Courting disaster by "demonstrating" Vmca
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Most of the examiners I fly with as a candidate close a mixture control during the take-off roll - but, as said above, there's nothing to say this exercise is as a result of engine failure - it could be dog running across the runway, runway incursion, door opening, annunciator light coming on, tower controller yelling "stop, stop, stop"...anything.
When I do the same exercise (to comply with the test profile) I just brief that I will say "Abort" (which I do at nominated Vr minus 15 knots). Close the throttles and stop or vacate.
I still say C Y B's fountain of all knowledge is speaking from personal choice or company ops manual - not any "mandate" from outside sources (and, if so, shouldn't really dictate it as law to those who look up to him/her/it).
When I do the same exercise (to comply with the test profile) I just brief that I will say "Abort" (which I do at nominated Vr minus 15 knots). Close the throttles and stop or vacate.
I still say C Y B's fountain of all knowledge is speaking from personal choice or company ops manual - not any "mandate" from outside sources (and, if so, shouldn't really dictate it as law to those who look up to him/her/it).
Why do it if it's not fun?
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Close the throttles and stop or vacate
FFF
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As to original post I agree with a later comment, the instructor concerned needs to go back to school and understand the relationship between altitude, vmca and stall speed.
One way around the problem with reaching the stall speed before vmca, with the increase in altitude (and a subsequent decrease in vmca as the live engine produces less thrust as you climb) is to limit the rudder travel (the instructor uses his foot), this simulates that you reach vmca ie there is no longer enough rudder authority to control the assymetric thrust from the live engine.
As to demonstrating/testing the student on a rejected take off, use a simulator to practise the engine failure (I cannot believe the amount of students that sit dumfounded as the aircraft veers off the runway (in the sim)the first time they get an engine failure on take off, despite briefing on their planned actions each time they start the sim!!!
) IMHO you would have to be a F%$%$ng idiot to pull a mixture lever back for real!
Why some people feel the need to practice bleed is beyond me!
Sage advice from previous post to brief the RTO before hand, tell ATC what you plan and simulate a door open or something similar. Final bit of the rant is before you post what you think is correct "from memory" get your book out and check! Stupid advice on here might lead to stupid actions in an aircraft!
One way around the problem with reaching the stall speed before vmca, with the increase in altitude (and a subsequent decrease in vmca as the live engine produces less thrust as you climb) is to limit the rudder travel (the instructor uses his foot), this simulates that you reach vmca ie there is no longer enough rudder authority to control the assymetric thrust from the live engine.
As to demonstrating/testing the student on a rejected take off, use a simulator to practise the engine failure (I cannot believe the amount of students that sit dumfounded as the aircraft veers off the runway (in the sim)the first time they get an engine failure on take off, despite briefing on their planned actions each time they start the sim!!!
) IMHO you would have to be a F%$%$ng idiot to pull a mixture lever back for real! Why some people feel the need to practice bleed is beyond me!Sage advice from previous post to brief the RTO before hand, tell ATC what you plan and simulate a door open or something similar. Final bit of the rant is before you post what you think is correct "from memory" get your book out and check! Stupid advice on here might lead to stupid actions in an aircraft!
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Surely stop then vacate?
High speed turnoffs are good for this - although you do NOT have to be going at a high speed to use them - indeed, normal speed (?) turnoffs are just as useful.
Depends on the nature of the incident. The runway incursion/door opening (whatever), may suggest get off the runway and start the taxi back without wasting too much more fuel. The 737 fire at Manchester, so many years ago, may (with hindsight) suggest stop and don't vacate.
Stop and then vacate doesn't seem to work smoothly for anything that immediately springs to mind.
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...and now I understand you, too.
Strange how a common language can still get so badly misconstrued, isn't it? Reminds us to be more careful when making comments to students.
On the subject though (yours) - in anything other than a Cessna 337, I would still CONSIDER the option of vacating (the aircraft) and let the bugger roll away from me.
Fires, failures - dramas of any kind - it would not be unreasonable to suggest that the aircraft has decided not to look after you any more - so I believe that you are under no moral obligation to look after IT.
By the time you realise that there actually is a serious drama, the aircraft already belongs to the insurance company.
Strange how a common language can still get so badly misconstrued, isn't it? Reminds us to be more careful when making comments to students.
On the subject though (yours) - in anything other than a Cessna 337, I would still CONSIDER the option of vacating (the aircraft) and let the bugger roll away from me.
Fires, failures - dramas of any kind - it would not be unreasonable to suggest that the aircraft has decided not to look after you any more - so I believe that you are under no moral obligation to look after IT.
By the time you realise that there actually is a serious drama, the aircraft already belongs to the insurance company.
Thread Starter
On the subject though (yours) - in anything other than a Cessna 337, I would still CONSIDER the option of vacating (the aircraft) and let the bugger roll away from me.
Hugh FD. Must say I have never heard of "piston slap" as reason for using the mixture to simulate engine failure. The Lycoming Flyer Key Reprints published in 2002 and on page 50 has this to say:
In our publications we then explained the reason for using the mixture to abruptly terminate power. By putting the the mixture control in ICO in a normal open or operating position, the pilot merely cut off the fuel but allowed the air to continue to fill the cylinders with resulting normal compression forces that are sufficient to cushion the deceleration of the engine and prevent the detuning of the crankshaft counterweights. However, any practice of simulated engine out condition at low altitudes should be best accomplished by a slow retardation of the throttle in accordance with the NTSB recommendation. This careful technique will protect the engine and at the same time provide for instant power if is needed.
With the throttle wide open and the mixture is cut initial cushioning is effective as discussed by Lycoming above. Unfortunately the effect is nullified a few seconds later by the closing of the throttle as part of the identification phase. With closed throttle very little air gets into the cylinders.
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killed a passer by
I did emphasise the word CONSIDER - but see no reason to leave a burning wreck in the middle of the runway if it can be moved (or move itself) out of the way.
Would have to think twice here, at the moment, as the grass is so dry it could start another major forest fire (and subsequently kill a few more squirrels, raccoons, possums etc).
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Unfortunately the effect is nullified a few seconds later by the closing of the throttle as part of the identification phase. With closed throttle very little air gets into the cylinders.
Centaurus,
Whilst that's true consider the s'down drill when the student is practising failures.......Case 1. Use mixture....If you use the mixture to 'simulate' the s'down then the student will have to retard the identified failed throttle to check they have correctly identified the failed engine (because both throttles will still be forward) and you keep the mixtures hidden so the student HAS to use dead foot/leg = dead engine to identify the failed engine and if they get it wrong and retard the live throttle then there is a significant yaw change. However Case 2. Use throttle........ if the throttle is pulled back by the instructor to simulate the failure and he/she hides the throttles behind paper/map etc until the stude correctly idents the failed engine and they get it wrong, what can you do? Just say try again or show them the throttle quadrant and say 'wrong'? Not a satisfactory demo IMHO or a satisfactory learning point for them.
With Case 1, they get a much closer drill to real life ie they actually get to retard the throttle as it is still forward and aligned with the other and get an actual and real result on the controls if they get it wrong.....for this reason I would much prefer to use the mixture for demos airborne. That said my schools SOP is to use the throttle so I use the throttle (Mostly)!
Regards...
Centaurus,
Whilst that's true consider the s'down drill when the student is practising failures.......Case 1. Use mixture....If you use the mixture to 'simulate' the s'down then the student will have to retard the identified failed throttle to check they have correctly identified the failed engine (because both throttles will still be forward) and you keep the mixtures hidden so the student HAS to use dead foot/leg = dead engine to identify the failed engine and if they get it wrong and retard the live throttle then there is a significant yaw change. However Case 2. Use throttle........ if the throttle is pulled back by the instructor to simulate the failure and he/she hides the throttles behind paper/map etc until the stude correctly idents the failed engine and they get it wrong, what can you do? Just say try again or show them the throttle quadrant and say 'wrong'? Not a satisfactory demo IMHO or a satisfactory learning point for them.
With Case 1, they get a much closer drill to real life ie they actually get to retard the throttle as it is still forward and aligned with the other and get an actual and real result on the controls if they get it wrong.....for this reason I would much prefer to use the mixture for demos airborne. That said my schools SOP is to use the throttle
so I use the throttle (Mostly)!Regards...
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A very good topic for discussion.
I have always found it best to explain things to
students in practical Laymans terms (ie common sense).
What is the AIM of Vmca demo exercise.
If you have an engine fail after TKOF then maintain Blueline, if you dont maintain
Blue line and speed decreases this is what can happen. The exercise will not be practised
after TKOF but at a safe altitude. At altitude less thrust = possible stall before loss of
directional control therefore Red line + 5/10 = minmimum speed before initiating recovery.
For the exercise I will simulate a failed engine by selecting one throttle to idle (slowly)
and the other throttle will be set at full power. Raise the nose slowly and approaching
redline +5/10 recover, if you dont initiate recovery I will call out RECOVER.
The C310 is generally Ok @ 5000'(Redline +5), However the BE55/58 BE CAREFUL (Redline +10)
came close to a spin when student said I have no more rudder and rolled the aileron for which I
closed throttle and intitated recovery and a pants change.
Relate to what is already known;
When conducting initial stall training and power off recovery,lower the nose increase airspeed
and increase power slowly and recover,this exercise is basically similar with the addition of
the asymmetric and associated yaw/roll etc which we no doubt discuss.
There is absolutely no reason to make a simulated scenario the real thing and becoming a test pilot.
Most people will initiate recovery as soon as the speed is identified even coming close to
redline therefore why explore what happens by continuing to decrease the speed even further.
Even during intitial stall training - stall warning and all will initiate recovery, even
the slow learners I have trained will do something.
Last week in C310 initial twin student says to me the the nose is not showing loss of control,
my comment was "would you ever fly at this speed" and "do you really want to find out what happens"
the answer obviusly was "No". I had already told him the above Baron aileron story on gnd.
Best advice I can give "KEEP YOUR FEET ON THE RUDDER PEDALS AND BE PREPARED TO TAKEOVER",
"DONT WAIT FOR ANOTHER 5KNOTS FOR RECOVERY, JUST TAKEOVER AND DO IT".
So without trying to Burn my comments I am NOT telling you all how to suck eggs. This is
simply what I do and I'm still breathing. Training is as safe as you make it.
Cheers
Naughty
I have always found it best to explain things to
students in practical Laymans terms (ie common sense).
What is the AIM of Vmca demo exercise.
If you have an engine fail after TKOF then maintain Blueline, if you dont maintain
Blue line and speed decreases this is what can happen. The exercise will not be practised
after TKOF but at a safe altitude. At altitude less thrust = possible stall before loss of
directional control therefore Red line + 5/10 = minmimum speed before initiating recovery.
For the exercise I will simulate a failed engine by selecting one throttle to idle (slowly)
and the other throttle will be set at full power. Raise the nose slowly and approaching
redline +5/10 recover, if you dont initiate recovery I will call out RECOVER.
The C310 is generally Ok @ 5000'(Redline +5), However the BE55/58 BE CAREFUL (Redline +10)
came close to a spin when student said I have no more rudder and rolled the aileron for which I
closed throttle and intitated recovery and a pants change.
Relate to what is already known;
When conducting initial stall training and power off recovery,lower the nose increase airspeed
and increase power slowly and recover,this exercise is basically similar with the addition of
the asymmetric and associated yaw/roll etc which we no doubt discuss.
There is absolutely no reason to make a simulated scenario the real thing and becoming a test pilot.
Most people will initiate recovery as soon as the speed is identified even coming close to
redline therefore why explore what happens by continuing to decrease the speed even further.
Even during intitial stall training - stall warning and all will initiate recovery, even
the slow learners I have trained will do something.
Last week in C310 initial twin student says to me the the nose is not showing loss of control,
my comment was "would you ever fly at this speed" and "do you really want to find out what happens"
the answer obviusly was "No". I had already told him the above Baron aileron story on gnd.
Best advice I can give "KEEP YOUR FEET ON THE RUDDER PEDALS AND BE PREPARED TO TAKEOVER",
"DONT WAIT FOR ANOTHER 5KNOTS FOR RECOVERY, JUST TAKEOVER AND DO IT".
So without trying to Burn my comments I am NOT telling you all how to suck eggs. This is
simply what I do and I'm still breathing. Training is as safe as you make it.
Cheers
Naughty
Centaurus:
Just at the moment I can't lay my hands on the SB I'm thinking of. Based on memory, it recommended mixture above 2000ft and smooth closure of throttle at lower levels. I thought the reason for preferring mixture was piston slap (caused by reduced pressure above the piston when throttle closed at high RPM) but it may well be that my memory has failed me and that the primary nasty was detuning of the balance weights. There's a more detailed discussion of the counterweight issue in SB245, but this specific SB does not cover IO360s, etc.
When I track down the one I'm thinking of I'll post the relevant text (unless I dreamt it).
HFD
Just at the moment I can't lay my hands on the SB I'm thinking of. Based on memory, it recommended mixture above 2000ft and smooth closure of throttle at lower levels. I thought the reason for preferring mixture was piston slap (caused by reduced pressure above the piston when throttle closed at high RPM) but it may well be that my memory has failed me and that the primary nasty was detuning of the balance weights. There's a more detailed discussion of the counterweight issue in SB245, but this specific SB does not cover IO360s, etc.
When I track down the one I'm thinking of I'll post the relevant text (unless I dreamt it).
HFD
Thread Starter
HFD. I am not sure, but I recall the de-tuning of the counterweights (must admit to ignorance on how they get buggered up) can also be caused by rapid throttle closure. In another words a snap closing of the throttle lever.
Page 50 of the Lycoming Flyer Reprints says this:
"Many flight instructors down through the years used the technique of abruptly cutting an engine with a multiengine candidate to test his emotional reaction and judgement with this extreme technique. (my comment is that testing emotional reaction is the job of a trained psychologist - not an enthusiastic amateur) Big radial piston engines with short stubby crankshafts could tolerate the abrupt technique. However, flat opposed piston engines with their long crankshafts and attached counterweights could not as readily take the abuse of suddenly snapping a throttle shut, particularly at take off or climb power. Use of the latter technique would tend to detune crankshaft counterweights and could possibly result in a nasty engine failure. Since it was common technique by flight instructors to terminate power abruptly to simulate an engine power loss, we had to protect the engine. As a result we published in our Engine Operator's Manual and in Service Bulletin No. 245, the recommendation that if power was abruptly terminated, it must be accomplished with the mixture control. Of course, this was intended for higher altitudes where a complete engine shut down could be conducted safely.
The student was to identify the dead engine by retarding the throttle to about 12 inches MP to simulate zero thrust, or similar to having the prop feathered. At that point the instructor could immediately return the mixture to an engine operating position and power would be available if needed. However, any practice of simulated engine out condition at low altitudes should be best accomplished by a slow retardation of the throttle in accordance with the NTSB recommendation. This careful technique will protect the engine and at the same time provide for instant power if it is needed."
End of quote.
For instructors the problem is getting hold of a copy of the Engine Operator's Manual and Service Bulletin No. 245. This of course is the CFI's responsibility to obtain these documents and ensure his staff read them. It probably never happens and techniques (faulty, or hopefully correct) then get passed down the line from instructor to student and so on indefinately and that is how myths are propagated.
Page 50 of the Lycoming Flyer Reprints says this:
"Many flight instructors down through the years used the technique of abruptly cutting an engine with a multiengine candidate to test his emotional reaction and judgement with this extreme technique. (my comment is that testing emotional reaction is the job of a trained psychologist - not an enthusiastic amateur) Big radial piston engines with short stubby crankshafts could tolerate the abrupt technique. However, flat opposed piston engines with their long crankshafts and attached counterweights could not as readily take the abuse of suddenly snapping a throttle shut, particularly at take off or climb power. Use of the latter technique would tend to detune crankshaft counterweights and could possibly result in a nasty engine failure. Since it was common technique by flight instructors to terminate power abruptly to simulate an engine power loss, we had to protect the engine. As a result we published in our Engine Operator's Manual and in Service Bulletin No. 245, the recommendation that if power was abruptly terminated, it must be accomplished with the mixture control. Of course, this was intended for higher altitudes where a complete engine shut down could be conducted safely.
The student was to identify the dead engine by retarding the throttle to about 12 inches MP to simulate zero thrust, or similar to having the prop feathered. At that point the instructor could immediately return the mixture to an engine operating position and power would be available if needed. However, any practice of simulated engine out condition at low altitudes should be best accomplished by a slow retardation of the throttle in accordance with the NTSB recommendation. This careful technique will protect the engine and at the same time provide for instant power if it is needed."
End of quote.
For instructors the problem is getting hold of a copy of the Engine Operator's Manual and Service Bulletin No. 245. This of course is the CFI's responsibility to obtain these documents and ensure his staff read them. It probably never happens and techniques (faulty, or hopefully correct) then get passed down the line from instructor to student and so on indefinately and that is how myths are propagated.
SB245D is available here: http://www.prime-mover.org/Aviation/...ins/sb245.html but it looks like I dreamt about the other SB.
HFD
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Vmca
Interesting forum and one in which there will always be a confliction of ideas and opinions. My own experience/comments are are follows:-
1. I have always simulated an engine failure close to the ground by closing a throttle, not the mixture. One reason is that by closing the mixture it could be argued that the instructor or examiner has deliberately shut the engine down which is at variance with the CAA and I believe FAA ruling about not practicing engine shut downs below 3000 feet agl.
2. As a CAA/JAR multi engine instructor I have never taught a student to demonstrate Vmca. He/she is, after all, a student not a test pilot and neither the CPL Skill Test nor the Multi Engine Class Rating require the student to demonstrate it. My understanding of the exercise is to demonstrate to the student those factors that affect the airspeed at which directional control is lost. There is a very long list of factors but on any one day and altitude and on any one aircraft type, only a few can be demonstrated. In practice these are
a. Critical engine (if applicable)
b. The use of bank towards the live engine
c. Whether or not the propeller of the failed engine has been feathered
The worst case scenario would be the loss of the critical engine, windmilling propeller and wings level. For the very reason that Naughty S described in the third paragraph of his last posting, I only give control of the rudder to the student for this and all the other demonstrations. Another reason for retaining control of everything but the rudder is that the rate of speed reduction is under my control and there is therefore less risk of the student mishandling the aircraft and spoiling the demonstration, plus the student does not have to concentrate on maintaining an accurate angle of bank where required.
In the worst case scenario mentioned above this inevitably results in full rudder being reached at an airspeed comfortably above stalling speed so there is absolutely no risk of a spin. The exercise then progresses through the other combinations. Since I teach on a Seneca I cannot demonstrate critical engine, but for those aircraft that do have one the next demonstration would be with the non-critical engine failed and and wings level This should result in a slightly lower airspeed at which full rudder is reached. Then back to the critical engine, this time with zero thrust set and wings level followed by the critical engine again with a windmilling propeller and bank towards the live engine. The latter two demonstrations could result in a critical speed below the stall speed. In this case the demonstration stops when the stall warner sounds and the student is asked to see if he or she can apply any more rudder. Inevitably the answer is that they can so it is not difficult to elicit friom them that they could have maintained directional control down to a lower airspeed. Since the airspeed is above stalling speed there is no risk of a spin but the student has been shown that bank and/or feathering the propeller will result in the ability to fly slower before directional control is lost.
3. The airspeed at which directional control is lost is invariably at a speed well below that at which the aircraft will normally be flown unless deliberately carrying out stalling. Therefore whenever teaching and practicing engine failures after take off the airspeed should always be comfortably above Vmca and the stalling speed.
4. I agree with those who have said that the rejected take-off does not have to be as a result of an engine failure. There are many reasons why a pilot would want to abandon take off and these can be introduced and practiced with no danger of departing the runway even if the student is slow in reacting.
This posting is not intended as a lesson in how to teach asymmetric flying and I am sure that there are many other equally good ways of getting the message across. However, there seems to be some confusion between Vmca and what I was taught to call Critical Speed, ie the airspeed at which directional control is lost. They are not the same thing.
1. I have always simulated an engine failure close to the ground by closing a throttle, not the mixture. One reason is that by closing the mixture it could be argued that the instructor or examiner has deliberately shut the engine down which is at variance with the CAA and I believe FAA ruling about not practicing engine shut downs below 3000 feet agl.
2. As a CAA/JAR multi engine instructor I have never taught a student to demonstrate Vmca. He/she is, after all, a student not a test pilot and neither the CPL Skill Test nor the Multi Engine Class Rating require the student to demonstrate it. My understanding of the exercise is to demonstrate to the student those factors that affect the airspeed at which directional control is lost. There is a very long list of factors but on any one day and altitude and on any one aircraft type, only a few can be demonstrated. In practice these are
a. Critical engine (if applicable)
b. The use of bank towards the live engine
c. Whether or not the propeller of the failed engine has been feathered
The worst case scenario would be the loss of the critical engine, windmilling propeller and wings level. For the very reason that Naughty S described in the third paragraph of his last posting, I only give control of the rudder to the student for this and all the other demonstrations. Another reason for retaining control of everything but the rudder is that the rate of speed reduction is under my control and there is therefore less risk of the student mishandling the aircraft and spoiling the demonstration, plus the student does not have to concentrate on maintaining an accurate angle of bank where required.
In the worst case scenario mentioned above this inevitably results in full rudder being reached at an airspeed comfortably above stalling speed so there is absolutely no risk of a spin. The exercise then progresses through the other combinations. Since I teach on a Seneca I cannot demonstrate critical engine, but for those aircraft that do have one the next demonstration would be with the non-critical engine failed and and wings level This should result in a slightly lower airspeed at which full rudder is reached. Then back to the critical engine, this time with zero thrust set and wings level followed by the critical engine again with a windmilling propeller and bank towards the live engine. The latter two demonstrations could result in a critical speed below the stall speed. In this case the demonstration stops when the stall warner sounds and the student is asked to see if he or she can apply any more rudder. Inevitably the answer is that they can so it is not difficult to elicit friom them that they could have maintained directional control down to a lower airspeed. Since the airspeed is above stalling speed there is no risk of a spin but the student has been shown that bank and/or feathering the propeller will result in the ability to fly slower before directional control is lost.
3. The airspeed at which directional control is lost is invariably at a speed well below that at which the aircraft will normally be flown unless deliberately carrying out stalling. Therefore whenever teaching and practicing engine failures after take off the airspeed should always be comfortably above Vmca and the stalling speed.
4. I agree with those who have said that the rejected take-off does not have to be as a result of an engine failure. There are many reasons why a pilot would want to abandon take off and these can be introduced and practiced with no danger of departing the runway even if the student is slow in reacting.
This posting is not intended as a lesson in how to teach asymmetric flying and I am sure that there are many other equally good ways of getting the message across. However, there seems to be some confusion between Vmca and what I was taught to call Critical Speed, ie the airspeed at which directional control is lost. They are not the same thing.
