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Topic Author
Posts: 2
Joined: Tue Apr 21, 2020 3:18 pm

### Throttle/Thrust Settings, How's It Work?

Forgive me for being a complete fetus in the aviation world, but I was hoping for some light on these topics.

1. Is there more than simply pushing the throttle to the desired power to takeoff, or anytime else? I thought you calculated how much thrust you'd need, and then you'd push the throttle to that level to takeoff. If the throttle does not directly equal power output at all times (which I think would be dumb), is there a setting that can allow for that to be the case?

2. How much flexibility do you have with power and climb rates? If you have a "lead foot", can you err on the side of faster acceleration and more power if you want? Can you use maximum power if you want, even if it's not required?

3. Are there any specific airports or runways that generally require maximum thrust and/or a steep climb rate at takeoff, so you'd know for sure planes would be operating full performance there?

4. If you wanted to, could you fly, or plan to fly, at near maximum climb rate for a significant portion of your ascent to cruising altitude? Who decides that?

5. At cruising altitude, are you always flying at your maximum cruising speed? If not, why not? If the reason is fuel, who cares? Do airlines keep track of which pilots have a heavy foot and which do not?

Thank you for this. I've done lots of reading and haven't been able to really figure these things out clearly. I appreciate it!

Woodreau
Posts: 1971
Joined: Mon Sep 24, 2001 6:44 am

### Re: Throttle/Thrust Settings, How's It Work?

Hello and welcome to a.net

1. For most airliners today, there is no physical connection between the thrust levers and the engine. There is a computer called a FADEC that controls the engine, the thrust levers are an input to that computer. The FADEC does the "magic" and does the minutiae of operating the engines that used to required the flight engineer to do. There are several settings on the thrust lever quadrant, one is a MAX setting which commands maximum thrust for the given conditions, a MCT/TO setting (setting for takeoff and maximum thrust setting for One Engine Inoperative), and a CLB setting (maximum for cruise flight) and a variable setting between CLB and IDLE. So for takeoff, you just push the thrust levers up two clicks. First click is the CLB detent, the second click is the MCT/TO detent. different airplane call these different things.

2. For takeoff the required performance is calculated and set in the FADEC, and normally takeoff thrust is derated to meet all of the required climb performance for the runway, airport, and atmospheric conditions at the calculated takeoff weight for the aircraft. If the thrust is derated, there is always the option to use MAX takeoff power at any time, and there are several times where you may only use MAX takeoff power (contaminated runway, windshear conditions, etc)

3. Yes. For different parameters of runway, atmosphere, engine bleed air usage, the weight of the aircraft and the payload, we'll get the "numbers" and there will be a weight associated with those numbers. As long as the aircraft weight is below that weight, the aircraft will meet the minimum climb requirements.

4. For climb, you normally set the thrust for maximum climb, setting the thrust levers to the CLB detent which is the maximum thrust available for climb and adjust the pitch to control the plane's airspeed or vertical speed. You normally don't vary the thrust for climb.

5. There is a planned cruise speed. and for the most part. I believe most crews just fly the flight planned cruise speed. There are some pilots that fly at max speed - if the speed deviates from the filed flight plan speed by more than 10% you're technically supposed to notify ATC. . ATC can always ask us to fly a specific speed or mach number for whatever reason, usually for sequencing. Some airlines do have a "fuel" score (my last airline did), but the current airline I fly at no one keeps track of how much fuel a pilot "uses"
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.

Posts: 3264
Joined: Sat Aug 24, 2002 11:41 am

### Re: Throttle/Thrust Settings, How's It Work?

Depends a lot on type of engine...

Pistons:
- A basic piston engine with a fixed pitch prop you'd typically be using RPM as a power setting and that's that, keep an eye on temperatures and things but RPM is your main setting. Throttle is your main engine control and directly affects RPM.
- A step up from that would be a piston with a constant speed prop, in which case you are using a combination of RPM and manifold pressure, if anything more manifold pressure. The aircraft I fly the checklist calls for basically a takeoff, climb, and cruise RPM, (back to takeoff setting on short final to be ready for a go around), and beyond that all of the actual power settings are done on the manifold gauge. You have two controls, a prop lever which will change your RPM and a throttle which will change your manifold pressure. Takeoff in that airplane calls for full power (everything full in unless you hit redline first), cruise power varies quite a bit depending on what yer doing. Trying to get somewhere I'll be at the higher end for a good cruise speed, if I'm just checking out some scenery or scouting out a trail for later I'll be throttled back quite a bit as slower is a better view and also keeps closer to the recommended maneuvering speed for tight turns and any surprise turbulence.
- More complex pistons with turbochargers and/or superchargers are similar to the regular constant speed prop, except temperatures can be a bigger deal on some of those to the point where sometimes temperatures can be your limiting factor.

Turboprops:
- Turboprops that I've experience with are two ways, first one is the old school dart with which what would be your "prop lever" just has three gated settings, feather, off, on. Normally just used to turn the engine on and off. The other is the throttle, which is connected to both the fuel control unit and propeller control unit on the engine and the propeller self governs to match the desired power setting. To operate that they look at RPM, Torque and temperatures. Takeoff they go full throttle and look for full RPM and at least x PSI of torque, then throttle back slightly to a lower RPM for climb, and then cruise they do an initial setting and then fine tune for temperatures.
- Newer ones I've worked on are similar, except you have a throttle and a propeller lever. Throttle is your power setting, propeller is your RPM setting. Usually RPM and torque you are setting a given % on each while keeping temperatures need to stay within a certain range.

Jets
Never worked on turbojets, but I know turbofans work in thrust. Main control is the "power lever" (at least in Boeing language).
- How you set power depends on the engine, example JT8Ds they were all over the Engine Pressure Ratio as a key measurement, the CFMs that measurement doesn't even exist to the pilots.
- The CFMs your main indications you'd be looking at are N1 % (front fan RPM), N2 % (engine core RPM), and EGT (exhaust temperature). Basically set power using your N1, then make sure the resulting N2 makes sense and EGT is within the proper range for that setting.
- Most newer turbine engines the power lever is connected only to a computer (Full Authority Digital Engine Control - FADEC) which then controls the engine.

_____

1. Is there more than simply pushing the throttle to the desired power to takeoff, or anytime else? I thought you calculated how much thrust you'd need, and then you'd push the throttle to that level to takeoff. If the throttle does not directly equal power output at all times (which I think would be dumb), is there a setting that can allow for that to be the case?

Yes.
- Some engines/aircraft say use full power (typically props), but when you do so you still have to ensure you don't go past red lines.
- Aircraft with a throttle and a prop lever make sure you have the prop set full fine before you punch full throttle, it can and probably will get very expensive very fast if you don't.
- Turbofans in airliners they do figure a power setting before they go. Everything that goes into it is a little beyond my pilot's license but there is a calculation they do, and usually in an effort to save fuel and maintenance if you aren't full max weight and are on a long runway the setting will be quite a bit less than full power. Why burn out the engine faster if you really don't need it.
- Usually you do set all of your engine controls to a normal takeoff position, and then use the throttle to directly control power.

2. How much flexibility do you have with power and climb rates? If you have a "lead foot", can you err on the side of faster acceleration and more power if you want? Can you use maximum power if you want, even if it's not required?

Quite a bit. Load, terrain, traffic, atc requests or restrictions, weather, schedule, mission, and a million other things will all be considerations when setting power in flight.

3. Are there any specific airports or runways that generally require maximum thrust and/or a steep climb rate at takeoff, so you'd know for sure planes would be operating full performance there?

For the big turbofan airliners most takeoffs are reduced thrust, but not uncommon for airports with short runways and hills to climb over to have full throttle takeoffs. Dawson City is 5000' with a hill on all four sides so the 737s coming and going there are pretty much always full thrust takeoffs. Up until about this time last year it was gravel too, I can still hear that JT8D crackling roar echoing down the valley for 10 minutes after departure, anyways.

4. If you wanted to, could you fly, or plan to fly, at near maximum climb rate for a significant portion of your ascent to cruising altitude? Who decides that?

Yes, but you'd burn more fuel and wear out your engines faster. Who decides entirely depends on the operation. Owner flying a private airplane doing what they want, small outfit pilots using judgement, big outfit following standard procedures, could be lots of things.

5. At cruising altitude, are you always flying at your maximum cruising speed? If not, why not? If the reason is fuel, who cares? Do airlines keep track of which pilots have a heavy foot and which do not?

Usually not. You can, but again you'd be buying more fuel and overhauling your engines more often. Usually they are closer to an economical cruise speed. Private pilots are a surprisingly cheap bunch, and usually want to enjoy the scenery anyway. Commercial operations exist to make money, and saving fuel will help accomplish that.
HS-748, like a 747 but better!

bhill
Posts: 1877
Joined: Thu Sep 13, 2001 8:28 am

### Re: Throttle/Thrust Settings, How's It Work?

..as a follow on, for FADEC implementations, do all the parameters need to be manually entered, like atmospheric conditions, aircraft weight, etc? Or are there sensors on the LG for weight/mass and weather sensors that feed the data directly into the FADEC?
Carpe Pices

mxaxai
Posts: 2059
Joined: Sat Jun 18, 2016 7:29 am

### Re: Throttle/Thrust Settings, How's It Work?

bhill wrote:
..as a follow on, for FADEC implementations, do all the parameters need to be manually entered, like atmospheric conditions, aircraft weight, etc? Or are there sensors on the LG for weight/mass and weather sensors that feed the data directly into the FADEC?

Manually. Usually there's a database for airport information (runway length etc.) and some systems can receive data like flight plans or weather from external sources.

On this particular aspect, the weight on the gear changes when wind blows around the aircraft. Weighing aircraft is a relatively rare event that's done in hangars, to control the test environment.

Topic Author
Posts: 2
Joined: Tue Apr 21, 2020 3:18 pm

### Re: Throttle/Thrust Settings, How's It Work?

Great replies, thank you! FYI, I am more interested in commercial airliners, the big boys.

Tell me pilots, does the throttle lever, with its settings at intervals with no change in between, going to a computer to decide, doesn't that take the fun away? I used to love the quote about racing car drivers, when someone would suggest their car was the fastest and that's why they won, that it's not because of that, "it's the driver in the driver's seat doing the driving." I personally hate how modern cars don't have a direct throttle hookup to the butterfly valve. You hit the gas and then a computer decides everything, from the gear to the gas... and usually it's not what I want. I drive a manual transmission from the 90s solely for those reasons. I know that piloting an a350 isn't a race, but you didn't sign up to be computer technicians, right? You signed up to fly airplanes. Yes, you're in "control", but you're not in control in the moments you would want to be. It seems like at least.

I want to clarify that when I was referring to being able to use full thrust whenever you wanted it, what I meant was, could you use maximum takeoff thrust even if conditions didn't require it? Just because you wanted to? And what about during the climb, or at altitude, can you still get the maximum takeoff thrust then? Could you climb for a period at maximum takeoff thrust if you wanted?

What if, for example, you saw there were a lot of plane spotters out watching you prepare to takeoff. Could you do a full power, steep climb out of there to give them a show? Thanks all.

Starlionblue
Posts: 20193
Joined: Fri Feb 27, 2004 9:54 pm

### Re: Throttle/Thrust Settings, How's It Work?

Forgive me for being a complete fetus in the aviation world, but I was hoping for some light on these topics.

1. Is there more than simply pushing the throttle to the desired power to takeoff, or anytime else? I thought you calculated how much thrust you'd need, and then you'd push the throttle to that level to takeoff. If the throttle does not directly equal power output at all times (which I think would be dumb), is there a setting that can allow for that to be the case?

2. How much flexibility do you have with power and climb rates? If you have a "lead foot", can you err on the side of faster acceleration and more power if you want? Can you use maximum power if you want, even if it's not required?

3. Are there any specific airports or runways that generally require maximum thrust and/or a steep climb rate at takeoff, so you'd know for sure planes would be operating full performance there?

4. If you wanted to, could you fly, or plan to fly, at near maximum climb rate for a significant portion of your ascent to cruising altitude? Who decides that?

5. At cruising altitude, are you always flying at your maximum cruising speed? If not, why not? If the reason is fuel, who cares? Do airlines keep track of which pilots have a heavy foot and which do not?

Thank you for this. I've done lots of reading and haven't been able to really figure these things out clearly. I appreciate it!

The following applies to airliners.

1. Yes there is a lot more than just pushing the thrust levers to the detent, but importantly it all comes before that action. Once you say "takeoff" and push the thrust levers up, all the calculations have already been done, which is why it seems deceptively simple.

A takeoff calculation is done (paper, ACARS to central computer, or EFB) based on weight, runway and environmental. This spits out thrust setting (derate, flex/assumed temp, or TOGA), v speeds and flap setting which are then entered in the FM. When the thrust levers are set to the appropriate detent, FADEC will set the demanded thrust level.

Manual thrust is always available. Sometimes it is the only thing available if autothrust is inop. For take-off, though, you'd always set it to either TOGA or derate/flex. It is the only way to ensure desired performance.

The thrust levers position is not directly proportional to thrust, because jet engine thrust is very far from linear to fuel flow (and thus mass flow). For the sake of the exercise, if we assume that thrust lever angle is proportional to fuel flow, the top 20% of thrust lever travel would probably give you more than 50% of the thrust variation.

2. Climb rates and thrust. Airliners typically climb at a fixed thrust setting, either max climb thrust or a derated climb thrust. By varying the speed, we can vary the climb angle and rate. For example if there is a minimum altitude close in, we would climb slower than normal, giving a steeper climb angle. It isn't quite as simple as just slowing down, though. Minimum speed, best angle of climb speed, and best rate of climb speed increase with altitude, so you have to be careful not to paint yourself into a corner, so to speak.

("Fixed thrust setting" isn't strictly true, because available thrust decreases with altitude, but FADEC handles that so it is transparent to the pilots.)

3. Certainly some airports will typically require higher thrust setting than others. Shorter runways and/or close in obstacles, require higher takeoff thrust settings. And some airports with very rough runway surfaces might have "minimum ground roll" calculation options that shortens the takeoff run. However, takeoff performance is calculated for every takeoff and varies widely. 20 tons weight more or less, or 10 knots of wind, will make a massive difference to performance numbers.

It isn't just thrust that varies. It is also flap setting. While on the 330 we typically use Flap 1, if the runway is short we might use flap 2 or even flap 3. In general, more flap gives a shorter takeoff roll, but worse initial climb performance.

4. In many places, climb restrictions, either charted or instructed by ATC, force tactical decisions on climb angle. We also often change climb rate to avoid triggering TCAS advisories, or to get above clouds that cause turbulence. Given no restrictions, we could choose to climb faster than "optimal", but since optimal is what the plane thinks is most efficient, that is what we should be doing. We work for a commercial operation, after all.

The saying for what to do in case we have a tight climb constraint goes "negotiate, decelerate, derate". First, negotiate with ATC to see if they can give you something less restrictive. If you can't, decelerate to increase climb angle. And if you can't do that either, remove the derate. Efficiency is key.

5. We almost never fly at max cruise speed. If we did, we would often find ourselves with too little fuel to get to the destination. The cruise speed on the day is dictated by the cost index, a number which represents the tradeoff between fuel and time. The lower the cost index, the less fuel we use and the slower we fly. However, slower means longer flight, meaning more time on the engines and airframe, more hours paid to the crew and so on. The cost index is set based on complex cost calculations on the day, and printed on the flight plan. We sometimes tactically deviate from the cost index, for example if we get a time constraint from ATC, but normally just stay on it.

Does the company keep track of cruise fuel consumption? Not at the captain by captain level, I think, but since fuel is the biggest cost we have, it is certainly a focus of attention. Again, we work for a commercial operation, so we take pride in being efficient.

Great replies, thank you! FYI, I am more interested in commercial airliners, the big boys.

Tell me pilots, does the throttle lever, with its settings at intervals with no change in between, going to a computer to decide, doesn't that take the fun away? I used to love the quote about racing car drivers, when someone would suggest their car was the fastest and that's why they won, that it's not because of that, "it's the driver in the driver's seat doing the driving." I personally hate how modern cars don't have a direct throttle hookup to the butterfly valve. You hit the gas and then a computer decides everything, from the gear to the gas... and usually it's not what I want. I drive a manual transmission from the 90s solely for those reasons. I know that piloting an a350 isn't a race, but you didn't sign up to be computer technicians, right? You signed up to fly airplanes. Yes, you're in "control", but you're not in control in the moments you would want to be. It seems like at least.

I want to clarify that when I was referring to being able to use full thrust whenever you wanted it, what I meant was, could you use maximum takeoff thrust even if conditions didn't require it? Just because you wanted to? And what about during the climb, or at altitude, can you still get the maximum takeoff thrust then? Could you climb for a period at maximum takeoff thrust if you wanted?

What if, for example, you saw there were a lot of plane spotters out watching you prepare to takeoff. Could you do a full power, steep climb out of there to give them a show? Thanks all.

I can only speak for myself but it does not take the fun away. Jet engines are finicky beasts, and before FADEC a flight engineer was needed to take care of them. FADEC is magic and should be worshipped.

As airline pilots we have a duty to the bottom line. We can't just use TOGA just because we feel like it, because that would increase cost. That being said, safety is paramount, and if the conditions warrant it (e.g. windshear forecast) we could certainly choose to use all the performance available.

The climbout is based on the conditions on the day. We can't climb steeper than what will maintain the speed. Most climbs are done at a set thrust (typically derated but sometimes max).

You have to remember the purpose of what airline pilots do, and it is not doing "cool stuff" like max performance takeoffs all the time. By no means does this decrease job satisfaction. We take pride in an efficient operation. Pushing on time, solving dispatch problems, getting that rotation just right, managing the climb to meet a tight restriction, avoiding weather in order to give a more comfortable ride, managing the descent profile just so, touching down in the zone smoothly. These things all give us job satisfaction. Even managing a single-engine go around in the sim to perfection, with callouts and actions unhurried and confident, makes me smile.

bhill wrote:
..as a follow on, for FADEC implementations, do all the parameters need to be manually entered, like atmospheric conditions, aircraft weight, etc? Or are there sensors on the LG for weight/mass and weather sensors that feed the data directly into the FADEC?

"Manually", but not in the FM itself. Takeoff performance is calculated separately, which spits out performance figures. The inputs are weight, runway and environmentals. This used to be done paper (before my time). A few years ago we entered data into an ACARS form, sent that off, and a few minutes later the printer spat out the figures calculated by a computer system located somewhere. Now we do it in the Airbus FlySmart software on our EFBs. You get the thrust setting, config (flap setting) and V speeds, which you then enter in the FM.
Last edited by Starlionblue on Wed Apr 22, 2020 12:33 am, edited 2 times in total.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

meecrob
Posts: 201
Joined: Sun Jun 19, 2016 6:15 pm

### Re: Throttle/Thrust Settings, How's It Work?

If you are speaking of plane performance only, then yes (Here's a lightly loaded 757 doing similar to what you describe - https://www.youtube.com/watch?v=eRiCHgQnf9s). If you mean from a regulatory/company operating procedures perspective, then it depends on if you still want your job after you zoom climb a commercial plane outside being given explicit permission to do so (such as at airshows, etc.)

e38
Posts: 748
Joined: Sun May 04, 2008 10:09 pm

### Re: Throttle/Thrust Settings, How's It Work?

With some of the questions you asked, and comments you made, you seem to have the impression that being an airline pilot is very similar to being a race car driver with our goal of always seeking a thrill, pushing the aircraft to its limits, or trying to impress our passengers or the local plane spotters.

Well, flying is a lot of fun, but most pilots who fly for commercial airlines are actually much more professional than that. Note comments by Starlionblue above (Reply # 7).

In your original post, question # 2, you asked, "Can you use maximum power if you want, even if it's not required?"

Sure you can, but why would you? To use additional power that isn't required for performance has the potential to reduce engine life in terms of higher temperatures and pressures. Why would we operate the aircraft in a manner that could increase the possibility of engine failure at some future time?

When you drive your car, how often do you "floor" the accelerator, go as fast as the vehicle can possibly go, and run the engine at or above "redline" for an extended period of time, just for fun?

In question # 5, you asked, "At cruising altitude, are you always flying at your maximum cruising speed? If not, why not? If the reason is fuel, who cares?"

Who cares? Seriously? So, flying at maximum cruise speed uses more fuel and requires a higher power setting. All of us want our company to be financially profitable--that helps our job security--so I'm not sure why any professional pilot would do something to intentionally increase fuel usage unnecessarily or increase the wear and tear (thus increasing maintenance costs) on our aircraft. So, the simple answer to your question is, "We care." (and, no, the airline where I work does not track how much fuel individual pilots use). Trying to operate the aircraft efficiently and economically is just something most pilots take pride and satisfaction in doing.

We normally fly an airspeed based upon a cost index, which is a performance value calculated by the flight planning program based upon aircraft weight, temperature and winds aloft, distance to destination, and other variables. The cost index is entered into the Flight Management Computer during pre-flight. It is designed to provide maximum economic performance for the aircraft and determines optimum cruise altitude, as well as climb, cruise, and descent airspeeds. The key takeaway from using a cost index is "optimum fuel burn" and "efficient operation of the aircraft." While handflying the airplane is fun, the use of automation also increases efficiency.

In your second post (Reply # 6), you asked, "I want to clarify that when I was referring to being able to use full thrust whenever you wanted it, what I meant was, could you use maximum takeoff thrust even if conditions didn't require it?"

Could you? Yes. We can always use full thrust for takeoff.
Would you? No, what would be the purpose of doing so if not required?

The answer is the same for your last question about plane spotters near the runway, "Could you do a full power, steep climb out of there to give them a show?"

Could you? Of course.
Would you? Absolutely not! We're not in this business for their entertainment. (yes, there probably are some young, low-time, less-than-professional, daring, thrill-seeking airline pilots out there that would do it, but they would be the exception, not the rule).

Hope some of this helps.

e38

SAAFNAV
Posts: 612
Joined: Wed Mar 17, 2010 5:41 pm

### Re: Throttle/Thrust Settings, How's It Work?

The OP does seem to have some misconceptions about flying.

Have a look at the famous book by D.P. Davies 'Handling the Big Jets: An Explanation of the Significant Difference in Flying Qualities Between Jet Transport Aeroplanes and Piston Engined Transport Aircraft'

If you're familiar with the internet, you can source a copy easily.... (tpb).

He goes into great detail about the amount of thrust vs lever angle, how it is different from smaller planes. The weight considerations, swepts wings etc.
It would definitely give you a bigger insight into what goes on in the life of a pilot. And it isn't like being a racecar driver.

As for driving a manual transmission... Great, if you like it, then do it. Some people (myself) included enjoy it to get it just right. But a bigger consideration is traffic. If you sit bumper to bumper, would you more enjoy an easier life with no clutch, or try to be a race driver?

As in driving, there are things in aviation which makes your life easier. Apart from a comfort point of view, it frees up mental capacity to focus on things that really matter, like avoiding mountains and other aircraft instead of juggling engine controls.
CFI/Gr. III, L-382 Loadmaster, ex C-130B Navigator

Woodreau
Posts: 1971
Joined: Mon Sep 24, 2001 6:44 am

### Re: Throttle/Thrust Settings, How's It Work?

Usually the difference between flying max cruise speed and the filed flight plan speed for a short flight (less than 6 hours) is minimal.

Max cruise for an A320 is M0.80, (if you turned autothrust off and manually controlled the thrust levers it is M0.82, but you'd be constantly adjusting the thrust levers throughout the cruise portion of the flight and the other pilot would think you're an idiot, call you out on it and call professional standards) normal cruise usually is around M0.78/M0.79 the difference between M.78 and M.80 is 12 knots. over a 6 hour flight (West Coast to Hawaii or East Coast to West Coast), that is 72 miles, or if you constantly adjusted the thrust levers to maintain M0.82 over those 6 hours, 144 miles... a difference of maybe 10 minutes (for 72 miles), 20 minutes for (144 miles). but the fuel consumed is significantly increased.

Flying at M.80 or M0.82, I get to the destination 10 or 20 minutes earlier. It doesn't matter. Now I spend those 10 or 20 minutes on the ground waiting for my gate to become available..

There are many ways to get satisfaction flying airplanes. I do enjoy extracting maximum performance from the aircraft but not in the way you imagine. Managing the energy of the aircraft in a descent is a very satisfying exercise. I enjoy beating the published fuel burn in the flight release (burning less fuel than they calculated I would burn) (and not by setting CI zero either or changing the CI to cheat.),

Or as of late, getting smooth landings that don't feel like carrier landings with an empty airplane.
Even ATC has noticed, planes that normally take forever to get to cruise altitudes, every airplane out there flying today climb like homesick angels getting back into the air, like they couldn't wait to leave the ground.
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.

gloom
Posts: 492
Joined: Thu Jun 30, 2016 4:24 pm

### Re: Throttle/Thrust Settings, How's It Work?

Woodreau wrote:
Usually the difference between flying max cruise speed and the filed flight plan speed for a short flight (less than 6 hours) is minimal.

Right.

I would like to raise one point though, to give a better view.

The difference between planned and real cruise could be even greater.
Depends on many factors, just to give you three to get the idea:
- cruise winds stronger than expected/planned/usual; I've seen and heard many times the cruise was reduced by .03 or .04 Ma in order to arrive closer to planned arrival time
- clearance to enter airspace rescheduled; sometimes during flight one of control centres changes its entry time due to planned traffic vs capacity; if it changes to later time by a few minutes, best you could do is slow down in order to try and match those times
- depending on airline SOPs, every single one can differentiate. Taking Ejets as an example, max cruise is Ma .82, some airlines would use them at .78, some at .74. If you look at LR settings, you could cruise as slow as .7Ma, as it is I believe max cruise range speed.

That all makes up for quite a difference.

Cheers,

Posts: 236
Joined: Tue Sep 11, 2007 8:13 am

### Re: Throttle/Thrust Settings, How's It Work?

Clearly this guy is a troll. I commend the calm responses by you all, but this guy sounds like he wondered into this place with all the wrong ideas in mind.
We are all just fanboys, our opinions don't make or break businesses.

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