250 kts below 10000?

[airline man]

Hi all,

Was wondering if anyone had a good idea about the magnitude of fuel savings when an aircraft is allowed 'no speed restrictions' on departure and is allowed to immediately accelerate to the FMC recommended climb speed.

My question isn't aircraft specific but basically applies to anything equal to or faster than an A320.

I'd like to know if it's worth it to request ATC for a high speed climb or would it be better to just sit silent till 10000ft.

Thanks

[HPbleed]

Always worth asking, I don't know the specific savings - it would depend on when you got the restriction lifted etc but every little helps.

[ImbracableCrunk]

I had a few Korean CAs claim it was 3% for a short flight. I dunno where they came up with that number. Of course they thought I was crazy when I suggested they could save even more by doing visual approaches.

[irishpilot1990]

You are asking is it worth speeding up? But you focused only on the savings! Remember the actual reasons behind 250kts below 100!!

Bird strikes result in less damage at the slower speed.
If everyone is doing 300 kts ATC are more likely to miss their mistakes and ours.

Was the rule not originally brought in following a mid-air collision or a few near miss!?

I am interested to see a figure for the fuel savings though, i suspect they must be very small as the slower speed penalty may be countered by the higher ROC to higher levels.

[jimmyg]

The Climb is far and away the most fuel expensive phase of the flight and every effort should be made to optimize fuel use per mile in this phase.

Power increases linearly with speed. Ram recovery; the degree of compression is exponential to speed. At low speed numbers this compression is not very significant, but does partially compensate for 'Thrust Equation' losses. They are about equal at approximately M0.5 (250 Kt in ball-park figures). With further speed increase, the exponentially increasing ram effect exceeds the linearly decreasing 'thrust equation' effect, and at about M0.75, thrust is back to static thrust. Much more of the engine's internal power is now used to propel the exhaust gases, much less is used to drive the compressor. Above this mach number, net thrust can and does exceed static thrust. Ram recovery is an important factor and directly affects thrust. At a fixed engine setting, due to the effects of the 'thrust equation', thrust declines with increasing speed up to about M0.5, where the decline bottoms out and then, due to ram recovery, begins to rise again reaching parity with static thrust at about M0.75 and may exceed static thrust thereafter. If there were no ram recovery, jet aircraft would do no better than propeller aircraft.

The best rate of climb occurs at a speed where there is maximum excess power. As jet engines directly produce thrust, not power, it is necessary to consider thrust multiplied by speed (Power = Force X Velocity). Thus, for a given thrust setting, power increases as TAS increases. Thrust actually ‘dips’ as speed increases, but then there is significant ram recovery at higher mach numbers, thus further increasing Power at higher speeds.

I frequently accelerate 'slingshot' above the low altitude speed limit of 250 KIAS from 5000 feet instead of the ‘standard’ 10000 feet. For the A320, this repeatedly saves 100 Kg of fuel per SECTOR and that’s only over 5000 feet. The risk is nominal due to bird strike versus performance rewards.

[aterpster]

irishpilot1990:

Was the rule not originally brought in following a mid-air collision or a few near miss!?

1. December, 1960: UAL DC-8 plows into TWA Connie over Brooklyn at 5 or 6,000 while blowing a holding fix (one VOR inop) doing barbar pole or there abouts.

This resulted in 250 below 10,000 within 30 miles of the destination airport. No speed restriction on departure once clear of the ATA (now Class D). Also resulted in regulation to report to ATC any en route loss of navigation capability.

2. March, 1967: TWA DC-9-10 going on short range flight (KPIT to either KCMH or KDAY) plows into a Beech Baron at 8,000 while going barbar pole or there abouts.

This resulted in 250 below 10,000 at all times.

[jimmyg]

Opting for the lower speed, let's say 230 KIAS climb to allegedly reach higher levels sooner. At your CAS/Mach changeover height for 280/M0.6 at FL200 feet, TAS at ISA is 370 Kt. At 230 KIAS at the same level, the TAS is 306 Kt, some 64 Kt slower at the same fuel flow. My low CI friends will need to find 64 Kt of Tailwind that you don't have just to remain equal. In the reverse direction, flying into a headwind, the faster climb wins again, as a given headwind component has a lesser percentage penalty upon KNM per unit of fuel at high speed than at low speed.

[dhardesthard]

I understand that 250 kts below 10,000 ft is a law and ATC cannot approve it except in an emergency so if there is an incident you are held accountable if you were exceeding 250 below 10,000. When ATC approves high speed climb or descent below 10,000 ft all he is telling you is that there is no conflict with traffic.

[de facto]

frequently accelerate 'slingshot' above the nominal low altitude speed limit of 250 KIAS from 5000 feet instead of the ‘standard’ 10000 feet. For the A320, this repeatedly saves 100 Kg of fuel per sector and that’s only over 5000 feet.

Operating in Kuwait,the land of cheap gaz,and going non standard for 5000 feet of supposely fuel saving?:E
How did you calculate this 100 kgs saving over 5000 feet between 250kts and your 'slingshot' higher speed?:suspect:

Speed range of 260-280kts save fuel on 320 but not on heavier types such as 330s...higher speed then save fuel..

My low CI friends will need to find 64 Kt of Tailwind that you don't have just to remain equal.

Your cost index friends may just following speeds that their relevant performance officers calculated to be the most 'appropriate' for that flight,using factors that you may not have necessary data or knowledge about.

[10W]

I understand that 250 kts below 10,000 ft is a law and ATC cannot approve it except in an emergency so if there is an incident you are held accountable if you were exceeding 250 below 10,000. When ATC approves high speed climb or descent below 10,000 ft all he is telling you is that there is no conflict with traffic.

Depends in which States airspace you are flying. It is legal in many places.

[ed1016nw]

Flying out of Dallas one is told to "go fast" as often as not, I think they want you out of their space ASAP

[FlightPathOBN]

There are getting to be more and more restrictions, or planned restrictions on departure speeds.

With an increased effort on throughput, departures are happening at reduced time separation, but then the ac are piling up and violating distance separation.

The solution is looking at more speed restrictions for the departures, if they cannot have a diverse departure path...

[ImbracableCrunk]

Boeing FCTM says ECON with no restrictions saves gas.

Couldn't this be tested on the ground by checking the fuel req'd in both conditions?

[McBruce]

According to Boeing performance manual based on 737-800 CFM56-7B26:

Trip fuel and time charts are based on an initial climb speed of 280 KIAS. Local ATC may require that 250 KIAS not be exceeded below 10000ft. Approximately 25kg of additional fuel is burned when this restriction is imposed.

[jimmyg]

At any time that ANY aircraft conducts a climb at less than, or more than, optimum range climb speed you will consume more fuel. This speed is typically slightly higher than best Rate of climb speed, and significantly higher than the best gradient speed.

The best Rate of climb can be refined further to optimize time and fuel. Remembering that up to 20 to 30 Knots off optimum will have only minimal effect upon excess power. An econ climb speed a little above best rate will have a negligible effect upon rate of climb, but put the aircraft 30 miles or so further down track at top of climb. The very slight increase in climb time and fuel is more than off-set by the extra distance covered in the ‘fuel expensive’ climb, and elimination of the incremental cruise.

Operation cost equations vary from organizations but are most always benefited by a time reductions. Low cost indices in many cases are opted for based purely on face value of misinformed accountancy rather than laws of physics and cost factors.

[de facto]

Low cost indices in many cases are a function of misinformed accountancy rather than laws of physics.

What are you smoking?
Tell that to Airbus....

An Airbus 320(that s what you fly?) will burn 45kgs more flying at 320 kts than 280 kts for a constant climb to FL350.

[jimmyg]

If you care to have a informed intelligent conversation rather than a childlike self depreciating " what are you smoking" Then I do not care to partake.

In all engineering endeavors, nothing proves the laws of physics and mathematics more succinctly than does the jet airplane.

I find it intriguing though, for most of us who don't have too high an opinion of our innate knowledge start off knowing nothing. A year or two later and with a few hundred hours, know that we know everything and then spend the rest of our careers coming to realize just how little we really do know.

Learning commences with humility.

[de facto]

Learning commences with humility.

True and by reading..

Here is a good start pointer, google airbus 'getting to grips with fuel economy' and airbus 'getting to grips with cost index'


The smoking thing was light hearted comment not meant to be pejorative.

[framer]

Irishpilot talked about a higher rate of climb to cruise altitude at 250kts. Thats not accurate. Best rate of climb will be above 250kts in most airliners. If you want to save gas in a 737 you accelerate low (ie 1000ft) and you accelerate to best rate (about 280kts). You'll save about 10kg by accelerating NADP2 instead of NADP 1 and you'll save about 25kg by going straight to best rate. (Boeing info as best as I can recall).
SR 22 talked about cost index flying resulting in low climb speeds anyway..... Thats not accurate. Cost index zero will give you the least fuel burn, which is the best rate, which is well above 250 kits .
If you really want to be efficient you'll depart with the least flap possible and accelerate to best rate of climb as low as you can. There will obviously be slight adjustments for head and tail winds but that's the guts of it.

[de facto]

Irishpilot talked about a higher rate of climb to cruise altitude at 250kts. Thats not accurate. Best rate of climb will be above 250kts in most airliners. If you want to save gas in a 737 you accelerate low (ie 1000ft) and you accelerate to best rate (about 280kts). You'll save about 10kg by accelerating NADP2 instead of NADP 1 and you'll save about 25kg by going straight to best rate. (Boeing info as best as I can recall).
SR 22 talked about cost index flying resulting in low climb speeds anyway..... Thats not accurate. Cost index zero will give you the least fuel burn, which is the best rate, which is well above 250 kits .
If you really want to be efficient you'll depart with the least flap possible and accelerate to best rate of climb as low as you can. There will obviously be slight adjustments for head and tail winds but that's the guts of it.


Agree,just that CI does not account for winds during climb and descent.The ECON speed is a speed where from the start of the climb segment to a point into the cruise segment,the cost of fuel and time cost is minimized.
To save a tad more,max rate speed can be used,a speed dependent on weight.
Accelerating early (800ft) NDP2 will obviously reduce fuel burn as drag is reduced earlier and speed increased.

[NARVAL]

Reading the comments on this subject, I realise that many captains are now very decided to save some pounds of fuel at all costs. Accelerating like a slingshot...sent a shudder through my old spine. Reminds me of gung-ho captains in my company who kept more than 300 knots until interceepting the localizer, when the controller agreed, "to save time for the company"...then would wait twenty minutes for the stairs to reach the aircraft because they were early at the block...
More important...Va is 250 knots on the A320 (or was in my days) and above VA...you do not have full deflection of the ailerons and spoilers...you have a reduced rate of roll to protect the airframe...if any strong avoidance tactics should be needed, you might hit the intruder...45 or 60 pouds of fuel lighter.But managers talk about saving fuel, so let us forget it...

[737Jock]

Narval, that is only valid for:
If alternate or direct law is active, full ailerons and rudder application should be confined to speeds below VA. If alternate or direct law is active manoeuvres involving angle of attack near stall should be confined to speeds below VA.

And

(Applies in alternate or direct flight control laws only).

The speed you quote is also incorrect!

FCOM LIM-13

[sudden Winds]

it's 25 kg in a 737NG. A bird strike at 300 kts is a bit more expensive than 25 kg of fuel. Having to pull 3 g to avoid a lost piper cub at 3000 ft and 300 kts is not good either.

Want to save fuel?

-ask your dispatcher to make sure CG is not too far forward.
-takeoff with less flaps, conditions permitting.
-keep airplane's takeoff config for early turns after takeoff, or flaps up speed for big turns after accel ht.
-do not use reduced climb.
-ask for off airway direct routings, if possible and safe.
-use a-p
-keep airplane properly trimmed, especially rudder.
-make good use of engine anti ice.
-use fmc computed speeds for the majority of the time.
-give the fmc as much info as you can, regarding temp and winds.
-make sure you've entered the correct CRUISE CG, so that your speed tapes display correct maneuver margins AND MAX ALT is not erroneously low, we've got ex Easy Jet 737NGs and it seems CAA requires a default value of 8% CG in perf init. I keep changing that, but some pilots disregard that completely.
-During cruise, use the recirc fan even if it´s noisier (I do not comply with this one in the older ex Virgin Blue planes that don´t have the vortex generators).
-try to stay within +/- 1000 ft from optimum alt.
-Use delayed flap approach whenever possible.
-Use flaps 30 for landing.
-Make a correct use of thrust reversers.
-shut down one engine for long taxiing after cooling, conditions permitting.
-make a good use of apu.

[exeng]

Please don't post the obvious.

Apart from the rediculous such as do not use reduced climb.

Reduced climb saves engine turbines at the lessor expense of fuel - thats why all airlines do this.

As for make good use of engine anti ice, what do you think most Pilots do - select it because they feel like it.

And Make a correct use of thrust reversers

Well I use idle or a reverse N1 that is comensurate with the prevailing landing conditions - that is what all Pilots are trained to do.

As for keep airplane properly trimmed, especially rudder. We are talking about Pilots are we not?

And [QUOTEmake a good use of apu]/QUOTE]. Good one that - delay the start on the taxi in until the last possible moment - then a distraction and I wait at the gate with an engine running till the gen is ready - been there so many times.

Keep it simple and there is just a small chance you may personally survive.


Regards
Exeng

[Sciolistes]

If you really want to be efficient you'll depart with the least flap possible and accelerate to best rate of climb as low as you can.
As expensive as fuel is, it seems engines are more so. Hence we are now using fixed derates, assumed temps and flap 1 takeoffs with non balanced calculations as much as possible which probably burns considerably more fuel for takeoff and climb.

[sudden Winds]

Exeng,

I will explain what I meant because it's OBVIOUS you didn't understand.

I was mentioning aspects that WILL help save fuel, but never said that those needed to become policies or were always the best courses of action.

1) reduced climb. If for some reason your estimated fuel on board on arrival is too close to reserve+alternate, that's one thing you can do, especially if flying with a tailwind.

2) you and probably everyone else in the airline you work for are perfect (except for forgetting to start the apu on time, according to your confession) but here in imperfectland I've seen improper use of engine (and wing) anti ice repeatedly.

Examples...keeping it on when OAT is less than -40°C during climb and cruise with no thunderstorms around AND failing to enter the altitudes for TAI ON and OFF in the forecast page. That DOES increase fuel burn.

Regarding the -40°C criteria, of course I don´t just automatically turn it off when OAT says -40.0001°C but I noticed pilots still using it while riding inside harmless cirrus with OATs well below -40°C. There's a reason for NOT using engine anti ice with OATs below -40°C.

4) APUs. We fly into a few airports where taxi times can be as much as 20-30 minutes after landing. During THOSE operations what I do is I tell my first officer WHERE we will start the apu. I use a location during taxi where I am a few minutes from the gate, I can still ask for a GPU if an APU fails to start and of course the apu will be started and transferred well before engine shut down (you may want to try this:} yourself) From my experience, B737NG APUs are extremely reliable and after a little over a year flying the NG I can remember one time when an APU failed to start. I do not combine engine out taxi WITH an apu still off tho.

You see the company I fly for is in the process of developing fuel saving procedures, but in the meantime I use my own as nothing has been written otherwise.

Next time you contact me spare me the dos and don'ts, will ya Mr Perfect?

[Denti]

@Exeng, reduced climb thrust doesn't really save any engine wear and therefore maintenance cost. Reduced take off however does. At least thats what boeing tells us, not to mention our own 15 years of experience operating the NG. Therefore we reduce the take off thrust as much as possible using both fixed derates and assumed temperatures for the last 10 or so years, however once we get an unrestricted climb clearance or at airports where it is given on the ground we select unreduced climb thrust manually. It is nice to get a load of additional thrust at climb thrust reduction and climb out of the "dangerous" below 10.000ft environment in 2,5 minutes.

Anyway, over here there is no speed limit below FL100 if one is within a class C airspace.

[FlightPathOBN]

Anyway, over here there is no speed limit below FL100 if one is within a class C airspace.

Denti, that is being looked at as we speak. On runways where there is no ability to have diverse departures, in order to increase capacity, there will be speed restrictions on departures.
This is to prevent the aircraft from running up on each other, to maintain min separation.

[LeadSled]

Folks,
For those of you operating in US airspace, read the "250Kt" rule carefully. ATC cannot ( unless it is one of the special trial airspace areas) give you a clearance to accelerate past 250, below 10,000.
However, the rule gives the PIC the authority to exceed 250 if he has a good reason for doing so.
What might that be?? For example, most aircraft with flaps out have a negative G limit of 0/zero, and there is no shortage of types where the minimum flaps up speed and turbulence penetration speed is well above 250 kt.
Most of the rest of the world can give you clearance to exceed 250, where it is an ATC restriction, not a statutory restriction.
Tootle pip!!

[bubbers44]

I was on an FAA check ride once when the controller said expedite to 9,000 ft so said when I slowed to 250 I would descend because he had traffic crossing at 10,000 ft ahead of us. Using full speed brakes was able to descend about 5 miles later but told the FAA guy, only the administrator can authorize over 250 below 10, not ATC. Any other time I would have done it. We were in the clear so was just protecting my license. I hate it when you have to do stupid things because you have to stay legal.

[GlueBall]

only the administrator can authorize over 250 below 10, not ATC.

...How about technical necessity, like 265Kts for zero flaps speed, or do you think that I will be dragging flaps to 10,000 feet? :ooh:

[bubbers44]

No, that would be minimum maneuvering speed which is authorized as covered in a previous post. I have had to use that speed in a 767 heavy a few times. You obviously don't leave flaps out to maintain 250 knots. The captain is authorized to use that higher minimum speed to operate his aircraft properly.

[aterpster]

bubbers44:

No, that would be minimum maneuvering speed which is authorized as covered in a previous post. I have had to use that speed in a 767 heavy a few times. You obviously don't leave flaps out to maintain 250 knots. The captain is authorized to use that higher minimum speed to operate his aircraft properly.

Indeed, it is done all the time, but only at a relatively small number of airports that have large airplanes and long range flights.

[NARVAL]

737Jock replied:
only in alternate direct law...
Thank you for your answer (except when you tell me the speed I quote 250 is incorrect...let us not split hairs, if it is 249 or 251, we are talking here of exceeding or not 250 knots at low altitudes)
There is something that escapes you, it seems to me. In alternate direct law ONLY, you have to respect the manoeuver speed by applying careful inputs on the stick.You are right there.
In normal law, do you believe for one moment that such a sophisticated airplane will let you violate the manoeuver speed and give you 25° deflection of ailerons at 300 knots? In normal law the plane looks after itself,, as flight control normal laws (I quote) covers "alleviation of manoeuver loads". Sorry to disagree with you on that subject, I remember au French BEA report, about a near midair where an A320 was implicated, and which said that due to its speed of 250 the pilot was able to fully deflect ailerons and spoilers. I shall try to find it, if you are interested.

[misd-agin]

767-300 at our max T.O. wt had a flap retract speed of 256kts. That was your clean min manuever speed and the speed you flew in the U.S.

Former 747 pilot told me their min man. speed was around 270 kts when heavy.

[737Jock]

Narval, the speed varies from 250 kts (10000ft) down to about 248 on a319. On A320 it comes down from 260kts to about 256kts.

No I do not think the aircraft will give full control deflections. It will give maximum flight envelope performance in normal law.

I am not disagreeing with anything just providing the correct references.

[exeng]

Apologies if I struck a nerve.

Your point: 1) reduced climb. If for some reason your estimated fuel on board on arrival is too close to reserve+alternate, that's one thing you can do, especially if flying with a tailwind.


Sorry but I disagree. If short in fuel then climb at max climb power and you will reduce overall burn at the expense of the engine hot end.

Your other point: Well thanks for the compliment but I don't believe any of us are.

Regarding the -40°C criteria, of course I don´t just automatically turn it off when OAT says -40.0001°C but I noticed pilots still using it while riding inside harmless cirrus with OATs well below -40°C.

Very good - you are correct to notice that.

Another point of yours: AND failing to enter the altitudes for TAI ON and OFF in the forecast page. That DOES increase fuel burn.

How would you measure that? Scientifically I would doubt you have ever had the means to carry out a proper statistical study based on your assumption. Regardless of what is entered in the FMC the outside conditions are the outside conditions that exist. The FMC is just another instrument to help us manage the flight - entering this altitude or another for A/I on or off is irrelevant. Just my opinion..... We used to fly the 737-200 which had no FMC but somehow we managed.

By the way I never tell my F/O where we will start the APU because I will not insult the intelligence of my colleagues - they know what is the best option for the airfield. Occasionally they have got it wrong in and I have failed to notice.

I've tried to leave out the 'do's and don'ts' and hope that my reply leaves you feeling that I have treated you with the respect that you and everybody else deserves.


Regards
Exeng

[framer]

The FMC is just another instrument to help us manage the flight - entering this altitude or another for A/I on or off is irrelevant.
It´s not really irrelevant and I think you´l find Sudden Winds is probably correct, that it saves fuel (although probably not much). It wouldn´t save fuel if you were in a mode other than VNAV, but lets face it, most aircraft leave their cruise altitude in VNAV.

[de facto]

Regardless of what is entered in the FMC the outside conditions are the outside conditions that exist. The FMC is just another instrument to help us manage the flight - entering this altitude or another for A/I on or off is irrelevant. Just my opinion
As Framer said,VNAV profile will be more accurate with proper data entered in the descent page of the fmc,including TAI on OFF.
EXENG,you must be aware of the N2 increase with EAI ON ,which means your idle will be higher hence adescent should be started earlier...if you delay the descent your fuel burn will increase for a fixed CI.
Same without fmc,youd have to increase your speed to to increase rate of descent if you selected tAI On,,maybe not by much,,but all counts ,even QNH setting in the descent page.
By the way I never tell my F/O where we will start the APU because I will not insult the intelligence of my colleagues - they know what is the best option for the airfield
You should have SOPS for that,no?

[ozgun]

İ am so sorry because i couldnt search the forum and i am in the middel of my flight . İ am wondering in an ils approach you are approaching vor and the minimum altitude is 9000 feet but in fms says 9000 feet or above , some pilot says you must cross vor at 9000 feet but fms says you can cross above this altitude, in jeppesen or somewhere is it written like you can cross above ?? İf you find this i will forward to my company . Thank you and sorry for the not searching

[onprofile]

Its all academic what the fuel savings are if any. Just remember how your airline management will factor it into your next pay cut. Fly safe.

[exeng]

Yes you are correct in respect of entering predictions for anti-ice use in the FMC. If your predictions are correct then you will save fuel. So I stand corrected.

Regarding APU use after landing - yes we do have SOP's but they are vague in wording. The essence of the wording is that APU starting should be delayed if a long taxi is expected.


Regards
Exeng

[Young Paul]

Save more fuel by having the APU running instead of an engine for a long taxi ... to or from the runway ... *ducks*

In the air, high speed also means that turns have larger radii, so if there are significant turns, that can represent a fuel penalty.

If you are stuck at (say) 6000 feet, to clear the stack of another airfield, then accelerating may not only save you time but also get you out of a controller's hair more quickly, which may please him/her.

[sudden Winds]

Exeng,

Fair enough.

Regarding how to guess cloud thickness what I do is I obtain a thorough weather briefing and I look at charts and satellite imagery. That gives me an idea. Is it always perfect? Of course not, but by doing it frequently I am able to obtain some good results every now and then.

The APU thing...let´s see. Long taxi routes with frequent stops. 20 to 30 minutes to the gate. Normal Procedure is to start the apu as soon as active rwy vacated. What I do is I tell my first offcers that we are NOT going to do that, but instead we are going to start the APU when joining GOLF (for example). That is a few minutes from the gate just in case. It serves two purposes, economy and ecology. So far no one has felt insulted.
Exceptions to that apu start delay thing that I do...
1. If the aircraft is rather light (around less than 55 tons in a 700, other conditions such as airport elevation, temperature, slope not conspiring) I turn on the apu and shut down one engine, after 2-3 minutes.
2. Extremely hot weather, long taxi, apu comes on, isolation valve closed, left engine bleed air switch off, apu bleed air switch on, for cooling.
If I have time and some minivolts are still energizing my brain, I try to think of those things.....those things in the back, called passengers.

Regards,
SW.

[james ozzie]

I really appreciated your simple outlining of the ram recovery and thrust equation story in your posting #6.

It reminded me of a particularly bruising and at times nasty debate in this forum a few years back, concerning thrust loss of jet engines at inceased speed.

I think this posting now of yours would have ended much of the arguing at that time.