Usind the Assumed Temp/Thrust Derate - the Engine failure scenario
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Usind the Assumed Temp/Thrust Derate - the Engine failure scenario
Hi Guys, just been reading our Flight Crew Training Manual (FCTM) and we have a new insertion, stating that;
"The fixed derate is considered a limitation for takeoff. Takeoff speeds consider ground and in-air minimum control speeds (VMCG and VMCA) at the fixed derate level of thrust"
It then goes on to say in the engine out case, you should not increase thrust on the live engine as loss of directional control may occur....
Can anyone give a reasonably easy to understand explanation as to why this may be.
Rgds
JJ757
"The fixed derate is considered a limitation for takeoff. Takeoff speeds consider ground and in-air minimum control speeds (VMCG and VMCA) at the fixed derate level of thrust"
It then goes on to say in the engine out case, you should not increase thrust on the live engine as loss of directional control may occur....
Can anyone give a reasonably easy to understand explanation as to why this may be.
Rgds
JJ757
Back to you SSG Version 1.0-1.9. Inside joke 
The reason is that those two speeds, Vmcg and Vmca, are determined by thrust. Increasing the thrust on the live engine would increase those numbers and, hence, affect adversely directional control. Further V1, Vr, and V2 are related (Old Smoke, help me here) to Vmcg and Vmca. V1 must be greater than Vmcg for you directional on the runway using aerodynamic controls only; Vr and V2 must also exceed Vmca by certain margins to ensure control airborne. If you increase thrust on that live engine, you can see that the numbers the take-off was predicated on have all increased and IF you followed the planned speeds at increased thrust, it could be bad.
GF
The reason is that those two speeds, Vmcg and Vmca, are determined by thrust. Increasing the thrust on the live engine would increase those numbers and, hence, affect adversely directional control. Further V1, Vr, and V2 are related (Old Smoke, help me here) to Vmcg and Vmca. V1 must be greater than Vmcg for you directional on the runway using aerodynamic controls only; Vr and V2 must also exceed Vmca by certain margins to ensure control airborne. If you increase thrust on that live engine, you can see that the numbers the take-off was predicated on have all increased and IF you followed the planned speeds at increased thrust, it could be bad.
GF
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I think that you've argued the case quite well galaxy flyer, no need to call for reinforcements!
757jetjockey, the author of those words included in your FCTM was a wise person indeed, I've had the pleasure of writing similar prohibitions in our own manuals.
Vmcg and Vmca are indeed predicated upon the Rated Thrust used. Even if a further thrust reduction occurs (as in the use of Assumed Temperature or Flex Thrust), Vmcg and Vmca are still based upon the Rated thrust used. This applies to derates, and similarly (in the reverse sense) to aircraft such as the Jungle Jet with APR OFF, and APR ARMED as Takeoff thrust choices.
Lower Vmcg in many cases leads to lower V1s, and everyone loves lower V1s. Lower V1 becomes particularly attractive when Wet or Contaminated runways are in use, because the appropriately lower Vmcg adds enormously to improved directional control (or JUST meets adequate directional control). Thus, increasing thrust beyond the derated Thrust at V1 may lead to serious directional control problems, or complete loss of directional control. In these circumstances, Reduced Thrust (Assumed Temp / Flex) COULD be increased to the Rated Thrust, but certainly NOT to Full Thrust Rating. My attitude to the latter point is to let "sleeping dogs lie", leave the thrust alone, and enjoy the improved directional control in the knowledge that sufficient performance exists in any case.
Similar arguments apply to V2, with the caveat that not a great number of takeoffs for long haul operations are V2/Vmca limited (because of the higher weights), but short haul operators who frequently use lower V2 speeds (because of the lower weights) governed by Vmca, may more frequently encounter Vmca limited V2 speeds. The problem is, when the engine failure occurs, do you have prior knowledge if your V1 or V2 is Vmc limited, and who does that? I don't, and I'm a performance nerd.
Thus, your operator has, in my opinion applied very sound policy.
During my performance nerding at my desk (not in the cockpit), I've found that the aircraft that I primarily handle for performance analysis is frequently V1/Vmcg limited, but the V2 speeds for all thrust ratings is the same. Thus I have incorporated into THAT aircraft's operating manuals, "Following engine failure during Takeoff, thrust must NOT be increased to the full rating until V2 speed is achieved"
EXTREME WARNING - The above-mentioned allowance to increase to Full Thrust after V2 has been reached applies to this particular aircraft only. It may not apply to your aircraft.
In short, using a lower Thrust Rating is primarily beneficial for the continued Takeoff case, particularly on wet or slippery runways. Using the Full thrust rating is primarily beneficial for the Rejected Takeoff case (where Vmcg is not a problem for more than a second or two).
Conversly, for APR equipped aircraft (like the jungle jet), APR OFF is primarily beneficial for the Rejected Takeoff case, whilst APR ARMED is primarily beneficial for the Continued Takeoff case (unless the runway is wet or slippery). (A few other factors come into this argument).
Best Regards,
Old Smokey
757jetjockey, the author of those words included in your FCTM was a wise person indeed, I've had the pleasure of writing similar prohibitions in our own manuals.
Vmcg and Vmca are indeed predicated upon the Rated Thrust used. Even if a further thrust reduction occurs (as in the use of Assumed Temperature or Flex Thrust), Vmcg and Vmca are still based upon the Rated thrust used. This applies to derates, and similarly (in the reverse sense) to aircraft such as the Jungle Jet with APR OFF, and APR ARMED as Takeoff thrust choices.
Lower Vmcg in many cases leads to lower V1s, and everyone loves lower V1s. Lower V1 becomes particularly attractive when Wet or Contaminated runways are in use, because the appropriately lower Vmcg adds enormously to improved directional control (or JUST meets adequate directional control). Thus, increasing thrust beyond the derated Thrust at V1 may lead to serious directional control problems, or complete loss of directional control. In these circumstances, Reduced Thrust (Assumed Temp / Flex) COULD be increased to the Rated Thrust, but certainly NOT to Full Thrust Rating. My attitude to the latter point is to let "sleeping dogs lie", leave the thrust alone, and enjoy the improved directional control in the knowledge that sufficient performance exists in any case.
Similar arguments apply to V2, with the caveat that not a great number of takeoffs for long haul operations are V2/Vmca limited (because of the higher weights), but short haul operators who frequently use lower V2 speeds (because of the lower weights) governed by Vmca, may more frequently encounter Vmca limited V2 speeds. The problem is, when the engine failure occurs, do you have prior knowledge if your V1 or V2 is Vmc limited, and who does that? I don't, and I'm a performance nerd.
Thus, your operator has, in my opinion applied very sound policy.
During my performance nerding at my desk (not in the cockpit), I've found that the aircraft that I primarily handle for performance analysis is frequently V1/Vmcg limited, but the V2 speeds for all thrust ratings is the same. Thus I have incorporated into THAT aircraft's operating manuals, "Following engine failure during Takeoff, thrust must NOT be increased to the full rating until V2 speed is achieved"
EXTREME WARNING - The above-mentioned allowance to increase to Full Thrust after V2 has been reached applies to this particular aircraft only. It may not apply to your aircraft.
In short, using a lower Thrust Rating is primarily beneficial for the continued Takeoff case, particularly on wet or slippery runways. Using the Full thrust rating is primarily beneficial for the Rejected Takeoff case (where Vmcg is not a problem for more than a second or two).
Conversly, for APR equipped aircraft (like the jungle jet), APR OFF is primarily beneficial for the Rejected Takeoff case, whilst APR ARMED is primarily beneficial for the Continued Takeoff case (unless the runway is wet or slippery). (A few other factors come into this argument).
Best Regards,
Old Smokey
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galaxy flyer,
Loved your little dig at "SSG Version 1.0-1.9". I guess that as SSG doesn't like "taking it to the fence", he/she will be using Full Takeoff thrust in ALL cases.
No more taking it to the fence eh SSG, I guess that "taking it to the ditch beside the runway" is a much improved option on a wet and slippery runway.
BTW ssg, as you state that you see we Airline automatons taking it to the fence ALL THE TIME, you must see an incredible number of engine failures. Those same dumb regulations that allow us to do reduced thrust takeoffs also require a 15% margin on runway length for the all engines takeoff. Thus, on the average 10,000 foot runways used by the airline automatons, we should be at 35 feet by 1,500 feet before the end of the runway. Maybe you have fences across the runway 1,500 feet before the end in your part of the world.
Standing by for SSG Version 1.10
Regards,
Old Smokey
Loved your little dig at "SSG Version 1.0-1.9". I guess that as SSG doesn't like "taking it to the fence", he/she will be using Full Takeoff thrust in ALL cases.
No more taking it to the fence eh SSG, I guess that "taking it to the ditch beside the runway" is a much improved option on a wet and slippery runway.
BTW ssg, as you state that you see we Airline automatons taking it to the fence ALL THE TIME, you must see an incredible number of engine failures. Those same dumb regulations that allow us to do reduced thrust takeoffs also require a 15% margin on runway length for the all engines takeoff. Thus, on the average 10,000 foot runways used by the airline automatons, we should be at 35 feet by 1,500 feet before the end of the runway. Maybe you have fences across the runway 1,500 feet before the end in your part of the world.
Standing by for SSG Version 1.10
Regards,
Old Smokey
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Thus I have incorporated into THAT aircraft's operating manuals, "Following engine failure during Takeoff, thrust must NOT be increased to the full rating until V2 speed is achieved"
Interesting comment. While I agree with it, I wonder if many of the 'new generation' pilots understand it. I have not seen it so written in any ops manual of the 10 airlines I've worked for. But, indeed, there was 1 airline where the SOP on V1 cut was to increase to full power. Hm? Another left it to captain's discretion. Hm?
You say a/c type might be significant. B732, 733, 737, 739, B757, B767. I can't remember which of them was go to full power, but I hazard a guess it was a B767-300 operator becasue they didn't undertand the a/c in many other areas either. The Ops manual was written by an old B707 pilot.
Interesting comment. While I agree with it, I wonder if many of the 'new generation' pilots understand it. I have not seen it so written in any ops manual of the 10 airlines I've worked for. But, indeed, there was 1 airline where the SOP on V1 cut was to increase to full power. Hm? Another left it to captain's discretion. Hm?
You say a/c type might be significant. B732, 733, 737, 739, B757, B767. I can't remember which of them was go to full power, but I hazard a guess it was a B767-300 operator becasue they didn't undertand the a/c in many other areas either. The Ops manual was written by an old B707 pilot.
Moderator
.. the next aircraft which ends up on its back in a smoking pile of aluminium, having cartwheeled across the runway head as a result of pushing the levers up after a failure ... won't be the first ...
there was 1 airline where the SOP on V1 cut was to increase to full power
maybe not too much of a problem at high weight ... at low weight/speed schedule .. probably/possibly a death wish.
there was 1 airline where the SOP on V1 cut was to increase to full power
maybe not too much of a problem at high weight ... at low weight/speed schedule .. probably/possibly a death wish.
I always liked the KC-135R (with CFM56s) procedure-idle the opposite engine! It then had about the same thrust as the original with water going!
There appears to be a SSG 1.10 as I.R.PIRATE on the Africa forum-if it isn't him- a good duplicate.
John, I always thought perf planning was hastily covered, after lunch, by the least interesting instructor (not you or OS) and everyone wanted off for the day. Too much stressed drilling thru charts, which bored the crowd, and not enough on the basic physics involved. It is not hard, but does require some thought. The FAA (thru Part 25) dumbs it down more. How many Vmcg threads have there been? And still most people do not understand the concept, the effects of runway condition and crosswinds.
There appears to be a SSG 1.10 as I.R.PIRATE on the Africa forum-if it isn't him- a good duplicate.
John, I always thought perf planning was hastily covered, after lunch, by the least interesting instructor (not you or OS) and everyone wanted off for the day. Too much stressed drilling thru charts, which bored the crowd, and not enough on the basic physics involved. It is not hard, but does require some thought. The FAA (thru Part 25) dumbs it down more. How many Vmcg threads have there been? And still most people do not understand the concept, the effects of runway condition and crosswinds.
Moderator
... which is why you, me, OS and mutt like to see them come up from time to time. It's a case of not being significant on every takeoff .. but if the weight is low and the speed Vmc limited .. then a bit of understanding might just avoid Capt Bloggs' getting himself into more strife than he needs.
We Aussies were quite fortunate ... AN, in the olden days, had a pretty good approach to performance for pilots .. the early course notes, put together by folk such as John Walsh, Roger Gabriel, et al (actually, I've never met Al .. but I guess he is a fine chap) covered the certification considerations in considerable detail. Likewise TAA's (subsequently Australian and now Qantas domestic) Pete Turner, Qantas' Wal Stack (Wal's original pilot course - a moderately thick paper - is quite prized by most folk ... I have several copies for auction ...). Certainly, with the operators for whom I did the ops engineering stuff .. the boys got the full going over with certification ins and outs ... and I have no doubt that OS does the same for his current clients. A lot depends on the attitude and desires of the Chief Pilot ...
Unfortunately, the "must know" philosophies have cut the available time down to nothing and, often, the presentations are made by folk whose knowledge is adequate rather than extensive.
C'est la vie, I guess ...
We Aussies were quite fortunate ... AN, in the olden days, had a pretty good approach to performance for pilots .. the early course notes, put together by folk such as John Walsh, Roger Gabriel, et al (actually, I've never met Al .. but I guess he is a fine chap) covered the certification considerations in considerable detail. Likewise TAA's (subsequently Australian and now Qantas domestic) Pete Turner, Qantas' Wal Stack (Wal's original pilot course - a moderately thick paper - is quite prized by most folk ... I have several copies for auction ...). Certainly, with the operators for whom I did the ops engineering stuff .. the boys got the full going over with certification ins and outs ... and I have no doubt that OS does the same for his current clients. A lot depends on the attitude and desires of the Chief Pilot ...
Unfortunately, the "must know" philosophies have cut the available time down to nothing and, often, the presentations are made by folk whose knowledge is adequate rather than extensive.
C'est la vie, I guess ...
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I spend about 4 hours on this subject alone in our type rating course. It always surprises me how little is understood (even less after the 4 hours). And that applies equally to ab-initio and long in the tooth pilots.
The whole thing is complicated some what by the use of ATTCS which boosts thrust in the case of an engine failure. But also does so in the case of wind shear. However the pilot can also manually select RSV thrust by pushing the thrust levers forward. Depending on the circumstances the thrust you get when you push to MAX could be Normal TO or TO-RSV or GA-RSV.
I know it saves money but the complication it adds can sometimes overwhelm the pilots.
The whole thing is complicated some what by the use of ATTCS which boosts thrust in the case of an engine failure. But also does so in the case of wind shear. However the pilot can also manually select RSV thrust by pushing the thrust levers forward. Depending on the circumstances the thrust you get when you push to MAX could be Normal TO or TO-RSV or GA-RSV.
I know it saves money but the complication it adds can sometimes overwhelm the pilots.
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I have no VC10 knowledge and it may well be that the Type is never Vmc limited nor, indeed, near limited. If that is the case, then the protocol may well be fine, depending on the overall effect of whatever thrust you get .. whether rated or some degree of more than rated thrust.
As I recall, some of the Citations are similar in that the Vmc limits are way below minimum speed schedules.
As I recall, some of the Citations are similar in that the Vmc limits are way below minimum speed schedules.
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Very interesting post by Old Smokey, allways a pleasure to learn something.
Actually we do have the same caution in our manuals for the derate case, however we do have at least a Vmcg table for each thrust setting so we can see if we are Vmcg restricted with our V1, sadly there is no information about Vmca (737-700). We dont use derate on our -300s allthough it is available, no clue why.
I dont know if its true, but using derate, assument temperature and improved climb can lead to pretty high V-speeds (V1 past 150 and Vr well past 160) on long runways, is it safe to assume that with such high speeds controllability is actually pretty much a non-issue if we get the dreaded engine failure after V1?
Actually we do have the same caution in our manuals for the derate case, however we do have at least a Vmcg table for each thrust setting so we can see if we are Vmcg restricted with our V1, sadly there is no information about Vmca (737-700). We dont use derate on our -300s allthough it is available, no clue why.
I dont know if its true, but using derate, assument temperature and improved climb can lead to pretty high V-speeds (V1 past 150 and Vr well past 160) on long runways, is it safe to assume that with such high speeds controllability is actually pretty much a non-issue if we get the dreaded engine failure after V1?
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Please can I clarify this to my own satisfaction. Airbus person.
My understanding is that this 'gotcha' of inreasing thrust after a V1 cut is only applicable to a derate take off (Boeing) as opposed to a flex thrust (assumed temp) take off (Airbus) - a generality I know. Am I correct?
My concern is operating to increased/improved V2 on a wet r/w when close in obstacle limited as has been debated before on this forum.
Regards
mcdhu
My understanding is that this 'gotcha' of inreasing thrust after a V1 cut is only applicable to a derate take off (Boeing) as opposed to a flex thrust (assumed temp) take off (Airbus) - a generality I know. Am I correct?
My concern is operating to increased/improved V2 on a wet r/w when close in obstacle limited as has been debated before on this forum.
Regards
mcdhu
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I agree with the argument as far as V MCG is concerned. VMCA is a different issue.
To use more than 5° of bank is no problem as long as you meet the required climb gradient.
So our FCTM only refers to the V MCG even after the amendment.
To use more than 5° of bank is no problem as long as you meet the required climb gradient.
So our FCTM only refers to the V MCG even after the amendment.
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My understanding is that this 'gotcha' of inreasing thrust after a V1 cut is only applicable to a derate take off (Boeing) as opposed to a flex thrust (assumed temp) take off (Airbus) - a generality I know. Am I correct?
Mutt
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If I may add to Mutt's observation .. include aircraft with pilot limited thrust .. ie those where the pilot can push the levers to command greater than rated thrust. Same concern/result as with derate.
The problem is at the lower weights with low speed schedules. In general, unless there is another problem involved, a simple engine failure ought not require that the levers be moved ....
To use more than 5° of bank is no problem as long as you meet the required climb gradient
some considerations..
(a) 5 deg is the max permitted for certification to keep everyone honest
(b) Vmc speeds are very sensitive to bank
(c) likewise climb performance OEI
(d) given that the optimum bank is somewhere around 2-3 degrees ... a substantial increase puts you in a significant sideslip situation at low speed .. is that a good idea ?
The problem is at the lower weights with low speed schedules. In general, unless there is another problem involved, a simple engine failure ought not require that the levers be moved ....
To use more than 5° of bank is no problem as long as you meet the required climb gradient
some considerations..
(a) 5 deg is the max permitted for certification to keep everyone honest
(b) Vmc speeds are very sensitive to bank
(c) likewise climb performance OEI
(d) given that the optimum bank is somewhere around 2-3 degrees ... a substantial increase puts you in a significant sideslip situation at low speed .. is that a good idea ?
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Some years ago I'm in the L1011 sim with the chief pilot, and his idea is to firewall the throttles of the remaining operating engines in the event of the one engine out scenario.
I try to explain that this is not only not a good idea, but downright dangereous.
He says...show me.
Whereupon we 'depart' at quite a low weight with a max derate thrust.
Number three fails just at rotation.
CP applies firewall thrust...and the machine promptly rolls over on its back....or rather is freezes just before doing so.
CP now has eyes as big as dinner plates, and says....'I never thought....'
Yep, he never did.
I try to explain that this is not only not a good idea, but downright dangereous.
He says...show me.
Whereupon we 'depart' at quite a low weight with a max derate thrust.
Number three fails just at rotation.
CP applies firewall thrust...and the machine promptly rolls over on its back....or rather is freezes just before doing so.
CP now has eyes as big as dinner plates, and says....'I never thought....'
Yep, he never did.