Can a 2 engines plane takeoff at MTOW when 1 engine quits,or only at lower weight?
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Can a 2 engines plane takeoff at MTOW when 1 engine quits,or only at lower weight?
Hi,
I can't seem to find a certain answer on the internet, so I dare putting this important question here?
For example, are the 2 engine planes MTOW (maximum takeoff weight) defined or calculated as to allow the planes to safely climb out from a very long runway with no obstacles ahead (which allows for the highest MTOW) when one engine quits? Or are there other design limitation which won't recommend a weight higher than MTOW, such as the maximum weight which the landing gear can carry, regardless of being able to takeoff with an engine loss? I personally believe that the highest MTOW should not be higher than it could allow any commercial aircraft to takeoff and safely climb out (at a much lower vertical speed rate though) in one engine, for aircraft with 2 engines as example.
Wikipedia says just that about the MTOW, but other sources say differently, telling that an aircraft with 2 engines may not safely climb out at MTOW if one engine quits, thus the weight must be limited below MTOW, so I still find this general rule unclear. I think that the PART 25 (or JAR 25) regulates the maximum allowable takeoff weight for any aircraft taking into account the remaining thrust available when 1 or more engines fail in order to still have the aircraft safely climbing out with the highest possible MTOW.
For example, can an MD-82 safely climb out when loaded at 149500lbs (the MD-82's highest MTOW) if one engine fails well above V1, let's say, exactly when the pilot starts pulling for takeoff, or they must do whatever possible to reject the takeoff and stop it even with the consequence of hitting ILS poles, etc. (which would be much better than taking off and crashing anyway)? In this kind of circumstance, if I were to choose between continuing to try and lift it off the ground (there is no turning back from this point, so If I made a terrible mistake, I'm done...) or doing whatever possible to brake it even if I have to make an off-runway excursion and having to chose on what obstacles I should hit if obstacles are unavoidable, I'd rather choose this, for there will be much higher chances of surviving rather than daring to takeoff and finding out that the speed will only keep on dropping after liftoff even with one engine screaming at max. RPM and even if I'll try to retract the flaps (but keep the slats out) and fly leveled in order to reduce the drag, the speed would still drop..., that would mean the end!
So, I wonder if the MD-82 for example, with it's tiny JT-8D 217C engines with 21000lbf (maximum for 5 minutes) each would be capable of safely climbing out when loaded at highest MTOW if one engine stops?
Thank you.
I can't seem to find a certain answer on the internet, so I dare putting this important question here?
For example, are the 2 engine planes MTOW (maximum takeoff weight) defined or calculated as to allow the planes to safely climb out from a very long runway with no obstacles ahead (which allows for the highest MTOW) when one engine quits? Or are there other design limitation which won't recommend a weight higher than MTOW, such as the maximum weight which the landing gear can carry, regardless of being able to takeoff with an engine loss? I personally believe that the highest MTOW should not be higher than it could allow any commercial aircraft to takeoff and safely climb out (at a much lower vertical speed rate though) in one engine, for aircraft with 2 engines as example.
Wikipedia says just that about the MTOW, but other sources say differently, telling that an aircraft with 2 engines may not safely climb out at MTOW if one engine quits, thus the weight must be limited below MTOW, so I still find this general rule unclear. I think that the PART 25 (or JAR 25) regulates the maximum allowable takeoff weight for any aircraft taking into account the remaining thrust available when 1 or more engines fail in order to still have the aircraft safely climbing out with the highest possible MTOW.
For example, can an MD-82 safely climb out when loaded at 149500lbs (the MD-82's highest MTOW) if one engine fails well above V1, let's say, exactly when the pilot starts pulling for takeoff, or they must do whatever possible to reject the takeoff and stop it even with the consequence of hitting ILS poles, etc. (which would be much better than taking off and crashing anyway)? In this kind of circumstance, if I were to choose between continuing to try and lift it off the ground (there is no turning back from this point, so If I made a terrible mistake, I'm done...) or doing whatever possible to brake it even if I have to make an off-runway excursion and having to chose on what obstacles I should hit if obstacles are unavoidable, I'd rather choose this, for there will be much higher chances of surviving rather than daring to takeoff and finding out that the speed will only keep on dropping after liftoff even with one engine screaming at max. RPM and even if I'll try to retract the flaps (but keep the slats out) and fly leveled in order to reduce the drag, the speed would still drop..., that would mean the end!
So, I wonder if the MD-82 for example, with it's tiny JT-8D 217C engines with 21000lbf (maximum for 5 minutes) each would be capable of safely climbing out when loaded at highest MTOW if one engine stops?
Thank you.
Last edited by MaverickSu35S; 11th Mar 2017 at 10:50.
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The Structural limit as quoted in the AFM is 1 of a number of things which can limit the MTOW of any aircraft.
For large aircraft (EASA CS-25) there is a general philosophy that the loss of the most critical engine at any time throughout the flight should result in a safe outcome.
So when operating to those rules the MTOW is the lowest of all the limiting weights.
These could be related to the length of the runway or the climb capability on one engine or the ability to clear obstacles in the take off path (one engine) which may require higher climb capability or of course the certified structural MTOW.
For large aircraft (EASA CS-25) there is a general philosophy that the loss of the most critical engine at any time throughout the flight should result in a safe outcome.
So when operating to those rules the MTOW is the lowest of all the limiting weights.
These could be related to the length of the runway or the climb capability on one engine or the ability to clear obstacles in the take off path (one engine) which may require higher climb capability or of course the certified structural MTOW.
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Lots of threads in PPRuNe talk to this topic.
Suggest you run a search on something like "takeoff weight limit" and have a read through the resulting links. Be aware that references to "mass" and "weight" are sensibly similar and relate to the practices adopted by particular States.
However, in addition to FE Hoppy's observations, the 10 second short brief is ..
(a) the certificated (ie TC and AFM) MTOW is the maximum weight for which all the relevant Design Standard requirements can be met. Often the limiting case either will be one of the structural considerations or one of the WAT limits.
The certificated MTOW is just that - regardless of the circumstances, the pilot may not takeoff at a weight in excess of the MTOW. Caveat - the Regulator may authorise occasional higher takeoff weights for special purposes, eg a ferry flight overseas to permit the carriage of additional temporary tankage fuel.
(b) on a day to day basis the MTOW may have to be reduced (and usually is) by one of a range of considerations. Often such a reduced weight limit will be referred to by other terms, eg RTOW (regulated TOW).
These other limits may be performance requirements (eg WAT limits, OEI obstacle climb, AEO/OEI runway distance limits, etc.), system limitations (eg brake energy limit), cruise limits (eg weight limitation to achieve a high LSA AEO/OEI), destination limits (eg runway or climb limit weight plus expected fuel burn).
The number of engines only changes the numbers, otherwise the philosophy is similar.
Suggest you run a search on something like "takeoff weight limit" and have a read through the resulting links. Be aware that references to "mass" and "weight" are sensibly similar and relate to the practices adopted by particular States.
However, in addition to FE Hoppy's observations, the 10 second short brief is ..
(a) the certificated (ie TC and AFM) MTOW is the maximum weight for which all the relevant Design Standard requirements can be met. Often the limiting case either will be one of the structural considerations or one of the WAT limits.
The certificated MTOW is just that - regardless of the circumstances, the pilot may not takeoff at a weight in excess of the MTOW. Caveat - the Regulator may authorise occasional higher takeoff weights for special purposes, eg a ferry flight overseas to permit the carriage of additional temporary tankage fuel.
(b) on a day to day basis the MTOW may have to be reduced (and usually is) by one of a range of considerations. Often such a reduced weight limit will be referred to by other terms, eg RTOW (regulated TOW).
These other limits may be performance requirements (eg WAT limits, OEI obstacle climb, AEO/OEI runway distance limits, etc.), system limitations (eg brake energy limit), cruise limits (eg weight limitation to achieve a high LSA AEO/OEI), destination limits (eg runway or climb limit weight plus expected fuel burn).
The number of engines only changes the numbers, otherwise the philosophy is similar.
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Thank you very much for your replies. I didn't know this forum already had this topic discussed, my bad I didn't do the search, but thanks again for letting me know about the regulations. The only thing I want to know is if the highest allowable MTOW (ex: for the longest runway in the world with no obstacles ahead) for the MD-82 (149500lbs) permits it to continue and takeoff with just one engine.
Best wishes!
Best wishes!
Quote (my emphasis):
"The only thing I want to know is if the highest allowable MTOW (ex: for the longest runway in the world with no obstacles ahead) for the MD-82 (149500lbs) permits it to continue and takeoff with just one engine."
At sea-level on a dry runway with zero gradient, certainly. Otherwise the whole concept of MTOW would in practice be meaningless? But, when considering the acceleration phase on the runway, there has to be an airspeed calculated below which it is not safe to continue in the event of an engine failure. The nominated V1 (decision) speed has to take that into account.
"The only thing I want to know is if the highest allowable MTOW (ex: for the longest runway in the world with no obstacles ahead) for the MD-82 (149500lbs) permits it to continue and takeoff with just one engine."
At sea-level on a dry runway with zero gradient, certainly. Otherwise the whole concept of MTOW would in practice be meaningless? But, when considering the acceleration phase on the runway, there has to be an airspeed calculated below which it is not safe to continue in the event of an engine failure. The nominated V1 (decision) speed has to take that into account.
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I read about a procedure for taking off with 3 engines on a 4 engine aircraft : full power on the two symmetrical engine, power up of the third engine when speed is enough.
Could it be possible to takeoff from the start with only one engine ? One would need a very long runway, use little power at the beginning (counteract the yawing moment with the nose wheel at first), then increase power gradually while the rudder gains efficiency, and if this allows to reach VMCG then full power can be applied and the a/c should be able to takeoff on only one engine.
Did anyone ever hear about something similar ?
Could it be possible to takeoff from the start with only one engine ? One would need a very long runway, use little power at the beginning (counteract the yawing moment with the nose wheel at first), then increase power gradually while the rudder gains efficiency, and if this allows to reach VMCG then full power can be applied and the a/c should be able to takeoff on only one engine.
Did anyone ever hear about something similar ?
Hi KayPam,
We had that strange discussion recently on another thread (possibly after the B777 diversion into Iqaluit). But I think this OP is addressing legal SOPs, not flights of fancy that, in the past, have often not ended well!
http://www.pprune.org/rumours-news/5...ml#post9662834
We had that strange discussion recently on another thread (possibly after the B777 diversion into Iqaluit). But I think this OP is addressing legal SOPs, not flights of fancy that, in the past, have often not ended well!
http://www.pprune.org/rumours-news/5...ml#post9662834
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Right, I forgot about altitude, but logically that should also be taken into account as for reducing the MTOW depending on available engine thrust for a given air density. But as you've said, for a near sea level altitude and for an air of no more than 35 Celsius (cooler air gives more engine thrust), if the plane is way past V1 (as I initially said) and V2 is reached (so the aircraft can safely keep climbing with just one engine), can an MD-82 continue to takeoff when it weighs 149500lbs? That's all I'd like to know.
Thank you
!
Thank you
!
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That's all I'd like to know.
That's a specific AFM question so it will require an answer from someone who can refer to the manual to check. What you really are asking is .. whether the takeoff is WAT-limited below the MTOW or not.
That's a specific AFM question so it will require an answer from someone who can refer to the manual to check. What you really are asking is .. whether the takeoff is WAT-limited below the MTOW or not.
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I don't think anyone here can realistically give an answer to that question. It depends on the runway. However, if the runway is not TOPL limiting and the TOPL exceeds the MTOW then yes it can sustain an engine failure after V1 and meet the required climb gradient.
Hi MaverickSu35S:
You forgot to mention altitude, and I forgot to mention temperature!
Quote:
"for a near sea level altitude and for an air of no more than 35 Celsius (cooler air gives more engine thrust), if the plane is way past V1 (as I initially said) and V2 is reached (so the aircraft can safely keep climbing with just one engine), can an MD-82 continue to takeoff when it weighs 149500lbs?"
As john tullamarine has said, and others imply, every take-off has to be looked at as a separate case, using the performance criteria for the MD-82. But as I said, it would be completely pointless to certificate an aeroplane with a given MTOW based on sound structural factors which nevertheless was higher than the maximum weight ever attainable when considering the performance regulations. The latter, by the way, is referred to as the RTOW (regulated take-off weight).
I don't have access to any take-off performance figures for the MD-82, but any aircraft that could not legally take-off at MTOW on a very long, dry, horizontal runway at sea-level in still air with a temperature of +15C (ISA) with no significant obstacles would be a lemon, to say the least. But now that you have stipulated +35C (ISA+20), that is a very different case.
As your MD-82 is already at V2, the only remaining performance factor will, as john says, be WAT (weight/altitude/temperature). A twin-engine aeroplane, if I remember correctly, must be capable of maintaining a climb gradient of 2.6% ** in still air in the second-segment climb (after gear retraction) on one engine. But don't trust my memory, and you'll need the MD-82 performance charts or tables, and someone who can show you how to interpret them.
** [EDIT] That should have read 2.4%
You forgot to mention altitude, and I forgot to mention temperature!
Quote:
"for a near sea level altitude and for an air of no more than 35 Celsius (cooler air gives more engine thrust), if the plane is way past V1 (as I initially said) and V2 is reached (so the aircraft can safely keep climbing with just one engine), can an MD-82 continue to takeoff when it weighs 149500lbs?"
As john tullamarine has said, and others imply, every take-off has to be looked at as a separate case, using the performance criteria for the MD-82. But as I said, it would be completely pointless to certificate an aeroplane with a given MTOW based on sound structural factors which nevertheless was higher than the maximum weight ever attainable when considering the performance regulations. The latter, by the way, is referred to as the RTOW (regulated take-off weight).
I don't have access to any take-off performance figures for the MD-82, but any aircraft that could not legally take-off at MTOW on a very long, dry, horizontal runway at sea-level in still air with a temperature of +15C (ISA) with no significant obstacles would be a lemon, to say the least. But now that you have stipulated +35C (ISA+20), that is a very different case.
As your MD-82 is already at V2, the only remaining performance factor will, as john says, be WAT (weight/altitude/temperature). A twin-engine aeroplane, if I remember correctly, must be capable of maintaining a climb gradient of 2.6% ** in still air in the second-segment climb (after gear retraction) on one engine. But don't trust my memory, and you'll need the MD-82 performance charts or tables, and someone who can show you how to interpret them.
** [EDIT] That should have read 2.4%
Last edited by Chris Scott; 20th Mar 2017 at 13:57. Reason: See **
"Could it be possible to takeoff from the start with only one engine ?"
G'day KayPam,
I did it once in the sim after the session was completed and we had a little free time.
How we did it was to use full rudder and nosewheel steering to keep tracking the centreline while slowly introducing thrust on the live engine. Once Vmcg had been achieved then full thrust on the live engine was used with a normal rotate at Vr and climbout at V2, the same as an engine failure after V1 excercise.
The aeroplane was a B767, unfortunately I can't remember the TOW or ambient conditions for this exercise but the B767 climbed away quite nicely at MTOW on one engine.
Cheers.
G'day KayPam,
I did it once in the sim after the session was completed and we had a little free time.
How we did it was to use full rudder and nosewheel steering to keep tracking the centreline while slowly introducing thrust on the live engine. Once Vmcg had been achieved then full thrust on the live engine was used with a normal rotate at Vr and climbout at V2, the same as an engine failure after V1 excercise.
The aeroplane was a B767, unfortunately I can't remember the TOW or ambient conditions for this exercise but the B767 climbed away quite nicely at MTOW on one engine.
Cheers.
Last edited by Bullethead; 12th Mar 2017 at 06:59.
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Pinpointed! That's what I'm looking for as well, but the most important was: if the MD-82 would be capable of climbing out when weighing 149500lbs in 1 engine even at sea level and at no more than 30-35 Celsius.
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"Could it be possible to takeoff from the start with only one engine ?"
G'day KayPam,
I did it once in the sim after the session was completed and we had a little free time.
How we did it was to use full rudder and nosewheel steering to keep tracking the centreline while slowly introducing thrust on the live engine. Once Vmcg had been achieved then full thrust on the live engine was used with a normal rotate at Vr and climbout at V2, the same as an engine failure after V1 excercise.
The aeroplane was a B767, unfortunately I can't remember the TOW or ambient conditions for this exercise but the B767 climbed away quite nicely at MTOW on one engine.
Cheers.
G'day KayPam,
I did it once in the sim after the session was completed and we had a little free time.
How we did it was to use full rudder and nosewheel steering to keep tracking the centreline while slowly introducing thrust on the live engine. Once Vmcg had been achieved then full thrust on the live engine was used with a normal rotate at Vr and climbout at V2, the same as an engine failure after V1 excercise.
The aeroplane was a B767, unfortunately I can't remember the TOW or ambient conditions for this exercise but the B767 climbed away quite nicely at MTOW on one engine.
Cheers.
Obviously not something to be attempted on a regular basis but rather something nice to know, "for science" and curiosity.
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So the AFM should also tell the MTOW in case of one engine out during the takeoff phase.
The AFM provides the tools to do the sums, providing that all relevant external data (wx, runway details, obstacles, etc) are input. The resulting, lowest weight becomes the relevant RTOW for the day.
Obviously not something to be attempted on a regular basis but rather something nice to know, "for science" and curiosity.
A routine and trained for exercise on four-engined machines. Only for interest in the sim, otherwise ... prototype Aero Commanders (May 1951) notwithstanding.
The AFM provides the tools to do the sums, providing that all relevant external data (wx, runway details, obstacles, etc) are input. The resulting, lowest weight becomes the relevant RTOW for the day.
Obviously not something to be attempted on a regular basis but rather something nice to know, "for science" and curiosity.
A routine and trained for exercise on four-engined machines. Only for interest in the sim, otherwise ... prototype Aero Commanders (May 1951) notwithstanding.
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Didn't someone actually do this in a Twin Otter?
There are some stories .. run a search in PPRuNe .. there was a thread I can recall on the subject
.. but the Aero Commander marketing exercise did occur and involved removing one prop and then flying a lengthy OEI flight.
There are some stories .. run a search in PPRuNe .. there was a thread I can recall on the subject
.. but the Aero Commander marketing exercise did occur and involved removing one prop and then flying a lengthy OEI flight.