MCT at cruise
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Hi Latetonite,
I am not saying that MCT can not be used as a max thrust limit ,you can do it all you want...and the same goes with using MCT when required,i am just saying that the standard has always been CRZ as a limit and thats what your FMC will give you when levelling in vnav.
Now please explain to me why a CRZ thrust limit(CRZ) is set as default rather than MCT?
I am not saying that MCT can not be used as a max thrust limit ,you can do it all you want...and the same goes with using MCT when required,i am just saying that the standard has always been CRZ as a limit and thats what your FMC will give you when levelling in vnav.
Now please explain to me why a CRZ thrust limit(CRZ) is set as default rather than MCT?
Last edited by de facto; 29th Sep 2013 at 15:22.
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Originally Posted by Bubbers
We had a situation in an MD80 on a short flight and my captain got a little slow at 36,500ft so called it out and he used alt hold and MCT to regain speed but it was too late. Using MCT actually lowered our N1 and we started to get buffeting so descended at 500 fpm.
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Now please explain to me why a CRZ thrust limit(CRZ) is set as default rather than MCT?
maximum cruise thrust
This thrust rating is used as a reference for the thrust available for cruise. It is not a true limit on cruise thrust, as the engines can be advanced to maximum continuous thrust in an emergency situation. It is usually designated as MCRT. It’s usually a slightly lower thrust rating than maximum climb thrust, although in some instances the two are the same. There is no time limit on the use of maximum cruise thrust.
Cruise is normally conducted at a thrust setting somewhat less than maximum cruise thrust. MCRT is the upper cruise thrust threshold for normal operation. Should the pilot wish to cruise at the fastest speed possible, he may advance the thrust levers to the MCRT setting and accept the resulting speed provided, of course, that it doesn’t exceed the maximum certified speed VMO/MMO. These are discussed in the chapter entitled “Speeds”.
Because maximum cruise thrust is not the basis for any performance level mandated by the aviation regulations, the data for MCRT doesn’t appear in the Flight Manual, but rather in the PEM and the QRH.
This thrust rating is used as a reference for the thrust available for cruise. It is not a true limit on cruise thrust, as the engines can be advanced to maximum continuous thrust in an emergency situation. It is usually designated as MCRT. It’s usually a slightly lower thrust rating than maximum climb thrust, although in some instances the two are the same. There is no time limit on the use of maximum cruise thrust.
Cruise is normally conducted at a thrust setting somewhat less than maximum cruise thrust. MCRT is the upper cruise thrust threshold for normal operation. Should the pilot wish to cruise at the fastest speed possible, he may advance the thrust levers to the MCRT setting and accept the resulting speed provided, of course, that it doesn’t exceed the maximum certified speed VMO/MMO. These are discussed in the chapter entitled “Speeds”.
Because maximum cruise thrust is not the basis for any performance level mandated by the aviation regulations, the data for MCRT doesn’t appear in the Flight Manual, but rather in the PEM and the QRH.
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De facto:
Think about the days without FMC's and VNAV.
The engines do not know you have it aboard anyway.
Even less they are caring wether you are in climb, cruise, descent or approach.
However, there is a Maximum Continous Trust they are rated for, in short: MCT. You can use this thrust setting until your next oil change.
At the point you will need MCT to maintain cruise altitude, you reached your maximum altitude for that speed.
As this is not an advisable operating, you fly lower.
Based on margin calculated, you will get a lower, Normal, 'max' Cruise setting, below the engines will operate for given weight, speed and ambient conditions.
This setting will also prevent the thrust levers going "al the way"( to what?), just to adapt for normal speed deviations, in which there is in fact no "hurry".
The FMC will do that for you.
Thrust this makes some sense.
Think about the days without FMC's and VNAV.
The engines do not know you have it aboard anyway.
Even less they are caring wether you are in climb, cruise, descent or approach.
However, there is a Maximum Continous Trust they are rated for, in short: MCT. You can use this thrust setting until your next oil change.
At the point you will need MCT to maintain cruise altitude, you reached your maximum altitude for that speed.
As this is not an advisable operating, you fly lower.
Based on margin calculated, you will get a lower, Normal, 'max' Cruise setting, below the engines will operate for given weight, speed and ambient conditions.
This setting will also prevent the thrust levers going "al the way"( to what?), just to adapt for normal speed deviations, in which there is in fact no "hurry".
The FMC will do that for you.
Thrust this makes some sense.
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Just a guess: it's just about economics.
Maximum Climb and Cruise ratings are contractually agreed between the engine manufacturer and the airframe manufacturer to achieve commercially acceptable targets of time between overhauls and parts replacement costs.
If CLB is equal to MCT the difference is obviously academic.
If CLB is equal to MCT the difference is obviously academic.
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de facto,
Yes, I have no problem step climbing to next level, when the FMC shows it as max. And consequently I have no problem selecting CON as thrust limit as pr. Boeing recommendation - routinely.
Now on the other hand, please tell me where Boeing recommends 1000 feet extra margin on the max altitude (which already has plenty of margin built in).
At some point one has to stop adding personal margins on margins already built into the systems.
Yes, I have no problem step climbing to next level, when the FMC shows it as max. And consequently I have no problem selecting CON as thrust limit as pr. Boeing recommendation - routinely.
Now on the other hand, please tell me where Boeing recommends 1000 feet extra margin on the max altitude (which already has plenty of margin built in).
At some point one has to stop adding personal margins on margins already built into the systems.
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At some point one has to stop adding personal margins on margins already built into the systems.
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Kramer,
Please do it every day..select MCT, i dont give a 
and fly at MaX altitude,you can also select flaps at 19 900 ft and select flaps 1 at 249kts while you are at it,you are the captain Sir.
Boeing doesnt recommend a 1000 ft margin...it is a margin i aim for to avoid ROuTiNeLy having to use speed brakes and MCT.
Exactly.
Yes, I have no problem step climbing to next level, when the FMC shows it as max. And consequently I have no problem selecting CON as thrust limit as pr. Boeing recommendation - routinely.
Now on the other hand, please tell me where Boeing recommends 1000 feet extra margin on the max altitude (which already has plenty of margin built in).
Now on the other hand, please tell me where Boeing recommends 1000 feet extra margin on the max altitude (which already has plenty of margin built in).
and fly at MaX altitude,you can also select flaps at 19 900 ft and select flaps 1 at 249kts while you are at it,you are the captain Sir.Boeing doesnt recommend a 1000 ft margin...it is a margin i aim for to avoid ROuTiNeLy having to use speed brakes and MCT.
If we actually weighed what they tell us, I would have no problem using the FMC numbers. Having the low and high speed buffet hooks touching is not my idea of a safe operation, yet, that is where the FMC will drive you if you believe it.
Last edited by de facto; 30th Sep 2013 at 05:26.
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Latetonite,
My aircraft is fitted with 2 Fmc and vnav.
Exactly so do you routinely need MCT?
Exactly...and what happens when the thrust is kept to a lower max?
Oups ...seems like Crunk nailed it.
Think about the days without FMC's and VNAV.
At the point you will need MCT to maintain cruise altitude, you reached your maximum altitude for that speed.
As this is not an advisable operating, you fly lower.
As this is not an advisable operating, you fly lower.
Based on margin calculated, you will get a lower, Normal, 'max' Cruise setting, below the engines will operate for given weight, speed and ambient conditions.
This setting will also prevent the thrust levers going "al the way"( to what?), just to adapt for normal speed deviations, in which there is in fact no "hurry".
This setting will also prevent the thrust levers going "al the way"( to what?), just to adapt for normal speed deviations, in which there is in fact no "hurry".
Just a guess: it's just about economics. Most of the time, you don't need MCT, so if Boeing says 94.6% is the limit, the engine/airframe will be that much more "fuel efficient." That 0.00001% of cruise at MCT costs more fuel. When marketing is digging for every dime, they can sell a less expensive CASM than the other guys.
Yes, I have no problem step climbing to next level, when the FMC shows it as max. And consequently I have no problem selecting CON as thrust limit as pr. Boeing recommendation - routinely.
Now on the other hand, please tell me where Boeing recommends 1000 feet extra margin on the max altitude (which already has plenty of margin built in).
Now on the other hand, please tell me where Boeing recommends 1000 feet extra margin on the max altitude (which already has plenty of margin built in).
I hope you don't ever get the temperature changes or wind changes that I've seen in the cruise over the years! You'll be re thinking your personal operating procedures pretty quickly if you do. The issue with operating at max isn't normally an aerodynamic one, it's more often than not a thrust available issue. If you get a temp change of plus fifteen or twenty degrees while banked at 15degrees you'll be leaving your flight level with the stick shaker going.
That's just my humble opinion, feel free to explain how wrong I am
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The issue with operating at max isn't normally an aerodynamic one, it's more often than not a thrust available issue.
If you get a temp change of plus fifteen or twenty degrees while banked at 15degrees you'll be leaving your flight level with the stick shaker going.
If you operate the aircraft as Boeing recommends, you do not need to add your own personal margins. Common sense should of course prevail, you do get weather charts in your briefing package don't you? And you do study those charts during your briefing I hope? 15-20 deg temperature change should be something you notice...
Then again I am not the one to report moderate turbulence as soon as we hit light chops.
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...and then just to clarify. I never said that I blindly climb to max altitude, every time it's available. I said I have no problem doings so, and do it routinely - that of course if I see an operational benefit in doing so.
Example cruising at FL360 top of clouds in light chops. FL380 becomes available as max altitude, I climb.
Common sense: I do not need to see FL384, 386 or 390 (or whatever people have for personal margin preferences), to initiate the climb.
And I am not stupid, I plan ahead. Which included looking if 380 also will be my max altitude in near future (wx charts, vertical profile etc), the FMC only tell you the current conditions, not what will happen along the route. You could have asked... but you went on to assume that I am stupid based on things that I did not write. De facto even worse, to assume that I also select flaps with 249 knot (why would I do so, based on what I wrote?). CRM...
Every decision I make in the cockpit is a conscious, considered decision, based on the facts at hand... Not an automated decision based on old wife's tales or "that I always do/need so".
Keep editing because more things pop into mind:
If you foresee that you are unable to keep the speed, a small tip (which I do not use routinely
) - instead of going "into a stall" (a bit dramatically put by you, lowspeed band comes first you know). Turn your altitude selector down, and use V/S -100 to -200 fpm, until you regained your speed. Then vs back to level and alt selector back to your altitude. Pretty simple and unnoticeable to ATC.
Example cruising at FL360 top of clouds in light chops. FL380 becomes available as max altitude, I climb.
Common sense: I do not need to see FL384, 386 or 390 (or whatever people have for personal margin preferences), to initiate the climb.
And I am not stupid, I plan ahead. Which included looking if 380 also will be my max altitude in near future (wx charts, vertical profile etc), the FMC only tell you the current conditions, not what will happen along the route. You could have asked... but you went on to assume that I am stupid based on things that I did not write. De facto even worse, to assume that I also select flaps with 249 knot (why would I do so, based on what I wrote?). CRM...
Every decision I make in the cockpit is a conscious, considered decision, based on the facts at hand... Not an automated decision based on old wife's tales or "that I always do/need so".
Keep editing because more things pop into mind:
If you foresee that you are unable to keep the speed, a small tip (which I do not use routinely
) - instead of going "into a stall" (a bit dramatically put by you, lowspeed band comes first you know). Turn your altitude selector down, and use V/S -100 to -200 fpm, until you regained your speed. Then vs back to level and alt selector back to your altitude. Pretty simple and unnoticeable to ATC.
Last edited by cosmo kramer; 30th Sep 2013 at 12:19.
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...and then just to clarify. I never said that I blindly climb to max altitude, every time it's available. I said I have no problem doings so, and do it routinely - that of course if I see an operational benefit in doing so.
Example cruising at FL360 top of clouds in light chops. FL380 becomes available as max altitude, I climb.
Example cruising at FL360 top of clouds in light chops. FL380 becomes available as max altitude, I climb.
Code:
As for bank, LNAV calculates safe bank angles that doesn't exceed thrust available. If using HDG select, bank angle selector is set to 10, routinely, when reaching cruise altitude... again pr. Boeing recommendation High Altitude Maneuvering (automatic pdf download)
Turn your altitude selector down, and use V/S -100 to -200 fpm, until you regained your speed. Then vs back to level and alt selector back to your altitude. Pretty simple and unnoticeable to ATC.
Last edited by de facto; 30th Sep 2013 at 15:05.
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you do get weather charts in your briefing package don't you?
instead of going "into a stall" (a bit dramatically put by you, lowspeed band comes first you know).
If tooling around at Max altitude a very clear understanding of what drives the PFD displays is a good idea. In that same situation, what happens to thrust available?
At -56 degrees the aircraft was capable of a 100fpm climb rate, what is it capable of now that the temp is -46 ?
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From boeing and Airbus :
Maximum Altitude
Maximum altitude is the highest altitude at which an airplane can be operated. In today’s modern airplanes it is determined by three basic charac- teristics which are unique to each airplane model. It is the lowest of:
• Maximumcertifiedaltitude(structural)thatisde- termined during certification and is usually set by the pressurization load limits on the fuselage.
• Thrust Limited Altitude – the altitude at which sufficient thrust is available to provide a specific minimum rate of climb.
• Buffet or Maneuver limited altitude – the altitude at which a specific maneuver margin exists prior to buffet onset.
Although each of these limits is checked by modern flight management computers the available thrust may limit the ability to accomplish anything other than relatively minor maneuvering.
The danger in operating near these ceilings is the potential for the speed and angle of attack to change due to turbulence or environmental factors that could lead to a slowdown or stall and subsequent high altitude upset.
Maximum Altitude
Maximum altitude is the highest altitude at which an airplane can be operated. In today’s modern airplanes it is determined by three basic charac- teristics which are unique to each airplane model. It is the lowest of:
• Maximumcertifiedaltitude(structural)thatisde- termined during certification and is usually set by the pressurization load limits on the fuselage.
• Thrust Limited Altitude – the altitude at which sufficient thrust is available to provide a specific minimum rate of climb.
• Buffet or Maneuver limited altitude – the altitude at which a specific maneuver margin exists prior to buffet onset.
Although each of these limits is checked by modern flight management computers the available thrust may limit the ability to accomplish anything other than relatively minor maneuvering.
The danger in operating near these ceilings is the potential for the speed and angle of attack to change due to turbulence or environmental factors that could lead to a slowdown or stall and subsequent high altitude upset.
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De facto,
I thought you were done here?
You forgot to quote on:
I am familiar with the performance characteristics, so for to me I don't see it as a big deal.
Coincidentally I had exactly this scenario last night, so I can back up with some numbers too. Cruising at 360 top of clouds with continuous light turbulence (what other usually report as moderate, for some reason). Max 381 with a 9 knots margin between low and high speed buffet (240 to 249, with 249 equal to approx .79). We climbed at it was smooth at FL380. We kept the speed at just below .79 (ECON cost index 55, can't remember the exact speed) and with the variations it was momentary slightly in the high speed buffet band at times (autothrottle acting more fast to correct so not a problem for me), and comfortably above the low speed band, so as to allow me to continue reading the book I brought along and drinking my coffee with out the risk of spilling any on my tie.
After 15-20 mins the margin increased to about 15 knots (still flying close to the upper band giving me 13-14 knots to low speed band).
Now where exactly do you see the problem in this?? Just because you are not familiar with the characteristics, doesn't mean that everyone else is wrong.
And the reason for the pdf was the the FCTM doesn't have those nice graphs that the pdf does. Yes, I am of course am familiar with the FCTM - try answering polite, it will get you futher (unless of course you "are done" here again).
Hobo, are you referring to 737 classic? If so, then I agree. It is quite uncomfortable if going into the high speed buffet band, but the NG is smooth as long as you are flying straight and level. Again, with a 200nm direct and no WX to avoid on the screen, I have no problem to climb and to let it run a few knots into the upper yellow band with the occasional speed variations.
Framer,
I remember a thread about a year ago, where we discussed correct flare/thrust reduction technique for the 737. It seemed to me at the time, that you were quite green?
Did you encounter an instant un-forcasted +20 deg temp. increase in clear weather?
Seems just as likely as encountering Godzilla at FL380.
I thought you were done here?
You forgot to quote on:
Flight crews intending to operate at or near the maximum operating altitude should be familiar with the performance characteristics of the airplane in these conditions.
Coincidentally I had exactly this scenario last night, so I can back up with some numbers too. Cruising at 360 top of clouds with continuous light turbulence (what other usually report as moderate, for some reason). Max 381 with a 9 knots margin between low and high speed buffet (240 to 249, with 249 equal to approx .79). We climbed at it was smooth at FL380. We kept the speed at just below .79 (ECON cost index 55, can't remember the exact speed) and with the variations it was momentary slightly in the high speed buffet band at times (autothrottle acting more fast to correct so not a problem for me), and comfortably above the low speed band, so as to allow me to continue reading the book I brought along and drinking my coffee with out the risk of spilling any on my tie.
After 15-20 mins the margin increased to about 15 knots (still flying close to the upper band giving me 13-14 knots to low speed band).
Now where exactly do you see the problem in this?? Just because you are not familiar with the characteristics, doesn't mean that everyone else is wrong.
And the reason for the pdf was the the FCTM doesn't have those nice graphs that the pdf does. Yes, I am of course am familiar with the FCTM - try answering polite, it will get you futher (unless of course you "are done" here again).
Hobo, are you referring to 737 classic? If so, then I agree. It is quite uncomfortable if going into the high speed buffet band, but the NG is smooth as long as you are flying straight and level. Again, with a 200nm direct and no WX to avoid on the screen, I have no problem to climb and to let it run a few knots into the upper yellow band with the occasional speed variations.
Framer,
I remember a thread about a year ago, where we discussed correct flare/thrust reduction technique for the 737. It seemed to me at the time, that you were quite green?
Did you encounter an instant un-forcasted +20 deg temp. increase in clear weather?
Seems just as likely as encountering Godzilla at FL380.