derated take off during Engine failure
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derated take off during Engine failure
Tm say if an engine failure occurs during take off, any thrust increase beyond the fixed derate limit could result in loss of directional control....
why we can loss control?
why we can loss control?
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With a fixed derate you use legally an engine with that lower thrust limit and the corresponding speeds. Especially Vmcg (minimum control speed ground) and Vmca (minimum control speed air) are based on the thrust setting.
If you increase the thrust beyond the fixed derate limit and your speed is near the approved Vmcg/a you might lose control as the controls cannot cope with that amount of thrust at that low a speed.
If you increase the thrust beyond the fixed derate limit and your speed is near the approved Vmcg/a you might lose control as the controls cannot cope with that amount of thrust at that low a speed.
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The greater the thrust, the greater the assymetry in case of an engine failure.
The greater the assymetry, the greater will the control forces required be.
With under-wing mounted enginges this can be a problem. I don't know about aircraft with the engines mounted in the tail though, anyone with experience on the falcon or MD?
The greater the assymetry, the greater will the control forces required be.
With under-wing mounted enginges this can be a problem. I don't know about aircraft with the engines mounted in the tail though, anyone with experience on the falcon or MD?
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It is to do with the Vm speeds; so I was instructed years ago. Further, the performance calculations have a little buffer between 100% perfect and the line duffer on the day. Thus they say it is not necessary to increase thrust to achieve the profile.
What I find disconcerting, and another dumb don in knowledge, is that people say it is not allowed to increase thrust. Some say they are nervous that once PF has the correct rudder inputed close to the ground it would be disturbing to cause an adjustment.
Personally, IMHO, there should be a 'note to self' in the training and during the manoeuvre: "choose 1.......a/c is performing as required......leave thrust alone. A/C is not climbing as required.......increase thrust and control a/c."
To not teach people the pro's & con's of use of thrust is negligent, but I see it every day.
What I find disconcerting, and another dumb don in knowledge, is that people say it is not allowed to increase thrust. Some say they are nervous that once PF has the correct rudder inputed close to the ground it would be disturbing to cause an adjustment.
Personally, IMHO, there should be a 'note to self' in the training and during the manoeuvre: "choose 1.......a/c is performing as required......leave thrust alone. A/C is not climbing as required.......increase thrust and control a/c."
To not teach people the pro's & con's of use of thrust is negligent, but I see it every day.
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Are you confusing a FLEX take off with a DERATED one? Very different beasts.
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Since increasing power reduces the controllability margin wouldn't decreasing power increase the controllability margin? Think about it. If you reduced the good engine's power to match the power of the bad engine lateral control issues would be reduced to zero.
Last edited by misd-agin; 21st Mar 2016 at 17:20. Reason: Added last sentence.
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I know nothing of Flex takeoffs. I understand the effect of thrust/speed on yaw & roll control. It is an effect at slow speed. VMCG is an on ground scenario. VMCA is airborne and again slow speed. If airborne and above V2 I suggest you should not be anywhere near VMCA. If I have the yaw & roll under control, but the ROC is suffering for an unknown reason, I feel capable of slowly increasing thrust to try and solve that problem while retaining control about the other 2 axis. That is what I've been trained to do, and in light twins, non perf A, was a regular airborne training manoeuvre with new pilots on type. Educating and illuminating, too.
I do not advocate increasing thrust as a common technique during an EFATO. (I have flown for one airline whose CP did advocate that as an SOP). What I do advocate is not teaching that it is not allowed.
I do not advocate increasing thrust as a common technique during an EFATO. (I have flown for one airline whose CP did advocate that as an SOP). What I do advocate is not teaching that it is not allowed.
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because the minimum v1, rotate and v2 speeds are restricted by the minimum control speeds and the minimum control speeds increase as rated thrust increases so increasing thrust beyond the rating used to define minimum control speeds and those speeds limited by them could put you in a position where the yaw effect of engine out is greater than can be countered aerodynamically at your scheduled speeds.
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This is becoming far too theoretical and in the ideal world for my simple way of thinking. I know the theory and the ratios & %'s for the various speeds. In the sim it works fine and has done for 40 years. In the real world, as they say on the rugby pitch, you play what's in front of you. The coach's best plans may need adjusting on the day. You need to be well aware of what you're doing. Perhaps there-in lies the hesitation. Too many treading into the darkness of the unknown nor understood.
Indeed there have been a/c whose rudder had too little authority, and with an EFATO it was necessary to reduce thrust on the live donk. That was to gain control in yaw and 2ndly roll. Assuming those 2 were acceptably under control I was only considering what was happening in pitch & ROC and seeing if anything needed to be done about that. I might feel rather sheepish trying to explain why I'd descended shallowly into farmer Fred's ploughed earth while having more power to call upon.
Indeed there have been a/c whose rudder had too little authority, and with an EFATO it was necessary to reduce thrust on the live donk. That was to gain control in yaw and 2ndly roll. Assuming those 2 were acceptably under control I was only considering what was happening in pitch & ROC and seeing if anything needed to be done about that. I might feel rather sheepish trying to explain why I'd descended shallowly into farmer Fred's ploughed earth while having more power to call upon.
This is becoming far too theoretical and in the ideal world for my simple way of thinking. I know the theory and the ratios & %'s for the various speeds. In the sim it works fine and has done for 40 years. In the real world
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VMCG means Jack all once you pass it and by V1 you are either on or above it.
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Hi flyhardmo & RAT 5,
Do you really understand the theory?
May I suggest you read: ASN Aircraft accident Boeing 707-436 G-APFK Glasgow-Prestwick Airport (PIK)
"At the light aircraft weights used for training, standardised takeoff airspeeds were used as follows: V1 - 125 knots, VR - 135 knots and V2 - 145 knots. Based on the prevailing conditions and actual aircraft takeoff weight of 94,580 kg, the true takeoff airspeeds were: V1 - 125 knots, VR - 125 knots and V2 - 142 knots; the VMCG and the VMCA were 125 knots and 119 knots respectively."
But they still crashed.
Please see the AAIB report: https://assets.digital.cabinet-offic...978_G-APFK.pdf
Para 2.4 which calculates the VMCA had risen to 160 kts with wings level.
You don't normally get that sort of in depth analysis if you crash the simulator.
We all know the theory behind it but practically nothing is stopping you from increasing thrust once above VMCA or V2.
Indeed there have been a/c whose rudder had too little authority, and with an EFATO it was necessary to reduce thrust on the live donk.
May I suggest you read: ASN Aircraft accident Boeing 707-436 G-APFK Glasgow-Prestwick Airport (PIK)
"At the light aircraft weights used for training, standardised takeoff airspeeds were used as follows: V1 - 125 knots, VR - 135 knots and V2 - 145 knots. Based on the prevailing conditions and actual aircraft takeoff weight of 94,580 kg, the true takeoff airspeeds were: V1 - 125 knots, VR - 125 knots and V2 - 142 knots; the VMCG and the VMCA were 125 knots and 119 knots respectively."
But they still crashed.
Please see the AAIB report: https://assets.digital.cabinet-offic...978_G-APFK.pdf
Para 2.4 which calculates the VMCA had risen to 160 kts with wings level.
You don't normally get that sort of in depth analysis if you crash the simulator.
Last edited by Goldenrivett; 22nd Mar 2016 at 09:02.
Only half a speed-brake
Yup. If you're above Vmca that had been calculated for 23k thrust, and decide to put in 27k, you may well find yourself inverted.
Another one here:
ASN Aircraft accident Airbus A330-321 F-WWKH Toulouse-Blagnac Airport (TLS)
Another one here:
ASN Aircraft accident Airbus A330-321 F-WWKH Toulouse-Blagnac Airport (TLS)
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The main desirable trait of this thread is the general admonition to be careful and cautious ..
I feel capable of slowly increasing thrust to try and solve that problem (my emphasis) ..
RAT 5's comment should be read carefully by all as it is written in blood. The certification animal doesn't look at thrust increases during a dynamic manoeuvre.
As a f'instance, an aeroplane with which I had some familiarity in a previous life had a reasonably well-behaved static Vmca and, indeed, could get to significant yaw angles. But life could get interesting in the dynamic situation.
I was involved in the on-site investigation of a fatal which (almost certainly - based on eye-witness debriefings) involved one of the pilot's panic advance of one throttle as the aircraft was about to impact the takeoff overrun. This particular aircraft had extremely good engines (very high mod status embodiment) and the thrust response, quite rapidly, saw the aircraft yaw/roll significantly and cartwheel after the wingtip impacted the runway strip end. (There were some related things which made the pilots' job much more difficult than it ought to have been but the thrust/yaw/roll/crash/burn/die exercise was, nonetheless, very obvious and devastatingly effective .. ).
If you elect to increase thrust (I'm not suggesting whether you should or should not) .. do it slowly so that the asymmetric effect can be assessed more easily and the requirement for rudder input adjustment made with some degree of confidence.
As an aside, the B707 report is worth reading to note the importance of bank angle on Vmca ..
I feel capable of slowly increasing thrust to try and solve that problem (my emphasis) ..
RAT 5's comment should be read carefully by all as it is written in blood. The certification animal doesn't look at thrust increases during a dynamic manoeuvre.
As a f'instance, an aeroplane with which I had some familiarity in a previous life had a reasonably well-behaved static Vmca and, indeed, could get to significant yaw angles. But life could get interesting in the dynamic situation.
I was involved in the on-site investigation of a fatal which (almost certainly - based on eye-witness debriefings) involved one of the pilot's panic advance of one throttle as the aircraft was about to impact the takeoff overrun. This particular aircraft had extremely good engines (very high mod status embodiment) and the thrust response, quite rapidly, saw the aircraft yaw/roll significantly and cartwheel after the wingtip impacted the runway strip end. (There were some related things which made the pilots' job much more difficult than it ought to have been but the thrust/yaw/roll/crash/burn/die exercise was, nonetheless, very obvious and devastatingly effective .. ).
If you elect to increase thrust (I'm not suggesting whether you should or should not) .. do it slowly so that the asymmetric effect can be assessed more easily and the requirement for rudder input adjustment made with some degree of confidence.
As an aside, the B707 report is worth reading to note the importance of bank angle on Vmca ..
Denti
One of the conditions to determine V1, at least in the Boeing world, is that it may not be less than Vmcg.
Logic demands this as well - given that after V1 you are committed to fly it will be unpleasant if you are unable to control the aircraft for a while.
One of the conditions to determine V1, at least in the Boeing world, is that it may not be less than Vmcg.
Logic demands this as well - given that after V1 you are committed to fly it will be unpleasant if you are unable to control the aircraft for a while.
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... but note that Vmcg is determined for prescribed wind component conditions .. if you are playing in the sand pit at light weights (ie low speed schedule) and in strong crosswinds ... all bets are off if the "wrong" side engine fails and you find yourself in the weeds.
The go-after-V1 mantra may need to be revised very quickly if you find yourself without adequate control (ie out of control).
.. in strong crosswind conditions at light weights on a local training exercise .. he who takes off without using speeds for higher weights .. is, indeed, a brave training captain.
Real world Vmcg can increase quite significantly with crosswind.
The go-after-V1 mantra may need to be revised very quickly if you find yourself without adequate control (ie out of control).
.. in strong crosswind conditions at light weights on a local training exercise .. he who takes off without using speeds for higher weights .. is, indeed, a brave training captain.
Real world Vmcg can increase quite significantly with crosswind.
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RAT 5's comment should be read carefully by all as it is written in blood.
John: Firstly I respect your knowledge and have learnt from many of your previous discussion points. This comment sounds most ominous. I wonder if I have understood it correctly, or if others have understood my comments correctly.
I have not advocated a technique of increasing thrust, ON THE GROUND, after an engine failure. I have not advocated, willy nilly, increasing thrust once airborne. I have certainly not even hinted at stuffing the lever to full thrust. What I've asked in debate & conversation is to consider what you might do, if using reduced thrust, when you find the a/c not accelerating or even sinking, or at any rate not climbing as you consider necessary? Who knows, an engine catastrophe might have prevented the gear retracting fully. What then to all your imperfect calculations?
It is simply a debate about whether pilots should be taught it is NEVER allowed to gently and smoothly increase thrust, once airborne, to assist in solving a performance problem without creating another. Once you reach a thrust setting to satisfy your needs then leave it.
Once again we are back to the level of education and depth of training. What I find disturbing is when asking cadets at FFS during TR courses: "what are VMCG & VMCA?" They might give you a perfect definition. Next question, "what do they mean in practical terms?" Often blank stares. You then move on to "what affects them; how can they change; how can you infringe them?" It is very sad to hear the silence.
John: Firstly I respect your knowledge and have learnt from many of your previous discussion points. This comment sounds most ominous. I wonder if I have understood it correctly, or if others have understood my comments correctly.
I have not advocated a technique of increasing thrust, ON THE GROUND, after an engine failure. I have not advocated, willy nilly, increasing thrust once airborne. I have certainly not even hinted at stuffing the lever to full thrust. What I've asked in debate & conversation is to consider what you might do, if using reduced thrust, when you find the a/c not accelerating or even sinking, or at any rate not climbing as you consider necessary? Who knows, an engine catastrophe might have prevented the gear retracting fully. What then to all your imperfect calculations?
It is simply a debate about whether pilots should be taught it is NEVER allowed to gently and smoothly increase thrust, once airborne, to assist in solving a performance problem without creating another. Once you reach a thrust setting to satisfy your needs then leave it.
Once again we are back to the level of education and depth of training. What I find disturbing is when asking cadets at FFS during TR courses: "what are VMCG & VMCA?" They might give you a perfect definition. Next question, "what do they mean in practical terms?" Often blank stares. You then move on to "what affects them; how can they change; how can you infringe them?" It is very sad to hear the silence.
Last edited by RAT 5; 22nd Mar 2016 at 10:53.
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Good sir, my apologies if my meaning was obscure.
I was not expressing any concern with your previous post .. only emphasising my concurrence with your admonition to play with thrust levers .. gently. We appear to be in heated agreement, generally ..
.. is to consider what you might do, if using reduced thrust, when you find the a/c not accelerating or even sinking, or at any rate not climbing as you consider necessary? Who knows, an engine catastrophe might have prevented the gear retracting fully. What then to all your imperfect calculations?
d'accord. Certification is all well and good ... and generally works fine in practice .. but is a postulated animal. As you observe, the real world doesn't always read the rules .. and, sometimes, the Commander is called upon to earn his/her dollar for the day by exercising command prerogative.
Once again we are back to the level of education and depth of training. What I find disturbing is when asking cadets at FFS during TR courses: "what are VMCG & VMCA?" They might give you a perfect definition. Next question, "what do they mean in practical terms?" Often blank stares. You then move on to "what affects them; how can they change; how can you infringe them?" It is very sad to hear the silence.
.. isn't that the oft-observed truth .. ?
It is my view that the main value of Tech Log is the depth of experience and technical expertise collectively put by a significant proportion of posters .. the potential educational value is of the greatest importance, especially for the new chums. Knowing who some of those posters are, in their real worlds .. it amazes me just how great the knowledge base is within PPRuNe ..
I was not expressing any concern with your previous post .. only emphasising my concurrence with your admonition to play with thrust levers .. gently. We appear to be in heated agreement, generally ..
.. is to consider what you might do, if using reduced thrust, when you find the a/c not accelerating or even sinking, or at any rate not climbing as you consider necessary? Who knows, an engine catastrophe might have prevented the gear retracting fully. What then to all your imperfect calculations?
d'accord. Certification is all well and good ... and generally works fine in practice .. but is a postulated animal. As you observe, the real world doesn't always read the rules .. and, sometimes, the Commander is called upon to earn his/her dollar for the day by exercising command prerogative.
Once again we are back to the level of education and depth of training. What I find disturbing is when asking cadets at FFS during TR courses: "what are VMCG & VMCA?" They might give you a perfect definition. Next question, "what do they mean in practical terms?" Often blank stares. You then move on to "what affects them; how can they change; how can you infringe them?" It is very sad to hear the silence.
.. isn't that the oft-observed truth .. ?
It is my view that the main value of Tech Log is the depth of experience and technical expertise collectively put by a significant proportion of posters .. the potential educational value is of the greatest importance, especially for the new chums. Knowing who some of those posters are, in their real worlds .. it amazes me just how great the knowledge base is within PPRuNe ..