EK407 Tailstrike @ ML
Ed - can you name a major airport with a sufficiently long runway where your V1 theory would be practical.
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Can we please just draw a line under this ridiculous notion that Flex/Assumed Temp thrust reduction is in some way unsafe.
Facts.
It reduces engine wear through lower EGT
It reduces the chances of VMCG problems
It allows far smoother climb out, imagine using full rated thrust in a very lightly loaded 757 with a 400oft level off SID, not fun for anyone
Oddly reduced thrust actually can help in an engine out situation, things happen slower and there is less chance of having control difficulties, plus you still have the protection by virtue of perf calcs that you will make all necessary performance criteria.
So can the idiot SLF who are prattling on about this please stop it.
If you put incorrect performance figures into the FMC and have incorrect speeds then yes, you are in a bit of trouble, but you could just as easily use full rated thrust and have some lunatic pop the speedbrake, retract flaps etc. That will kill you as well.......
As for the V1 > Vr argument, well words fail me. By definition it cannot be, fact.
Facts.
It reduces engine wear through lower EGT
It reduces the chances of VMCG problems
It allows far smoother climb out, imagine using full rated thrust in a very lightly loaded 757 with a 400oft level off SID, not fun for anyone
Oddly reduced thrust actually can help in an engine out situation, things happen slower and there is less chance of having control difficulties, plus you still have the protection by virtue of perf calcs that you will make all necessary performance criteria.
So can the idiot SLF who are prattling on about this please stop it.
If you put incorrect performance figures into the FMC and have incorrect speeds then yes, you are in a bit of trouble, but you could just as easily use full rated thrust and have some lunatic pop the speedbrake, retract flaps etc. That will kill you as well.......
As for the V1 > Vr argument, well words fail me. By definition it cannot be, fact.
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Clown (how apt)
I think you are confusing "unsafe" and "increased risk". If you cannot see that there is an increased risk in using reduced thrust that delays rotation until near the end of the available runway for every take off, then I would ask YOU to kindly desist posting.
No one has answered this: Is the increase in risk associated with reducing the thrust for take-off balanced against the decrease in risk (as outlined in the Clown's post) AND the commercial benefit?
If it is, surely as PIC (and the acceptor of the risk), you are aware of the numbers involved, or your employer has told you not to worry, as THEY accept the risk on your behalf?
Can we please just draw a line under this ridiculous notion that Flex/Assumed Temp thrust reduction is in some way unsafe.
No one has answered this: Is the increase in risk associated with reducing the thrust for take-off balanced against the decrease in risk (as outlined in the Clown's post) AND the commercial benefit?
If it is, surely as PIC (and the acceptor of the risk), you are aware of the numbers involved, or your employer has told you not to worry, as THEY accept the risk on your behalf?
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judge.oversteer
As I said, it was just an example to show that selected thrust may be as low as 60% of maximum thrust. I believe the fixed de-rates may be operator selected depending on the engine type. Even the sub-types may have a different "fixed" de-rate. (T/O 1, T/O 2)
Those percentages were for the RR with the Trent core, G and H cores may be different, as will GE and PW.
Climb de-rates (CLB 1, CLB 2) also washout at different rates.
I am sure an engine specialist can give you more information.
As I said, it was just an example to show that selected thrust may be as low as 60% of maximum thrust. I believe the fixed de-rates may be operator selected depending on the engine type. Even the sub-types may have a different "fixed" de-rate. (T/O 1, T/O 2)
Those percentages were for the RR with the Trent core, G and H cores may be different, as will GE and PW.
Climb de-rates (CLB 1, CLB 2) also washout at different rates.
I am sure an engine specialist can give you more information.
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FrequentSLF (and others)
I am happy to use reduced thrust whenever it is available. Treat the engines with a little TLC and they will serve you well.
As many have said, the CORRECT reduced thrust does not reduce safety.
We are assuming that some sort of Flex Thrust error caused EK's problem and that the repairs will be expensive individually for EK. You have to compare this with the global savings made by using Flex/De-rate on a daily basis.
[ Compare the useful life of an F1 engine (maybe 1000 miles/6 hours) with that of a well driven taxi (maybe 250,000miles/10,000 hours) and you may see my point of view.
]
I am happy to use reduced thrust whenever it is available. Treat the engines with a little TLC and they will serve you well.
As many have said, the CORRECT reduced thrust does not reduce safety.
We are assuming that some sort of Flex Thrust error caused EK's problem and that the repairs will be expensive individually for EK. You have to compare this with the global savings made by using Flex/De-rate on a daily basis.
[ Compare the useful life of an F1 engine (maybe 1000 miles/6 hours) with that of a well driven taxi (maybe 250,000miles/10,000 hours) and you may see my point of view.
]
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You have to compare this with the global savings made by using Flex/De-rate on a daily basis.
Can you see what I am getting at? I'd just like someone to come out and declare that the risk numbers have been done, and that crews are aware of exactly what risk they are accepting. I'd expect that as airlines are big businesses with large sums of money at stake, someone, somewhere has done this.
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ferris
Sorry you did not like my analogy.
Try this one:
Most engines are rated for 5 minutes (10 minutes in case of an engine failure) at max thrust. Try this for every takeoff and the engines will run out of useful life at a much faster rate than a similar engine treated with TLC. Thermal and physical stresses are so much greater at max thrust compared with max continuous or Flex/De-rate. That is why there is the time limit.
I think your 1 minute is a little mean for a 13 hour sector at close to max takeoff weight. I am just guessing (and from experience) that the average sector length probably is less than 7 hours for a 744/340 so twice the number of applications of high thrust per day/year.
Returning to the humble motor car for a moment. Do you ALWAYS use full throttle when moving off, or would you normally use sufficient power for a slightly more sedate departure?
Recommended reading:-
http://www.smartcockpit.com/data/pdf..._and_Climb.pdf
and more discussions
Why Derate? — Tech Ops Forum | Airliners.net
Sorry you did not like my analogy.
Try this one:
Most engines are rated for 5 minutes (10 minutes in case of an engine failure) at max thrust. Try this for every takeoff and the engines will run out of useful life at a much faster rate than a similar engine treated with TLC. Thermal and physical stresses are so much greater at max thrust compared with max continuous or Flex/De-rate. That is why there is the time limit.
I think your 1 minute is a little mean for a 13 hour sector at close to max takeoff weight. I am just guessing (and from experience) that the average sector length probably is less than 7 hours for a 744/340 so twice the number of applications of high thrust per day/year.
Returning to the humble motor car for a moment. Do you ALWAYS use full throttle when moving off, or would you normally use sufficient power for a slightly more sedate departure?
Recommended reading:-
http://www.smartcockpit.com/data/pdf..._and_Climb.pdf
and more discussions
Why Derate? — Tech Ops Forum | Airliners.net
Last edited by Sir Richard; 7th Apr 2009 at 05:24. Reason: Links added
Originally Posted by John R
Ed - can you name a major airport with a sufficiently long runway where your V1 theory would be practical.
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Full runway length
As the person who originally brought this subject up, I'd like to say that I was not implying it was poor airmanship not to use the full length of the runway. As has been shown above, there are sometimes valid reasons for not using the full length.
That said, not using the full length available is fine if everything goes OK, but it does seem that there are those very rare occasions when the runway behind you at the start of the take off run may have been just enough extra to get out of serious trouble.
That said, not using the full length available is fine if everything goes OK, but it does seem that there are those very rare occasions when the runway behind you at the start of the take off run may have been just enough extra to get out of serious trouble.
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Ex Cargo Clown
This idiot SLF has still something to say (nice to know that professionals have to resort to name calling when have nothing else to say)
as correctly said by No Land 3
Is exactly my logic. Now Ex Cargo Clown would you explain me why am I an idiot?
Thanks to all that have express their opinion about taking off at max trust.
The next logic question will be, why don't you set the trust that you want/need instead of flex/temp? Would not be easier to spot an error on the input of all the data?
This idiot SLF has still something to say (nice to know that professionals have to resort to name calling when have nothing else to say)
Can we please just draw a line under this ridiculous notion that Flex/Assumed Temp thrust reduction is in some way unsafe
Actually CDRW makes a perfect point about the logic you are using SLF. It's directly analogous, albeit taken to its logical extreme.
Economics are part of life, and in aviation we balance risk vs reward.
Economics are part of life, and in aviation we balance risk vs reward.
Thanks to all that have express their opinion about taking off at max trust.
The next logic question will be, why don't you set the trust that you want/need instead of flex/temp? Would not be easier to spot an error on the input of all the data?
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Big Surprise !
That's exactly what is done........
Input the Flex/De-rate and /or Assumed Temperature,
N1 or EPR is calculated and displayed,
Thrust levers or Autothrottle moved to achieve that N1 or EPR
Even in the good old days of steam driven clockwork aeroplanes, (Super VC10 and B747-100/200 spring to mind) these calculations were done from the books, the N1/EPR was bugged and the trusty F/E set the appropriate thrust.
Not too difficult.....
That's exactly what is done........
Input the Flex/De-rate and /or Assumed Temperature,
N1 or EPR is calculated and displayed,
Thrust levers or Autothrottle moved to achieve that N1 or EPR
Even in the good old days of steam driven clockwork aeroplanes, (Super VC10 and B747-100/200 spring to mind) these calculations were done from the books, the N1/EPR was bugged and the trusty F/E set the appropriate thrust.
Not too difficult.....
Last edited by Sir Richard; 7th Apr 2009 at 07:58.
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Because you do not have direct access to the FADEC.
Access is via the FMC which "talks" to the FADEC.
There are many levels of redundancy for all these calculations,
ACARS RTOW calculations are rejected if rubbish is input.
Similarly, the FMC will reject many inappropriate inputs.
The old fashioned paper calculations mentioned above seemed to work without FADEC and other modern electronic gizmos.
When the various electronic calculators are unavailable, there is usually a paper backup method available with tables for weights/temperatures/pressures and wind components for the available runways.
[This was in reply to another question posted by SLF...which seems to have disappeared !
]
Access is via the FMC which "talks" to the FADEC.
There are many levels of redundancy for all these calculations,
ACARS RTOW calculations are rejected if rubbish is input.
Similarly, the FMC will reject many inappropriate inputs.
The old fashioned paper calculations mentioned above seemed to work without FADEC and other modern electronic gizmos.
When the various electronic calculators are unavailable, there is usually a paper backup method available with tables for weights/temperatures/pressures and wind components for the available runways.
[This was in reply to another question posted by SLF...which seems to have disappeared !
]
Last edited by Sir Richard; 7th Apr 2009 at 08:49.
SLF; what you propose would be reasonable if every take-off would be field limited; i.e. dependent on the length of pavement available. In practice, other limits apply as well, like obstacle and climb limits being independent limitations of the pavement length.
Since it is basically impossible to have all this data -up to date and everything; think of construction sites with cranes in a departure area- of every airport available in the aircraft, tables are mostly provided from an operations department which are guaranteed correct and up to date.
Since it is basically impossible to have all this data -up to date and everything; think of construction sites with cranes in a departure area- of every airport available in the aircraft, tables are mostly provided from an operations department which are guaranteed correct and up to date.
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This will continue to go in circles as people, who obviously have no basic knowledge or understanding of the subject, continues to insist that something is wrong and should be changed. Arguing for the sake of it, it seems.
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Flex Toga
Probably shown before but here is an Emirates A340-500 where a pilot selected TOGA 1/2 way during the take off roll. Interesting to see how close V1 and VR are. This flight was a light 3 hour flight.
YouTube - Take off from Sydney
YouTube - Take off from Sydney
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So the anti-Flex/derate brigade's argument is, always full-rated unless an error has been introduced due to manual errors in calculating.
So by that rationale what about RVSM ? Maybe we should have min vertical separation of 2000 ft, maybe more, just in case someone mishears a clearance/put the altitude into the MCP incorrectly and it isn't cross-checked. Actually best make that 4000ft just to be safe.
What about departures at MAUW or MZFW. Surely they have to carry a greater level of "risk" as they are at the very edge of performance. Let's offload 2 tonnes of freight, actually make that 5 tonnes, just to be sure.
The fact are that there is no greater risk of Flex/Assumed Temp departures when done correctly. All figures are calculated that even the worst case scenario (engine failure at V1) is catered for as far as runway length goes, with the necessary safety margins.
If your argument is to use full-rated thrust to remove a possible error being introduced (incorrect V speeds or thrust set) then think about it this way, maybe gear shouldn't be retracted after takeoff, this will reduce the risk of the crew forgetting to lower it before landing.
How does that meerkat put it, oh yes, "Simples"
So by that rationale what about RVSM ? Maybe we should have min vertical separation of 2000 ft, maybe more, just in case someone mishears a clearance/put the altitude into the MCP incorrectly and it isn't cross-checked. Actually best make that 4000ft just to be safe.
What about departures at MAUW or MZFW. Surely they have to carry a greater level of "risk" as they are at the very edge of performance. Let's offload 2 tonnes of freight, actually make that 5 tonnes, just to be sure.
The fact are that there is no greater risk of Flex/Assumed Temp departures when done correctly. All figures are calculated that even the worst case scenario (engine failure at V1) is catered for as far as runway length goes, with the necessary safety margins.
If your argument is to use full-rated thrust to remove a possible error being introduced (incorrect V speeds or thrust set) then think about it this way, maybe gear shouldn't be retracted after takeoff, this will reduce the risk of the crew forgetting to lower it before landing.
How does that meerkat put it, oh yes, "Simples"
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SLF comment
Dear All,
I feel that is time to stop the discussion on the pro and cons of reduced power setting on take-off.
Various professionnals explained in great details the setting actually used and the in-built safety margin.
Shouldn't we wait for the preliminary report instead of wasting bandwith?
Regards
Willy
I feel that is time to stop the discussion on the pro and cons of reduced power setting on take-off.
Various professionnals explained in great details the setting actually used and the in-built safety margin.
Shouldn't we wait for the preliminary report instead of wasting bandwith?
Regards
Willy
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This performance is all very simple really as long as you input the correct data. This nonsensical discussion of flex (used by EK)/derate (not used by EK) and TOGA shows that many here don't have any grasp of 'Performance A' and associated requirements.. And yes, a heavy 345 taking off with flex will often be rotating in the reds after a 4000m take-off roll, but as long as it clears the 'screen height' by 35' after an engine fails at V1 that's all that matters!!
As for the video on youtube a few posts back - if you listen they're just seeing 'how it goes' at TOGA when the aircraft is light.. Trust me, it's off like a scalded cat at light weight and TOGA...
As for the video on youtube a few posts back - if you listen they're just seeing 'how it goes' at TOGA when the aircraft is light.. Trust me, it's off like a scalded cat at light weight and TOGA...