? Noshows? Extra gas? Did they fill you with overflow from earlier cancelled flight?

-Lastly, does the number make sense? Remind yourself of the type you are flying. How much does it weigh empty? How much do 170 Canadian holidaymakers weigh? How much gas to Carribean from Montreal? (soo, 155, 55+20=75. Fits, 75 tonnes on loadsheet, makes sense as well)

 

How much is 300 people from Prague to Dubai? Do we have cargo? Why does it only leave 10 tonnes for fuel?

[777simmer 117]

You're right that I'm not going to get everyone to agree with me (and I'm not going to try), but let me answer my own questions:

 

The root cause was incorrect entry, correct. BUT, what did that incorrect entry result in? It resulted in a LOWER POWER SETTING being used than was required (and this is the crux of the problem - why CREATE a problem by using less power than is available?).

 

What did the lower power setting result in? MORE RUNWAY LENGTH REQUIRED FOR TAKEOFF. They DELIBERATELY made the runway shorter as it was by using FLEX (pretty stupid IMHO), but because of the screwed up entry, IT WAS EFFECTIVELY REDUCED TO THE POINT THE AIRCRAFT HAD INSUFFICIENT RUNWAY.

 

Now to the cause of the tail strike: THEY PANICKED, APPLIED TOGA, and OVER-ROTATED in a desperate bid to get airborne before the (now inevitable) end of the runway.

 

See, if they had just used TOGA, they would not have had a problem, and we would not be discussing it now. Another A340 would still be serviceable, and 300+ passengers would not have been affected by the event.

 

In short, FLEX/ATM reduces options, and reduces safety (runway length is like altitude - better to have more of it in front than behind).

 

Best regards,

Robin.

 

 

Many decisions are made on a daily basis to fly from A to B as economical (yet safe) as possible.

What you dont seem to get is that Flex/Derate is normal.

Used by every flight every day when conditions allow.

 

Procedures are established to cross check data entries but I dont know, maybe in this case the crew did not follow procedures. (dont know, I have not investigated this incident).

 

To say lets not use Flex/Derate anymore is the same as saying we should no longer use the following cost reducing methods:

 

Minimum safe fuel policy (yes this includes holding fuel and alternate fuel), lets get rid of that and from now on lets all fly with full fuel tanks only!

 

ETOPS flights, lets get rid of that and only fly from overhead one airport to another just in case something happens.

 

Oh and lets plan with (and carry fuel for) 20 Alternate Destination Aerodromes rather than one!

 

And, you know what, just in case the Cat3B Autoland feature fails, lets fly on Sunny days only!

 

 

What about a load sheet that was not done right (accidents have happened because of that too)

Flights have had problems taking of or their fuel calculation way off because they where haevier than calculated or their Cg way off. Upps Wrong numbers!

What do we do about that? fill up airplanes with 50% capacity of Pax/Cargo to prevent the thing from ever being heavier than Max TO Mass?

 

Comon,

Flex/Derate is not up for debate.

It is normal daily business and it is safe and it is there to stay.

 

Of course if you make mistakes (entering the wrong weight for example) things can go downhill fast.

This counts for pretty much everything we do in aviation and it is one of the reasons why it such an interesting and rewarding bussiness.

[777simmer 117]

Oh, and I just thought of one more thing :-)

 

As we all know, as temperature increases, air density decreases and thus engine performance decreases.

So when it is hot, engine power is less.

 

Now imagine it is 20 degrees C outside.

What we do with Flex/Derate is, we tell the engine to produce the same thrust it would be able to produce if it were for example 35 C outside.

 

Saying it is unsafe to take off with 35C because the engines then deliver less power than max, means we can close Dubai ;-)

[nawarren 83]

Hi All,

 

As well as saving money from less wear on the engines, derates also put less stress on the engines in a critical phase of flight, i.e. takeoff. This helps prevent engine failures etc. on takeoff. It's a win win for the airlines and they will always try and derate whenever they can.

 

Derate has another advantage to busy crews, in that things will happen slower than at max thrust, they will be less likely to bust an altitude limit, or overspeed the flaps. To blame derates for the cause of this crash is missing the point entirely.

 

The simple fact is the crews made a basic error that could have had far harsher consequences. I  do not judge them for it, as it's easy sitting on a sofa with 20 20 hindsight to be an expert. I'm afraid there will always be such accidents with humans in the loop.

 

Cheers

 

Neil

 

Cheers

 

Neil

[3-2-1-Now 126]

Anyway, don't bother, some people are just against some things no matter arguments. I sense a similar case here.

 

Well, the controlability issue is a pretty compelling reason in favor of Flex/ATM, especially at lighter weights. I'm safety first, sod the cost (within reason) - that is not to say safety at any cost, because that is equally ridiculous.

 

Best regards,

Robin.

[Fabo 213]

If you are safety first - that is a good thing. You have now shown signs of actual approachability, hopefully it will keep that way and we shall create a fruitful and interesting discussion.

 

You do have to learn to consider deeper layers though. Aside from controlability, there has been cited a concern of safety in more stressed engines running at marginal values each takeoff. It is indeed logical that this wears the engines more and makes the risk of failure higher.

 

Regarding your cited incident in the EK case in SYD, by using full TO thrust you are bit removing the problem, which is what should be the main point. Incidents stemming from incorrect weight management are not exactly uncommon, it is just that the Sydney one was pretty big (in error and in potential outcome). The problem is not in use of derated thrust, rather in other factors such as (in general, not always EK case specifically) lack of proper rest, fleet switching, mission type changes, lack of proper controls in place.

 

It can be said that by forcing full TO thrust use, you are not lowering the risk, rather you are making the inherent risk higher - it is proven that bad behaviour is more widespread when the outcome is covered by something else; by removing the possibility for weight related negligence to promote itself through effects on takeoff, you are placing an incentive for carelessness. Such carelessness might later prove to be fatal, when proper calculations regarding local atmospheric conditions are not made, "it is under MTOW, it will make out at full thrust"

 

More to come tomorrow. I should have been sleeping for two hours.