Climb gradient after engine failure
Moderator
when using RTOW charts how does one account for a forecast temperature inversion?
One needs to look at both Hp and OAT at the inversion. Depending on the presentation of the chart and the inversion height delta, you might either correct both for pressure and temperature or run the inversion temperature back down to aerodrome level at a suitable lapse rate.
Main thing is to be aware that a significant inversion is going to present you with problems if you lose one during the takeoff so you should do something sensible to keep some extra (T-D)/W up your sleeve for the possibility. If your company procedures don't address the problem, then the above suggestions will give you a fighting chance.
Derated-TO is a max. thrust.
Doesn't matter which brand we are talking about. Flex is reduced throttle, derate is a defacto lower thrust engine bolted onto the aircraft. Flex plus derate is a combination of the two.
With flex you can run the thrust back up to the (relevant) derate or max thrust setting but, I suggest, slowly to avoid any nasty surprises.
With derate, you need to be aware of the very real potential for Vmcg/Vmca problems if you increase thrust significantly during a low speed schedule takeoff. This latter is quite a probable situation for those operators which use derate to get a better RTOW out of shorter contaminated runways - the reduced Vmcg/Vmca permits a lower speed schedule to fit better with the runway length.
One needs to look at both Hp and OAT at the inversion. Depending on the presentation of the chart and the inversion height delta, you might either correct both for pressure and temperature or run the inversion temperature back down to aerodrome level at a suitable lapse rate.
Main thing is to be aware that a significant inversion is going to present you with problems if you lose one during the takeoff so you should do something sensible to keep some extra (T-D)/W up your sleeve for the possibility. If your company procedures don't address the problem, then the above suggestions will give you a fighting chance.
Derated-TO is a max. thrust.
Doesn't matter which brand we are talking about. Flex is reduced throttle, derate is a defacto lower thrust engine bolted onto the aircraft. Flex plus derate is a combination of the two.
With flex you can run the thrust back up to the (relevant) derate or max thrust setting but, I suggest, slowly to avoid any nasty surprises.
With derate, you need to be aware of the very real potential for Vmcg/Vmca problems if you increase thrust significantly during a low speed schedule takeoff. This latter is quite a probable situation for those operators which use derate to get a better RTOW out of shorter contaminated runways - the reduced Vmcg/Vmca permits a lower speed schedule to fit better with the runway length.
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OAT plus INVERSION TEMP = Temp used for takeoff calculation.
If using FLEX/ASS then you will have lower temperature.
If using TOGA, then you will have a weight reduction........
Not many airlines use inversion temperatures due to the weight loss
...... gotta disagree, you cannot run it back to max thrust due to lack of VMCG protection......
Mutt
If using FLEX/ASS then you will have lower temperature.
If using TOGA, then you will have a weight reduction........
Not many airlines use inversion temperatures due to the weight loss
With flex you can run the thrust back up to the (relevant) derate or max thrust setting but, I suggest, slowly to avoid any nasty surprises.
Mutt
Mutt
How about, "set thrust to the rated thrust"? In other words, from the ATM thrust to rated for the planned thrust rating, but not to a higher rating.
GF
How about, "set thrust to the rated thrust"? In other words, from the ATM thrust to rated for the planned thrust rating, but not to a higher rating.
GF
Moderator
Not many airlines use inversion temperatures due to the weight loss
Of course .. but, then, if you lose the engine, don't be surprised to find yourself dead in the water at the inversion ... all dressed up with nowhere to go.
... gotta disagree, you cannot run it back to max thrust due to lack of VMCG prot
You're misreading my intent, good sir.
(a) if flex only then the pilot MAY increase the thrust to the full thrust rated setting
(b) if derate without flex, no increase is permitted
(c) if derate with flex, the pilot MAY increase the thrust to the relevant derate rated thrust setting
Having seen a couple of embarrassments with thrust overswings, including one nasty fatal, any increase pemitted and availed needs to be done steadily to avoid the risk of unnecessary and, potentially, hazardous gyrations. My view is to leave the thing alone unless you are REALLY terrified of hitting the hard bits.
How about, "set thrust to the rated thrust"?
Indeed.
And, if all else fails ... and you are at rated thrust .. and still going down or are going to hit the hard bits ... it is a case of choice ... crash under control and do the best you can .. or trade a bit of extra thrust against a bit more bank as required to keep the heading under control .. and just hope that the extra sideslip doesn't bite you along the way.
One keeps in mind the reality that, on the day, the real Vmca is most likely going to be a bit lower than book so it probably isn't all doom and gloom.
If you are at a low enough weight to be in the Vmca problem region, (moreso for twin than quads) the bird probably is accelerating like a cat on a hot tin roof and, by the time it is sorted out, you will be well above the book V2 problem area.
Generally, I wouldn't be too worried about the Vmcg problem as the risk of increasing thrust is more likely to occur in the air rather than on the ground. Vmca is the one which worries me.
Main concern is in the steady state condition where the pilot has got the situation under control, is on speed .. but still going nowhere. If the operating throttle is just shoved up ... that's when he/she might find out about the sting in the tail.
Very occasionally, a crew is faced with a set of circumstances which accord with the observation that one just ought not to have got out of bed that day ... the sort of day where one earns the entire year's salary in a few minutes and either gets a pat on the back .. or a lot of tut-tuts by the Monday morning quarterbackers.
Of course .. but, then, if you lose the engine, don't be surprised to find yourself dead in the water at the inversion ... all dressed up with nowhere to go.
... gotta disagree, you cannot run it back to max thrust due to lack of VMCG prot
You're misreading my intent, good sir.
(a) if flex only then the pilot MAY increase the thrust to the full thrust rated setting
(b) if derate without flex, no increase is permitted
(c) if derate with flex, the pilot MAY increase the thrust to the relevant derate rated thrust setting
Having seen a couple of embarrassments with thrust overswings, including one nasty fatal, any increase pemitted and availed needs to be done steadily to avoid the risk of unnecessary and, potentially, hazardous gyrations. My view is to leave the thing alone unless you are REALLY terrified of hitting the hard bits.
How about, "set thrust to the rated thrust"?
Indeed.
And, if all else fails ... and you are at rated thrust .. and still going down or are going to hit the hard bits ... it is a case of choice ... crash under control and do the best you can .. or trade a bit of extra thrust against a bit more bank as required to keep the heading under control .. and just hope that the extra sideslip doesn't bite you along the way.
One keeps in mind the reality that, on the day, the real Vmca is most likely going to be a bit lower than book so it probably isn't all doom and gloom.
If you are at a low enough weight to be in the Vmca problem region, (moreso for twin than quads) the bird probably is accelerating like a cat on a hot tin roof and, by the time it is sorted out, you will be well above the book V2 problem area.
Generally, I wouldn't be too worried about the Vmcg problem as the risk of increasing thrust is more likely to occur in the air rather than on the ground. Vmca is the one which worries me.
Main concern is in the steady state condition where the pilot has got the situation under control, is on speed .. but still going nowhere. If the operating throttle is just shoved up ... that's when he/she might find out about the sting in the tail.
Very occasionally, a crew is faced with a set of circumstances which accord with the observation that one just ought not to have got out of bed that day ... the sort of day where one earns the entire year's salary in a few minutes and either gets a pat on the back .. or a lot of tut-tuts by the Monday morning quarterbackers.
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Ocampo,
" Derrated-TO is a max. thrust. Can someone with a bit more of experience in Mr. Boeing's aircrafts confirm this?
Boeing DO indeed state that "Derrated-TO is a max. thrust", for several very good reasons -
(1) Even if you are using Reduced Thrust (Assumed Temperature Method or ATM) with a Derate, Vmcg and Vmca are based upon the full applicable Derated thrust. V1, Vr, and V2 are based upon this set of Vmc speeds. Advancing thrust to the FULL rating following engine failure at Vmc limiting speeds for a Derated Thrust Takeoff would be courting disaster.
(2) The rules specify just how much thrust reduction is possible using Reduced Thrust (ATM) as a percentage of Maximum Thrust. By introducing new sets of Maximum Thrust (e.g. TO-1, TO-2), much larger thrust reductions (as related to FULL Takeoff Thrust) are possible.
Thus, Derated TO IS a maximum thrust.
Other areas where you may find this is in Boeing recommendations such as contaminated runway operation etc., where they state that ATM shall not be used, and Maximum Thrust used, with the immediately following reminder that Derated Thrust/s are Maximum Thrust/s.
Once you are out of the Vmc danger zone (above V2 for FULL TO), you may, if operationally necessary, advance the engine/s to FULL TO with impunity, AEO or OEI. For every Takeoff that I do with Derated Thrust (which is most of them) I always check the V2 speed for FULL TO, "just in case".
John_T, you had to mention the Tennant Bl**dy Creek inversion didn't you! As a young sprog Flying Doctor pilot about 32 years ago, I had a night takeoff there which came to a stop at about 200 ft AGL. The not-so-large aircraft (8,800 Lb) just sat, and sat, and sat at 200 ft, until VERY shallow climb resumed. I've 'enjoyed' the Middle East's inversions on numerous occasions, but none came close to Tennant Bl**dy Creek's mother of all inversions. I recently saw TNK again from 38,000 feet, definately the best way to see it, still get shivers about the night that Young Smokey never made it to Old.
Regards,
Old Smokey
" Derrated-TO is a max. thrust. Can someone with a bit more of experience in Mr. Boeing's aircrafts confirm this?
Boeing DO indeed state that "Derrated-TO is a max. thrust", for several very good reasons -
(1) Even if you are using Reduced Thrust (Assumed Temperature Method or ATM) with a Derate, Vmcg and Vmca are based upon the full applicable Derated thrust. V1, Vr, and V2 are based upon this set of Vmc speeds. Advancing thrust to the FULL rating following engine failure at Vmc limiting speeds for a Derated Thrust Takeoff would be courting disaster.
(2) The rules specify just how much thrust reduction is possible using Reduced Thrust (ATM) as a percentage of Maximum Thrust. By introducing new sets of Maximum Thrust (e.g. TO-1, TO-2), much larger thrust reductions (as related to FULL Takeoff Thrust) are possible.
Thus, Derated TO IS a maximum thrust.
Other areas where you may find this is in Boeing recommendations such as contaminated runway operation etc., where they state that ATM shall not be used, and Maximum Thrust used, with the immediately following reminder that Derated Thrust/s are Maximum Thrust/s.
Once you are out of the Vmc danger zone (above V2 for FULL TO), you may, if operationally necessary, advance the engine/s to FULL TO with impunity, AEO or OEI. For every Takeoff that I do with Derated Thrust (which is most of them) I always check the V2 speed for FULL TO, "just in case".
John_T, you had to mention the Tennant Bl**dy Creek inversion didn't you! As a young sprog Flying Doctor pilot about 32 years ago, I had a night takeoff there which came to a stop at about 200 ft AGL. The not-so-large aircraft (8,800 Lb) just sat, and sat, and sat at 200 ft, until VERY shallow climb resumed. I've 'enjoyed' the Middle East's inversions on numerous occasions, but none came close to Tennant Bl**dy Creek's mother of all inversions. I recently saw TNK again from 38,000 feet, definately the best way to see it, still get shivers about the night that Young Smokey never made it to Old.
Regards,
Old Smokey
Moderator
... which came to a stop at about 200 ft AGL
That's the one .. and there we was sat in our Friendly with both dog whistles screaming away at wet power ... going nowhere .. and, as I recall, we weren't at the RTOW for the day. Engine failure ? .. didn't want even to think about it.
Talk about putting the wind up two pilots. Almost enough to cause a crew to be moved to praying to the Almighty for succour. I don't recall if either of us actually got to praying .. but there certainly were a few inappropriate quasi-religious invocations uttered as we watched the bumpy bits sail past at window height ...
That's the one .. and there we was sat in our Friendly with both dog whistles screaming away at wet power ... going nowhere .. and, as I recall, we weren't at the RTOW for the day. Engine failure ? .. didn't want even to think about it.
Talk about putting the wind up two pilots. Almost enough to cause a crew to be moved to praying to the Almighty for succour. I don't recall if either of us actually got to praying .. but there certainly were a few inappropriate quasi-religious invocations uttered as we watched the bumpy bits sail past at window height ...
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Flex
Thank you, Old Smokey, for quite a nice explanation. No doubts on the Derated Thrust.
I do, however, have another doubt. Here goes:
If FLEX is still a reduced set of thrust, why can you select Max. Thrust with FLEX but you can't with D-TO? Is it because Vmc speeds with FLEX are not calculated to the respective thrust reduction, but to TO/GA thrust?
BTW, some "trick" that I've learned in a few sims I've witnessed is that on the 3rd segment you are supposed to select MCT, but if you decide, you can continue on TO/GA up until the time limit is almost up, whether it is 5 or 10 mins; that way you can get a bit more of thrust in those moments you need the most. Is it good practice to do the above? Recommended or not?
Thanks in advance
I do, however, have another doubt. Here goes:
If FLEX is still a reduced set of thrust, why can you select Max. Thrust with FLEX but you can't with D-TO? Is it because Vmc speeds with FLEX are not calculated to the respective thrust reduction, but to TO/GA thrust?
BTW, some "trick" that I've learned in a few sims I've witnessed is that on the 3rd segment you are supposed to select MCT, but if you decide, you can continue on TO/GA up until the time limit is almost up, whether it is 5 or 10 mins; that way you can get a bit more of thrust in those moments you need the most. Is it good practice to do the above? Recommended or not?
Thanks in advance
Moderator
If FLEX is still a reduced set of thrust, why can you select Max. Thrust with FLEX but you can't with D-TO?
You are still missing the difference between flex and derate - if you are at the derate setting, you ARE ALREADY at Max Thrust.
Think in the following way -
(a) for an aircraft, the certification set of rules is addressed considering the maximum power (thrust) which the engine is able to produce.
If, by some means, you operate at power output levels higher than those used for the certification then you invalidate the certification basis for the aircraft ie you are not allowed to do this.
(b) full power T/O - if you conduct a T/O using the maximum power permitted from the engine, you are conducting a full power T/O
(c) flex - you may operate the engine at a lower power setting by using less than full throttle. This is what you are doing in a flex T/O - conducting the T/O intentionally at a power setting less than the maximum that the engine is capable of producing on the day. That doesn't cause any certification problems (and, providing you have done the sums correctly, won't produce any operational problems). It follows that you will not produce any certification problems if, during the T/O you elect to return to the maximum power output envisaged by the certification basis.
(d) derated T/O - now pull the original engine out and install a modified engine of smaller power output capability. This is quite common within a family of aircraft (motorcars, etc). If you now conduct a T/O using the new full T/O power capability, you are operating to the maximum power available for this particular model engine but, compared to the higher powered version, it is a lower power output, for which the term we use is derated (ie the new max thrust rating is less than [hence derated from] the higher/highest rating. However, for the derated engine, if you are operating at max power (thrust) you are operating at full thrust FOR THAT DERATE.
(e) derated and flex T/O - exactly as at (c), you may operate the derated engine at a lower than maximum (now the derated level) power setting by using less than the throttle setting necessary to achieve the derated power output level. It follows that you will not produce any certification problems if, during the T/O you elect to return to the maximum power output envisaged by the certification basis. However, this maximum power level is now the derated level, not the original engine's higher level. If you exceed the derated level, you will invalidate the certification basis for the aircraft. Keep in mind that derate requires the OEM to schedule separate AFM data for the derate ie you have, in effect, multiple AFMs and you must use the one appropriate to your chosen level of derate on the day.
(f) with an aircraft engine, we want to be able to have our cake and eat it too - ie sometimes we want to operate to the maximum rating and, on other times, to a derated rating. However, we don't physically swap engines back and forth - that just wouldn't work in practice.
What we can do to achieve the same thing, in principle, is constrain the engine not to operate at power outputs higher than the declared reduced rating level. This can be done either by computer control or manual setting of lower power output using the engine gauges.
In doing this we are conducting a derated T/O - intentionally operating a bigger (higher thrust) engine at a lower certificated power setting. This must be done in a manner to emulate installing a lower power engine ie you must not permit the engine to operate at a power output higher than the new, lower certification rating otherwise you invalidate the certification basis for the derate setting.
Does this seem to be a round about way to achieve a goal ?
Absolutely so. Wouldn't it just be simpler to keep reducing the flex setting and not worry about the intermediate step of setting a derate setting ? Probably, but there are a couple of important things which prevent us using that simpler approach in the first instance and would deny us an advantage in the second.
(a) maximum flex setting. The rules prevent our using more than a specified maximum flex thrust reduction. See, for example, FAA AC25-13 which amplifies the FAR 25 requirements that the actual thrust be no less than 75% of rated thrust. Given that, with some of the larger engines, it is feasible to use significantly greater flex settings than this, we need to use the "trick" of derated flex to get past the initial certification restriction.
(b) as the certification is based on the maximum power output, if we use a derate then we can get some side benefits, such as a reduction in Vmcg/Vmca. Such a benefit shows up in a reduced minimum T/O speed schedule .. which may require a lesser TOD for low weight takeoffs, allowing better payload out of shorter runways.
[Caveat - I have used power and thrust interchangeably but intend power for turboprops and thrust for turbofans]
Is it because Vmc speeds with FLEX are not calculated to the respective thrust reduction, but to TO/GA thrust?
Precisely - and the important thing is that you can have several sets of Vmcg/Vmca data, provided that the OEM choses to schedule these in the AFM.
you can continue on TO/GA up until the time limit is almost up, whether it is 5 or 10 mins
really a matter for the operator to choose for routine use.
In the event that you REALLY need the extra thrust on the day because of some out of left field consideration, I suggest that the 5/10 minute limit is not going to be very high in your list of priorities on the day. A case of whether we are talking routine or emergency conditions.
You are still missing the difference between flex and derate - if you are at the derate setting, you ARE ALREADY at Max Thrust.
Think in the following way -
(a) for an aircraft, the certification set of rules is addressed considering the maximum power (thrust) which the engine is able to produce.
If, by some means, you operate at power output levels higher than those used for the certification then you invalidate the certification basis for the aircraft ie you are not allowed to do this.
(b) full power T/O - if you conduct a T/O using the maximum power permitted from the engine, you are conducting a full power T/O
(c) flex - you may operate the engine at a lower power setting by using less than full throttle. This is what you are doing in a flex T/O - conducting the T/O intentionally at a power setting less than the maximum that the engine is capable of producing on the day. That doesn't cause any certification problems (and, providing you have done the sums correctly, won't produce any operational problems). It follows that you will not produce any certification problems if, during the T/O you elect to return to the maximum power output envisaged by the certification basis.
(d) derated T/O - now pull the original engine out and install a modified engine of smaller power output capability. This is quite common within a family of aircraft (motorcars, etc). If you now conduct a T/O using the new full T/O power capability, you are operating to the maximum power available for this particular model engine but, compared to the higher powered version, it is a lower power output, for which the term we use is derated (ie the new max thrust rating is less than [hence derated from] the higher/highest rating. However, for the derated engine, if you are operating at max power (thrust) you are operating at full thrust FOR THAT DERATE.
(e) derated and flex T/O - exactly as at (c), you may operate the derated engine at a lower than maximum (now the derated level) power setting by using less than the throttle setting necessary to achieve the derated power output level. It follows that you will not produce any certification problems if, during the T/O you elect to return to the maximum power output envisaged by the certification basis. However, this maximum power level is now the derated level, not the original engine's higher level. If you exceed the derated level, you will invalidate the certification basis for the aircraft. Keep in mind that derate requires the OEM to schedule separate AFM data for the derate ie you have, in effect, multiple AFMs and you must use the one appropriate to your chosen level of derate on the day.
(f) with an aircraft engine, we want to be able to have our cake and eat it too - ie sometimes we want to operate to the maximum rating and, on other times, to a derated rating. However, we don't physically swap engines back and forth - that just wouldn't work in practice.
What we can do to achieve the same thing, in principle, is constrain the engine not to operate at power outputs higher than the declared reduced rating level. This can be done either by computer control or manual setting of lower power output using the engine gauges.
In doing this we are conducting a derated T/O - intentionally operating a bigger (higher thrust) engine at a lower certificated power setting. This must be done in a manner to emulate installing a lower power engine ie you must not permit the engine to operate at a power output higher than the new, lower certification rating otherwise you invalidate the certification basis for the derate setting.
Does this seem to be a round about way to achieve a goal ?
Absolutely so. Wouldn't it just be simpler to keep reducing the flex setting and not worry about the intermediate step of setting a derate setting ? Probably, but there are a couple of important things which prevent us using that simpler approach in the first instance and would deny us an advantage in the second.
(a) maximum flex setting. The rules prevent our using more than a specified maximum flex thrust reduction. See, for example, FAA AC25-13 which amplifies the FAR 25 requirements that the actual thrust be no less than 75% of rated thrust. Given that, with some of the larger engines, it is feasible to use significantly greater flex settings than this, we need to use the "trick" of derated flex to get past the initial certification restriction.
(b) as the certification is based on the maximum power output, if we use a derate then we can get some side benefits, such as a reduction in Vmcg/Vmca. Such a benefit shows up in a reduced minimum T/O speed schedule .. which may require a lesser TOD for low weight takeoffs, allowing better payload out of shorter runways.
[Caveat - I have used power and thrust interchangeably but intend power for turboprops and thrust for turbofans]
Is it because Vmc speeds with FLEX are not calculated to the respective thrust reduction, but to TO/GA thrust?
Precisely - and the important thing is that you can have several sets of Vmcg/Vmca data, provided that the OEM choses to schedule these in the AFM.
you can continue on TO/GA up until the time limit is almost up, whether it is 5 or 10 mins
really a matter for the operator to choose for routine use.
In the event that you REALLY need the extra thrust on the day because of some out of left field consideration, I suggest that the 5/10 minute limit is not going to be very high in your list of priorities on the day. A case of whether we are talking routine or emergency conditions.
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I think that John_T's last post should be made into a sticky!!!
Mind you, in doing so, it would reduce performance related discussion in this forum to about 20%, spoil a lot of lively discussion......
Seriously, if any PPRuNers had any doubts of the how, when, where or why of Thrust Ratings, Derates, Reduced Thrust (ATM or Flex), then it's cut and paste time for J_T's post, starting with a LOT of Instructors (who are, after all, mandated to pass on such knowledge).
Regards,
Old Smokey
Mind you, in doing so, it would reduce performance related discussion in this forum to about 20%, spoil a lot of lively discussion......
Seriously, if any PPRuNers had any doubts of the how, when, where or why of Thrust Ratings, Derates, Reduced Thrust (ATM or Flex), then it's cut and paste time for J_T's post, starting with a LOT of Instructors (who are, after all, mandated to pass on such knowledge).
Regards,
Old Smokey
Moderator
I am at the Asian Aerospace Show
Someone further up the food chain will be there but not me, I'm afraid. I'm sure you'll have an ale on my behalf ....
Someone further up the food chain will be there but not me, I'm afraid. I'm sure you'll have an ale on my behalf ....
Moderator
how do you learn the inversion layer temperature?
The met man is your friend ... normally measured using a radiosonde as, for example, in this link.
Probably not available for each and every airport but that would be a matter for some research into your local AIP.
The met man is your friend ... normally measured using a radiosonde as, for example, in this link.
Probably not available for each and every airport but that would be a matter for some research into your local AIP.
Ask the met man for his opinion of the Skew-T chart for the location in question. It is a plot of temp and humidity over the airport. Quite a bit of information, some obscure, but will clearly reveal an inversion layer. Hope his language isn't French. 
Places that have strong inversions are pretty well known.
GF
Places that have strong inversions are pretty well known.GF
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(relevant)
learn the inversion layer temperature?
Mutt
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Thank you for your posts and special thanks to certain gurus.
To add few information to previous quote, here a quote from this link:Assumed Temperature Thrust Reduction
a)For takeoff and approach, there is an assumption of one engine failure regarding the climb gradient. Why not such assumption on landing (3.2% with all engine operating)?
b)How a takeoff thrust time limit (5/10 minutes) can affect the aircraft (take off climb gradient, takeoff path,…)? Does this occur in reality (a fact and not only a theory) only during takeoff or even during go-around (missed approach, engine failure)?
Feedback appreciated
Regards
(f) with an aircraft engine, we want to be able to have our cake and eat it too - ie sometimes we want to operate to the maximum rating and, on other times, to a derated rating. However, we don't physically swap engines back and forth - that just wouldn't work in practice.
What we can do to achieve the same thing, in principle, is constrain the engine not to operate at power outputs higher than the declared reduced rating level. This can be done either by computer control or manual setting of lower power output using the engine gauges
What we can do to achieve the same thing, in principle, is constrain the engine not to operate at power outputs higher than the declared reduced rating level. This can be done either by computer control or manual setting of lower power output using the engine gauges
When an engine is de-rated, the full (un-de-rated) thrust is no longer available because this would require changes to the EEC, HMU, fuel pump, engine ID plug and the loadable software; non of which can be done by the pilot in-flight.
a)For takeoff and approach, there is an assumption of one engine failure regarding the climb gradient. Why not such assumption on landing (3.2% with all engine operating)?
b)How a takeoff thrust time limit (5/10 minutes) can affect the aircraft (take off climb gradient, takeoff path,…)? Does this occur in reality (a fact and not only a theory) only during takeoff or even during go-around (missed approach, engine failure)?
Feedback appreciated
Regards
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Hi AeroTech,
You've asked two very good questions -
a)For takeoff and approach, there is an assumption of one engine failure regarding the climb gradient. Why not such assumption on landing (3.2% with all engine operating)?
There is such an assumption on landing. The 3.2% gradient which you've quoted is with (i) All engines at TOGA thrust, (ii) Gear DOWN, and (iii) Flaps at the landing setting. Approach Climb Gradient must be provided for, and AFM data provides for a 2.1% Gradient with (i) One Engine operative, the remainder at TOGA thrust, (ii) Gear UP, and (iii) Flaps at the Approach Climb setting. (Flaps at the Approach Climb setting are typically at or close to normal Takeoff Flap settings). There is no lower altitude limit where Approach Climb (i.e. Engine Inop) may be used, it would also apply at the DH for a Cat III landing.
PANS-OPS and TERPS provide for a minimum 2.5% Gradient during missed approach, providing 100 ft of Obstacle Clearance. It is up to you, the pilot to compensate for the 0.4% difference between AFM Approach Climb "guarantees" and the required 2.5%. (You may use either of an increased approach minima, or consult performance data to guarantee 2.5% OEI Climb Gradient, or greater if required for the location).
b)How a takeoff thrust time limit (5/10 minutes) can affect the aircraft (take off climb gradient, takeoff path,…)? Does this occur in reality (a fact and not only a theory) only during takeoff or even during go-around (missed approach, engine failure)?
Very much so, particularly for the 5 minute limited aircraft. An actual example is probably the best explanation. I was working OEI Escape Routes and obstacle data for an Australian airport with numerous obstacles in the 2nd segment climb, and a "further out" higher obstacle in the 3rd Segment. The obstacles in the 2nd Segment required a somewhat increased OEI gradient, but still provided quite useful and commercially viable RTOWs for the Runway. So far, so good.....
Although the "further out" obstacle actually subtended a quite modest gradient to the runway, and thus didn't affect 2nd Segment, it DID require 3rd Segment MAA to be increased to 1650 ft AFL. Your every day 2 engined aircraft can usually handle MAA of 1100 to 1200 ft within the 5 minute limit for Takeoff Roll, 1st Segment, 2nd Segment, and 3rd Segment acceleration to Clean configuration within 5 minutes. The (actual case) 1650 ft MAA required well in excess of 5 minutes at Takeoff thrust to reach Clean configuration. The only solution was to ARTIFICIALLY "bump up" the 2nd Segment climb gradient to somewhat more than required, in order to achieve MAA in a shorter time, and constrain the time to Vcl within 5 minutes. Thus, 2nd Segment weight limits for the higher gradient significantly reduced the RTOW for the runway, reducing these to marginally commercially viable. (A 10 minute limited aircraft would have had no problem).
So...... The time limit at Takeoff thrust can directly impact upon Limiting Takeoff Weights.
Regards,
Old Smokey
You've asked two very good questions -
a)For takeoff and approach, there is an assumption of one engine failure regarding the climb gradient. Why not such assumption on landing (3.2% with all engine operating)?
There is such an assumption on landing. The 3.2% gradient which you've quoted is with (i) All engines at TOGA thrust, (ii) Gear DOWN, and (iii) Flaps at the landing setting. Approach Climb Gradient must be provided for, and AFM data provides for a 2.1% Gradient with (i) One Engine operative, the remainder at TOGA thrust, (ii) Gear UP, and (iii) Flaps at the Approach Climb setting. (Flaps at the Approach Climb setting are typically at or close to normal Takeoff Flap settings). There is no lower altitude limit where Approach Climb (i.e. Engine Inop) may be used, it would also apply at the DH for a Cat III landing.
PANS-OPS and TERPS provide for a minimum 2.5% Gradient during missed approach, providing 100 ft of Obstacle Clearance. It is up to you, the pilot to compensate for the 0.4% difference between AFM Approach Climb "guarantees" and the required 2.5%. (You may use either of an increased approach minima, or consult performance data to guarantee 2.5% OEI Climb Gradient, or greater if required for the location).
b)How a takeoff thrust time limit (5/10 minutes) can affect the aircraft (take off climb gradient, takeoff path,…)? Does this occur in reality (a fact and not only a theory) only during takeoff or even during go-around (missed approach, engine failure)?
Very much so, particularly for the 5 minute limited aircraft. An actual example is probably the best explanation. I was working OEI Escape Routes and obstacle data for an Australian airport with numerous obstacles in the 2nd segment climb, and a "further out" higher obstacle in the 3rd Segment. The obstacles in the 2nd Segment required a somewhat increased OEI gradient, but still provided quite useful and commercially viable RTOWs for the Runway. So far, so good.....
Although the "further out" obstacle actually subtended a quite modest gradient to the runway, and thus didn't affect 2nd Segment, it DID require 3rd Segment MAA to be increased to 1650 ft AFL. Your every day 2 engined aircraft can usually handle MAA of 1100 to 1200 ft within the 5 minute limit for Takeoff Roll, 1st Segment, 2nd Segment, and 3rd Segment acceleration to Clean configuration within 5 minutes. The (actual case) 1650 ft MAA required well in excess of 5 minutes at Takeoff thrust to reach Clean configuration. The only solution was to ARTIFICIALLY "bump up" the 2nd Segment climb gradient to somewhat more than required, in order to achieve MAA in a shorter time, and constrain the time to Vcl within 5 minutes. Thus, 2nd Segment weight limits for the higher gradient significantly reduced the RTOW for the runway, reducing these to marginally commercially viable. (A 10 minute limited aircraft would have had no problem).
So...... The time limit at Takeoff thrust can directly impact upon Limiting Takeoff Weights.
Regards,
Old Smokey