The West: Plane Safe After Engine Trouble
Tiger 77, Capt Claret,
Thanks for the clarification.
My understanding of the way it works, then, is that the system will auto arm when the 3 conditions are met. But having auto armed, it cannot then auto disarm, otherwise it will never feather a prop.
So, it must be a manual process to disarm it. Anybody can confirm that?
If it does work this way, then what happens on a rejected takeoff - does a prop feather when you pull the power off, or is there some other condition required for actual autofeather (e.g torque differential) that prevents that?
I now understand why the autofeather didn't function in the Jundee case, but am curious as to why Embraer would have designed the system to not work for those cases.
I'm sure they had a good reason, but a more simple system (that used only lever position and an "arm" switch) would have feathered the prop as the power was increased in the go around.
Apologies for the thread drift.
Thanks for the clarification.
My understanding of the way it works, then, is that the system will auto arm when the 3 conditions are met. But having auto armed, it cannot then auto disarm, otherwise it will never feather a prop.
So, it must be a manual process to disarm it. Anybody can confirm that?
If it does work this way, then what happens on a rejected takeoff - does a prop feather when you pull the power off, or is there some other condition required for actual autofeather (e.g torque differential) that prevents that?
I now understand why the autofeather didn't function in the Jundee case, but am curious as to why Embraer would have designed the system to not work for those cases.
I'm sure they had a good reason, but a more simple system (that used only lever position and an "arm" switch) would have feathered the prop as the power was increased in the go around.
Apologies for the thread drift.
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Aircraft...
Yep, after takeoff at around 1500ft agl we turn the autofeather switch off which disarms the system.
During the RTO the power levers are pulled back to less than 62 deg, and the system dis-arms because one of the 3 conditions is no longer met.
I believe most autofeather systems work in this way, its just a limitation of the system. It was primarily designed to assist the pilot while close to the ground at high power setting to reduce the drag asap after an engine fails.
Cheers,
Tiger.
So, it must be a manual process to disarm it. Anybody can confirm that?
If it does work this way, then what happens on a rejected takeoff
I now understand why the autofeather didn't function in the Jundee case, but am curious as to why Embraer would have designed the system to not work for those cases.
Cheers,
Tiger.
Ahh, the endless discussions that can be had over autofeather.
Tiger 77, I thank you once again and appreciate your patience. Not everybody's cup of tea I know, but I find that the technicalities of aircraft systems can be enormously fascinating.
This suggests that the system can auto disarm.
But, if it auto disarms, shouldn't the failure of an engine then cause an auto disarm (i.e because no longer would both the torques be above 62%)?
Tiger 77, I thank you once again and appreciate your patience. Not everybody's cup of tea I know, but I find that the technicalities of aircraft systems can be enormously fascinating.
During the RTO the power levers are pulled back to less than 62 deg, and the system dis-arms because one of the 3 conditions is no longer met.
But, if it auto disarms, shouldn't the failure of an engine then cause an auto disarm (i.e because no longer would both the torques be above 62%)?
The autofeather is generally designed for the engine after take-off case (as already stated.) In the DHC8, to pre-arm it you push the autofeather button as part of the after start checks and then when power is applied to both engines the autofeather actually arms. Then if you lose power on one engine, that engine's prop will autofeather, if you lose power on both engines, the system disarms.
The most likely cause of a reduction in power on both engines is that you are rejecting the take-off, you don't want anything feathering at that point because then you lose the braking effect of the discing propellors.
So to recap. For the system to arm it must be selected on, have both power levers above a certain angle and both torques above a certain amount. Basically the aeroplane is waiting for something it recognises as being the start of the take-off roll. Then any power reduction on a single engine is assumed to be a single engine failure requiring the prop to be feathered and a power reduction on both engines is assumed to be a reject not requiring any feathering.
The DHC8 autofeather is not approved for any phase of flight other than take-off. It sounds like the EMB120 is approved for approach, but the system design still seems to be focussed on the EFATO scenario. The EMB120 system would also work fine if the engine failed during a go-around.
It makes sense if you think about it. There are many situations where you may have a small split in the torques at low power settings and you don't want the prop to be feathering all the time, could get embarrasing.
The most likely cause of a reduction in power on both engines is that you are rejecting the take-off, you don't want anything feathering at that point because then you lose the braking effect of the discing propellors.
So to recap. For the system to arm it must be selected on, have both power levers above a certain angle and both torques above a certain amount. Basically the aeroplane is waiting for something it recognises as being the start of the take-off roll. Then any power reduction on a single engine is assumed to be a single engine failure requiring the prop to be feathered and a power reduction on both engines is assumed to be a reject not requiring any feathering.
The DHC8 autofeather is not approved for any phase of flight other than take-off. It sounds like the EMB120 is approved for approach, but the system design still seems to be focussed on the EFATO scenario. The EMB120 system would also work fine if the engine failed during a go-around.
It makes sense if you think about it. There are many situations where you may have a small split in the torques at low power settings and you don't want the prop to be feathering all the time, could get embarrasing.
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From the maunal (somewhat abbreviated)
Automatic Feathering
The automatic feathering system will automatically feather the propellers whose relevant engine under-goes a power loss during takeoff or go-around
The system is ARMED when the following conditions are met simultaneously
- AUTO FEATHER switch ON
- Torque of both engines above 62.0 + or – 1.4%
- Both power lever above 62 degree power lever angle (PLA)
The automatic feathering system is activated whenever torque of one engine drops below 23,6 + or – 2.5%
So Aircraft, the autofeather does not 'auto Disarm' in the context I think you are thinking of, but rather it is armed ie, meets all three conditions simultaneously, or its 'not armed'.
Because the torque on final approach is no where near 62% (but rather closer to 20-25%, the automatic feathering system is disabled. Why it didn't feather on the go around has already been explained but just to clarify, only two conditions were met ie; the PLA above 62 degrees and the Autofeather switch ON. The 3rd condition (simultaneously is the word) was never met. It's hard to spool up a failed engine to 62%.
The props will only feather in a go-around if the engine failed during the go-around.
There are however two other ways to feather the EMB-120 prop (3 ways in total) and that is
1. Electrically, activated by either the ELEC FEATHER switch or by the Fire Extiguishing handle or
2. Mechanical, the way we all know and that is by the condition lever (feather position)
Hope this helps (any current Braz drivers may wish to add or correct some of this)
Mono
From the maunal (somewhat abbreviated)
Automatic Feathering
The automatic feathering system will automatically feather the propellers whose relevant engine under-goes a power loss during takeoff or go-around
The system is ARMED when the following conditions are met simultaneously
- AUTO FEATHER switch ON
- Torque of both engines above 62.0 + or – 1.4%
- Both power lever above 62 degree power lever angle (PLA)
The automatic feathering system is activated whenever torque of one engine drops below 23,6 + or – 2.5%
So Aircraft, the autofeather does not 'auto Disarm' in the context I think you are thinking of, but rather it is armed ie, meets all three conditions simultaneously, or its 'not armed'.
Because the torque on final approach is no where near 62% (but rather closer to 20-25%, the automatic feathering system is disabled. Why it didn't feather on the go around has already been explained but just to clarify, only two conditions were met ie; the PLA above 62 degrees and the Autofeather switch ON. The 3rd condition (simultaneously is the word) was never met. It's hard to spool up a failed engine to 62%.
The props will only feather in a go-around if the engine failed during the go-around.
There are however two other ways to feather the EMB-120 prop (3 ways in total) and that is
1. Electrically, activated by either the ELEC FEATHER switch or by the Fire Extiguishing handle or
2. Mechanical, the way we all know and that is by the condition lever (feather position)
Hope this helps (any current Braz drivers may wish to add or correct some of this)
Mono
AerocatS2A, Monopole,
Thanks for your posts. Just one little piece of the puzzle remains.
If, to be armed, the 3 conditions have to be met (simultaneously), and the removal of one of the conditions means that it automatically disarms, how does it ever manage to feather a prop when the engine failure itself removes one of the conditions (the 62% torque condition)?
Looking at the EFATO example: as the levers are advanced for takeoff, and as the torque (of both engines) increases past 62%, the system arms (the switch is "on"). That is all perfectly straightforward.
But, after getting airborne, an engine fails and the torque of that engine begins to rapidly decrease. That torque will rapidly drop past 62% on its way down to some negative value.
According to everything written so far, the system should disarm itself because both torques are no longer above 62% - this implies that it could not feather the prop!
But, I should assume, this is not what happens. Presumably the system remains armed and proceeds to feather the prop. How is it that the system remains armed?
And, another little question:
Why the great rush to disarm it?
Thanks for your posts. Just one little piece of the puzzle remains.
If, to be armed, the 3 conditions have to be met (simultaneously), and the removal of one of the conditions means that it automatically disarms, how does it ever manage to feather a prop when the engine failure itself removes one of the conditions (the 62% torque condition)?
Looking at the EFATO example: as the levers are advanced for takeoff, and as the torque (of both engines) increases past 62%, the system arms (the switch is "on"). That is all perfectly straightforward.
But, after getting airborne, an engine fails and the torque of that engine begins to rapidly decrease. That torque will rapidly drop past 62% on its way down to some negative value.
According to everything written so far, the system should disarm itself because both torques are no longer above 62% - this implies that it could not feather the prop!
But, I should assume, this is not what happens. Presumably the system remains armed and proceeds to feather the prop. How is it that the system remains armed?
And, another little question:
... after takeoff at around 1500ft agl we turn the autofeather switch off which disarms the system.
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As quoted
At this point the ARMED indicating light extinguishes and the prop is feathered.
Not negative, but Zero
I may be incorrect on this one, but from memory there is an eight second delay in the system to allow the torque to reach below 23.6% from which the autofeather system then feathers the prop.
Mono
The automatic feathering system is activated whenever torque of one engine drops below 23.6 + or – 2.5%
That torque will rapidly drop past 62% on its way down to some negative value.
Presumably the system remains armed and proceeds to feather the prop. How is it that the system remains armed?
Mono
The whole point of the autofeather system is to feather a prop if torque drops on one of the engines. So once it is armed it is specifically waiting for one engine to fail. It recognises one engine as having failed by noting a drop in torque on one engine while both power levers remain above the specified angle.
This is its primary purpose, so it looks for that scenario first. It is simply a matter of it feathering when an engine failure is recognised, and the feathering takes precedence over disarming the system. The system disarms when the three conditions are no longer met AND an engine failure hasn't occured.
As far as getting it off quicksmart, autofeather systems (particularly the one in the Dash 8) have a habit of working when you don't want them to. So once you are out of the relatively high risk take-off performance scenario, you get rid of it.
This is its primary purpose, so it looks for that scenario first. It is simply a matter of it feathering when an engine failure is recognised, and the feathering takes precedence over disarming the system. The system disarms when the three conditions are no longer met AND an engine failure hasn't occured.
As far as getting it off quicksmart, autofeather systems (particularly the one in the Dash 8) have a habit of working when you don't want them to. So once you are out of the relatively high risk take-off performance scenario, you get rid of it.
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Hey all,
All the above facts are correct with regard to the auto-feather system. Aircraft, et al. Once all three conditions are met the system becomes armed. Failure of one of those three parameters while the system is still armed will cause a propellor to feather. Once the feathering action has been initiated then the system automatically disarms to protect against the other propellor feathering as the windmilling blade will allow the continued operation for an auxillary generator and hydraullic pump.
Normal operations mean that the system is disarmed once above the minimum safe altitude or lowest safe altitude depending on how you operate the aircraft.
Monopole, the system will act to feather the prop the instant one of the conditons is not met.
Once it acts the system then disarms for the reasons mentioned above.
All the above facts are correct with regard to the auto-feather system. Aircraft, et al. Once all three conditions are met the system becomes armed. Failure of one of those three parameters while the system is still armed will cause a propellor to feather. Once the feathering action has been initiated then the system automatically disarms to protect against the other propellor feathering as the windmilling blade will allow the continued operation for an auxillary generator and hydraullic pump.
Normal operations mean that the system is disarmed once above the minimum safe altitude or lowest safe altitude depending on how you operate the aircraft.
Monopole, the system will act to feather the prop the instant one of the conditons is not met.
Once it acts the system then disarms for the reasons mentioned above.
Monopole, the system will act to feather the prop the instant one of the conditons is not met.
Disarming the Dash 8 Autofeather
This is for the Dash 8, but as mentioned above, the various systems have similar designs.
To disarm the autofeather it is not just a matter of removing one of the conditions that arms it.
The DHC8 autofeather can only be disarmed by:
Pushing off the autofether switchlight.
Retarding one or both power levers to flight idle.
Both engine torques dropping to below approixmately 38%.
From this you can see that if both power levers remain advanced but the torque drops on ONE engine, then none of the disarm conditions are met. The system remains armed and the failed engine's prop is feathered.
To disarm the autofeather it is not just a matter of removing one of the conditions that arms it.
The DHC8 autofeather can only be disarmed by:
Pushing off the autofether switchlight.
Retarding one or both power levers to flight idle.
Both engine torques dropping to below approixmately 38%.
From this you can see that if both power levers remain advanced but the torque drops on ONE engine, then none of the disarm conditions are met. The system remains armed and the failed engine's prop is feathered.
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It will feather if the torque drops below a certain amount. It won't feather if you retard the power levers or deselect the autofeather button. In that case it just disarms.
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Another reason for getting rid of autofeather is on some systems (and I dont know this one) the auto-ignition is inhibited, thus removing any chance of a relight upon flameout.
This is interesting in the context of many operators who arm autofeather at transition on descent.
This is interesting in the context of many operators who arm autofeather at transition on descent.
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Prelim report http://www.atsb.gov.au/publications/...703952_001.pdf
Brazdriver, your quote from page 1 when you had just obtained (probably bought) a job with said company
From the ATSB:
and
and
Care to review your comments?
Very professional crew on board! 
The stick shaker operated twice during the go-around, but because stick shaker operation was not a flight recorder parameter, the timings of those events could not be established. The recorded flight data indicated that the aircraft remained on the limit of its performance limits for about 1 minute 21 seconds after the go-around was initiated. The avoidance of a ground collision during that period was fortuitous.
and
The crew was surprised by the significant roll and yaw, consequences of asymmetric thrust, and did not complete the standard go-around initial actions of setting engine power and selecting flaps 15, and retracting the landing gear.
After the flaps reached 25°, aircraft performance deteriorated further with the speed in the range 95 to 97 kts for 12 seconds, and the altitude decreasing to about 50 ft AGL. The flaps were fully retracted and the landing gear retracted 3 minutes 6 seconds after the go-around was commenced.
Care to review your comments?
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zzzzzzzzzzzzzzzZZZZZZZZZZZZZZzzzzzzzzzzzzzzzzzzZZZZZZZZZZZZz .....
<snort>
What time it is... is it???
Wow, I've been asleep since 19 Sep 2007 waiting for somebody to post on this thread. Did I miss anything?
Way to revive a dead thread.
Nuhfink to see 'ere. Nighty night.
FRQ CB
<snort>
What time it is... is it???
Wow, I've been asleep since 19 Sep 2007 waiting for somebody to post on this thread. Did I miss anything?
Way to revive a dead thread.
Nuhfink to see 'ere. Nighty night.
FRQ CB
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Interesting thread, particularly the autofeather/autocoarsen subthread. I have a personal story here.
A flight test aircraft was rigged with a "Kill switch" to stop fuel flow to the critical engine, independent of normal cockpit controls. A V1 cut was accomplished, with normal SE climbout in autocoarsen. After the desired performance point was demonstrated, a restart was attempted; but as the throttle was advanced above idle "all hell broke loose" with much shuddering and shaking. The engine was again shut down, and a SE landing was completed. This was unusual to me as a ground observer, so I met the aircraft on the ramp.
The chief test pilot cornered me and, very agitated, asked what the hell was happening. It was two or three minutes before I could get a word in edgewise.
Finally I was able to ask one question: "Was autocoarsen still armed?"
Instantly the heat was off. He knew exactly what had happened, and their flight test card was rewritten to include that vital disable step.
A flight test aircraft was rigged with a "Kill switch" to stop fuel flow to the critical engine, independent of normal cockpit controls. A V1 cut was accomplished, with normal SE climbout in autocoarsen. After the desired performance point was demonstrated, a restart was attempted; but as the throttle was advanced above idle "all hell broke loose" with much shuddering and shaking. The engine was again shut down, and a SE landing was completed. This was unusual to me as a ground observer, so I met the aircraft on the ramp.
The chief test pilot cornered me and, very agitated, asked what the hell was happening. It was two or three minutes before I could get a word in edgewise.
Finally I was able to ask one question: "Was autocoarsen still armed?"
Instantly the heat was off. He knew exactly what had happened, and their flight test card was rewritten to include that vital disable step.
