Starboard engine shutdown. Turns to the right or to the left?.
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Starboard engine shutdown. Turns to the right or to the left?.
I am an Atco at a medium sized International Airport and last Saturday whilst working on Radar I received details from the Parent Centre of an emergency diversion into my airfield by an overflying aircraft that had shutdown the starboard engine due to high oil temperature.
I vectored the aircraft to the airport overhead giving it initial descent.
I asked the pilot what direction of turn he would ideally prefer and the reply was ' To the right,thanks'.
This was perfect for me as I could easily vector the aircraft from the overhead to downwind righthand, then right base, then right turn 40 degree leg and finally the pilot could make the localiser capture with a right turn for the Westerly runway.
The aircraft, a Saab 340 landed safetly with the starboard propeller fixed in a stationary manner.
I have only flown single engined aircraft and have limited knowledge of asymmetric procedures.
It seemed perfectly natural for me to accept the decision to turn to the right as the inertia or thrust (apologies if incorrect terms) from the port engine would make turning to the right the easier option.
However, after discussing the incident with colleagues, someone suggested that the turn should be made towards the live engine ( ie. left) as there might be a danger of stalling the starboard wing if a turn to the right is made.
I would be very grateful if anyone could enlighten me on this issue as it will be discussed at our next Safety Review Meeting and I would like to make sure that all my ATCO colleagues are aware of the correct procedures.
Many thanks.
W. A.
I vectored the aircraft to the airport overhead giving it initial descent.
I asked the pilot what direction of turn he would ideally prefer and the reply was ' To the right,thanks'.
This was perfect for me as I could easily vector the aircraft from the overhead to downwind righthand, then right base, then right turn 40 degree leg and finally the pilot could make the localiser capture with a right turn for the Westerly runway.
The aircraft, a Saab 340 landed safetly with the starboard propeller fixed in a stationary manner.
I have only flown single engined aircraft and have limited knowledge of asymmetric procedures.
It seemed perfectly natural for me to accept the decision to turn to the right as the inertia or thrust (apologies if incorrect terms) from the port engine would make turning to the right the easier option.
However, after discussing the incident with colleagues, someone suggested that the turn should be made towards the live engine ( ie. left) as there might be a danger of stalling the starboard wing if a turn to the right is made.
I would be very grateful if anyone could enlighten me on this issue as it will be discussed at our next Safety Review Meeting and I would like to make sure that all my ATCO colleagues are aware of the correct procedures.
Many thanks.
W. A.
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Turning towards a dead engine is slightly riskier in that it would be easier to 'depart' after overbanking,but it makes turning far easier. Trying to turn into the live engine can be harder work, but safer.
I was at Franborough in the 60s when a Breguet Atlantique doing a low level display on one engine unfortunately did a 90 degree bank into the dead engine and lost it. Easier turn, but far riskier. As for stalling a lower wing, I think it makes no difference.
I was at Franborough in the 60s when a Breguet Atlantique doing a low level display on one engine unfortunately did a 90 degree bank into the dead engine and lost it. Easier turn, but far riskier. As for stalling a lower wing, I think it makes no difference.
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With many older aircraft (speaking light aircraft here), the POH mentions that turning toward the operating engine is preferred, as it is less prone to error on the pilots part to overbank, and thereby loose airspeed/altitude.
However, for a professional pilot, in a transport aircraft, it should make absolutely no difference, other than the effort required.
When I originally did my B707 training at PanAmerican, a circling approach (following an NDB letdown) was combined with one (outboard) engine out (idle thrust), all turns being accomplished toward the 'inop' engine.
An overshoot, followed by a two engine out (again, idle thrust) visual circuit, all turns again toward the 'inop' engines.
This makes life a bit easier, as slightly less rudder is required.
Now, on the other hand, TWA (many years ago) lost a 707 during flight training, when the FAA inspector in the obs seat, reached up and switched the rudder boost OFF during a OEI go-around.
Predictable result...the aircraft rolled over and crashed on the airfield boundry.
Not learning from previous accidents, a RAAF 707 also had the rudder boost switched OFF by a check pilot, with OEI...I don't recall if the aircraft was recovered, or lost.
Perhaps one of our OZ folks can comment.
Moral to the story...operate the aircraft BY THE BOOK,, for optimum results.
FAR too many accidents/incidents have been caused by folks who positively should know better.
However, for a professional pilot, in a transport aircraft, it should make absolutely no difference, other than the effort required.
When I originally did my B707 training at PanAmerican, a circling approach (following an NDB letdown) was combined with one (outboard) engine out (idle thrust), all turns being accomplished toward the 'inop' engine.
An overshoot, followed by a two engine out (again, idle thrust) visual circuit, all turns again toward the 'inop' engines.
This makes life a bit easier, as slightly less rudder is required.
Now, on the other hand, TWA (many years ago) lost a 707 during flight training, when the FAA inspector in the obs seat, reached up and switched the rudder boost OFF during a OEI go-around.
Predictable result...the aircraft rolled over and crashed on the airfield boundry.
Not learning from previous accidents, a RAAF 707 also had the rudder boost switched OFF by a check pilot, with OEI...I don't recall if the aircraft was recovered, or lost.
Perhaps one of our OZ folks can comment.
Moral to the story...operate the aircraft BY THE BOOK,, for optimum results.
FAR too many accidents/incidents have been caused by folks who positively should know better.
Do a Hover - it avoids G
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Sorry, while I was away typing you have had your points answered.
But for the record this was what I was going to say:
Well done you for wanting to understand the pilot problem when asymmetric.
There are two issues with asymmetric flying - handling and performance.
Handling first. Depending on the aircraft type, if all engines are a full power and the aircraft is at low speed when an engine quits (just after unstick for example) there will be a major handling issue as the aircraft will try to yaw and roll towards the failed engine. If no pilot (or autopilot) action is taken the aircraft could well finish up inverted in less than 5 seconds. To prevent this and stay on the pre failure track up to full rudder may be needed as well as some bank towards the live engine (up to 5 deg is allowed for certification purposes). If we assume the worst case of no autopilot help and where all the foot forces needed to stop the yaw are greater than the rudder trimmer can provide, then the pilot can be left with a residual effort needed on the rudder into the good side.
At this stage old hands brought up on aircraft that would not meet today’s criteria are likely to prefer to do all turns AWAY from the failed engine. Then if your foot slips or knee buckles the subsequent roll and yaw will be initially TOWARDS wings level. If the same thing happened when turning into the bad engine you would be on your way towards inverted more quickly.
But, and it is a big but, if you cope with the initial failure and get the thing reasonably trimmed out, then from a handling point of view you are no longer asymmetric and should be able to turn either way without worrying. You may still be quite concerned that during a circuit to land things are not as pleasant as normal and so might wish to fly a left hand circuit from the left seat and right hand from the other just to make your view and judgement of events a little easier.
Performance issues. These are again very type dependant. A lot of light twins (not the one you mentioned) may NOT be able to maintain height on one engine. In which case even if the pilot deals with the handling OK then he still may have a major problem getting back to a runway or open space to put it down before running out of height. This could make one direction of turn more preferable than the other.
In the specific case you mentioned perhaps the pilot flying was in the right hand seat…..
But for the record this was what I was going to say:
Well done you for wanting to understand the pilot problem when asymmetric.
There are two issues with asymmetric flying - handling and performance.
Handling first. Depending on the aircraft type, if all engines are a full power and the aircraft is at low speed when an engine quits (just after unstick for example) there will be a major handling issue as the aircraft will try to yaw and roll towards the failed engine. If no pilot (or autopilot) action is taken the aircraft could well finish up inverted in less than 5 seconds. To prevent this and stay on the pre failure track up to full rudder may be needed as well as some bank towards the live engine (up to 5 deg is allowed for certification purposes). If we assume the worst case of no autopilot help and where all the foot forces needed to stop the yaw are greater than the rudder trimmer can provide, then the pilot can be left with a residual effort needed on the rudder into the good side.
At this stage old hands brought up on aircraft that would not meet today’s criteria are likely to prefer to do all turns AWAY from the failed engine. Then if your foot slips or knee buckles the subsequent roll and yaw will be initially TOWARDS wings level. If the same thing happened when turning into the bad engine you would be on your way towards inverted more quickly.
But, and it is a big but, if you cope with the initial failure and get the thing reasonably trimmed out, then from a handling point of view you are no longer asymmetric and should be able to turn either way without worrying. You may still be quite concerned that during a circuit to land things are not as pleasant as normal and so might wish to fly a left hand circuit from the left seat and right hand from the other just to make your view and judgement of events a little easier.
Performance issues. These are again very type dependant. A lot of light twins (not the one you mentioned) may NOT be able to maintain height on one engine. In which case even if the pilot deals with the handling OK then he still may have a major problem getting back to a runway or open space to put it down before running out of height. This could make one direction of turn more preferable than the other.
In the specific case you mentioned perhaps the pilot flying was in the right hand seat…..
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Notso Fantastic, 411A,and John Farley,
Many thanks for your infomative and very helpful replies.
My unit Training Officer will be adding this information into our local training plan.
Many thanks for your infomative and very helpful replies.
My unit Training Officer will be adding this information into our local training plan.
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Help the guy....
It is interesting to note that (and this is true mainly for the lighter piston twins) that most accidents involving an engine-out situation takes place well after the pilot has recovered the situation and is manuevering to land.
My opinion wrt to this issue is the fact that most pilots seem to get into the "get on the ground ASAP" mode and then things go pear-shaped when they try to fly and plan and talk on the radio and read the plate and, and, and....
From an ATC point of view, except obviously where the guy is burning, calm him down and slow him down so as to give ample opportunity for planning the approach. It normally helps if the circuit is clear and radio chatter is kept down to a minimum.
Also keep in mind that although an twin loses 50% of its power during an engine failure, it loses more that 70% of its performance and as mentioned previously, most piston twins fly to the scene of the accident on one engine only....
My opinion wrt to this issue is the fact that most pilots seem to get into the "get on the ground ASAP" mode and then things go pear-shaped when they try to fly and plan and talk on the radio and read the plate and, and, and....
From an ATC point of view, except obviously where the guy is burning, calm him down and slow him down so as to give ample opportunity for planning the approach. It normally helps if the circuit is clear and radio chatter is kept down to a minimum.
Also keep in mind that although an twin loses 50% of its power during an engine failure, it loses more that 70% of its performance and as mentioned previously, most piston twins fly to the scene of the accident on one engine only....
Moderator
I don't think one very important point has been made in previous posts ...
The normally quoted (certification - ie flight manual) Vmca usually is determined with 5 degrees into the live engine(s).
Real world Vmca, however, is STRONGLY bank dependent.
Therefore, while airspeed is low, one ought not to bank away from the live engine lest the real world Vmca increase both rapidly and significantly - this effect can rush up on the unsuspecting pilot and he/she might well find him/herself to be a mere spectator in the ensuing crash (unless thrust be reduced in time to avert inverting, crashing, burning, and dying ...).
Once the speed is up to normal good margins above published certification Vmca the concern is not so significant.
Be aware that the variation in real world Vmca with bank angle generally is neither linear nor insignificant - we are not talking a knot or two here but, perhaps, many tens of knots depending on the bank angle ....
Most sims with which I have played demonstrate the effect reasonably well. A stick and rudder skills exercise I work students up to involves a takeoff liftoff failure/seizure at minimum weight, min speed, and max aft cg. Almost invariably, until the student gets on top of the rapid speed at which things happen (refer John Farley's post, above), the aircraft rolls towards the failed engine during the failure control sequence, Vmca rises rapidly, and the roll accelerates - aircraft goes in inverted. Of course we freeze the sim once the situation gets out of control as there is little, if any, training benefit to be had by letting it go any further. Point is, suggest you don't forget this Vmca - bank angle relationship.
The normally quoted (certification - ie flight manual) Vmca usually is determined with 5 degrees into the live engine(s).
Real world Vmca, however, is STRONGLY bank dependent.
Therefore, while airspeed is low, one ought not to bank away from the live engine lest the real world Vmca increase both rapidly and significantly - this effect can rush up on the unsuspecting pilot and he/she might well find him/herself to be a mere spectator in the ensuing crash (unless thrust be reduced in time to avert inverting, crashing, burning, and dying ...).
Once the speed is up to normal good margins above published certification Vmca the concern is not so significant.
Be aware that the variation in real world Vmca with bank angle generally is neither linear nor insignificant - we are not talking a knot or two here but, perhaps, many tens of knots depending on the bank angle ....
Most sims with which I have played demonstrate the effect reasonably well. A stick and rudder skills exercise I work students up to involves a takeoff liftoff failure/seizure at minimum weight, min speed, and max aft cg. Almost invariably, until the student gets on top of the rapid speed at which things happen (refer John Farley's post, above), the aircraft rolls towards the failed engine during the failure control sequence, Vmca rises rapidly, and the roll accelerates - aircraft goes in inverted. Of course we freeze the sim once the situation gets out of control as there is little, if any, training benefit to be had by letting it go any further. Point is, suggest you don't forget this Vmca - bank angle relationship.
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JT has brought up a very good point, vital in fact.
Speed, or more precisely excess thereof, is indeed beneficial in these circumstances, as is the need to keep bank angle in check.
It was twenty five years ago that AA had their very unfortunate accident with a DC10 in ORD.
Interesting to note that this scenario was programmed into DC10 simulators later on, to see if there was a way to recover.
Only a few plonked the nose down and went for excess airspeed, to control the wing down tendancy, during the roll.
These recoveries were successful.
In many cases, airspeed is your friend...sometimes your only friend.
Speed, or more precisely excess thereof, is indeed beneficial in these circumstances, as is the need to keep bank angle in check.
It was twenty five years ago that AA had their very unfortunate accident with a DC10 in ORD.
Interesting to note that this scenario was programmed into DC10 simulators later on, to see if there was a way to recover.
Only a few plonked the nose down and went for excess airspeed, to control the wing down tendancy, during the roll.
These recoveries were successful.
In many cases, airspeed is your friend...sometimes your only friend.
Last edited by 411A; 4th Jun 2004 at 04:46.
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with alacrity
Just some of my thoughts on the matter. The whole "turning away from the dead engine issue" seemed to be given far too much importance at the college of knowledge. To put it into perspective - all of those Senecas, Seminoles, Duchesses etc. which are instrument training and flying full instrument procedures (depending upon exactly which airport you work at) are doing so effectively on one engine. These procedures often involve turns in both directions, and on different days different engines will be shut down. So every day you will find aircraft turning towards the dead engine.
This concept has achieved far too much importance and I heard an OJTI in the SE expounding this principle with regard to an Hs125 only last summer.
In simple terms only start to worry if the pilot tells you or if the aircraft was built a long time ago (eg Miles, Percival, DH etc.). Obviously this is a gross simplification, but it is somewhere to start from!
The next pearl of college wisdom I seem to remember was "can you take a frequency change". In an ideal world emergency traffic would like a discrete frequency if possible. We don't care who clears us for the approach and on what frequency. It is nice to operate knowing that every call will be for us. I accept that it is not always possible, but again it is something to consider.
If my recent experience is anything to go by, I think the hot topic of the day should be really be "sterile runways". Emergency traffic will not thank you if it is forced to go-around and airports with 2 parallel runways really have little excuse. ASAP would be my answer to when I would like it to be sterile, but in the real world I accept that wide base/40nm away might be the best I can hope for.
As always - this has no basis more reliable than my own meandering experience.
G W-H
Just some of my thoughts on the matter. The whole "turning away from the dead engine issue" seemed to be given far too much importance at the college of knowledge. To put it into perspective - all of those Senecas, Seminoles, Duchesses etc. which are instrument training and flying full instrument procedures (depending upon exactly which airport you work at) are doing so effectively on one engine. These procedures often involve turns in both directions, and on different days different engines will be shut down. So every day you will find aircraft turning towards the dead engine.
This concept has achieved far too much importance and I heard an OJTI in the SE expounding this principle with regard to an Hs125 only last summer.
In simple terms only start to worry if the pilot tells you or if the aircraft was built a long time ago (eg Miles, Percival, DH etc.). Obviously this is a gross simplification, but it is somewhere to start from!
The next pearl of college wisdom I seem to remember was "can you take a frequency change". In an ideal world emergency traffic would like a discrete frequency if possible. We don't care who clears us for the approach and on what frequency. It is nice to operate knowing that every call will be for us. I accept that it is not always possible, but again it is something to consider.
If my recent experience is anything to go by, I think the hot topic of the day should be really be "sterile runways". Emergency traffic will not thank you if it is forced to go-around and airports with 2 parallel runways really have little excuse. ASAP would be my answer to when I would like it to be sterile, but in the real world I accept that wide base/40nm away might be the best I can hope for.
As always - this has no basis more reliable than my own meandering experience.
G W-H
Real world Vmca, however, is STRONGLY bank dependent.
So in what sense is there a dependence? What exactly do you mean by "Vmca" in looking at its bank dependence? I don't think you can even use a "keep it straight" criterion here, because we are discussing turns. What do I run out of? Aileron? Rudder? or something else?
Moderator
The certification (AFM figure) Vmca typically is worked up by tests involving a progressive reduction in speed to determine a static Vmca (typically for 5 degrees bank into the operating engine(s)) - a maximum limited by the rules to keep the manufacturer honest) and then checked for compliance with the dynamic requirements (dynamic Vmca).
If one runs quasi certification tests to determine a static "Vmca" for different bank angles, the results show something typically a bit like a tangent curve relationship. There is nothing magical about the AFM (certification) Vmca - it is just the speed resulting from doing the tests in one specific manner specified in the design standards rules. Change the boundary conditions and the value varies.
So, for instance, if the certification Vmca is whatever for 5 degrees into the operating engine(s), the "Vmca" for more than 5 degrees will reduce, while that for bank angles less than 5 degrees (and then bank angles towards the dead engine) will progressively (and then comparatively rapidly) increase. As bookworm would be well aware this is principally to do with sideslip effects on the moment balance.
The magnitude of this variation is not insignificant. As I recall, for one large 4-engine bomber, the delta for 5 degrees toward the dead engine is something in the order of 35 kt higher than that for 5 degrees toward the live engines - food for thought ?
As an aside, keep in mind that excessive excursions in sideslip set one up for a spin departure.
During a turn, the sideslip consideration still applies although the pilot generally has no way of knowing what sort of sideslip angle applies at the time (sailplanes and Concorde notwithstanding).
Normally we are concerned with trying to fly straight and my comments were directed more at the problems associated with the initial failure control.
What do you run out of if the bank is the wrong way ? .. rudder .. at which stage the yaw is unable to be checked and the roll takes over. An interesting sequence to watch.
If one runs quasi certification tests to determine a static "Vmca" for different bank angles, the results show something typically a bit like a tangent curve relationship. There is nothing magical about the AFM (certification) Vmca - it is just the speed resulting from doing the tests in one specific manner specified in the design standards rules. Change the boundary conditions and the value varies.
So, for instance, if the certification Vmca is whatever for 5 degrees into the operating engine(s), the "Vmca" for more than 5 degrees will reduce, while that for bank angles less than 5 degrees (and then bank angles towards the dead engine) will progressively (and then comparatively rapidly) increase. As bookworm would be well aware this is principally to do with sideslip effects on the moment balance.
The magnitude of this variation is not insignificant. As I recall, for one large 4-engine bomber, the delta for 5 degrees toward the dead engine is something in the order of 35 kt higher than that for 5 degrees toward the live engines - food for thought ?
As an aside, keep in mind that excessive excursions in sideslip set one up for a spin departure.
During a turn, the sideslip consideration still applies although the pilot generally has no way of knowing what sort of sideslip angle applies at the time (sailplanes and Concorde notwithstanding).
Normally we are concerned with trying to fly straight and my comments were directed more at the problems associated with the initial failure control.
What do you run out of if the bank is the wrong way ? .. rudder .. at which stage the yaw is unable to be checked and the roll takes over. An interesting sequence to watch.
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I am acknowledging report.
Many thanks for the PM, I have learned so much from all the replies. TRUCE is an annual training programme short for Training for Unusual Circumstances and Emergencies.
I would like to add that during the scenario I described,the aircraft was transferred to a discrete frequency and the runway made sterile very early on into the incident.
I was just looking for handling characteristics and did not want to ramble on about other factors.
Once again
Thanks to you all.
I am acknowledging report.
Many thanks for the PM, I have learned so much from all the replies. TRUCE is an annual training programme short for Training for Unusual Circumstances and Emergencies.
I would like to add that during the scenario I described,the aircraft was transferred to a discrete frequency and the runway made sterile very early on into the incident.
I was just looking for handling characteristics and did not want to ramble on about other factors.
Once again
Thanks to you all.
So, for instance, if the certification Vmca is whatever for 5 degrees into the operating engine(s), the "Vmca" for more than 5 degrees will reduce, while that for bank angles less than 5 degrees (and then bank angles towards the dead engine) will progressively (and then comparatively rapidly) increase. As bookworm would be well aware this is principally to do with sideslip effects on the moment balance.
With no change in rudder input, won't you end up slipping out of the turn as usual, whichever way you go? I can understand how you might run out of rudder trying to keep it in balance turning into the live engine, but not the dead one.
What do you run out of if the bank is the wrong way ? .. rudder .. at which stage the yaw is unable to be checked and the roll takes over. An interesting sequence to watch.
As an aside, keep in mind that excessive excursions in sideslip set one up for a spin departure.
Moderator
Bookworm,
(a) although it will vary a bit with Type, I think you will find that 5 deg bank to the operating engine(s) results in some slip to the low side. Back around Vmca you will have run out of rudder ? .. otherwise the Vmca generally could be lower ?
(b) re the turns .. it will depend strongly on what the actual slip is doing as to what happens with control (keep in mind that we are concerned here with turns at/near Vmca .. somewhat faster and the problems are far less a concern). Regardless of the origin of the slip, if you start slipping toward the dead engine you will have a turning moment increase toward the dead engine .. and need more rudder to control it .. consider it a bit like crosswind generated turning moments on takeoff or landing ? There will also need to be some degree of rudder delta for the turn in any case.
(c) try drawing a plan diagram of the aircraft - consider engine, rudder, and sideslip forces and related turning/rolling moments.
(d) main problem if (real world) "Vmca" runs away is that things can happen fairly quickly and the pilot's options can disappear while he/she watches. The action might be intuitive .. eg apply a roll moment input .. but the consequence of the action might not align well with the pilot's expectation.
(e) yaw and slip are much misunderstood. One way to consider it is that yaw is something which a pilot generally does or creates by control inputs while slip is the aerodynamic airflow consequence of the pilot input ?
(a) although it will vary a bit with Type, I think you will find that 5 deg bank to the operating engine(s) results in some slip to the low side. Back around Vmca you will have run out of rudder ? .. otherwise the Vmca generally could be lower ?
(b) re the turns .. it will depend strongly on what the actual slip is doing as to what happens with control (keep in mind that we are concerned here with turns at/near Vmca .. somewhat faster and the problems are far less a concern). Regardless of the origin of the slip, if you start slipping toward the dead engine you will have a turning moment increase toward the dead engine .. and need more rudder to control it .. consider it a bit like crosswind generated turning moments on takeoff or landing ? There will also need to be some degree of rudder delta for the turn in any case.
(c) try drawing a plan diagram of the aircraft - consider engine, rudder, and sideslip forces and related turning/rolling moments.
(d) main problem if (real world) "Vmca" runs away is that things can happen fairly quickly and the pilot's options can disappear while he/she watches. The action might be intuitive .. eg apply a roll moment input .. but the consequence of the action might not align well with the pilot's expectation.
(e) yaw and slip are much misunderstood. One way to consider it is that yaw is something which a pilot generally does or creates by control inputs while slip is the aerodynamic airflow consequence of the pilot input ?
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First i'd like to thank With Alacrity for asking this question and encouraging understanding between pilots/controllers. Top marks mate, and i hope we can respond in kind when needed.
My personal answer to your question would be to keep all turns toward the live engine unless circumstances dictate otherwise eg terrain after take off (although, at least with my company, i will probably be following a laid down engine out contingency procedure rather than the normal departure procedure). Enroute (high speed) and in descent (idle power) a turn in either direction is acceptable, although if required to make a circuit prior to landing i would prefer it to be toward the live engine. Asking the pilot what he/she will accept, as you did, is spot on.
This "turn toward the live engine" reminds me of the piston "over-squared" rule in that they are sometimes touted as hard and fast rules. Not so! Just the why and when need to be understood.
The 5 degrees AoB is a certification limit which keeps the acft manufacturers working to a similar set of rules. By banking the acft towards the live engine/s we are changing the plane in which the forces on the acft are at work. With this bank towards the live engine/s part of the acft's weight is working with the rudder by "pulling" the nose toward the live engine (CoG fwd of CoP). Also we are slipping the acft and so increasing the AoA of the rudder plus using the aft fuselage and tail fin to "push" the tail in the appropriately helpful direction. This relieves the need for rudder input, or more appropriately allows a full rudder Vmca to be at a lower speed than at wings level. Theoretically you could increse the AoB towards the live engine/s further while slowing below Vmca and maintain the acft flying straight ahead BUT this sacrifices the all important performance- hence the 5degree limit.
Banking toward the dead engine/s makes these forces work against you and so inceases your Vmca, as John was saying. The L100 Hercules AFM has an excellent graph illustrating this but i can't find it for the life of me right now. From memory the Vmca increases in the order of 20kts for a 5degree bank toward the dead engine.
The "when" is up to commonsense keeping in mind that Vmca is determined at full rated thrust on the live engine/s and that some acft have rudder pressure reducers which operate at a flap setting or at an airspeed.
HJ
My personal answer to your question would be to keep all turns toward the live engine unless circumstances dictate otherwise eg terrain after take off (although, at least with my company, i will probably be following a laid down engine out contingency procedure rather than the normal departure procedure). Enroute (high speed) and in descent (idle power) a turn in either direction is acceptable, although if required to make a circuit prior to landing i would prefer it to be toward the live engine. Asking the pilot what he/she will accept, as you did, is spot on.
This "turn toward the live engine" reminds me of the piston "over-squared" rule in that they are sometimes touted as hard and fast rules. Not so! Just the why and when need to be understood.
The 5 degrees AoB is a certification limit which keeps the acft manufacturers working to a similar set of rules. By banking the acft towards the live engine/s we are changing the plane in which the forces on the acft are at work. With this bank towards the live engine/s part of the acft's weight is working with the rudder by "pulling" the nose toward the live engine (CoG fwd of CoP). Also we are slipping the acft and so increasing the AoA of the rudder plus using the aft fuselage and tail fin to "push" the tail in the appropriately helpful direction. This relieves the need for rudder input, or more appropriately allows a full rudder Vmca to be at a lower speed than at wings level. Theoretically you could increse the AoB towards the live engine/s further while slowing below Vmca and maintain the acft flying straight ahead BUT this sacrifices the all important performance- hence the 5degree limit.
Banking toward the dead engine/s makes these forces work against you and so inceases your Vmca, as John was saying. The L100 Hercules AFM has an excellent graph illustrating this but i can't find it for the life of me right now. From memory the Vmca increases in the order of 20kts for a 5degree bank toward the dead engine.
The "when" is up to commonsense keeping in mind that Vmca is determined at full rated thrust on the live engine/s and that some acft have rudder pressure reducers which operate at a flap setting or at an airspeed.
HJ
(a) although it will vary a bit with Type, I think you will find that 5 deg bank to the operating engine(s) results in some slip to the low side.
Back around Vmca you will have run out of rudder ? .. otherwise the Vmca generally could be lower ?
What eventually stops us from decreasing speed still further? I'm not sure: could be running out of aileron, could be mainplane stall as we demand more and more lift, or it could be a fin stall. But something will. So I find absolute Vmca.
So far so good: we're still going straight.
(b) re the turns .. it will depend strongly on what the actual slip is doing as to what happens with control (keep in mind that we are concerned here with turns at/near Vmca .. somewhat faster and the problems are far less a concern).
Regardless of the origin of the slip, if you start slipping toward the dead engine you will have a turning moment increase toward the dead engine .. and need more rudder to control it .. consider it a bit like crosswind generated turning moments on takeoff or landing ? There will also need to be some degree of rudder delta for the turn in any case.
So we develop a yaw rate into the dead engine. I can't check that yaw with rudder, but I can check it with bank angle. I've moved further from mainplane stall (less bank), further from fin stall (less slip). I'm not certain what would happen to the aileron input -- we've reduced the slip so we're not having to fight the lateral stability, but we are yawing towards the dead so we may need to hold that off a little.
What about a turn toward the live engine? So I bank still further into the live engine. I'm now closer to mainplane stall because there's still more bank. I'm also closer to fin stall as I'm demanding more yaw from the fin. And of course if I was limited by running out of aileron, I can't bank towards the live engine.
So I still can't see why a turn towards the dead engine is more problematic.
(d) main problem if (real world) "Vmca" runs away is that things can happen fairly quickly and the pilot's options can disappear while he/she watches. The action might be intuitive .. eg apply a roll moment input .. but the consequence of the action might not align well with the pilot's expectation.
(e) yaw and slip are much misunderstood. One way to consider it is that yaw is something which a pilot generally does or creates by control inputs while slip is the aerodynamic airflow consequence of the pilot input ?
Moderator
Bookworm,
Hopefully, one of the more experienced TPs who has plenty of OEI test experience will wade in here ....
However, I shall make an attempt to explain my thinking ...
(a) certification Vmca (or Vmc, if you prefer) generally will be limited by 5 deg bank into the operating engines, as this is permitted as a limitation by the design standards. The figure may not be established with a greater bank angle. ... if you choose to play with bank, then you can use slip to reduce or increase real world Vmca .. but beware setting up a slip situation which might lead to a spin departure. I think that we are talking much the same talk here ... ?
(b) if you are looking at a max rudder situation at 5 deg favourable bank (or zero slip bank angle - argument remains similar for both cases) and then bank away, the slip-generated yaw cannot be controlled unless you bank back to more than the starting bank angle (if you are able to do so .. ) to check the yaw and then, eventually, steady the configuration down to the original bank angle. Consider that we are looking at slip angles from both sides of the nose ... from the live side with 5 deg favourable and from the dead side with, for instance, wings level or unfavourable bank into the dead engine ... it can become a very slippery ride ... I guess that, in some aspects, it is a bit like the rudder/aileron cross-over situation which a well-known heavy twin became even better known for after some problems with rudder ....
(c) you can get bitten badly regardless which direction slip you are getting involved with ... but the increasing real world Vmca problem (which can sneak up quickly and dramatically) only occurs as the pilot intentionally (or unintentionally in the case of a low speed takeoff failure ..) banks away from the live engine(s). With a failure, say, during the takeoff flare and with near Vmca speed schedules, the yaw (and roll), especially in a swept wing jet, can be very dramatic with the pilot being totally overwhelmed in a few seconds ... with a bit of exposure practice and the confidence to apply roll inputs aggressively, the problem reduces markedly ....
(d) yaw rate .. and, I guess, slip "rate" complicate the exercise by introducing a dynamic consideration
If I have not helped out here, please feel free to ignore my ramblings ...
Hopefully, one of the more experienced TPs who has plenty of OEI test experience will wade in here ....
However, I shall make an attempt to explain my thinking ...
(a) certification Vmca (or Vmc, if you prefer) generally will be limited by 5 deg bank into the operating engines, as this is permitted as a limitation by the design standards. The figure may not be established with a greater bank angle. ... if you choose to play with bank, then you can use slip to reduce or increase real world Vmca .. but beware setting up a slip situation which might lead to a spin departure. I think that we are talking much the same talk here ... ?
(b) if you are looking at a max rudder situation at 5 deg favourable bank (or zero slip bank angle - argument remains similar for both cases) and then bank away, the slip-generated yaw cannot be controlled unless you bank back to more than the starting bank angle (if you are able to do so .. ) to check the yaw and then, eventually, steady the configuration down to the original bank angle. Consider that we are looking at slip angles from both sides of the nose ... from the live side with 5 deg favourable and from the dead side with, for instance, wings level or unfavourable bank into the dead engine ... it can become a very slippery ride ... I guess that, in some aspects, it is a bit like the rudder/aileron cross-over situation which a well-known heavy twin became even better known for after some problems with rudder ....
(c) you can get bitten badly regardless which direction slip you are getting involved with ... but the increasing real world Vmca problem (which can sneak up quickly and dramatically) only occurs as the pilot intentionally (or unintentionally in the case of a low speed takeoff failure ..) banks away from the live engine(s). With a failure, say, during the takeoff flare and with near Vmca speed schedules, the yaw (and roll), especially in a swept wing jet, can be very dramatic with the pilot being totally overwhelmed in a few seconds ... with a bit of exposure practice and the confidence to apply roll inputs aggressively, the problem reduces markedly ....
(d) yaw rate .. and, I guess, slip "rate" complicate the exercise by introducing a dynamic consideration
If I have not helped out here, please feel free to ignore my ramblings ...
Last edited by john_tullamarine; 15th Jun 2004 at 13:02.
Some inputs to this thread appear to be incorrectly coupling issues and unnecessarily adding fears to safe flight.
Determination of Vmca is a certification test. In ‘normal’ asymmetric flight, providing speed is respected a hazardous condition should not be encountered. Vmca is bank dependant but not unsafe and if you respect speed the margins are sufficient.
Vmca is defined either by control limit or stall limit depending on aircraft type and / or weight / configuration. If the aircraft is slipping at the control limit it does not imply that the aircraft will spin, nor in the other case if the stall is reached before control is limiting. However, stalling with slip and rudder does not bode well for continued controlled flight, but these concerns are much more for the test pilot than the average pilot who, again, should respect all speed limits.
Background reading on asymmetric flight etc can be seen here: Turboprop PSM+ICR, Asymmetric Fight
For ATC who wish to help a crew after an engine failure, by all means be aware of the pilot’s problems, but don’t attempt to fly the aircraft for him.
In Europe, maybe elsewhere, ATC follow the ASSIST guidelines:
Determination of Vmca is a certification test. In ‘normal’ asymmetric flight, providing speed is respected a hazardous condition should not be encountered. Vmca is bank dependant but not unsafe and if you respect speed the margins are sufficient.
Vmca is defined either by control limit or stall limit depending on aircraft type and / or weight / configuration. If the aircraft is slipping at the control limit it does not imply that the aircraft will spin, nor in the other case if the stall is reached before control is limiting. However, stalling with slip and rudder does not bode well for continued controlled flight, but these concerns are much more for the test pilot than the average pilot who, again, should respect all speed limits.
Background reading on asymmetric flight etc can be seen here: Turboprop PSM+ICR, Asymmetric Fight
For ATC who wish to help a crew after an engine failure, by all means be aware of the pilot’s problems, but don’t attempt to fly the aircraft for him.
In Europe, maybe elsewhere, ATC follow the ASSIST guidelines:
- Acknowledge, Make sure you understood the nature of emergency and acknowledge accordingly.
- Separate, Don’t forget to establish / maintain separation from other aircraft and terrain.
- Silence, Impose silence on your control frequency if necessary. Don’t disturb urgent cockpit actions by unnecessary transmissions.
- Inform, Inform your supervisor and other sectors / units concerned.
- Support, Give maximum support to pilot and crew.
- Time, Allow pilot’s sufficient time to work on their problem.
Some inputs to this thread appear to be incorrectly coupling issues and unnecessarily adding fears to safe flight.
Determination of Vmca is a certification test. In ‘normal’ asymmetric flight, providing speed is respected a hazardous condition should not be encountered. Vmca is bank dependant but not unsafe and if you respect speed the margins are sufficient.
Determination of Vmca is a certification test. In ‘normal’ asymmetric flight, providing speed is respected a hazardous condition should not be encountered. Vmca is bank dependant but not unsafe and if you respect speed the margins are sufficient.
I think it goes without saying that in many aspects of aviation certification limits are designed with sufficent margin that you should be OK provided you stay within them. But I don't think that invalidates the examination of what happens at the edge of the envelope.
There is undoubtedly a long-standing rule of thumb in aviation that discourages turning into the dead engine. It came from somehwere. John T has made a case for the origin of that RoT being a real aerodynamic effect. While I read everything that John writes with some reverence because he's right a lot more often than I am, he has not won me over in this particular case. John F has hinted that it may have an origin more closely related to what happens if you can't maintain rudder pressure before you're able to apply trim.
While the guidance to the original poster is correct in that it doesn't really matter which way you turn with a decent number on the ASI, I for one think it was worth having the debate.