737NG-Engine Failure during a Double Derate take off
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To inject an element of practicality into this...are we really going to need full rated thrust with an engine failure at low weight, leading to controllability issues? Where I would be considering full rated thrust following an engine failure would be somewhere like Sharm el Sheikh to the UK at max weight and 35+ degrees with a strong likelihood of a turbulent departure. Minimum speed considerations would not be an issue then. A lightweight departure on, for example, a ferry flight, would not present the same need for a thrust increase above the calculated figure. Something to be covered at the briefing stage methinks.
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Let's do not forget that the Power output at low speeds, is normally proportionally higher on turboprops compared to Jets.
Bit of a red herring, I suggest. The message we should be getting across to the newchums, in particular, is that thrust increases during the OEI exercise and especially at low weight and speed schedules ... are fraught with potential hazard. For the very great majority of OEI situations, there is no need to resort to increasing thrust ..
the answer would be the product of a risk assessment on what is more dangerous: Terrain closure Vs Yaw/Roll de-stabilizing moment....
Absolutely ! However, perhaps it is better to crash right way up with the aircraft under reasonable control .. rather than upside down and out of control ?
Must say I do not like Your tone on this one, considering You do not know what You are talking about.
My apologies .. not trying to be confrontational. Of course, you are entitled to your opinion.
Turboprops and B737-800,,, please?
While the details differ, the overall resulting effect is similar.
bump, may be needed when heawy ,,,not light
Agreed. However, the thrust of the discussion is to get the message across that there be dragons potentially lurking at very low weights and speed schedules.
We might just have to disagree on philosophy, perhaps ?
To inject an element of practicality into this..
Absolutely the case in practice.
For those who prefer to dismiss the concern out of hand .. I should relate that, with sim exercises intended to highlight the problem, even very experienced pilots (who had not seen the low weight/speed handling problems previously) found themselves caught out until they had the opportunity to play with the dragon.
Bit of a red herring, I suggest. The message we should be getting across to the newchums, in particular, is that thrust increases during the OEI exercise and especially at low weight and speed schedules ... are fraught with potential hazard. For the very great majority of OEI situations, there is no need to resort to increasing thrust ..
the answer would be the product of a risk assessment on what is more dangerous: Terrain closure Vs Yaw/Roll de-stabilizing moment....
Absolutely ! However, perhaps it is better to crash right way up with the aircraft under reasonable control .. rather than upside down and out of control ?
Must say I do not like Your tone on this one, considering You do not know what You are talking about.
My apologies .. not trying to be confrontational. Of course, you are entitled to your opinion.
Turboprops and B737-800,,, please?
While the details differ, the overall resulting effect is similar.
bump, may be needed when heawy ,,,not light
Agreed. However, the thrust of the discussion is to get the message across that there be dragons potentially lurking at very low weights and speed schedules.
We might just have to disagree on philosophy, perhaps ?
To inject an element of practicality into this..
Absolutely the case in practice.
For those who prefer to dismiss the concern out of hand .. I should relate that, with sim exercises intended to highlight the problem, even very experienced pilots (who had not seen the low weight/speed handling problems previously) found themselves caught out until they had the opportunity to play with the dragon.
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are we really going to need full rated thrust with an engine failure at low weight, leading to controllability issues
This reduces impact of any failure on departure, such as a bird strike or engine failure, while minimising time to cruise level afterwards and thus saving fuel.
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John, if you take off with double de-rate, you basically cut a good margin from the Actual temperature Vs Assumed Temperature.
If on top of that you add improved climb speed profile, your initial margin from the highest obstacle in the first, second and third segment is reduced even furthef.
If you Take Off from a relatively flat area, the my risk assessment would say that the directional control stability could be of higher importance.
If you take off from a field surrounded by high obstacles / terrain, my personal risk assessment brings me to believe that the worst danger is the terrain.
On the B737-NG JET, with light weights, high flap settings, -60ºC of temperature and -2000ft, your directional control cannot be impaired by the over trust because you are flying with more than 15 Kts overall margin from the Dragon nest.
But if you, John, want to be super-safe, maybe it is just better not to fly at all! Let the dragon fly for you.
Greetings from a newchum!
If on top of that you add improved climb speed profile, your initial margin from the highest obstacle in the first, second and third segment is reduced even furthef.
If you Take Off from a relatively flat area, the my risk assessment would say that the directional control stability could be of higher importance.
If you take off from a field surrounded by high obstacles / terrain, my personal risk assessment brings me to believe that the worst danger is the terrain.
On the B737-NG JET, with light weights, high flap settings, -60ºC of temperature and -2000ft, your directional control cannot be impaired by the over trust because you are flying with more than 15 Kts overall margin from the Dragon nest.
But if you, John, want to be super-safe, maybe it is just better not to fly at all! Let the dragon fly for you.
Greetings from a newchum!
soundlover, et al, the risk assessment is not quite as is suggested.
First the thread title might be misleading; consider a takeoff with engines rated at a value less than maximum, but where this is the new max thrust. Then a reduced thrust takeoff would be allowed under existing rules.
These ensure that in the event of engine failure the minimum speeds do not jeopardise the flight handling safety margin, or the climb performance detracts from the obstacle clearance safety margin. Thus like-for-like, a ‘double derate’ takeoff provides equivalent safety.
It is only when additive and rare circumstances are considered that many aspects of this debate apply, but even then, the safety of any operation requires other considerations, e.g. consider the wind shear risk before takeoff.
Whilst all of the non-additive situations provide a safety margin, the value of the margin or the rate at which the limit could be approached are not identical; in this instance low weight / speed being more demanding.
Thus whatever reasoning there might be for applying more power in rare circumstances, the risk assessment should consider the aspects above, particularly where the bottom line of doing nothing is no more hazardous than for any take-off with or without the ‘additive’ situations, but alternatively acting hastily, or with surprise, or misjudgement of the situation, then the actions could seriously reduce the safety margins and the the ability to maintain control.
Safety is the art of knowing where the ‘edge’ is and maintaining a sufficient margin for any error – yours or others.
Engine Malfunction Recognition and Response.
http://www.faa.gov/documentLibrary/m...ar/AC25-13.pdf
http://www.theairlinepilots.com/foru...atedthrust.pdf
First the thread title might be misleading; consider a takeoff with engines rated at a value less than maximum, but where this is the new max thrust. Then a reduced thrust takeoff would be allowed under existing rules.
These ensure that in the event of engine failure the minimum speeds do not jeopardise the flight handling safety margin, or the climb performance detracts from the obstacle clearance safety margin. Thus like-for-like, a ‘double derate’ takeoff provides equivalent safety.
It is only when additive and rare circumstances are considered that many aspects of this debate apply, but even then, the safety of any operation requires other considerations, e.g. consider the wind shear risk before takeoff.
Whilst all of the non-additive situations provide a safety margin, the value of the margin or the rate at which the limit could be approached are not identical; in this instance low weight / speed being more demanding.
Thus whatever reasoning there might be for applying more power in rare circumstances, the risk assessment should consider the aspects above, particularly where the bottom line of doing nothing is no more hazardous than for any take-off with or without the ‘additive’ situations, but alternatively acting hastily, or with surprise, or misjudgement of the situation, then the actions could seriously reduce the safety margins and the the ability to maintain control.
Safety is the art of knowing where the ‘edge’ is and maintaining a sufficient margin for any error – yours or others.
Engine Malfunction Recognition and Response.
http://www.faa.gov/documentLibrary/m...ar/AC25-13.pdf
http://www.theairlinepilots.com/foru...atedthrust.pdf
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Don't understand that obsession with increasing thrust (well, it sounds a bit like ssg). Take off performance calculations take into account the current conditions, obstacle situation and any other special conditions. We do fly into airports with quite a bit of terrain around like SZG or INN and have all the special approvals one can get for those airports, we wouldn't even think about increasing thrust until cleaned up there, there is simply not need to do so. It is much easier to fly the airplane, don't fiddle with any thrust issues and follow the EOSID. And of course the lowest V speeds we use are well into two figure territory on the NG.
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you basically cut a good margin
May I emphasise that, as a pilot and performance engineer, I have absolutely no problem using derate plus ATM plus overspeed schedules when appropriate .. providing that the folks doing the sums are competent. Unfortunately that doesn't always apply from what anecdotes I hear from time to time ..
If you Take Off from a relatively flat area, the my risk assessment would say that the directional control stability could be of higher importance.
Concur
If you take off from a field surrounded by high obstacles / terrain, my personal risk assessment brings me to believe that the worst danger is the terrain.
Caveat - if the sums have been done competently and the monitored performance is appropriate (we do all know what sort of ROC we are looking for on the day, don't we ?) then, in the absence of some obvious performance problem (is the actual wind significantly different from what was anticipated ?), terrain clearance isn't likely to be of any real consequence .. which should increase the control problem risk potential in the HRA.
On the B737-NG
As I made clear, I cannot speak specifically to the NG as I didn't fly it. However, with a rapid thrust increase, 15kts might end up being diddly squat as a buffer regardless of Type and Model.
But if you, John, want to be super-safe
Not looking to be super safe - life is a risk whichever way one looks at it - only as safe as I can reasonably achieve. Knowledge of these various and oddball things is quite material to that aim, I suggest.
Greetings from a newchum!
Welcome aboard the Tech Log sandpit.
well, it sounds a bit like ssg
Come to think of it, we haven't seen our friend around for quite some time, now ...
May I commend PEI_3721's and Denti's repective commentaries, immediately above, to the readership ?
May I emphasise that, as a pilot and performance engineer, I have absolutely no problem using derate plus ATM plus overspeed schedules when appropriate .. providing that the folks doing the sums are competent. Unfortunately that doesn't always apply from what anecdotes I hear from time to time ..
If you Take Off from a relatively flat area, the my risk assessment would say that the directional control stability could be of higher importance.
Concur
If you take off from a field surrounded by high obstacles / terrain, my personal risk assessment brings me to believe that the worst danger is the terrain.
Caveat - if the sums have been done competently and the monitored performance is appropriate (we do all know what sort of ROC we are looking for on the day, don't we ?) then, in the absence of some obvious performance problem (is the actual wind significantly different from what was anticipated ?), terrain clearance isn't likely to be of any real consequence .. which should increase the control problem risk potential in the HRA.
On the B737-NG
As I made clear, I cannot speak specifically to the NG as I didn't fly it. However, with a rapid thrust increase, 15kts might end up being diddly squat as a buffer regardless of Type and Model.
But if you, John, want to be super-safe
Not looking to be super safe - life is a risk whichever way one looks at it - only as safe as I can reasonably achieve. Knowledge of these various and oddball things is quite material to that aim, I suggest.
Greetings from a newchum!
Welcome aboard the Tech Log sandpit.
well, it sounds a bit like ssg
Come to think of it, we haven't seen our friend around for quite some time, now ...
May I commend PEI_3721's and Denti's repective commentaries, immediately above, to the readership ?
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In Summary...
Thank you folks for sharing your expertise and a lot of valuable insight into the various issues associated with this.
In Summary:[LIST][*]The manufacturer does not recommend you do it
[*]unless you establish a procedure (e.g.Matey,Thomson policy.) [*]Difficult to teach the next gen unless it is documented 
[*]if push comes to shove it can still be done, albeit very gently and at a safe speed above full rated VMCA (which needs to be predetermined.) 
[*]Not many operators out there who have established a "procedure"[LIST]
thanks once again to All who contributed
cheers
In Summary:[LIST][*]The manufacturer does not recommend you do it
[*]unless you establish a procedure (e.g.Matey,Thomson policy.) [*]Difficult to teach the next gen unless it is documented [*]if push comes to shove it can still be done, albeit very gently and at a safe speed above full rated VMCA (which needs to be predetermined.) [*]Not many operators out there who have established a "procedure"[LIST]thanks once again to All who contributed
cheers
