Are Flex / De Rated take offs safe?

[ssg]

Curious if airline pilots are happy always burning up as much runway as possible to save on supposed engine wear?

[F4F]

Safe? Yes, they are. Have done 'em / seen 'em done for years, and until proven the other way, no problem.
Supposed engine wear? Well, heard that on the 320 Bus series the savings are in the order of $150 per degree of flex... good and easy way of saving dough :ok:
SOP? Yes, in most airlines flexing is part of the SOPs. TOGA might of course be used in windshear and eventually LOVIS ops.
Happy about it? Any decrease in safety due to flexing as opposed to using full thrust for TO should be small. Continuing this line of thinking one could argue about fuel planning, auto brake used on lo instead of hi, etc etc

Well, increasing safety to a max one could finally stay on the ground ;)

live 2 fly 2 live

[BOAC]

F4F - troll feeding not permitted here.

[PENKO]

Do you ever take off at MTOW? :ok:
Same idea, however a flex TO is inherently safer!
Now, if you accept MTOW take offs, if you accept departing at shorter rwy's, if you accept tail wind take offs, if you accept to take off when the temperature is higher than standard, if you accept derated engines, if you accept intersection take offs...then why would flex be a problem?

Good question though.
:)

[mutt]

As an airline, we have done approximately 1,800,000 takeoffs during the last 15 years using reduced thrust, to date we havent had 1 incident where the result would have been different if that takeoff was at Maximum Installed Power.

So to answer your question, the answer is YES.....

Mutt

[toolowtoofast]

120 million?

21,917 a day?

man, you guys are busy!

[Old Fella]

Sorry toolowtoofast, 1,800,000 de-rated takeoffs in 15 years is what Mutt posted. That is about 330 per day, not unreasonable for a large airline. Don't know for whom Mutt works, but if it is a major carrier he is quite likely 'spot on'.

[The Real Slim Shady]

When Flex / Derate / assumed meets all the runway and obstacle clearance requirements it has a further, mostly, hidden benefit: if an engine fails the thrust on the live is lower hence more rudder deflection is available to stabilise the flightpath.

Edited to change the word "control" to deflection"

[Mad (Flt) Scientist]

Is it "safe" - yes. Even if Mutt's single incident were in fact a Hull Loss, a rate of 1 per 2 million FH is about half the overall acceptable accident rate, and therefore would likely not be of major concern. But it also clearly is not "as safe", since that one incident did, in fact, occur.

Like all the "lines in the sand" which form part of the underlying assumptions behind the regulations to which aircraft are built and then operated, as we get smarter about operating nearer to the lines on a routine basis there must be concern over degraded average margin of safety. That's one reason for there being an element of "regulatory creep", to stay ahead of (or not too far behind ...) the "design creep" that occurs.

[SNS3Guppy]

From my perspective as a pilot, we've used reduced thrust where able in most types of aircraft I've flown, certainly most all turbine equipment, including agricultural, corporate/charter airplanes, and airline equipment. It's been a practice in most types of operations I've flown, from firefighting to ambulance to crop dusting/ag, to cargo, charter, corporate, government, and yes, airline. Where it's safe to do, allows ample takeoff and stopping margin, allows adequate obstacle clearance etc, it's perfectly acceptable.

A reduced thrust takeoff means that one always has the option of pushing up the power as required, though all the performance calculations take into account climb gradients, going, stopping, and obstacle clearance without having to do so. This includes an engine failure; when we calculate reduced thrust takeoff performance, the performance data assumes losing an engine and continuing the takeoff...still at reduced power, still able to make the required gradients. Stopping is a no-brainer; the power will be retarded, ground spoilers deployed, and the aircraft stopped on RTO brakes where installed, or manual braking. Not rocket science, and it's all factored in...without reverse I might add. Reverse only shortens that distance.

Our operations manual spells out exactly when a reduced thrust takeoff can be used, and when it can't. Every reduced thrust takeoff is planned with the specific runway and runway conditions in mind, including any appliable NOTAMS such as temporary obstacles or reductions in length. Every takeoff is planned with an engine failure in mind, as is the departure path after takeoff. Nothing is left to chance.

We utilize reduced thrust takeoffs, and reduced power climbs as part of the nearly universal standard noise abatement departure procedures. We also have reduced climb thrust above 10,000'.

From a mechanic's perspective, reduced engine temperatures make for substantial increases in engine and component life. I've been an aircraft mechanic and inspector as long as I've been a pilot, going back to my early teenage years. I've been working on large radial engines, small pistons, turboprops, turbojets and turbofans for several decades now. I've had these engines apart, boroscoped them, handled every internal part as a regular function of inspection and repair. The differences in operating techniques or procedures show up in burned blades, cracked cans, metal creep, etc. A ten percent reduction in power equates roughly to a ten percent increase in engine life. If this can be done safely, all the more power to the operator...increased engine life also equates to improved engine safety, longevity of components, increased mean time between failures for stressed and hard use items such as turbine wheels and blades, etc.

A common method of operating reduced thrust is to use an assumed temperature. This isn't a wild idea made up by flight crews, but comes directly from the engine and airframe manufacturers after ample testing and design. One assumes a takeoff at a much higher density altitude based on a plethora of criteria and data, and determines if the aircraft could be safely flown off the current runway under those conditions. If it could still do so, still meeting all go and stop criteria applicable to each segment of the takeoff, then it can also be taken off at a reduced power which replicates a takeoff at the higher assumed temperature. The performance data is recalculated using the reduced power to ensure it matches, and when all data adds up, the reduced power is established for the takeoff. Nothing precludes pushing up the power at any point in the takeoff where required, nor performing a full power takeoff if required. However, it isn't required, and where a reduced power takeoff is performed based on an assumed temperature calculation, an engine may be lost and the takeoff continued at that reduced power, and still meet all the takeoff criteria.

[mutt]

Old Fella, .... toolowtoofast correctly pointed out that i had miscalculated...i therefore edited my original post.

Even if Mutt's single incident were in fact a Hull Loss, It wasnt a hull loss....plus that was 1.8 million takeoffs, not hours.

Mutt

[ssg]

Most won't disagree that trying to baby the engines to overhaul might help save some engines...I just wont do it on take off...

Increasing ground roll, decreasing stop distances, decreasing reaction times to a crisis in furthurance of saving a buck on overhaul 5 years later seems counter intuitive...especialy with 200 people in the back....

I wonder how many lives could have been saved had ther pilots hit V1 5000 feet earlier, and had more time to accelerate, they were faster when they tried to horse it off, or more runway to stop on.

But hey, a thousand flights a day using flex can't be wrong..and someone thinks it must save some money...but not all airlines use it, they chose safety first, probably more from a liability standpoint rather then a love of safety...

I hear Flex is used primarily to keep the 3000 pilots flying the fleet from overtemping, over torquing, ect the engines..really about keeping pilots from breaking the engines and less about trying to save on overhaul costs...

Operators could have thier pilots fly around at 5% less on cruise to probably get the same intangible results on overhaul costs...

None the less...

When you have one pilot flying the plane, vs 1000, it's probably a good idea to put in place some margin on operating limitations...always a throttle jockey in there that will add 5% over max rated on take off by accident, then it might be a tear down inspection...flex could eliminate type of error...now if guys are using FADEC ect...this is moot...

Even so..John T brought up a good point where the argument at Quantas was how far should flex go..the crews bitching for some kind of margin...rather then being forced to make every take off a 'fly it to the fence' type of thing...

Anyone in here that flies planes that other people fly will probably hope that the last ten guys were easy on the plane..In corporate, typicaly, your the only one that flies the plane...so that type of error is very much reduced...

I know corporate pilots that have threatened to quit because the idea of a partnership and having a bunch of newbies fly the creampuff without them not being there, was to them unsafe...to many variables..not to mention increased operating costs, like brakes, ect from having a bunch of pilots run though the plane vs one..

Well, I hope the next time I fly on airlines, I can push a button on my seat that says says 'vote yes or no for flex take off today"

[Port Strobe]

Isn't the idea of the assumed temp method that it reduces wear on the engine such that x number of years down the line someone doesn't set rated thrust then have it go bang at an inopportune moment hence providing a safety margin in itself although it appears somewhat immeasurable. As has been mentioned one always has the discretion of setting full thrust at any stage without any penalty. What are ssg's thoughts on taking off at RTOM which is field length limited given the assumptions that go into how heavy the aircraft is declared to be? This would have the same effect on an assumed temperature take off if I understand it correctly but at least you could be happy in the knowledge you have full thrust set.

[FE Hoppy]

assumed temp reduced thrust take offs are safer than taking off at perf limited max weight as assumed temp calculations assume a lower 1/2 rho.

Is it unsafe to take off at max weight?


The statistics for long term engine wear and the chance of engine failure are conclusive. Anyone with any doubt should talk to RR or GE. They will be happy to send you some data.

So yes Flex/De Rated take offs are not only safe but statistically safer than full thrust take offs.

[ssg]

If Flex made sense to save money, trust me every cheap skate millionare with a jet would make his pilot do this as well.

Not one thing from Garret, RR, or Pratt has come through that has told us that it would save money in real terms...

[Old Smokey]

It seems, ssg, that no amount of argument can sway you from the conviction that the only significant reason for using Flex / Reduced thrust is cost savings.

The truth is that significant cost savings do occur, but, (and it's a big but), even if no cost savings arose, I would (and do) strongly advocate it's continued use for safety reasons.

The probability of engine failure is directly proportional to the stress placed on the engine, and the widespread use of Flex / Reduced thrust very significantly reduces engine stress, and thus very significantly reduces the probability of engine failure. One of the predicaments faced by the statisticians in assessing the reduction in the number of engine failures is that as the said engines did not fail, no absolute figure can be placed on the engine failures prevented by the use of Flex / Reduced thrust. The one good comparison that CAN be made is with operators who previously used full thrust for all takeoffs, and then changed policy to using reduced thrust. The failure rate decreased dramatically.

So, even if no cost savings arose, or even if it was slightly more expensive, the increase in safety due to decreased engine failure rate makes such policy worthwhile.

Regards,

Old Smokey

[Ashling]

Its common sense to look after your jet.

Sure you can take off at rated power all the time if you want you can also deploy the flaps at limiting speeds all the time. Same end result, they will fail more often perhaps with catastrophic results. So you have to figure whether any added safety margin due to reduced time on the ground outweighs the negative of an increased number of failures. The judgement of clever people who look into all this is that reduced thrust take offs are safer and cheaper than the rated alternate. You can disagree if you like SSG but I first suggest you write to the engine and aircraft manufacturers and ask the same question.

Remember too you can often have a spread of V1s depending on whether your operator is go or stop minded.

Also operators specify when you must use rated thrust eg contamination, strong winds, unserviceabilities etc to cater for situations when the risk benefit balance shifts the other way. Limits are also placed on the maximum reduction allowed. I think its 25% but I could be wrong on that number.

The calculations are normaly very conservative. We don't normaly take any benefit from a headwind or QNH (although we could) and allow for 1.5 times a tailwind and correct for a low QNH. If your taking these comfort factors out its because your payload critical and will be rated power in any case.

As others have said if you lose an engine you can increase power if you wish to give more margin but SSG you must understand this is not required to continue safely. You can stick with the reduced thrust if you so wish.

The Airforce do it too by the way.

SSG Reaction times are not reduced. You stop up to V1, at or after it you keep going. Same decision same reaction time wherever on the runway you happen to be. Less runway left certainly however I very much doubt if it makes anything like 5000' of difference as you have a limit to how much you can reduce by and in reality the derates are often not that large.

Horse it off the runway? You need to get this cowboy mentality out of your head SSG. I've had many engine failures in the sim at V1 and have never horsed the aircraft anywhere. Always a smooth rotation and the aircraft has done as it should so maybe the people who build the sims are in on the bill of goods as well.

The vast majority of airliners now have FADEC or EECs of some type that will look after the engines so overboosting is not an issue now for the vast majority.

Out of interest, as I have no experience of Business Jets, do they operate to Perf A? Some of them? All of them?

[ssg]

All the airline pilots in here that have removed, replaced, bid. boroscoped, bought, sold, leased, argued for parts, and decided which components to install on thier new jet engines...please raise your hands..

I didn't think so.

All the airline pilots in here that have flown one plane to overhaul then actualy seen how thier actual flying habits have affected those particular engines..please raise thier hands

I didn't think so.

--------------
Engines are certified and built based max thrust take offs, max cruise speeds ...to make it to designated overhaul times...say 3500-5000 hours.

I won't argue that taking better care of an engine, or running them right doesn't help...they do..that's why my overhauls and hots are really cheap...but if you trying to tell me that the trade off between flying it to the fence in a Flex take off is the exta safety of un worked, more reliable engine...that's really a stretch..

And it still won't make a diff when that flock of birds, bad fuel, puddle of water goes into your ultra reliable, unworked, babied engine, at the end of the runway....

[Denti]

In the airlines we do not necessarily have fixed overhaul times but rather overhaul on condition of parts. As i said before we had engines that could remain over 40.000 hours on the wing, flying shorthaul operation with a take off every 70 minutes, because they were looked after in daily operations. And that means largely flying them less stressed by using flexed/assumed temperature/derated thrust methods.

We have to do the calculation (and guess what, pilots do technical jobs as well, many of them started as certified mechanics) and the costs saved as well as the amount of maintenance required because of wear is several magnitudes lower than on engines that have to do a full rated thrust take off every single time.

[barit1]

There's the added factor of operating your aircraft at a more nearly constant thrust-to-weight ratio. What does that mean?

It's pucker factor. If you typically operate from long runways, at moderate TOGW, at moderate density altitudes, and use rated thrust all the time, you get spoiled.

But then comes that long leg out of MEX. The book says you are fine, but the plane seems so doggy and you've never used so damn much r/w before and HOLY **** WILL WE EVER MAKE VR????!!!

OTOH If you're used to flex takeoffs, that MEX takeoff (while within AFM limitations) won't seem so terrifying.

[stilton]

The benefits of flex/assumed temp/ reduced power take offs are undisputed.

I doubt there is an Airline in the world that is not doing them as routine.

As already well stated, not only are there benefits in less long term wear and tear, but it vastly reduces the stresses on any particular take off, directly reducing your chances of engine failure.

More is always there if you need it, in the sim, however with an engine failure at or after v1, normally we do not push the power up on the remaining engine (s) unless we absolutely need it.All performance is calculated on that reduced power.

Like to be very careful with what we have left !

[mutt]

Not one thing from Garret, RR, or Pratt has come through that has told us that it would save money in real terms. You obviously dont talk to engine manufacturers very much.

For the B787 engine guarantees, the manufacturer wants us to operate it with an average of 28% reduced thrust to comply with "THEIR" requirements! For the RB211, a 1% EPR reduction results in a 12% increase in blade life, plus in our case brought the engines up to the guarantee levels.

I just wont do it on take off. Then i suggest that you dont fly for an airline, we have constant ACARS monitoring of the engine conditions, any pilot who constantly refuses to use reduced would get to have "tea and biscuits".

Even our corporate fleet that includes 747-400's use reduced :)

You seem to have a concept that reduced will always put you right over the fence, this is totally wrong, look at any B777 taking off for a relatively short sector, ie, 6 hours. Look how much runway he used, and i will almost guarantee that he was using reduced!


Mutt

[ssg]

Ok Mutt..what is the overhaul hour and cycle limitation on these engines...what do fan blades cost on this engine...what was your last estimate for a overhaul when you put it out to bid...how long are your engines going before Hots...

----------

I don't have a problem with flex...empty plane, long runway, repostion flights, ...big deal.

With 200 people in the back, crappy weather, obsticles ahead, ice in the forcast...and some operators use flex to the nth, as far as they can take it..

You agree with that?

[nomorecatering]

Still getting my head around the flex concept, particularly the bit where u do one set of calculations, then recalculate for the (higher?) temp.

Do bizjets such as CJ3 have a flex power schedule?

On such aircraft that will do maybe 200hrs per year, and is often sold before a hot section or engine overhaul time is reach, is there a benefit? I can understand the benefits of an airline aircraft doing 10 sectors a day year on year.

I am lead to belive that flex power take-offs use a little more fuel because due to the lower initial climb thrust the time to cruise alt is longer and more time is spent on in the lower high fuel consumption altitudes during the climb.

Do I also read it right that for max range achievable on the aircraft, full power and max climb power then long range cruise? Would be interested in seeing some comparisons.

Assuming a new CJ3 is delivered, and flown by the same crew. How does one look after turbine engines. What abuses them. In short, how would you get your engines to a hot section/overhaul in the best condition.

[barit1]

There's a great read on the subject here (http://www.b737.org.uk/assumedtemp.htm). It's written around the 737, but the principles apply to other ships.

Actually, since I'm a graphical kind of guy, I like a graphical presentation but I have not yet found one online. It should include a chart of typical airfield-limited performance weights vs OAT, and a chart of N1 (or EPR) vs OAT. Using these it's fairly easy to understand how ATM or flex is computed.

And don't forget, even though you're running the engine at a thrust level equivalent to a 40C day, the wing is flying in (e.g.) 20C air. Thus your V1, Vr etc. TAS is quite a bit lower. All this means extra margin. :)

[Ashling]

SSG

Would you, or someone else who flies biz jets, tell me what performance rules you chaps use please.

[SNS3Guppy]

Would you, or someone else who flies biz jets, tell me what performance rules you chaps use please.


I'll answer that. Light transport category airplanes use the same performance rules that large transport category aircraft use. The training standard is the same, too. Most have reduced thrust takeoff calculation data available. The same SOP's apply in business class turbojet aircraft that apply when flying a B373 or 747. The posters arguing to the contrary are doing so based on their own ideas, and certainly not what's been taught them at well recognized and industry approved training centers.

Still getting my head around the flex concept, particularly the bit where u do one set of calculations, then recalculate for the (higher?) temp.


There exist several programs for operating on reduced thrust. Assumed temperature is just one of them. It's used in business class turbojets as much as large Boeing products. As you know, an aircraft will experienced reduced takeoff performance with an increase in density altitude. With an increase in temperature, we experience an increase in density altitude. We experience an increase in takeoff distance. If we then compare that distance to our present field and find that we can meet all the safety requirements to take off (including stopping and going, appropriate climb gradients, obstacle clearance, etc), then we can operate with a thrust setting that equals that same performance.

As an example, using example numbers which are for illustration only, we have a 10,000' runway. We calculate a full thrust takeoff and find we can takeoff in 5,500'. We then run an assumed temperature thrust reduction analysis, and determine that at 40 degrees C, we would use 7,000' of runway. Our peformance calcualtions show that we can reduce power enough to use that 7,000' of runway and still climb out, or stop from V1, safely using the reduced thrust. The assumed temperature is a reference number only, and at no time are we prevented from pushing up the power to maximum thrust if required. However, the performance data assumes the reduced performance, and shows that we are able to lose an engine at that lower thrust and continue the takeoff with the reduced thrust to give all the necessary performance (climb gradients, etc).

Normally reductions based on assumed temperature are done up to 25% of maximum thrust (meaning 75% thrust avail). Other systems are available to calculate reduced thrust. We use a computer based program that takes everything into account including specific conditions, NOTAM'd runway conditions, etc. We don't use more than a 25% reduction. A whole litany of conditions exist and are clearly spelled out in our Aircraft Operations Manual detailing when we can and can't use reduced thrust. We have the option at any time at pilot discretion of using full thrust, and we're required to do so at least every seven days for no other reason than that's one of our requirements; a full thrust takeoff logged every seven days.

Assumed temp is just one method of determining a reduced thrust setting. Rather than an arbitrary number, it's a reference that compares takeoff performance under a known given set of conditions (increased density altitude), in order to start with meaningful data to compare to the runway and departure conditions in use. If the performance experienced at the assumed higher temperature could still work right here, right now in these conditions, then we can reduce thrust to replicate the same distances and performance we'd experience at that higher temp. In so doing, we reduce engine operating temperatures, save wear, tear, money, fuel, and still meet every margin of acceptable safety.

[Ashling]

Thanks Guppy

[NoNameRecord]

Here's a powerpoint presentation on the subject:

http://www.captainpilot.com/performance/Assumed%20or%20derate.ppt


From Boeing:

http://www.captainpilot.com/performance/04_Takeoff.pdf


http://www.smartcockpit.com/pdf/plane/boeing/B737/instructor/0024/

Cheers

[barit1]

ssg -

Methinks you don't comprehend where V1 comes along the length of the runway. If you're doing the numbers right, you'll always have sufficient stop distance after V1, regardless of where Vr abides.

In any case, you'll always be safer when the assumed temp is 40C, than when the actual temp is 40C.

So far you haven't shown us any sign that you understand these basics. :confused:

[Denti]

Guppy, you might be right in principle, however the regulations governing GA and airlines are different, at least if mentioned GA aviation is not working under an AOC and of course everything just applicable in europe (JAR), dunno enough about the rules in other parts to comment about that.

We had the problem with a small business jet we operated some years ago (yes, we are an airline, but still can operate small stuff), it couldn't operate under JAR OPS rules into a certain airport, but it could quite happily outside of JAR OPS. To be able to fly into the home airport of the ownder of that jet we had to get a special permission that we could fly without having to factor the landing distance according to JAR OPS, as a result it was only allowed to fly there for private flights of the owner but not for normal charter operation.

[airfoilmod]

OK You may have commitment issues. I think you don't (won't) understand V1. You still want a choice after V1, which is commitment time. If you won't adhere to Runway calcs., (your own, if you actually take the time to consider them), then don't. I think you have trouble with authority (even if it's your own!). V1 is, after all, a command. You don't get that V1 is a commitment to fly, not a notice of enhanced awareness.

"Fly The Force, Luke". No. No. No.

[thegreek]

Barit, the link that you posted about FLEX Temp clears up a lot of questions, great !!

But surprised me with this:

"It Increases fuel burn.
Strange, but true. This is because:

Assuming an uninterrupted climb, it will take longer to reach the more economical cruise altitude than a full thrust climb.
Engines are less efficient when not at full thrust. "

[SNS3Guppy]

Guppy, you might be right in principle, however the regulations governing GA and airlines are different, at least if mentioned GA aviation is not working under an AOC and of course everything just applicable in europe (JAR), dunno enough about the rules in other parts to comment about that.


This is because you're considering the wrong regulations. Operational regulations are irrelevant. What you need to consider are certification regulations. A two engine transport category airplane, be it a Lear 60 or a B737, must still meet the same performance standards and design criteria with respect to minimum gauranteed performance, and they're still flown the same...especially with respect to takeoff and landing. Transport category aircraft are transport category aircraft, big or small.

Now there are certain things you can do, and get away with in small, light transpor category aircraft that you can't in big airplanes; I've taken off in a Lear 25 and turned downwind at 18,000'. Not something you'll do in a heavily loaded B747. However, each must still meet the same minimum performance criteria. And the training for each is very similiar. Moreover, approved training programs for either one don't teach to stop after V1, and do provide for reduced thrust operations.

But surprised me with this:

"It Increases fuel burn.
Strange, but true. This is because:

1. Assuming an uninterrupted climb, it will take longer to reach the more economical cruise altitude than a full thrust climb.
2. Engines are less efficient when not at full thrust. "



During a reduced thrust takeoff, very often when climb thrust is set after takeoff, it may be to increase thrust, rather than reduce it. During a standard noise abatement departure, climb trust is a thrust reduction. However, during a reduced thrust takeoff, setting climb thrust may mean increasing it to the climb thrust setting.

Turbine engines are most efficient at a high power setting. You can imagine the loss of efficiency at lower power settings somewhat like driving a car up a hill in the wrong gear; inefficient. Part of the reason that a jet engine is most efficient at high altitude is that the powerplant is required to run at a more efficient RPM. At lower altitudes, excepting climb, the power is pulled back into a less efficient power range.

The problem as you can guess is that at low altitudes, airspeed limitations prevent pushing the power up too far. At altitude, the power can be pushed up into an efficient range without exceeding airspeed limitations. At altitude in most turbojet airplanes, you run out of available power before you exceed airspeed limitations...meaning you can cruise in an efficient range. At low altitudes, reducing power even further decreases efficiency...which is part of the reason (performance being the other) that power is often increased after a reduced power takeoff.

Our typical profile includes a departure at reduced thrust, with climb thrust set at 1,000' above the departure elevation. At 10,000' we'll reset the climb thrust, often to a reduced climb by a given percentage; we use .04 EPR if our weight is more than 600,000 lbs, and .06 epr if weight is below that value. This isn't a great reduction, but it's also another place we reduce power slightly below maximum climb values for engine longevity. Around 24,000' we find that we need to restore the climb power to the maximum value for performance reasons, and continue up to our cruise altitude at that power setting.

[Denti]

This is because you're considering the wrong regulations. Operational regulations are irrelevant. What you need to consider are certification regulations. A two engine transport category airplane, be it a Lear 60 or a B737, must still meet the same performance standards and design criteria with respect to minimum gauranteed performance, and they're still flown the same...especially with respect to takeoff and landing. Transport category aircraft are transport category aircraft, big or small.

Right, certification wise there is no difference if both are certified to the same regulation. However there are still different operational regulations and those govern performance calculations as well. In fact the safety margins imposed on airline operation are much higher than on non AOC operation, especially for performance calculations. And therefore they do matter if the question is to what regulation you operate an aircraft, which was exactly the question asked by Ashling.

Of course you are right, V1 is V1, and aborting after V1 is not teached in either case.

[thegreek]

Very clear sns... Thanks a lot.

[lomapaseo]

'If your sitting in the back of an airliner, and the pilot uses 4000ft to get off the runway, and has 6000 ft to stop if he aborts...vs buring up 7000 ft of runway and having only 3000 ft to stop...because they wanted to save buck....which one would you choose.

'Sounds like they are endangering peoples lives to save a buck'



I believe that many are in this business to make a buck and their customers don't expect "pedal to the metal"

On the other hand you could alswys attain a performance increase by off loading some of the passengers.

[Junkflyer]

Its also pretty clear you can't grasp the concepts behind flying large jets safely.

[mutt]

it's in every flight manual that I ever looked at...reduced power climbs use more fuel.and in every Airplane Flight Manual that i have ever looked at, they dont show ANY DATA for ALL ENGINES! Therefore I dont see where you are getting your information from!

is just a tactic by your boss's to keep you from over temping, torqueing, over limiting your engines Sorry but we have FADEC's! As i said to you before, go talk to your local RR/PW/GE rep and tell him that you are going to use their engines at full power, ask them how long will they guarantee the engine.

Mutt

[ssg]

I don't have to ask, my engines come off at 3500 hrs whether I like it or not...

Are you trend monitoring? Basicaly using them untill something is broke?

[barit1]

That's progress for you...:ugh:

[barit1]

"It Increases fuel burn.
Strange, but true. This is because:

1. Assuming an uninterrupted climb, it will take longer to reach the more economical cruise altitude than a full thrust climb.
2. Engines are less efficient when not at full thrust. "

To address each point:

1. On a snapshot basis, I have to agree. However, if you routinely employ reduced thrust, your engine fuel burn remains closer to a new spec, and thus the long-term effect is a trip (and fleet) fuel savings. (It's not only EGT we're preserving, but fuel burn as well) :ooh:

2. Not all engines are really "less efficient when not at full thrust". The best modern engines actually have an SFC "bucket" or J-curve i.e. most efficient at cruise. :ooh::ooh:

[SNS3Guppy]

"Full thrust" is a misleading term, as it may cause one to suppose it means whatever power a full thrust lever setting can deliver. Instead it is better read to mean the maximum power setting under a given set of conditions...which will nearly always be substantially less than the maximum temperatures, EPR's, EGT's, TiT's, ITT's, N1's or RPM's that the engine can actually deliver.

For most turbine engines, 90% N1 or RPM is closer to the max limit under a set of conditions, and closer to the most efficient operating range for that engine. That, of course, is very "ballpark," and not at all specific to a given type.

[ssg]

Increases TODR.
Therefore you may come to rest on the stopway after a stop from V1.

[barit1]

And yet you want to stop AFTER V1??? :eek:

[Sir Richard]

SSG

I guess it's "pedal to the metal" every time the lights go green at an intersection ?:ugh:..Your Ferrari wouldn't last too long :E

(And carefully used engines can stay on the wing for much longer than 3,500 hours, in excess of 14,000 springs to mind.....ask RR !):D

[barit1]

ssg, you have quite a gap in your education. Engine hours mean virtually nothing in the airline world, and haven't for three decades.

Airline engines are now removed either for cycle limits (rotating parts and pressure vessels) or for condition monitoring alerts. They may even be removed for excess fuel burn.

Any engine removed at 3500 hours would trigger a technical investigation by the airline and the OEM. It's not unusual for an engine to run 20,000 hours or more. :)

(When a KC-135R had a FOD during Desert Storm - 1991 - there was no USAF maintenance crew in-theatre that had any experience in engine change on the bird, and a contractor crew had to be flown in...)

[ssg]

Since airline engines don't follow TBO hourly limits (loaded question- hint hint)

Just how do they determine when to overhaul the engines...?

And since I know what cycles are...which pressure vessels on the engines are you talking about...

[Junkflyer]

Boresope inspections and trend monitoring are among methods used to plan for engine repair/replacement. A Pratt JT-9Q engine runs upwards of $2,000,000 for parts alone to refurbish the hot section.

[Pugilistic Animus]

SSG---you should really look up reduced thrust rules for yourself http://rgl.faa.gov/Regulatory_and_Guidance_Library%5CrgAdvisoryCircular.nsf/0/4B385BB9E4E9C4DA862569D00076ACF7?OpenDocument then argue with performance experts and the like ---

[ssg]

Nothing sucks worse then barely having enough runway, barely getting second segment, barely having the numbers...and flex forces pilots to simply reduce power to fit thier runway and climb gradient...how fun...

If Flex just gets you balanced field and second segment numbers, then the pilots better have it together for every emergency...time has proven they don't...extra runway saves lives...shorter fields adds risk...

You can't dispute, reduced thrust burns up more runway, less time to stop if need be.. The sooner you get off the ground, and up in the air, the further you are away from impacting terra firma...the more runway you have infront of you during an abort, pre, during, or post V1, the better the chance of keeping people alive..

Just because flex turns every takeoff into an excuse to burn up more runway to save corporate some money on the overhauls doesn't mean it's safer. If the argument is to keep your 10000 hour trend monitored engine up in the air another 10000 hours..then take a walk in my shoes...our engines come off at 3500 hours whether we baby them or not. So we use them...

Now which is safer my engines with 2000 hours or yours with 10000 hours?
Even if the blades look nice every inspection, take it from a guy that had a number one bearing failure at 35000 ft...you can't boroscope for that...oil analyis means didly unless it's a slow, slow problem...that gets caught at the next 150 hour insp...

And if I sit in the back of your airline, burning up 8000 ft of runway, at 70% power,...it's little comfort to me when I see the plane rotate and then grass starts going by...

Besides if flex ever did get popular in corporate, which it's not...I just can't see some GV burning up 8000 ft of runway at 50% power, billionare in the back, white knuckles watching the plane lift off at the fence...

He will walk up to the capt and ask why the plane lifted off so slow.......'because I was trying to save you money' .....that's where Flex ends in corporate

You guys want to run the planes to the end of the runway to squeeze some more time out of your engines..fine...but the rest of us don't...and look at our safety record....not to bad huh?

We can afford to go max rated, we can afford to burn up less runway, we can afford to be as safe as possible..

If your going to make the case..that airliners don't fly to the fence using flex, then don't point the ire at me...start looking around this forum, guys that tell me it takes 7000 feet to get a loaded 737 off the ground...so what about a 747, or Airbus then? Considering the world isn't full of 12000 ft runways...we are left with an average of say....8-10k ft runways...so does flex help to push balanced field from 7000 ft in a 737 to 10k? ...now the pilot doesn't want to reject, fear of hitting the fence...so he goes...and flies this time his unflyable aircraft to the end...into the Potomic, into a Hotel, into a market in Goma...into....

[Diesel8]

Yes, using TOGA on every takeoff would increase the stopping margin.

If that is you only contention, then by all means, I hope you always use 12K plus foot runways, anything else would be unsafe, right?

As plenty have mentioned, large aircraft engines are normally trend monitored and that is what determines when overhaul is neccessary, not a number of cycles or hour limits.

Is Flex/derate unsafe, the numbers would say no. Plenty would say, as they have here, that the greatest stress is put on an engine when it operates at TOGA power.

You want to use TOGA on every takeoff, by all means, nothing can be said that will change your mind. The airlines will continue to use Flex/Derate and the large engine manufacturers will continue to recommend it!

[Pugilistic Animus]

Ssg, I've fixed the link---


NO--the parameter that's limiting at full thrust is not necessarily the one that limits on reduced thrust---one could be ASD limited the other Obstacle limited---the main justification was given by the likes of Mutt, Old Smokey---and the other who routinely use this procedure and have satisfactory operational experience using the procedure---now point out to me the EXACTLY the dangers of this method?

[ssg]

I read AC25-13...thank for taking the time to post this.

And your point...that Reduced thrust 'may' increase engine life and reliability?

Look I will throw you guys a bone..if I had a 40,000 hr engine, a million cycles on the bearings, a lake of burning lava at the end, and a ten hour trip over the Polar Ice cap to do for the next year, in this plane...no money for engines, airline was broke, we had to do the trip,..yeah I would baby those engines like you wouldn't believe..flex, reduced cruise, watch the temps like a Hawk, stay away from FOD and birds, no runups on the dirty ramps...you name it...anything to save those engines....

But is that a safe operation? If you guys can't afford to overhaul your engines at the same intervals as the rest of us...maybe it's not so safe...and it's forcing you to take chances...

If Flex is so integral to extending engine overhaul times based on boroscopes...maybe we should talk about just how far out you guys are taking these engines..and what you will do to keep from having to pay to fix you engines...and your planes...

Let me bore you with a story...in younger years, as a flight instructor in twins, one of our Cessna 310s had a gear problem, nose gear wouldn't come down...so the pilot landed the plane..didn't feather any engines, let the nose come down, trashed two props and two engines...as per the book.. Someone else got to pay the fix.

If it had been my plane, I would have shut down one engine, feathered a prop, bumped the starter to flatten the two blades...assured my landing on our 8000 ft field, then shut down my last good engine, bumped the blades around...nose hits..no blades or engine tear downs...costs me a little skin and paint....

Now which is safer...using power to the end, or being a cowboy to save a buck? If I worked for you guys, there is a little cowboy in me that likes pushing it sometimes,, but I might see passenger after passenger load up and rethink that...

Trust me, I get Flex..but I don't have to pay the bills, I can afford to be safe, my boss isn't cheap, he can afford the engines, and has...we don't need to take chances to save a buck...it's not worth it..

[Right Way Up]

SSG,
Do you ever accept intersection takeoffs?

[Old Fella]

It seems to me that ssg may in fact be a watchmaker, the way he keeps winding people up. Or maybe he is just a self indulgent reader who knows how to fix the world and who enjoys reading his own solutions. It is fairly obvious that one thing ssg cannot do, that is accept the view of others even if they have combined years of experience many times longer than ssg has been on the planet. Time for a change.

[acebaxter]

Besides if flex ever did get popular in corporate, which it's not...I just can't see some GV burning up 8000 ft of runway at 50% power, billionare in the back, white knuckles watching the plane lift off at the fence...


I don't think that's legal. Sure isn't on the aircraft I operate. 8% N1 reduction is the limit. In addition to that limit is my own. I always leave myself at least a 1000kg margin. My aircraft is not new and neither am I.

[Ashling]

SSG if your talking about 50% thrust reductions you clearly have not much of a clue about flex.

[ssg]

Right...in a jet, no, unless by myself...I tend to choose the longest runways when possible.

-------------

Ashling...Did I say Flex? Did I say Airbus ...Did I say reduced thrust, or Derated?

[Ashling]

You said Flex when you spoke of a 50% reduction.

[Denti]

You guys want to run the planes to the end of the runway to squeeze some more time out of your engines..fine...but the rest of us don't...and look at our safety record....not to bad huh?


Give us some numbers. I really want to see your safety record. And no, not that of your singular outfit but that of GA in general compared to airlines in general. Are you really sure you can beat airlines?

Taken from the NTSB database,

Accident rate for 100.000 flight hours (there is no data as to departures and miles for part 135 non scheduled service)

CFR 135 non scheduled (on demand air taxi as they call it)

2005 1.70
2006 1.42
2007 1.69

CFR 121 scheduled (airline service)

2005 0.176
2006 0.139
2007 0.128

You might want to enlighten yourself on http://www.ntsb.gov/aviation/Stats.htm.

Doesn't really look like your safety record is so outstanding compared to airlines after all, perhaps you should print out those figures and give them to your owner to read up while you do your TOGA takeoffs.

[Ashling]

You said Flex when you spoke of a 50% reduction. Flex being Airbus's equivalent of Boeings assumed temperature reduced thrust. The max reduction is 25% as far as I am aware.

A de rate is different to flex and some operators use it to get around VMCG problems. You can add flex to your derate in which case, granted, you may well get down to something like 60% of full rated thrust. However not all operators have derates available to them or if they do use them. I believe they're used to balance up engines (we could have a mix of 20K and 22k engines a while ago so you de rated the 22k down to 20K to match the other one), address a VMCG problem or restrict a very light powerfull aircraft to normalish performance in a busy ATC environment. I think thats correct but others will have much more experience of de rates than me

[ssg]

Corporate is the safest sector...look it up...

In the mean time...some bedtime reading for you ...

In early March, CNN obtained documents from the House committee investigation that alleged the discount airline kept dozens of aircraft in the air without mandatory inspections -- and in some cases, with defects the inspections were designed to detect.

Boutris and Peters said FAA managers knew the XXXXX planes were flying illegally and did nothing about it, according to the documents.

The airline also flew at least 47 planes beyond a mandatory inspection of the fuselage, or skin, of the planes for possible cracks, the inspectors said. When the inspections were carried out, six of the planes were found to have possibly dangerous cracks, they said.

------------------
Gosh just makes you wanna go out and fly on an airline doesn't it..I mean the total committment to safety, the stand up professionalism....wow...very impressive...

[Denti]

Corporate is the safest sector...look it up...


Nah, if you're so sure of that why don't you just give us the numbers? You surely have them at your fingertips.

Yes, the FAA really let things slip by and all that stuff happened. And surprisingly enough the statistics from the NTSB (which is independent from the FAA by the way) still shows CFR 135 operators producing more than 10 times the number of accidents than airlines do per 100k flight hours.

I really would love to see your figures proving me wrong, best if they come from a respected source like the NTSB of course.

[mutt]

Besides if flex ever did get popular in corporate, which it's not Incorrect....... we also operate a corporate fleet with both fixed and assumed temperature thrust reductions. You have this fixation that our aircraft will scrape over the fence, believe me, they dont!

Mutt

[OutOfRunWay]

Using TOGA for takeoff cannot possibly be the safest way.

Logically using the ultimate derate - down to 0% power is the most safe, as you can securely sit around on your stand without going through all this risky flying business. :8

Of course, your passengers might murder you..

OORW

[ssg]

Mutt, You have never seen airliners routinely use up all the runway to get off?

The US corporate fleet isn't allowed to run thier engines out to 20000 thousand hours based on the say so of a guy with a boroscope...engines come off at time and cycle limits...there is no incentive to reduce power for take off to extend engine life, because, the engines come off when they come off, evidentely, thousands of hours before the airliners do.

While reduced power is available in some of the larger corporate jet, it tends to be used, as I have,...when the runway is very long, the airplane is light, the assigned alt is very low, nice day...ect ect...and the numbers are such that balanced field for the reduced numbers usualy have another 5000 ft added to them...very safe..

While I can't speak for all corporate operators, any more then anyone here to can speak for all airline operators, I have never in 20 years of flying had anyone tell me they were reducing thrust so they could 'add reliability' to thier engines...I have never seen anyone burn up more runway using reduced thrust so 'thier flight will be safer'

[airfoilmod]

Sir- I'm honestly interested in your opinion, my friend flies the X for a local Company, loves the power and mystique.

Your last post was directed to Mutt, but if I may, could I ask you a couple questions?

I have seen airliners of all description "use all the Runway". I have seen a video of a Tupe using the overrun, launching a climb at 200fpm, scary.
If the discussion is about V1, my assumption is that when the crew calculate the numbers, the Runway Length is a definite player. I am not clear what consideration you are giving to the takeoff roll Post V1, doesn't that involve using addl Runway? Once V1 is attained, and I think this is important, what you are looking for is enough Runway left to Launch, not enough left to stop. All considerations relative to Takeoff have a "fresh" point, a time certain where they become irrelevant, as the Flight has transitioned from a Truck with Wings to an Aircraft with wheels. I may not be understanding all your posts, but I am left with the conclusion that you are demanding that the Runway left after V1 be of sufficient length to allow a stop. It is Not. It isn't supposed to be. Am I missing your point?

I should have posted this on the V1 thread, my apologies- Airfoil

[mutt]

but I am left with the conclusion that you are demanding that the Runway left after V1 be of sufficient length to allow a stop.Last time i counted, there were 5 versions of the FAR detailing accelerate stop requirements, YOUR aircraft may have been certified to a different standard to the one parked beside you, so in some cases, you are allowed to pass V1 and react, but in more modern aircraft, it is assumed that VEF occurs 1 second prior to V1 and that you have initiated your action by V1. The Boeing Takeoff Safety guide advocates that if you reach V1, its go time!

You have never seen airliners routinely use up all the runway to get off?Right from the cockpit, its amazing how rapidly a Classic747 eats up a Field Length Limited runway :)

I have never in 20 years of flying had anyone tell me they were reducing thrust so they could 'add reliability' to thier engines...I have never seen anyone burn up more runway using reduced thrust so 'thier flight will be safer'

You obviously havent spoken to the right people :) Here ended the discussion as we will never convince you until such time that you start flying an aircraft where the engine life isnt constant :)

Now considering that you consider us dangerous, i will give you the topic for your next thred...... Is a 15feet screen height safe on a wet runway?

It was fun.... thanks..

Mutt

[ssg]

If post V1, you have a problem, prior to rotation...you see 8000 feet left, a 1000 ft stopway, and Iowa corn fields beyond...In just about all GA planes including large corporate jets, the question of being able to stop is moot...yes you can...

The question to fly your burning wreck up into the clouds under these circumstances is also moot..you don't do it...

---
After days of arguing with posters on the mertis of post V1 aborts, it turns out I was right...please see SR71s Boeing link on the 'would you abort after V1thread' . I owe SR71 lunch and my sanity..

There is a concept of Min and Max V1s, which will lead to an excellent discussion I think..

Turns out my method of simply 'looking out and seeing if I have enough runway to stop' post V1, has been mathematicaly figured out my Boeing.

On a long runway, in our plane, we could say rotate at 3000 ft and 95 kts.... or you chose to stay on the ground, and continue to accelerate, there is a place, way down farther on the runway, at a certain speed at which you need to start slowing down, inorder to stop before the end of the runway.. this is a v speed like any other... That could be 10000ft and at a speed of 160kts...that could be a V1max...but not technicaly as it's after VR, but for the purposes of stopping, this is the last place on the runway, at a certain speed to do it...

So I will crown a new v speed..the last chance to stop the aircraft after Vr...: Vssg.

:)

In a small plane, they can rotate, take off, land, do it a couple of times before running out of runway..in a small jet, maybe twice...and how do they do this...'hey george...got enough runway infront of us...looks good to me' an they do it...

So here is the Flex or reduced thrust problem....

So now we are sitting here with all this runway infront of us...tons of room to stop...balanced field is 5000ft on a 12000 ft runway..lots of margin for a post V1 stop, lost of safety.....and someone says..

'Let's try to baby the engines today...use reduced power on take off...with the new settings balanced field is now 10000 feet. Let's go.'

So the plane burns up 7000ft, V1...go...just prior Vr, which would be around 10000 ft....both Thrust reversers pop out..11000 ft, pilot realizes he can't fly with both TRs out, pulls the levers 12000ft...he barrels into the corn field..houses, hotel. ect...

He did everything right on that flight, he had the numbers, he was trying to save money, ..everyone is dead...

Had he chosen not to use Flex, or reduced thrust, and hit VR with a TR problem at 5000 ft, he would have made it...7000 ft to slow the plane down...

If on a thousand flights in a year this operator had chosen not to burn up every available ft of runway, every time he took off, to save a buck on engine maintanance, and use up all his margin of safety...how much safer would that be?

[Right Way Up]

Why is the argument ended SSG? Just because there is a range of V1s, there is still only one V1 used during a takeoff. If in your opinion the aircraft is unflyable V1 is irrelevant anyway.

[FE Hoppy]

ssg

V1min, Vmax and V1 balanced are not news to most of us! They were to you half way through your discourse.


Now tell me, on any given day do you know which was used in your calculation?

Those of us who use (or produce) runway analysis on a daily basis can find it in the header on most types.

However, we do not see the the options not used in the calculation. The choice is made by company ops and perf departments based on statistical data and analysis of each runway.

If your company would prefer to bias engine failures to be above V1 and so take them airborne they will use V1min. If their are obstacles that limit your take off perf you may wish to use a high V1 thus giving better climb perf but biasing towards more stops.

Statistics show stopping in big jets is less safe so many if not most large companies prefer low V1s.

However if V1min is used the crew are not presented with V1 max or balanced or any other choices.

The reason for not presenting a range of speeds is that at the moment of failure during a take off the crew need to act, not think about whether or not to act. The thinking time is included in the V1 calculation. It is the time between Vef and the first action to stop at V1. This time can vary depending on the certification standards used and systems fitted.

Now your moving goalposts in the previous thread stated with a very simple question. In the case of an engine fire would you stop after V1. The correct answer to that question in NO.

To the question would you ever try to stop after V1 the answer is yes. But the reasons would need to be compelling.

Most runway analysis indicate what is the limiting factor for the take off and as long as it isn't field length OEI or VMBE there is some chance of stopping but that chance diminishes with every nano second you think about doing it.

When we think about using less than rated thrust it is because we accept that there is a maximum take off weight we are certified to use with rated thrust and our current weight is less than that.

If we are prepared to take off at max take off weight there is no argument against taking off with the lowest thrust allowed when we are below max take off weight.

In fact the latter is safer than the former for many reasons.

And it saves a lot of money, which makes our companies profit, which they pass on to us in pay scales, which we use to buy books about aeroplane performance!!!!!!!


end of.

[Pugilistic Animus]

Ssg there are also some aerodynamic safety benefits to using reduced thrust---what are they?----why?

[Pugilistic Animus]

Noise reduction is an aerodynamic benefit:confused:

btw: VMCG doesn't necessarily become lower depends on what's written in the TCDS--no? as Chris Scott once 'schooled' me on the airbus and on that type as well as a Vmcg is fixed therefore it would be a benefit---on a new [with the appropriate data] Boeing No ---it can change with a DERATE!!!
unless you know everything about a type never second guess performance:eek:

and 150 knots is not the time to be in the charts:}


me haces muy cansado---ay

[ssg]

And the 'unoffical' benefit is?

[Pugilistic Animus]

When you pick your limiting temp---did you just trick the atmosphere too? the airfoils? is reverse thrust also lowered to the assumed temp [unofficial]? had the PA/DA actually changed?


now you can tell me the benefit you are a CFI-no?


PA

[Denti]

Increasing ground roll, decreasing stop distances, decreasing reaction times to a crisis in furthurance of saving a buck on overhaul 5 years later seems counter intuitive...especialy with 200 people in the back....

The thing is, for us it is indeed years later. For your airplane operated to the same standards and usage as an airliner it would be twice a year since we actually use our airplanes to do what they were build for, flying. We have to use our aircrafts (and their engines) up to way over 6000 hours a year, with an overhaul interval of 3500 hours that you apparently need because your engines run out of limit that fast (i wonder why) we would have to keep around one extra pair of engines in the shop per every two airplanes just to keep them flying, and that would need around 7 to 20 million bucks (depending on type) of additional investment just for a pair of them.

[ssg]

PA: So what your saying is that the aerodynamic benefit to flex is picking your own limiting temp? Next!
------------------------
Denti, if you and I bought our first old trashed 737 and tried to make a go of a single jet airline, our own money on the line..do or die..sure save a buck anywhere we can but be legal about it...no problem...now flash forward, billions of dollars later, hundreds of new planes on the line, we have something to lose, ..why push the safety envelope at that point....greed?
I am curious what is the WE have to pay for engines, unless you own the airline, your an employee, and management is not on yourside. You know besides mismanagement, a plane crash is pretty much the only single event that can literaly take down an airline and a company..why risk it...

Besides cutting corners on maintanance, I can't see a more dangerous policy at an airline then to tell all the crews to burn up more runway, to cut it closer to the fence...that just asks for trouble.

[Pugilistic Animus]

NO!--that's how you do the procedure:cool:

[Pugilistic Animus]

better actual acceleration lift changes with acceleration=more lift with given unit time/distance-- the wings are working at a lower pressure altitude because the temp is only 'assumed' for the engines, but the engineers don't take that benefit in account and it gives a margin---

And better stopping [before V1]with reverse becasue you get full rated RT [that's why it unofficial because in part 25 dry RT doesn't exist,]also spoilers and retardation devices are better in the denser air



SNS3Guppy do you see why I said "you gotta wash'em out in ground school"?;)

[ssg]

lbetter actual acceleration lift changes with acceleration=more lift with given unit time/distance-- the wings are working at a lower pressure altitude because the temp is only 'assumed' for the engines, but the engineers don't take that benefit in account and it gives a margin---

-- The engineers don't take it into account because it doesn't exist as a benefit.....so using your logic...the slower we go (flex acceleration)the more lift with a given time/distance? lol..even so...ok I will bite....you said 'benefit'..how does this BENEFIT...flex doesn't make us go faster, but slower, it doesn't reduce runway length but increases it, less initial air over the wings.=.less active control imputs and feedback along the runway untill later in the roll, less time to find out of an aerodynamic problem exists...we know Flex uses more fuel as well...so what are you saying...that we create more lift flying slower....or that flex, somewhere in the box, some computer program creats a force field of extra lifting energy at slower speeds...

And better stopping [before V1]with reverse becasue you get full rated RT [that's why it unofficial because in part 25 dry RT doesn't exist,]also spoilers and retardation devices are better in the denser air

- So flex power changes the air density around the aircraft, helping spoilers and retardation devices So flex causes a FORCE FIELD? around the aircraft to create denser air over the spoilers and retardation devices?

[Pugilistic Animus]

negative!!!! I mean even though you've limited the TO perf---it not as limiting as it seems because of ---let me see--- the laws of physics

think it out ----it's ok to be wrong I've been wrong many many times and I am man/ and pilot enough to admit it--and I then learned the correct answer---you've left the learning process already--yet the mountains wont move for you---your dug in deep redeem yourself now---also Old Smokey, John Tullamarine and Mutt ARE performance experts--so you should pay them for teaching you something new about performance--and I think Cessna, Mr. B and Airbus also mayknow a thing or two about performance...

edited to add that V in the 1/2 rhoV^2 ===TAS!!!!;)---I reread your post;);)

[galaxy flyer]

SSG

Vssg is really refusal speed, a well-known concept, see also accelerate-stop.

Au contraire, my corporate jet engines (GE, RR and Honewell) are "on condition", it is a very nice selling point indicating lower costs. One of our models has flex power built into the FMS perf, btw.


BTW, after 4,000 hours in the C-5, we frequently did reduced power take-offs even at high gross weights when performance allowed. In fact, we weren't allowed not to except in exceptional circumstances. Not even to bring V1 up to Vgo. I thought it a good idea for all the reasons detailed here.

GF

You're general aviation mindset really needs to be open to life in the big leagues. Light twin ideas have no place in transport category airplanes.

[ssg]

Some reading on rejected take offs....


The RTO maneuver has been a fact of a pilot’s life since the beginning of aviation. Each takeoff includes the possibility of an RTO and a subsequent series of problems resulting from the actions taken during the reject. Historically, the RTO maneuver occurs approximately once each 3,000 takeoffs. Because the industry now acknowledges that many RTOs are not reported, however, the actual number may be estimated at 1 in 2,000 takeoffs. For example, an unreported RTO may occur when a takeoff is stopped very early in the takeoff roll because the flight crew hears a takeoff warning horn, stops to reset trim, then taxis back to the runway and continues takeoff.

According to these statistics, a pilot who flies primarily long-haul routes, such as in our Boeing 747 fleet, may be faced with an RTO decision only once in 20 years. In contrast, a pilot in our DC-9 short-haul fleet who makes 30 takeoffs per month may see an RTO every 7 years. Unfortunately, the pilot in each of these fleets must be prepared to make an RTO decision during every takeoff.


Boeing studies indicate that approximately 75 percent of RTOs are initiated at speeds less than 80 kt and rarely result in an accident. About 2 percent occur at speeds in excess of 120 kt. The overruns and incidents that occur invariably stem from these high-speed events.

A takeoff may be rejected for a variety of reasons, including engine failure, activation of the takeoff warning horn, direction from air traffic control (ATC), blown tires, or system warnings. In contrast, the large number of takeoffs that continue successfully with indications of airplane system problems, such as master caution lights or blown tires, are rarely reported outside the airline’s own information system. These takeoffs may result in diversions or delays, but the landings are usually uneventful. In fact, in about 55 percent of RTOs the result might have been an uneventful landing if the take-off had been continued, as stated in the Takeoff Safety Training Aid published in 1992 with the endorsement of the U.S. Federal Aviation Administration (FAA).

Some of the lessons learned from studying RTO accidents and incidents include the following:


More than half the RTO accidents and incidents reported in the past 30 years were initiated from a speed in excess of V1.
About one-third were reported as occurring on runways that were wet or contaminated with snow or ice.
Only slightly more than one-fourth of the accidents and incidents actually involved any loss of engine thrust.
Nearly one-fourth of the accidents and incidents were the result of wheel or tire failures.
Approximately 80 percent of the overrun events were potentially avoidable by following appropriate operational practices.

--------------
The Korean Air cargo jet which crashed near Stansted Airport had an engine on fire as it was taking off, eyewitnesses have told the BBC.

The jet crashed in a ball of flames in nearby fields, killing all four crew members.

[ssg]

The Airbus was the first fully electronic automated plane, with no eletromechanic controls or cables. During their first commercial record of a take off, they lost an aircraft and a team of pilots and technicians due computer problems on board - by Captain Bill

http://www.sumo.tv/watch.php?video=3011028

[galaxy flyer]

Negative, the F-16 was first fully electronic plane in service. But the Concorde drivers here will contest that, as it had very nearly a fly by wire system. You really should learn to think and listen first.

[Diesel8]

ssg,

what does this accident have to do with the discussion at hand. It didn't happen during takeoff but during a flyover.

Here is the cause, in case you feel like learning something:
http://aviation-safety.net/database/record.php?id=19880626-0

[galaxy flyer]

Nice one, Para. Except those of us in corporate aviation will have to live down the headlines. He is, unfortunately, not alone in general aviation. I had a boss who believed that it was dangerous to climb at V2+10 and the plane needed to be rapidly accelerated to climb speed. Even rotated to about 5 degrees and "let the plane fly off". Climb gradient didn't enter into his procedure, he could see the obstacles.

[BraceBrace]

Those who feel unsafe during a flex/assumed temperature takeoff... then how do you feel like takeing off on a 35°C day?

Jet engines are "pressure" limited up to a certain temperature, up to which they are certified to give max rated thrust. This certain temperature is sometimes called flat rate temperature, or FRT. Either you use N1/EPR/IEPR values, these parameters are designed for pilots to keep the thrust at the max limit. We look up the values calculated by engineers, and use these in day to day life.

If OAT is above this FRT, the engine is limited in temperature increase. And even though we still use N1/EPR/IEPR/..., the idea behind them, the rules to calculate these values, change. That's the whole reason that makes this story possible. Assumed is not an invention or anything, it's been a part of aircraft jet engines since day 1. The higher the OAT above the FRT, the lower the thrust you are allowed to get from it. We might not see that directly, it is calculated in the N1/... values you use. In a way, you always do a kind of derated takeoff anyway above FRT (even though some might not realise this). If you would even try to get all thrust out of the engine, we are operating it outside it's limits. THAT is dangerous.

The FRT's I know for jet engines nowadays are in the 15 to 25°C region. So any day OAT is above this temperature, you are sort of derating anyway. Reading this thread I get the scary feeling some people think they always get the max thrust out of it...

So what's the difference? Assuming a temperature of 20° on a 10° day, or doing a takeof on a sunny day with 35°C if your FRT is 25°C. The first one is actually safer since real density is higher, giving slightly better "general" performance than on a 35°C day.

The "you have some safety margin extra with full thrust".... Yes, you have it that day, but if you want to fly on a 35°C day, to me, you consider that specific takeoff as being a safe thing to do that day, and the day after, and the day after,... so why can't you use assumed day in day out? It's the same thing.

[ssg]

I can't choose how hot the day is...but I can choose on cold days not to make the plane act like it's high, hot, and heavy..I can also choose on hot days to take less fuel but fly higher, up to FL450...which can mitigate the effects of even a hot day...

My risk exposure over a year and appr. 500 flights is much less the way I do it, vs the flight dept that doesnt..

End result in laymans terms: If I don't fly it to the fence on every flight then I have a better chance of not rolling it up should some failure or issue occur...

[mutt]

Agh, its annoying to read something that is completely incorrect, so I’m back…..

Ssg, I suggest you educate yourself by reading FAA AC25-13 and FAA AMC 25-13. The Boeing training course presentation entitled Reduced Thrust and the Airbus “getting to grips with flex thrust”. You will then see that your statement of:

[quote] The engineers don't take it into account because it doesn't exist as a benefit.....so using your logic...the slower we go (flex acceleration) the more lift with a given time/distance?[\quote] Is incorrect. But I will stress that the comparison is between a Take Off at a specific OAT compared to Assumed OAT, it isn’t a comparison between Full Rating and Flex.
For this we are using a B777 at a weight of 235,000 kgs (That’s 518,086 lbs SSG..) S.L. Airport with 11,500 feet runway, no obstacles, Fixed Derate of 10%. That’s about average for us to do a 6 hour sector under our normal conditions.
What Pugilistic Animus was trying to point out to you is the difference between taking off at with OAT 50C, compared to OAT 25C assumed to 50C.
OAT 50C
Takeoff Distances
All Engine Takeoff Distance = 9680 FEET
All Engine Takeoff Run = 9045 FEET

One Engine Inoperative Takeoff Distance = 10055 FEET
One Engine Inoperative Takeoff Run = 8994 FEET

Accelerate-Stop Distance = 10055 FEET (1445 feet runway available)

OAT 25C assumed to 50C.
Takeoff Distances
All Engine Takeoff Distance = 9552 FEET
All Engine Takeoff Run = 8922 FEET

One Engine Inoperative Takeoff Distance = 9943 FEET
One Engine Inoperative Takeoff Run = 8897 FEET

Accelerate-Stop Distance = 9943 FEET (1557 feet runway

You can see that there is a 100 feet difference in the accelerate stop.

If we were going to use Maximum Thrust all of the time, the figures would be:
OAT 25C
Takeoff Distances

All Engine Takeoff Distance = 6298 FEET
All Engine Takeoff Run = 5783 FEET

One Engine Inoperative Takeoff Distance = 6930 FEET
One Engine Inoperative Takeoff Run = 6244 FEET

Accelerate-Stop Distance = 6930 FEET

So Accel Stop = 6,930 feet whilst with DER1/Assumed it would be 9,943 feet. It’s this difference in runway length that we are trading against reducing the takeoff thrust. But remember we still have 1,557 feet of runway left.

Even with full 10% fixed Derate and 25% Assumed Temperature Derate, we get this:
Takeoff Distances

All Engine Takeoff Distance = 10764 FEET
All Engine Takeoff Run = 10088 FEET

One Engine Inoperative Takeoff Distance = 11050 FEET
One Engine Inoperative Takeoff Run = 9857 FEET

Accelerate-Stop Distance = 11050 FEET

So even with 35% of a thrust reduction, we can still operate a 6 hour sector, and if in the event of an engine failure at VEF, we could continue the takeoff or stop with 450 feet of runway remaining.
So as you can see, we are never scraping over the fence on the way to immediate doom.
Finally to expand on what Pugilistic Animus was trying to explain to you, this comes from Boeing, I don’t know the aircraft type. It should be split into 3 columns, so it might be easier for you to paste it into excel due to formatting restrictions in Pprune.

Details / OAT40C / OAT15C Assumed 40C
EPR / 1.376 / 1.376
V1 (IAS/TAS) / (147/153) / (147/147)
VR (IAS/TAS) / (155/162) / (155/155)
V2 (IAS/TAS) / (162/169) / (162/162)
Thrust @ V1 /30960/31210
Thrust @ VR / 30610/30880
Thrust @ V2 / 30300/30570
So the inherent benefits that PA was taking about are shown in the speeds IAS vs TAS and the available thrust.
Using reduced thrust reduces the jet engines internal operating pressures and temperatures, which results in:
[list]
Reduced Stress and wear on the engine.
Reduced costs on parts and maintenance
Increased Engine Life
Increased Reliability
Improved operational safety and efficiency.
These words are taken straight from Mr Boeing….
That should keep you busy for a while….

Mutt (No time to edit)

[Right Way Up]

I can also choose on hot days to take less fuel but fly higher, up to FL450

Why fly so high SSG. Its much safer flying at lower levels. What if you have an explosive decompression. By being so higher you are reducing the safety margin for a safe emergency descent. As you have said your boss would much rather be safe than save money.

[SNS3Guppy]

A few business aircraft cruise up to FL510, but most remain at or below FL410. Operating above those altitudes is an option for non-RVSM equipment, and aircraft wishing to avoid both weather and most of the other traffic. A lot more direct clearances above FL410.

[Right Way Up]

Guppy,
The question was put up against the argument for safety vs cost that SSG keeps banging on about.

[ssg]

Software engineers approximations put into a fuel controller...having deviations of 100 ft over a ten thousand ft span on a 50c day..is not an 'aerodynamic advantage' ...as P.A. baited me with..

Anything other then actual OAT numbers are approximations and not some magical way of defying aerodynamic laws...

Max on your 11500 ft field is 7000 ac/stop...derate/assumed is 10000ft.
I can choose with 250 people to have 1500ft of margin after a reject or I could choose 4500 ft of margin after a reject.

Now since all the airliner guys are 'go' in here and abhor rejects, even they would have to admit that such a dangerous maneuver as a reject is better served with 4500ft margin.

--Now Mutt..you picked a 11500 ft field..you and I know that this plane is probably overgross, and the pilot is trying to squeeze that assumed 10000 ft accel/stop into a more realistic 9000 ft field with a 1000 ft stopway..

So yeah..he went right over the fence...and they do it in front of me every day...

Thanks for the numbers...

[Denti]

Denti, if you and I bought our first old trashed 737 and tried to make a go of a single jet airline, our own money on the line..do or die..sure save a buck anywhere we can but be legal about it...no problem...now flash forward, billions of dollars later, hundreds of new planes on the line, we have something to lose, ..why push the safety envelope at that point....greed?
I am curious what is the WE have to pay for engines, unless you own the airline, your an employee, and management is not on yourside. You know besides mismanagement, a plane crash is pretty much the only single event that can literaly take down an airline and a company..why risk it...



The thing is, we do not produce worse safety than you do, the fact is, proven by NTSB figures, we produce 10 times less accidents than your type of operation does. I am still awaiting your figures disproving that.

And yes, private aviation often does not have the cost pressures commercial aviation has, that is in fact one of the major differences. However, even with those cost pressures we are much better at delivering a safe flight than GA aviation is, although some sectors of GA are as good as airlines in that regard, however more than enough of that sector are not.

And as to WE, well, all employees at my airline are investors in said airline, one previous big investor granted us 50% of his earnings he made with that investment as shares in our airline.

[mutt]

--Now Mutt..you picked a 11500 ft field..you and I know that this plane is probably overgross, and the pilot is trying to squeeze that assumed 10000 ft accel/stop into a more realistic 9000 ft field with a 1000 ft stopway..
I picked 11500 ft coz its almost the length of the shortest runway at my local airport, the actual length is 11800 ft. So nothing devious in its selection. If the runway was shorter, the weights would be lower, and most certainly the takeoff weight would be lower. This would also probably mean that flex value would be much lower or zero.

The numbers are from the B777 Electronic Flight Manual, they are certified by the FAA and hence do not lie! So please get away from statements like these...So yeah..he went right over the fence...and they do it in front of me every day.... as you have no justification to back it up.....

Mutt

[BOAC]

If that was a ssg 'gem', it deserves a posting holiday! How demeaning, disrespectful and insulting do you have to be in here?

JT - you up yet?

[BraceBrace]

SSG, flex/assumed takeoff is not the same as "hot & high".

Hot & high is high density altitude takeoff. Low pressure at higher altitudes in involved there as well, leading to higher required airspeeds for the same groundspeed. Not only you have lower thrust (if it's hot that high anyway), you need to accelerate to higher groundspeeds as well for the same true airspeed you need on takeoff. That's not the case for reduced thrust takeoff at low altitudes.

[galaxy flyer]

SSG

Since you fly above FL 410, do you wear an O2 mask at all times? If you are single-pilot do you wear a mask at all times above FL350? In fact, if you are single-pilot are you not worried about the safety issue of single pilot? After all, the pilot is single greatest cause of accidents.

Stop banging on mx costs, airline engines routinely stay on the wing for 20,000+ hours. They are not overhauled anymore. PERIOD.

[Pace]

Guppy

I posted this at the end of the other thread !

>So now that you are back peddling, please answer the question, how do you ensure your obstacle clearance following an engine failure? (referring to SSG)<

Mutt

A few years ago I was involved with a forum for Microsoft Flight Simulator. I did some development work with addon companies, wrote reviews and was fairly active in their forums.

The problem with all these forums is that they are open to a lot of people who hide behind a cloak and claim to be something they are not.

There was one guy in particular who challenged the real world pilots on those forums and fair enough some of the stuff he came up with was quite convincing.

But in other ways his approach was very purile and he made major blunders.
We discovered that this experienced so called pilot was infact a 12 year old kid who was merrily googling his answers on the internet and somehow getting a kick by playing out his act. He fooled a lot of airline and corporate pilots for some time.

Pace

[galaxy flyer]

I'll give an ultimate example-US Navy

Fighters routinely catapult off the ship in "cold" power (non-afterburning) to save engines, better control, the F-14 had better stagnation margins. What is the problem? In fact, in the 14, pilots wanted to use cold power, due to engine stalls ingesting steam.

GF

[Denti]

Denti - You got my answer


Indeed, no, you didn't answer my question.

You told us all that Corporate is the safest sector...look it up..., so i asked you to provide the figures. After all the only figures provided are from the NTSB proving that indeed exactly that part of aviation produces 10 times as many accidents as airline aviation.

So you still have to provide the answer to my question: Where are the figures proving that corporate aviation is the safest sector in all of aviation.

[PK-KAR]

You and I know guys are using Flex, planning right into the stopway.
Who says when using flex U HAVE to take the stopway into account?

and that is why they fly right over the fence and call it legal.
Right over the fence? hey, if I get an engine failure at V1 and make 35ft or higher at the end of the runway (and higher over the end of the clearway), with no other obstacles in front, good enough for me. If the obstacles become a problem if I derate and have N-1 @ V1, and the non-derate clears it, why should I derate?

Only an idiot, or someone that truly doens't care about safety, or the passengers in back...would time after time choose to burn up more runway then he has too because 'corporate says we will save some money'. I mean what kind of a tool, would believe that ending up at the end of the runway, with and engine on fire , with only a thousand feet to go, then a stopway is safer then having another 4500 ft to go
If you're implying that everyone derates to the extent that it won't meet their TODR and ASDR, then you're the idiot. You can derate to the extent that your TODR and ASDR matches TODA and ASDA (you can include or not include the stopway, your choice)... Of course, for you, it's not safe because using that method you cannot abort past V1 eh? Btw, how much past V1 do you want to abort anyway? Vlof? V2? VMBE? Vmo?

To put it simply, you can only derate as far as the resultant take off and climb profile meets the regulations! Now if you think the regulatory requirements of "flying off the fence everytime" then change the regulations... Shoving a higher screen height, you can still derate!

Guess what, derate to the extent that you still got a spare, means you have a lower Vmcg, so derate to the extent that your ASD and TOD still gives some spare (without the use of stopway) with VMCG as your V1, and will be able to fulfill your seemingly lifelong ambition, that is to abort past V1 everytime and still stop in time!

Who you trying to kid anyways? The Teletubbies?

There was a case here where an engine is known to have high EGT (it was creeping up with each take off), and the ops guys with the maintenance guys wants to pull the engine off line. The aircraft came in for a C check. It was estimated that the maintenance would cost 30k USD. Another aircraft was coming out of maintenance, but the engines hadn't finished, the management insisted to get the aircraft flying at all cost despite the ops and maintenance guys saying no.

It was going to be a long weekend, and extra flights were already planned, and it was that aircraft that was gonna take the extras. So, ops placed the aircraft on mandatory derate (except when wet). With extra load, some take offs wouldn't be legal on a derate, ops wanted to offload, the management wanted to keep the load, and yes, ssg, they said what you said... "it'll take a shorter runway, so if the engine quit, there's more stopping distance!"

Guess what? Not only that the management didn't want to off load... Halfway through the 16th flight out of the shop, the engine seized and the engine had to be sent to the shop. Engine repair costs? 300k USD! That's one extreme example of derate cost savings... *grin* (it was a CFM56-3)

But normally, if I was given the right numbers, the savings per flight on a 737-classics using derate t/o and climb whenever possible (with the company policy of not using stopway as ASD calculations), was about USD 50 per cycle, with all runways within the company's network being 2500m or less (except 5 airports, which had 3000m runways). The aircraft would normally do 8 - 10 cycles a day, so it'll save about 100 k- 150k USD a year by derating. That'll pay a few people's salaries over here.

We discovered that this experienced so called pilot was infact a 12 year old kid who was merrily googling his answers on the internet and somehow getting a kick by playing out his act. He fooled a lot of airline and corporate pilots for some time.
Well Pace, ssg could be on of them! LOL. I could be one of them, heck, any one of us could be a 12 yr old sim pilot with too much time on their hands.

Over here we got someone who went around with a fake crew tag, and convinced enough people he was a crew member with his talk, until he ran into a gate agent who knew the game and called security. If you wanna see someone leaving the terminal with such speed, you should have seen this guy!!!!

On the other hand, I've met a captain who thinks a 72kt wind aloft will break your plane apart and uses LDA against his TODR. :ugh: I avoid paxing on his airline with good reason! But then, that fake guy I mentioned above uses this airline as his claimed employer... now why am I not surprised... ;)

PK-KAR

[mutt]

I don't think you fly a plane Oh cool, this sounds like you give me your ATP certificate number and I will give you mine...... :):)

Why is it that people must resolve to personal insults when they starting losing a technical discussion? Its most unbecoming!!!!!

Mutt

[PK-KAR]

Trickle451...
1st 2 posts in this and the abort v1 topic... very interesting. :=:D:oh:

Trading safety for a buck, yes, and NO. It's not that simple as "it's safe" or "it's not safe". It's safe, relatively safe, comfortable risk, unacceptable risk.
The first two is what we're after. The last 2, don't belong in aviation.

No doubt in here he was fighting the rising tide of those that couldn't stand up to thier boss and say 'wait a minute...is this the safest it could be?'
The safest it could be is not to take the flight at all! To do the flight, there are risks, now, how much risks is acceptable? The regulations state what must be able to performed to an legally acceptable risk level.

That's how you take your shilling. If you want it the safest way, don't do the flight. Heck, even keeping the aircraft on the ground or in the hanggar has it's risks. There is no safest... only safer.

Mods/Admins... IP check please... :E:rolleyes:

PK-KAR

[trickle451]

Mr. Hoppy,

I don't have the statistical data to make the case for or against flex. I did just read however , that statisticaly, you have about the same chance of losing a tire as you do an engine..

If I was lining up on a 7000 ft field, I would much rather lose that tire on a 4000ft take off run then on 6000 ft take of run. More time to deal with it.

Longer runs, just like longer braking distances heat up the tires more. Also longer runs tend to pick up more goodies on the runway, such as parts from other planes, the result I am sure we can all sadly remember.

[FE Hoppy]

Mr. Hoppy,

I don't have the statistical data to make the case for or against flex. I did just read however , that statisticaly, you have about the same chance of losing a tire as you do an engine..

If I was lining up on a 7000 ft field, I would much rather lose that tire on a 4000ft take off run then on 6000 ft take of run. More time to deal with it.

Longer runs, just like longer braking distances heat up the tires more. Also longer runs tend to pick up more goodies on the runway, such as parts from other planes, the result I am sure we can all sadly remember.

exactly how do you:
a) Identify a tyre burst?
b) Calculate your new stopping distance?

You may also like to check out the manufacturers recommendations with regard to high speed stops!

[trickle451]

The last tire that blew on me, was in a landing actualy,.excessive nose down, veering to the right...took all opposite control forces to maintain directional control including directional thrust management, with extremely heavy braking. Had I been a little faster on at touchdown, the nose tire would have separated from the nose gear, and what turned out to be simply changing a tire, would have resulted in an incident at the very least. I was in a turboprop...had this been a jet, with less assymetrical thrust to counter the veering, and faster speeds, this would have been an accident, as I wouldn't be able to control the direction and the gear would have impacted, metal to pavement after the tire separated..

I am convinced that a blown tire on take off would create the following scenario

-1 Directional control issues
-2 Vibration (thumping)
-3 Excessive drag / Force impeding acceleration

Obviously if you identify this prior to V1, you stop. If you never identify it it you might not get off the ground at all. Post V1 the issue would be trying to accelerate past v1 to Vr. Same result.

Some of the latest accidents suggest the pilots kept chasing V1 or VR all the way down the runway, when they ran out of runway...some tried to pull the plane off at the end, others didn't...same result.

Base on personal experience I don't think identifying a blown tire is difficult, it's a violent experiece...just like in a car...the issue is trying to figure out with your new speed paradigm if you can make it to take off, or if you should stop...all your pre briefed V speeds just went out the door...

[Right Way Up]

Obviously if you identify this prior to V1, you stop

Why is the recommendation from manufacturers not to abort high speed with a burst tyre. Of course if you believe the Spantax crash that killed 50 people was a resounding success then you might think it is a good idea! :ugh:

[FE Hoppy]

Trickle,
read this then get back to us please!
http://www.faa.gov/other_visit/aviation_industry/airline_operators/training/media/takeoff_safety.pdf
:ugh:

[PK-KAR]

If I was lining up on a 7000 ft field, I would much rather lose that tire on a 4000ft take off run then on 6000 ft take of run. More time to deal with it.

Longer runs, just like longer braking distances heat up the tires more. Also longer runs tend to pick up more goodies on the runway, such as parts from other planes, the result I am sure we can all sadly remember.

Anyways... now VERY ROUGHLY AND CRUDELY...
Say a 732... My TOFL 7000ft,TOEPR 2.15 SL, 30C... 54 tons, I'm carrying 50 tons... I can derate the T/O to 47C, and it'll give me EPR of 1.96... now here's a very simplified derate effect...
54 Tons V1Bal = 143kts, Stopping distance from 143kts = 2500ft.
at 50 tons I get V1Bal = 135. From 135kts, stopping distance = 2250ft and TOFL 6500ft

AccelgoV1 dist (54tons)= 4500ft
AccelgoV1 dist (50tons)= 4250ft no derate.

Now, I derate to 40C and presto, my AccelgoV1 dist = 4500ft... stopping dist from v1 is 2250... my ASD = 6750ft, I still got 250ft of margin.

My accelgov1 dist is the same if I'm at 54tons no derate or 50tons with AOAT40C.

Now, r u trying to tell me now that because I need longer distance, I should carry 50 tons with no derate instead of 50 tons with derate, for saving 250ft of runway?
OK, how about I just load up 5 extra tons of fuel, so I use up that 250ft of runway and putting my signature "added safety measure" on the dispatcher's copy just for the sake of "oh derate is dangerous?"

Sure, I'd rather stop with 2750ft left from 135kts instead of 2500ft left from 135kts. BUT, I'd prefer 2500ft left from 135kts than 2500ft left from 143kts.

And, given the engine reaction time to go to idle from the take off thrust from 2.15 EPR and 2.05EPR, let's just assume the worst, 0.2 secs... I'm only left with 200ft added margin left! (it trundle down at 250ft/sec-ish at that speed)...

Now U want me to add the $30-50 bucks worth of extra engine wear and fuel burnt for... say, 200ft of margin, while I have an adequate 250ft of extra margin in the beginning... so the price of the extra margin in the above scenario is $0.15 per ft by not derating. Now, does the cost of changing tires due to tireburst is equivalent to 15 cents a foot?

The aircraft will do 4000 hrs and 3500 cycles this year (assuming it flies for 350 days in a year, no other downtime including for overhauls).

By not derating, you're spending an extra $100k a year to reduce your tireburst risk which on an average year will cost a fraction of that.

While insurers love added safety margins, the extra margin (to lower the premium) is offset by the fact that it's not a cost saving, therefore can increase risk in other areas (such as financial, which then leads to other operational risks), including engine failure risk. Your insurance, might actually go up!

Now, you tell me, which costs more? changing a tire or shoving the engine into the repair shop? And remember, you've already spent that extra 100,000 USD... that's 2 captain's worth of pay where I am... all that for 250ft of margin above another 250ft I already have after derate? at 4.5 to 6 crew sets per aircraft, you can pay 1 whole crew set per year with that amount of money here (including cabin crew). By derating, the company can actually afford an extra crew set, which means, up to 20% less flying hours in a year, now, that means, you can do 80hrs a month instead of 100hrs (and then find short term crew when your annual limits are up), which lowers fatigue, which means safer operations! Fatigue is a higher risk than derating or not derating! Now, therefore, with this more valuable increase in safety through cost savings from the derate, the insurers will give you a lower insurance premium...

So, now, when you do have a tireburst or an engine failure at V1, your crew can handle it better and safer! Further reducing repair costs when these mishaps happen (you can't eliminate risk! If you want to, get another job!)

hey, guess what? MORE SAFETY AND COST SAVINGS THROUGH DERATING!

So, Ssg/trinkle/whatever your next username will be, still trying to say that derating is UNSAFE?

The last tire that blew on me, was in a landing actualy,.excessive nose down, veering to the right...took all opposite control forces to maintain directional control including directional thrust management, with extremely heavy braking. Had I been a little faster on at touchdown, the nose tire would have separated from the nose gear, and what turned out to be simply changing a tire, would have resulted in an incident at the very least. I was in a turboprop...had this been a jet, with less assymetrical thrust to counter the veering, and faster speeds, this would have been an accident, as I wouldn't be able to control the direction and the gear would have impacted, metal to pavement after the tire separated..
Now would you rather have a tired crew who flies 100hrs a month going through that or a fresher crew doing 80 a month going through that experience?

Now, does your plane have 4 or more main landing gear wheels?

If you never identify it it you might not get off the ground at all. Post V1 the issue would be trying to accelerate past v1 to Vr. Same result.
A 732 had a tireburst the other week, a friend of mine was on board. It was a few knots before V1, 7000ft runway. Guess what the crew did? GO... accelerated as normal, and it was a non event except for the notable vibrations for a few secs. Had time to prepare the tire change, prepare for whatever was to be expected on arrivals... Waaaaay better than stopping, with 1 less tire (discount the brakes on that wheel), possible directional difficulty on braking, etc, etc... and causing everyone to panic and may lead to pax trying to get out without crew instructions.

Base on personal experience I don't think identifying a blown tire is difficult, it's a violent experiece...just like in a car.
Had a double blowout on 1 side two months ago... shocker, but no big deal.

Why is the recommendation from manufacturers not to abort high speed with a burst tyre. Of course if you believe the Spantax crash that killed 50 people was a resounding success then you might think it is a good idea!
I guess Trinkle/Ssg never had an airline take off briefing... it'll cover what will make an abort between 80 and V1... on planes with 4 or more main landing gear wheel... :E

PK-KAR

[galaxy flyer]

PK-KAR

It is the fuel savings that launching in cold power, the thrust isn't needed, reduces stress on engines (just like derate, reduced power on airliners) and, esp, in older reheated fan engines, increased stall margins down the stroke. Ever see the video of an F-14 losing an engine just off the bow? It ain't pretty, level at best.

GF

[SNS3Guppy]

Can't argue with an early pre-V1 reject speed if a blown tire, but they state I have to get that actual number from my airplane manufacturer...do you know what it is in a Ferrari jet.?..would I have to dial up the underworld to talk to the designer long dead gone for 50 years?


No need. The takeoff data is already before you. You needn't contact the dead, just be able to read a simple performance chart and abide by the numbers.

If you don't have directional control issues, then don't risk a high speed reject...especially if you think you have a failed tire or wheel. If you do have directional control issues, then the matter is settled for you. Clearly you're not going anywhere if you can't maintain directional control.

Try to make this connection...loosing a tire on an 18 wheeler is a little different then losing a tire on a Yugo.


Try making this connection: people experience tire blowouts every day and don't lose control. A little vibration...yes. Pulling to one side; sometimes. Connect it further; lose that tire at the end of the road...gonna run off the road into obstacles when you can magically pull back and get airborne, and go back to the beginning of the road? Go fly.

The point is everyone on this forum doesn't drive a heavy...SOPS are different for each operation..


You're right. Many of us do both, or have experience in both...and yes, the procedures are basically the same. Specific aircraft procedures apply to each type, but competent professional training centers teach the same that airlines teach with respect to runway behavior and policies regarding stopping or going.

Then again, you've had ONE tire experience, and are now an expert. :rolleyes:

[PK-KAR]

Good paper..
Good sarcasm... :E

Can't argue with an early pre-V1 reject speed if a blown tire, but they state I have to get that actual number from my airplane manufacturer...do you know what it is in a Ferrari jet.?..would I have to dial up the underworld to talk to the designer long dead gone for 50 years?
WHICH Ferrarijet? I've heard that term being used from the 732A to the 752 to the 345, down to the Lears and some of the Citations.

Assumptions that regardless if you saved lives and equipment, might still not have been a good decision, or that tire blowouts might not be felt, are assumptions from someone driving a desk.
The guys driving the desk are the guys paying your salary. They employ risk managers to convert operational risk to terms they understand, numbers. The guys fondling the yoke and throttles while trundling down the runway are the ones who make the business run, and the guys carrying the wrenches and test pens make sure the business keeps running, and the guys receiving the phone calls make sure those who want to pay to use the business actually gets on the plane and sits behind the guys fondling the yoke and throttles so that the desk drivers can get the money and pay the risk managers, the guys with the wrenches and test pens and, yes, the guys fondling the yokes and throttles again. It's all a chain and an appreciation of safety and risk management is needed for the business to run sustainably. Your (or your former self) previous posts reflect that you see it in boxes, you do what you do, and no one else understands what you do.

If the tire blow out isn't felt, no directional issues, and not keeping you from getting to VR, then it's a non issue at that point...it's not affecting performance...
But you say it does and did not mention it before. You put a blanket statement that a derated take off is less safe. It's not the case at least MOST of the time, and it's safe enough for most of the remaining time.

flies in the face of the Goma crash, were there was actualy a pilot to talk to who said 'after the tire blew, the plane wouldn't accelerate'
Goma? Hewa Bora DC9? Or another crash.
Anyway, this topic is about derates right? Any evidence that derate was used in that crash? The events of the crash is not that clear anyways, one source says the aircraft suffered an engine fire after 300m of take off run leading to an uncontained engine failure? Surely, at an airport of about 5000ft elevation, you think a DC-9-51 would have passed V1? I think NOT. The reversers were indicated to be deployed at the time of impact... now, did someone not do their PERF figures right that day? Or did they just decided to flaunt the Vspeeds and decide stop/go at a time they picked out of the blue?

Another source said the aircraft went through a puddle and resulted in loss of thrust in one engine. Another said tireburst. Air Safety Week mentioned BOTH tireburst AND engine failure.

It's a 6500ft-ish long runway but there are information that only 5250ft or 5900ft of it was usable.

Given the above and the poor state of the runway/airport, do you think they'd derate? If they did then I'm not surprised the airline is banned from going into the EU.

Or perhaps, since someone was adamant about aborting after V1... here's another danger...
They elected to take off to the South when the runway was wet, with standing water, while other aircraft were waiting for the runway to dry out. Nothing wrong with the TOW. They had about 50-80 pax, depending on who you listen to, and were apparently 4,000 lbs below performance limit.

The captain briefed, reducing V1 to 100 kts, with VR around 125, but didn’t change the speed card.

At 100 kts the F/O called “V1”

At about 125 kts, at the point of rotation No. 2 engine failed. (Or possibly barked with a compressor stall)

It was then that the captain elected to abort the take off.

They had so much speed that the airplane actually became airborne. When it slammed back onto the runway they took the nose gear off and subsequent braking with the main gear bouncing off the runway took some tires out.

They shot off the end of the runway at high speed, down the embankment into the residential and market complex. The airplane caught fire and came to rest by the mosque.

All of the crew, including all of the flight attendants managed to escape injury and the fire while most of the pax and people at the market were burned to death.

- Standing water on the runway MAY have caused the engine to stall or fail
- The Captain's decision to abort the takeoff at Vr instead of taking-off

No accident investigation report, so, no official information. Moot example. NEXT...

The issue here is not just reject speeds but if the plane isn't accelerating when you do say..ok..this isn't working I can't get to VR.
If that's the case, there's only 1 solution... STOP! STOP! STOP! PRAY!

Perhaps you don't have it in your manual...
"Aborting past V1 should only be considered if airborne flight is unattainable or that safe flight is practically impossible."

After V1, can't accelerate to Vr, is speed increasing? No? in most cases then, Abort. There is decision, and there is judgement. I'm sure you learnt ADP vs conventional in school...

So are you going to apply big jet SOPS to that that Cessna Twin or light jet you just bought?

The point is everyone on this forum doesn't drive a heavy...SOPS are different for each operation..
The point is to everyone in this forum, is, you love your lights and scream out loud the policies of the heavies are unsafe, and when proven what is not safe with your lights is safe with the heavies, you say they're two different things.

The rules and SOP I adhere to are in accordance to what I operate. Going on a C402, a burst tire and loosing control means I stop. If the burst tyre happen at a speed where the wing of the burst tyre can be lifted , I go. Lost the left tire once on t/o but wasn't me doing the take off, and we could lift the left wing up. If I get an engine failure, I know beforehand how much climb rate I'm gonna make. Still past V1, I go, unless I brief or have been briefed otherwise (depending on the circumstances of the airport... yes, bushflying keeps you on your toes just like the flying heavies). If I get engine failure and burst tyre at anytime prior to lift off, it's a stop. Took off from a gravel runway once and the props were getting hit and the leading edge was getting hit. We went... but if a tireburst and an engine failure happened between V1stop and Vr, we'd stop. We agreed beforehand that the tyreburst meant V1=Vr, but engine failure decision was v1stop.

Going on a twin airliner, as you said so yourself, different game. BUT, don't argue about being on a light saying the heavy is wrong and when shown it's safe on the heavy you run back and use the "but I was talking about lights" as an excuse. It's disgusting.

GF,
It is the fuel savings that launching in cold power, the thrust isn't needed, reduces stress on engines (just like derate, reduced power on airliners) and, esp, in older reheated fan engines, increased stall margins down the stroke. Ever see the video of an F-14 losing an engine just off the bow? It ain't pretty, level at best.
Never saw the F14 stumper... saw the single on the E4 stumper, and other types. I might have seen the Vigilante one... None of them were pretty! At least a tireburst on a sling, you can't do much except for have people watch sparks coming out of the contact.

[SNS3Guppy]

If your just about to hit V1, hear a thump, then a firelight, and the plane starts to decelerate...or the airspeed just stays there...hmmm...do you think you will get to VR?


Problem before V1...you're rejecting. Problem after V1, you're going.

Stick to one screen name. I realize that ssg got pounded and had no credibility, but coming back as a different name doesn't give you any more credibility when you're posting the same tripe over and over.

Clearly if the airplane can't fly then it can't fly. If you're talking a business jet, you're going to have enough power to accelerate to Vr from V1 with a blown tire. If you can't maintain directional control, then clearly you have to stop...that doesn't even dignify a discussion on the subject. However, you don't seem to have any significant real world experience if it always comes back to "in the simulator...".

If you had a tire or wheel failure approaching V1, was the problem you weren't accelerating because you were riding the brakes on the opposite side?

[SNS3Guppy]

- I have learned


So you say, but you didn't come here to learn, nor have you done so. You came here to preach a failed sermon based on conjecture, ignorance, and emotion, with no useful information. You certainly did not come here to learn.

Let's see what you've learned...

- I have come up to speed on Flex/Assumed (1 day?)wth Mutt / Pug running away from my questions...I gather they were your best. A nice way for corporate to save money, having the pilots fly 200 people a little closer to the end of runway...and possiblly thier last flight..


Mutt, a professional performance engineer with a major airline operating internationally, didn't run away from your questions, but provided you great detail and numbers, as well as asked you questions you couldn't answer. You haven't come up to speed on assumed temperature or flex, as you still seem to fail to grasp even the most basic aspects of either one. Whereas no safety margins are reduced or compromised, and whereas safety is enhanced on multiple levels with reduced thrust takeoffs, clearly you missed not only the boat but the wake it left behind. You appear lonesome and confused waiting on the darkened dock.

- I have learned that you boroscope your own engines instead of hourly limits, flying them to ridiculous times..visions of South West Congressional Hearings are floating by...


You haven't learned. Airlines work in concert with manufacturers and their respective airworthiness authorities in maintaining powerplants through full and complete maintenance programs. On-condition maintenance for some components, specific hard life time limited items for others. If an operator, with a full maintenance and repair facility cannot boroscope one's it's own engines, then who can?

Your words betray an absolute lack of maintenance experience. From my perspective of not only an ATP, but a mechanic and inspector with more than a few years of experience behind me, you have a great deal to learn, but refuse to be taught. Where honeywell or P&W or any other manufacturer may set time limited or cylce limited overhaul intervals on certain small engines used in light business turbojet aircraft, different standards are set for other powerplants such as are used on many airline-class aircraft.

Perhaps you take offense that the engine manufacturers set standards for the engines...but the engine manufacturers set the standards for the same engines you fly supposedly fly, too. You seem to feel that all engines should be maintained by the same time intervals as the powerplants with which you've come in contact during your extremely limited experience. You apparently haven't been educated on the fact that non-charter, non-airline engines are often maintained on an on-condition basis, and many charter and airline departments have authorizations based on very close observation and documentation to significantly extend overhaul intervals, too. I've worked for several such organizations myself; companies which had such advanced experience with the particular powerplant that the manufacturer and the FAA provided authorization to extend the life of the engine by significant numbers.

Powerplants on test cells have run nonstop for years, over a decade, with little more than fuel and oil provided...including some of the same powerplants you have theoretically flown. Imagine that...did you know that?

You've learned nothing, but continue to run your mouth (or keyboard as the case may be). Why don't you tell us about these "South West congressional hearings." What hearings might those be? Are you familiar in the least, beyond a mindless google search, of the circumstances surrounding the media circus regarding Southwest Airlines? Clearly not. You might try educating yourself. No one else can.

- I have learned that airline pilot logic is that if we put less power through our engines, but take away all available runway stopping margins, the flight is safer


Powerplants run at reduced temperatures and power settings last longer, are safer, more reliable, and more dependable. Reduced power takeoffs are according to data provided by the manufacturer, under manufacturer approval, and fully approved by the overseeing aviation authorities (such as the FAA, CAA, etc), and meet every single safety margin there is. There is no loss of stopping ability or distance, when the takeoff is calculated to be stoppable from V1. The point on the runway varies with the power setting, but the required runway is always available. You've learned nothing about "airline pilot logic," which is actually aircraft and powerplant manufacturer logic, Federal Aviation Administration logic, Airline logic, Flight Safety International logic, CAE Simuflite logic, corporate logic, NBAA logic, etc. Seems you're the lone turnip out there that can't comprehend it. Safety is never compromised when calculations are done properly.

- I have learned that airline pilots, after about a 1000 posts will eventualy cave that it's possible a plane won't fly after V1, but that is a dark, dark prospect to an airline pilot who has built his balanced field into the stopway, is probably running overgross....and is told he HAS to go after V1...it's like you have to admit your religion is false..


We have learned that you've repeatedly attempted to introduce popular media articles regarding overruns or entirely irrelevant fly-by's in an effort to discuss this topic, but that you've ignored all the data provided by performance experts, using the factory numbers which show you and your ideas to be wrong and a lie.

You've failed to grasp the fact that the field doesn't need to be balanced, is seldom balanced, and has no reason to be balanced...and when it is, it's often by coincidence. Yet you keep coming back to it like a student pilot to his beginner's textbook.

You've claimed ten thousand hours of flying you don't have, and perhaps the only truthful statement you've made is that you've been rejected by an airline...for which you seem to have nothing but a case of sour grapes. You need to bear in mind that your own failures and your own inadequacies are not the fault of others here, but yours alone. You've claimed to have been trained at FSI...but FSI doesn't teach stopping after V1; you either didn't go, or lied about the training you received, but we've learned that no matter what name you choose to log in under, you still lie. No credibility.

- I have learned about V speeds ad nauseum, and thanks to those that linked all sorts of advisory circulars and educational .pdfs Those links and my ability to sort the info gave me enough bullets to take on all comers, and if I might ad, fight off guys that supposedly do this for a living.


If you count making yourself a laughing stock among some very respected professionals who really see you for what you are, then you've done well. Otherwise, thus far all you've managed to do is continuously lose credibility every step of the way. You still seem to fail to grasp the concept of V1; you've learned nothing.

- I have learned that 'taking the shilling' and 'doing what the SOPS say is basicaly a subsitute for safety..and very few in here are able to stand up to the social will of the group or the need to sit in a plane.


If by "taking the shilling" you mean that pilots are willing to compromise safety for pay, you haven't a clue. Where no lack of go distance, stop distance, and obstacle clearance exists due to very advanced and detailed calculations for every takeoff and every landing (when was the last time YOU performed a runway analysis or determined your obstacle clearance criteria with an engine failed on the go...or that you actually flew something other than a laptop computer??)...safety isn't compromised. As a professional aviator, I'm first to the seen of the crash, standing at the head of the line in front of anyone riding in back. I don't compromise safety; not by using reduced thrust, not by continuing after V1...every aspect of what I do is fully backed up by the performance capabilities of the airplane and methods and practices that aren't just written in ink, but in blood. That includes the knowledge that stopping is far less safe than going.

"Taking the shilling" means exercising the judgment to complete the flight safely, and that' what we're paid to do. Exercise the judgement to be safe. Reduced thrust takeoffs are safe.

My Operations Manual spells out all the conditions under which I can and can't make the flight. One overriding statement nullifies any issues regarding reduced thrust and that is that the PIC ALWAYS has the authority and discretion to make a full thrust takeoff if he desires. The truth is that it's often unnecessary, for many reasons that have been hereto discussed, with NO compromise to safety.

You've learned nothing.

- No one has standed out...maybe a comment here or there, to help..but no warriors or heros. I know you tried, thanks...but you caved to social pressure.


Standed out?

- At the end of the day..no one stated what was best for the passengers, but only what was good for saving a buck.


Reduced thrust takeoffs are best for the passengers. Reduced thrust increases safety margins on many levels, from reduction of minimum control speeds, to more reliable, safer engine operation over extended periods, fewer failures, extended mean time between failures, and ultimately, even the financial needs of the passenger are attended with reduced costs. Safety is always the chief concern, and reduced thrust caters to safety first and foremost. Clearly you have learned nothing.

Maybe one of these days I will see you in a sim or be called to consult at your company, I suggest you keep your opinions behind the veil of internet privacy...in the a room full of pilots, books, pen and paper, they would be hard to justify, and might cost you your job. I have no quams going toe to toe with people in an area of my expertise. If I had been schooled here, I would have admitted. I did learn some things, important things, but also saddened by the lack of horse sense, morality, and decision making skills that should be ineherent in a person that flies proffesionaly for a living. My goal was not to gauge, but be educated, and I was.


No, your goal wasn't to be educated. You won't be seen in any sim I'm flying, and I don't play with microsoft sim, so chances are slim that you'll see me...or most of the other people here. There is no chance you'll ever be called to consult at any company where I fly. You see, I've done the kind of the flying you've done, a great deal of it, plus more, and know the type of training you should have received...but you fly in the face of all of it. I've seen your kind washed out of training programs at Simuflite and FSI. I've known more than a few of your kind who are dead now due to your need to operate by your own understanding. There's always someone who thinks they can reinvent the wheel, and you're that someone. The shame of it is that you don't appear to have a clue just how many folks are laughing at you right now.

You go right on believing whatever you want to believe. You will, anyway. One can only hope that you aren't flying an actual aircraft, or that if you are you quit soon, lest someone innocent die at your expense.

Time to put your latest alter-ego on the ignore list.

[john_tullamarine]

Likewise, this has been a spirited thread.

Procedural points to keep in mind ..

(a) several folk have complained about some of ssg's posts. Be aware that I am following along behind and I alter/delete posts which I think are a bit out of line .. not just ssg's .. any ...

(b) so long as the posts are not too far out of order and the subject remains reasonably on flying matters the thread can remain here to stir up objective passions

(c) if individuals get to the stage where they feel that the thread is going in circles or whatever, there always remains the option to ignore it .. when enough lose interest it will, like near all threads ... sink into the abyss.

As a moderator, it is not my personal task to be the arbiter of what content should or should not be in threads .. only that they reasonably follow PPRuNe requirements.

The only "rule" we have here is that outright rudeness etc., will be modified or deleted as we consider appropriate


Now that I have finally caught up with the leading edge of this thread .. it is evident that ssg/trickle451 is now pursuing an unuseful path .. one of my colleagues has beat me to the punch and given the poster some time out. As you all would be aware, we have a great tolerance in this forum .. but, occasionally, the odd individual does take too great a liberty with that tolerance.

[barit1]

Although ssg has many of us pushed to the point of exasperation, I've felt this thread was useful if only to expose us all to the fringe element, to try to understand their motivation. Operational economics was certainly not his motivation.

And even more revealing were the issues ssg nicely sidestepped.

PS Thank you JT for bringing a new word into my vocabulary - unuseful :ok:

[rubik101]

There are thousands of engines operating on the wing after considerably more than 60.000 hours. I have no idea what the longest lived engine is before its first shop visit but I am sure it is well in excess of this figure.
I have experience of a CFM 56 in Germany that has been on the wing over 70.000 hours.
I have heard of RRs on B757 that are also well in excess of this number.
I am only guessing, as would you be, but if every take off were made at Max Thrust, I suspect these numbers would be considerably lower.
The answer to the question originally posed, so eloquently and thoroughly answered here, is yes.

[john_tullamarine]

It has been suggested that Angels60 is our erstwhile friend ssg. I don't know if that is, or is not, the case.

Can I ask that we give him the benefit of doubt for the time being and see how his posts go ... ?

[Angels 60]

Well I think we should give him the benefit of the doubt...:)

Just curious with regard to this thread..doesn't Flex/assumed/derate add to take off distances, extend balanced field, and create more space for a problem between V1 and VR?

Personaly I would rather miss that crowbar on the runway at 8000 ft by hitting VR at 5000ft instead....

[SNS3Guppy]

Increased "space" between V1 and VR is not necessarily a function of reduced thrust.

If one can show adequate stopping distance from V1, it doesn't matter where on the runway it occurs. Or that mythical "crowbar" exists. However, if indeed there's a directional control problem waiting, reduced thrust provides for reduced assymetrical thrust issues and higher controllability during a rejected takeoff.

Ironically, we've had two aircraft recently experience engine fires during takeoff, with reduced thrust...both of which continued and returned to land safely. More importantly, with the reduced thrust calculation, there is no need to increase power on the "good" engine(s) throughout the entire exercise. The necessary performance, stopping or going, can all be done on the reduced thrust and still meet every margin every clearance, every gradient, every required criteria.

What do you call a runway that's five thousand feet longer than it needs to be? Long enough. What do you call a runway that's a thousand feet longer than it needs to be? Long enough. What do you call a runway that's as long as it needs to be? Long enough.

Extended engine life and reliability is more than a passing interest in safety. An engine which has been operated with reduced thrust takeoffs for it's life tends to live a lot longer, be more reliable, suffer less failures (or in other words experience longer mean times before failures--mtbf), cost less, and produce less problems.

Conversely, an engine which has been abused and pushed to it's limits regularly will have a higher probability of failure, and engines so operated have considerably reduced mean times and overhaul intervals.

Reduced thrust is safer, both in the short, and in the long run.

[FE Hoppy]

I'm waiting for some one to bring ATTCS into this topic. Then the fun will really start!!

There is a nice section in CS25 if anyone want's to read up first.

I'm intimate with an aeroplane where one uses reduced thrust on top of derated thrust and ATTCS.

Some of the posters on here are going to have a very hard time coming to terms with that..............................

[Angels 60]

No doubt less engine stress leads to a probabity of more reliabity and longevity...we are getting into the areas of engineering, FOD possibities, bird strikes, puddles, ice, oil consumption issues, bearing failures, and a whole host of things that can lead to or lead away from the possibility of engine failures..

If all we ever worried about was an engine failure on take off, then I tend to think reduced thrust would further that argument quite a ways...

An AC circular I once read indicated that tire blowouts were just as likely to happen statisticaly as an engine failure.

One tire blowing on an airliner is no biggie, unless it's the Concorde I guess, on a light jet it can be catastrauphic...

V1-VR, a scary place to have a problem...if that number could be shrunk down a little, less exposure, somehow with more thrust, or changing flap positions, ect I might feel a little better trying to 'find' VR if I am committed after V1.

[barit1]

V1-VR, a scary place to have a problem...if that number could be shrunk down a little, less exposure, somehow with more thrust, or changing flap positions, ect I might feel a little better trying to 'find' VR if I am committed after V1.

If that's a real issue with you (I'd like to see statistics supporting this), and if you have a range of V1's available, I suppose this could bias you to V1max.

But in the 2008 airline universe - Is it a significant issue? (I'll acknowledge that fewer tires on your bird might alter the picture)

[Angels 60]

Well Barit, as someone mentioned, the perfectly safe flight is one that never took off.

Risk/Reward type of thing seems at play here. I have found there is always some Achilles heel in some operation. Like a main rotor in a helo coming off, or your last parchute doesn't open...that's that. I like options.

I do not mind taking calculated, mitigated risks, just hate the idea of being in position where I could've prevented something and didn't when it happened, and now it's too late...

[Denti]

V1-VR, a scary place to have a problem...if that number could be shrunk down a little, less exposure, somehow with more thrust, or changing flap positions, ect I might feel a little better trying to 'find' VR if I am committed after V1.

Personally i like my V1 cuts (four times a year in the simulator) to happen quite a while before Vr. Why? It is much easier to operate the airplane that way. Better controllability, perfect reference to runway centreline even in LVP, makes any kind of engine failure even more a non-issue than it allready is.

[Diesel8]

yeah I would baby those engines like you wouldn't believe..flex, reduced cruise, watch the temps like a Hawk, stay away from FOD and birds, no runups on the dirty ramps...you name it...anything to save those engines....

It is called airmanship, try it, you might like it.

[barit1]

Well Barit, as someone mentioned, the perfectly safe flight is one that never took off.

Yeah, but then you have to contend with terrestrial hazards. :}

As I said many times, there is NO SUCH THING as "safe"! Safety is a variable that can only be measured in specific units (events per 1,000,000 trips, e.g.). And on this basis, you'd be hard-pressed to beat most airlines.

(Out here in flyover country, we had a support pylon under an Interstate overpass demolished by a RR locomotive, being towed on a trailer by a long-haul trucker. What are the odds of THAT? :eek: )

BTW, my name has three syllables. :=

[Angels 60]

The answer to this thread...No

[Wizofoz]

The answer to this thread...No

I guess that's why airlines who use de-rate have that terrible saftey record

You can use your excuses for caning your engines all you want- after all, you only fly for a bunch of rich guys, you don't actually have to make money out of aviation- but the stats on airline saftey re the use of derate are unassailable.

By the way- is your aircraft equipped with the absolute most powerful version of its engine, or a flat rated version? If it's the latter, YOU use de-rate on EVERY takeoff!!

[Angels 60]

I have only heard one compelling argument for the use of flex...that If I was a corporate airline executive... be hoping that running those 50000 hr engines a little longer, might help increase my yearly bonus..

[flyingflatfour]

The introduction of FLEX take-offs on the AVRO-RJ fleet in my previous company (about 5 years ago) led to a fierce debate amongst pilots.

Chiefs were telling us to flex as much as possible to save mucha €€, we pilots could not believe that we had to increase power after "thrust reduction"...

Being an unexperienced pilot back then, and after 5 years of asking my collegues about how they operate, I finally made up my own mind.

1) FLEX does save maintenance costs
2) FLEX does burn more fuel

I made some calculations and actually, the extra fuel burn would offset the maintenance costs by 50% on the RJ. That was a few years ago with a barrel below 50 $ IIRC.

3) Performing a FLEX take-off at an average gross weight on a long runway gave us as much margin as a a REF take-off at max take-off weight on a long runway. In both cases we would not take-off in balanced field conditions, so plenty of margin.
4) Performing a FLEX take-off in balanced field conditions (short runway + average gross weight or long runway + high gross weight + high temps for isntance) is just as tricky as a REF take-off at max performance take-off weight on a medium or short runway (balanced field and/or WAT limited). You have to remind that there is no margin left, you HAVE to perform a static take-off from the calculated take-off position (including the calculated line-up position LUF, LUZ, LUH) and you better make sure every other parameter that was used for take-off is met on the runway (actual OAT on a hot runway vs the ATIS OAT, actual wind component, actual gross weight maybe different than the one you used for calculations, etc etc)

The conclusion of 4) is that in fact, because you are performing a FLEX take-off, you no dot realise that you are in the same position as a REF take-off. Performing a REF take-off, your attention is probably going to be at a higher level. Which means that you might tend to forget about the static take-off, etc.


My personal conclusion is that I used to visualize my margin. For instance, if we were to take off from full length, I would calculate from an intersection. That was going to be my margin.

I also used to increase my assumed weight by two tons (5% for an RJ) so that if I ever was in a situation were we were balanced field or WAT limited, hence a decrease in assumed temperature, we would still have that margin to play with.

Furthermore, when the assumed temp would start decreasing for the actual weight, I used to calculate a "REDU" take-off power, which in the RJ is a 10% derate from REF.


That way everybody was happy, so was I, and we always new how big our margins were in case we needed them.

[tankdriver45]

Flex/Assumed/Derated:

Longer take off rolls =

More chance to hit birds, FOD, blow a tire
Less runway to stop in a reject
Gives pilots less reaction time to an event
More V1 -VR Spread
Further down runway, closer to obsticles
Less obsticle clearance on climb out

Fierce debate among pilots? You bet...when managment wants to put put people at risk to save a buck, not surprised that the smart pilots step up and say something...

[mutt]

I would guess that SSG, Angels 60 and tankdriver45 are all the same person :)

Mutt

[tankdriver45]

I would guess that maybe he cares about safety too...

Mutt..as to my identity...Guppy, the legend in his own mind, 135 air ambulance hack, is running around banning everyone that he doesn't like, that doesn't agree with him, or put's up a logical argument against his.

I wouldn't be here unless I thought the passengers at large might actualy benefit from these discussions, not to mention my own passengers...

Mutt, you have a brain, I can tell that..don't sell out...you want people in here that can run with you. talk the big concepts, advanced stuff...or this becomes a forum for your buddies, nothing interesting happens, no intelligent talk...no fun, nothing learned.

And if you didn't hear what I said, then no worries...I can come in here, time after time, after time, and basicaly bang the same drum...untill maybe someone listens...

[Brian Abraham]

I would guess that maybe he cares about safety too
That would be OK if he had one iota of knowledge about which he sprouts. He does get around. SNS3Guppy has his number.

You're flying a helicopter, now? You were a fixed wing captain with 10,000 hours and seven type ratings, flying a citation, and had just been rejected by Alaska airlines when you posted as ssg and then as Trickle451...both of your former identities which have recently been banned.

Now you're a helicopter pilot. Who'd have guessed?

[tankdriver45]

Brian.. I remember kids like you..in the sandbox...you wouldn't give me back my shovel, you grew up in a troubled home, nothing I could say would sway you..

So I went over and sat on your head, pushing sand into your mouth untill you cried for your mommy..lesson learned, and like Pavlov's dog every time you picked up a shovel in the yard or a fork at dinner, you remembered the taste of sand in your mouth. It's the only thing that works..

On the flight line, if you can't figure out what a helicopter does at high speed, you don't get the job...so it's back to Microsoft Flight Sim.

[BraceBrace]

95% of all takeoffs I calculate (737) are climb limited and I believe (correct me if I'm wrong) most twin engine commercial airliners are climb limited most of the time. NOT field limited so there's always extra runway to play with on the ground. You will hardly ever get a bigger V1/Vr spread, with V1 being fairly close to Vr.

The 146/Avro is 4 engined high wing, that's different but I would be surprised to see a short field performance jet being field limited on general commercial airports (not considering the exceptions of course). But I don't know the type.

Really, if you think reduced thrust takeoffs are too close to the limit, you haven't done any wet/contaminated/improved takeoff. With a wet or contaminated takeoff V1 is reduced (for a contaminated usually up to minimum control speed), and screen height at the end is reduced as well (35ft, not 50ft clearance).

Passing V1 on a reduced is relaxed, passing V1 on an improved takeoff makes you think and wonder is the aircraft is still capable to stop.

PS: improved takeoff is always full thrust by the way...

[F4F]

Well tankdriver45, Angels 60 and other SSGs, now having so convincingly proved your worth by showing the world (of PPRune) how safe your operation is, you surely won't mind sharing with us some other ways you "improve" the safety of your daily flying, will you, please, please (some ideas: mandatory 3 hours flight prep, 10T extra fuel each leg, lower FL to increase TUC, no flights if any risk of CBs or icing, increased DH/MDA for each approach, VMC only flying, HW only departures and arrivals etc, etc, remember those are only a couple of pointers :suspect:)


live 2 fly 2 live

[Denti]

Brace, think about improved climb performane. We use it pretty often now, but it is somewhat uncomfortable to learn since you get very high Vrs with usual V1s and rotations in the red lights are usual even on 4000m runways in lightweight 733/737-7.

However you actually increase safety that way since you have a much better initial climb performance and with usual V1 more than enough space to abort if you get any problems before that. We are still climb limited with it, but it allows us to carry several tons extra or reduce thrust even more.

[barit1]

GIV drivers, if they work for a publicly traded co., have some incentive to optimize costs. I know this from the local DJIA co. operations.

On the other hand, if a private company, often they have a freer hand to play with their toys - GIVs or bigger, mega-yachts, etc. I have a guess which category ssg etc. flies.

My 10R once went on busman's holiday in NZ - he said there's a substantial cottage industry in the City of Sails, doing home theatre installations in visiting mega-yachts! :)

[BraceBrace]

Denti, we only use the improved if we're climb limited and can't make it the normal way. But we don't reduce the thrust then, so there's some increased safety most of the time, I agree.

I've heard of airlines using improved as a standard, then of course you always have extra margin if you were climb limited. On long runways this creates indeed a big safety margin.

[Denti]

Yep, we're one of those, pilots discretion though. We can combine derate, assumed, improved climb and forward CG performance if we really want. On long runways that can get very weird results and ATC isn't really happy when we have a longer groundrun than a fully loaded A340.

[The Real Slim Shady]

Denti why would you try to use derate and assumed then improved climb????

Improved climb is used when you have excess TORA available and the higher speeds allow you to lift more weight, hence you wouldn't be assuming and the chances of derate would also be lower.

[Denti]

Well, yes, if you want to lift more weight. However if you have a given weight and want to use less thrust despite being climb limited improved climb is a way to achieve that. The downside is that you use a lot of runway and get very high Vr and V2 which in turns increase runway occupancy time considerably, hence ATCs dislike of that practice, especially on crowded airports. By the way, V1 is not higher than normal and can even be lower since Vmcg is lower due to a derated thrust setting.

[mutt]

I've heard of airlines using improved as a standardIts part and parcel of flying an Airbus...... Optimized V-speeds ....

Mutt

[PK-KAR]

F4F,
Me being away for a few days and he already got another user id and got banned too? I must have missed a lot.

I guess next, he would be arguing that the Brussels Kalitta is a case of dangerous derate! :ugh:

[Pugilistic Animus]

His deleted post from his banned personality should be a stick in JB---he now has me rolling;

RTO's after V1, but attempting to fly off BLO Vmc:eek::}
Decents blo MDA/H:=
and landing in the face of TS's:\

LOVIN IT:}

PA

[SNS3Guppy]

his imput has taken what is a very boring forum and made it very interesting? Don't you think?


No, that's why he was banned. His input contributed nothing.

You've very recently joined, I see...

[Pugilistic Animus]

I see Guppy got fooled again:hmm:

[SNS3Guppy]

He's a sly one, alright. Nearly as subtle as a wounded ox during mating season in a briar patch full of stinging nettle and horseflies. Nearly.

[PK-KAR]

Do I see SSG v4.0 ?
Interesting v4.0 joined as soon as v3.0 was banned.
And always links the current version with the previous ones.
Yes, it makes it interesting albeit frustrating and painful...
but after seeing the same patterns again and again, sorry, SSG, it's getting boring.

I guess this one has tooo much time on his/her hands... corporate or not, pilot or not.

I think someone should make a "Bad Flying Advise" series and shove what Ssg and his "successors" preaches there... well, it'll be bad advise for those who carry cattle class (aka cattle flyers aka SLFs) at the back.

PK-KAR

[White Knight]

Of course it's safe.... Purleez..