reduced-thrust take-off
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Pilot's discretion. The performance data printout lists numbers for a variety of thrust settings, flap settings, and bleed configurations. Normally some form of reduced thrust is used as long as it provides a particular cushion (the difference between actual take-off weight and the performance limit weight for that particular thrust setting). Many times full take-off thrust is required.
Reduced thrust? Really Mutt, next you'll be telling me you use those flap thingys for take-off as well! 
I'd have to justify not using full power for take-off!
Throttles fully forward every time!
Sadly however, not many times now left!
Regards
Bellerophon
I'd have to justify not using full power for take-off!
Throttles fully forward every time!
Sadly however, not many times now left!
Regards
Bellerophon
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Thank you all for the replies. The reason I asked the question is I know reduced thrust takeoff will prolong on-wing life of the engines and reduce maintenance cost. I just wonder how much beancounters have to say in this matter. I guess the beancounters could always order derated engines so the pilots would not have a choice.
I guess the beancounters could always order derated engines so the pilots would not have a choice.
The Reverend
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I guess the beancounters could always order derated engines so the pilots would not have a choice.
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Thrust or trust?
I fly the 737-500, in my company were asked to ecomical as possible without breeching safety, so in my opinion it's up to the ''Flight Commander'' he has not earned those four gold bars on his shoulder for nothing. Usuall we use between 85% and 96% of N1 for take off, but depends on the lenght of the runway, we can use 100% of N1 somtimes....
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An additional safety item to note:
Provided the necessary performance minima can be attained, then reduced thrust will reduce the minimum control speed for the takeoff (NB not the certification speed, but the actual practical limit of the day). Any transient following a failure will be less dramatic than with full power applied.
It's not entirely a max power (safety) vs reduced thrust ($$$) argument.
Provided the necessary performance minima can be attained, then reduced thrust will reduce the minimum control speed for the takeoff (NB not the certification speed, but the actual practical limit of the day). Any transient following a failure will be less dramatic than with full power applied.
It's not entirely a max power (safety) vs reduced thrust ($$$) argument.
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The B757 RB211 E4 is so over powered that a reduced thrust T/O is almost always used. As a result of this, every 3-4 weeks it is a requirement of most companies I have worked with, that a full power T/O is carried out to ensure full power is available in the event of an emergency.
The other time that a full power T/O is required is when a thrust reverser is locked out (I think this is the case on every a/c type).
The other time that a full power T/O is required is when a thrust reverser is locked out (I think this is the case on every a/c type).
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I think that Mike Jenvey has given a very articulate answer to your question, and the Mad Scientist and mono have brought in other worthwhile considerations. It can be made to look like a very complex problem, but in reality you have the crux of the answers in the three posts mentioned. As an aside, we use a flex derate when possible. And that is often at quite heavy weights, it is NOT necessary to be lightweight. We have conditions, such as contaminated runways, de-icing fluid etc where flex derates are not permitted, but for the vast majority of departures we'll flex if possible. Originally, we worked out a pen and paper method, using pad weights, which got us a 'safe' derate. About 6 years ago we went to a computer programme which does the calculations to the nth degree. After one year of using the computer calcs, the maintenance department gave us a staggering reduction in engine overhaul costs. We do about 7000 departures a year on my fleet, and the savings resulting from the computer flex derates worked out to approximately $1400US per takeoff! And that was when compared to the paper calculated derates. With 7000 takeoffs per annum, that seems like a worthwhile savings to me. We have since gone to a 2nd iteration of the software which is yielding even greater savings. In todays competitive environment it can only be a dinosaur who would 'always use full throttle regardless'. Companies won't survive with that attitude. I am certainly not averse to building in a small fudge factor for me, the wife, the kids, and the whole song and dance, to ensure that I'm at a comfortable height when the end of the runway disappears under the nose. I don't see the need though, to be at 3,000 feet when I'm still over the concrete.
What must override the bean counters though, is that the whole flex temperature scenario must be prefixed with the thought that one accident will wipe out any cost savings for several years, therefore minimum aircraft performance must always be respected. And that is one of the reasons the four bar chappie gets the medium sized bucks (unless he gets the big ones with a national carrier).
To sum up then, use a flex derate system wherever prudent, while maintaining safety margins, and damn all bean counters.
What must override the bean counters though, is that the whole flex temperature scenario must be prefixed with the thought that one accident will wipe out any cost savings for several years, therefore minimum aircraft performance must always be respected. And that is one of the reasons the four bar chappie gets the medium sized bucks (unless he gets the big ones with a national carrier).
To sum up then, use a flex derate system wherever prudent, while maintaining safety margins, and damn all bean counters.
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"As a result of this, every 3-4 weeks it is a requirement of most companies I have worked with, that a full power T/O is carried out to ensure full power is available in the event of an emergency."
Is there not a CAA regulation which surrounds this too? I recall a Spotty M Captain telling me... every 28 days or something as a requirement to prove that the engines can still actually "do it" if required.
Anyone know if this is just company or actually regulatory?
Is there not a CAA regulation which surrounds this too? I recall a Spotty M Captain telling me... every 28 days or something as a requirement to prove that the engines can still actually "do it" if required.
Anyone know if this is just company or actually regulatory?
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Folks,
Flex/derate/redu take-offs produce significant savings in engine maintenance and are a practical commercial solution. Bean counters and ops managers should be as one, both on the benefits and on the circumstances that those at the potential accident site may choose to trade the financial benefits for the safety benefits.
Alas, in my experience the OEM part power predictions do not always give me the confidence that I need that the marginal engine will produce the goods when I want it. My very true friends, the engine specialists, are as equally dedicated as am I to a favourable outcome. The very good ones understand that they will always be spectators to a failure of the engine manufacturer's performance guarantees and therefore accept that my need for rated thrust comfort on a sensible timeframe has people management benefits that far exceed the small cost attributable to a weekly full power check.
Yes, I also used to love the total conversion of kerosene to heat and noise without regard to cost. I am older now and appreciate that the joys of my youth may well have exceeded what the community could afford to pay in the long term for my youthful exuberance. There is always a two way street and there is always a need for balance.
Stay alive,
Flex/derate/redu take-offs produce significant savings in engine maintenance and are a practical commercial solution. Bean counters and ops managers should be as one, both on the benefits and on the circumstances that those at the potential accident site may choose to trade the financial benefits for the safety benefits.
Alas, in my experience the OEM part power predictions do not always give me the confidence that I need that the marginal engine will produce the goods when I want it. My very true friends, the engine specialists, are as equally dedicated as am I to a favourable outcome. The very good ones understand that they will always be spectators to a failure of the engine manufacturer's performance guarantees and therefore accept that my need for rated thrust comfort on a sensible timeframe has people management benefits that far exceed the small cost attributable to a weekly full power check.
Yes, I also used to love the total conversion of kerosene to heat and noise without regard to cost. I am older now and appreciate that the joys of my youth may well have exceeded what the community could afford to pay in the long term for my youthful exuberance. There is always a two way street and there is always a need for balance.
Stay alive,
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Dull Certification Stuff
FAA Advisory Circular (AC) 25-13 (dated 1988) is frequently used as a means (not a "rule) to certificate aircraft for reduced thrust takeoff. You'll probably find it on a dusty e-shelf at their website (www.faa.gov, or something). There is a JAA equivalent, which is very similar.
Section 5:
....you can use flex if......
Paragraph 5e:
"A periodic takeoff demonstration is conducted using the airplane's (full) takeoff thrust setting and the event is logged in the airplane's permanent records. An approved engine maintenance procedure or an approved engine condition monitoring program may be used to extend the time interval between (full) takeoff demonstrations."
So, there you have it. It is likely that the use of flex on any given type is certified on the basis that a full thrust takeoff is done every now and then. However, somebody may have proven that the means to extend the period are so robust and trustworthy that it's been stretched to infinity (and beyond?).
Section 5:
....you can use flex if......
Paragraph 5e:
"A periodic takeoff demonstration is conducted using the airplane's (full) takeoff thrust setting and the event is logged in the airplane's permanent records. An approved engine maintenance procedure or an approved engine condition monitoring program may be used to extend the time interval between (full) takeoff demonstrations."
So, there you have it. It is likely that the use of flex on any given type is certified on the basis that a full thrust takeoff is done every now and then. However, somebody may have proven that the means to extend the period are so robust and trustworthy that it's been stretched to infinity (and beyond?).
