Rossair 1900D Engine Failure / Runway Overrun at Wilson?
Thread Starter
Rossair 1900D Engine Failure / Runway Overrun at Wilson?
Does anyone have additional details about the engine failure on takeoff of the Rossair 1900D at Nairobi Wilson yesterday, and the subsequent accident when the aircraft landed back at Wilson and then over-ran the end of the runway?
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It was'nt an engine failure! The prop governor played up and the pilot decided to shut down the engine. Mistake number one. Mistake number two, the pilot decided to return to Wilson, instead of going to Kenyatta. Mistake number three, the pilot landed deep at Wilson, and blew the tyres due to excessive braking.
The machine is fixed and is flying again. Mistake number four, the pilot probably does'nt have a job anymore!
The machine is fixed and is flying again. Mistake number four, the pilot probably does'nt have a job anymore!
What 2 do?
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It was not the engine that was worked on that caused the trouble, & clipboard since you R soo critical, were you on board when this all happend? You must be one of those invinsible examiners we all dred!
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The engine does not need to be shut down in the event of a Primary governor failure. It will automatically run on the Overspeed governor (assuming props are set at max for the take off). Should that fail then the Fuel Topping governor would kick in and the engine could still be run however the engine/prop would present a continuous cycle of surging. ....Very annoying yaw/ noise!
Thread Starter
MJBow2:
Your remarks are substantially correct, but your theory about the effect of control by the Nf governor following failure of both the primary and overspeed governors could be misleading to some readers.
If both propeller governors on an engine failed, oil supply to the propeller will be unrestricted, and the propeller will then move towards a very fine blade angle, leading to a gross overspeed. If sufficient power is being delivered to the propeller to achieve an overspeed as the Nf governor sees it (that being selected propeller speed +6%), fuel supply will then be reduced until the propeller is no longer >6% above selected propeller speed. Following a few momentary oscillations, the propeller speed will stabilize on the threshold of activating the Nf governor, and the net effect will be a zero thrust condition - caused by the FCU only supplying sufficient fuel to maintain the propeller at selected Np +6%.
If, following failure of both governors, not enough power is being supplied to the propeller to cause it to reach selected Np +6% (e.g. power lever at idle position), then the propeller blade angle will decrease until it reaches the normal angle for ground idle, at which point the beta reverse valve will intervene to regulate oil supply as the actual blade angle reaches idle blade angle.
It is critical that pilots flying PT6A series engines understand that in the event of a failure of the primary propeller governor, the propeller lever must always be moved to the full forward (maximum RPM, or takeoff speed) setting. If the propeller lever is at the maximum RPM setting, then the overspeed governor will take control of the propeller following failure of the primary governor, before the propeller speed reaches the threshold at which the Nf governor is set to intervene. If the propeller lever is moved back ONE TINY BIT from the maximum RPM position following a failure of the primary governor, then the Nf governor will intervene prior to the overspeed governor. The overspeed governor setting is a fixed value, whereas the Nf governor setting is variable - it is equal to selected propeller speed +6%.
In summary - if you encounter a propeller problem at any time during the takeoff phase of flight - make sure all the levers are forward. You won't have time to troubleshoot, and if you have any levers pulled back - most especially the propeller lever, in the case of a primary governor problem - you could easily lose all the propulsion from the powerplant with the problem. If you have the levers forward, you just drive away, with the propeller speed of the engine with the failed primary governor being controlled by the overspeed governor - just the way Pratt & Whitney designed it.
Your remarks are substantially correct, but your theory about the effect of control by the Nf governor following failure of both the primary and overspeed governors could be misleading to some readers.
If both propeller governors on an engine failed, oil supply to the propeller will be unrestricted, and the propeller will then move towards a very fine blade angle, leading to a gross overspeed. If sufficient power is being delivered to the propeller to achieve an overspeed as the Nf governor sees it (that being selected propeller speed +6%), fuel supply will then be reduced until the propeller is no longer >6% above selected propeller speed. Following a few momentary oscillations, the propeller speed will stabilize on the threshold of activating the Nf governor, and the net effect will be a zero thrust condition - caused by the FCU only supplying sufficient fuel to maintain the propeller at selected Np +6%.
If, following failure of both governors, not enough power is being supplied to the propeller to cause it to reach selected Np +6% (e.g. power lever at idle position), then the propeller blade angle will decrease until it reaches the normal angle for ground idle, at which point the beta reverse valve will intervene to regulate oil supply as the actual blade angle reaches idle blade angle.
It is critical that pilots flying PT6A series engines understand that in the event of a failure of the primary propeller governor, the propeller lever must always be moved to the full forward (maximum RPM, or takeoff speed) setting. If the propeller lever is at the maximum RPM setting, then the overspeed governor will take control of the propeller following failure of the primary governor, before the propeller speed reaches the threshold at which the Nf governor is set to intervene. If the propeller lever is moved back ONE TINY BIT from the maximum RPM position following a failure of the primary governor, then the Nf governor will intervene prior to the overspeed governor. The overspeed governor setting is a fixed value, whereas the Nf governor setting is variable - it is equal to selected propeller speed +6%.
In summary - if you encounter a propeller problem at any time during the takeoff phase of flight - make sure all the levers are forward. You won't have time to troubleshoot, and if you have any levers pulled back - most especially the propeller lever, in the case of a primary governor problem - you could easily lose all the propulsion from the powerplant with the problem. If you have the levers forward, you just drive away, with the propeller speed of the engine with the failed primary governor being controlled by the overspeed governor - just the way Pratt & Whitney designed it.
Last edited by V1... Ooops; 5th Feb 2005 at 09:03.
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V1...OOOPS, brilliant reply my man!
You see guys, here is a man that knows his PT6 engines and aircraft systems. No need for me to say anything further.
It was NOT the changed engine on 5Y-RAE that was the cause of the problem, so there is nothing more to say about that or the fact that it had an engine change. That is all irrelevant. The engineer who signed off the aircraft fit for flight, is a reputable and an experienced, licensed engineer. If he was happy that the aircraft was safe for flight, I would have been happy too.
The issue here is the fact that a minor problem resulted in the execution of certain procedures, which I don't entirely agree with.
I am of the opinion, and I reiterate that it is ONLY MY opinion, that the 15000 hour, airline experienced pilot, made a number of cardinal errors, and one can go into an in-depth discussion here between what is right and wrong, or what should have happened. Unfortunately it still does'nt change anything. It happened, and we should all learn from it.
Safe flying is cultivated thru good training. Having the ability to deal efficiently and effectively with "on-board emergencies" comes with good training and experience. Think safety all the time and evaluate all the options available to you during an emergency. Don't make decisions under pressure.
Every pilot WILL get a fright when something goes wrong in flight, but deal with it in the most effective manner. Stick with your airplane.... and fly the airplane........ until it no longer wants to fly!
Happy and safe flying out there guys!
You see guys, here is a man that knows his PT6 engines and aircraft systems. No need for me to say anything further.
It was NOT the changed engine on 5Y-RAE that was the cause of the problem, so there is nothing more to say about that or the fact that it had an engine change. That is all irrelevant. The engineer who signed off the aircraft fit for flight, is a reputable and an experienced, licensed engineer. If he was happy that the aircraft was safe for flight, I would have been happy too.
The issue here is the fact that a minor problem resulted in the execution of certain procedures, which I don't entirely agree with.
I am of the opinion, and I reiterate that it is ONLY MY opinion, that the 15000 hour, airline experienced pilot, made a number of cardinal errors, and one can go into an in-depth discussion here between what is right and wrong, or what should have happened. Unfortunately it still does'nt change anything. It happened, and we should all learn from it.
Safe flying is cultivated thru good training. Having the ability to deal efficiently and effectively with "on-board emergencies" comes with good training and experience. Think safety all the time and evaluate all the options available to you during an emergency. Don't make decisions under pressure.
Every pilot WILL get a fright when something goes wrong in flight, but deal with it in the most effective manner. Stick with your airplane.... and fly the airplane........ until it no longer wants to fly!
Happy and safe flying out there guys!
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You are qite right clipboard, fly this wonderfull errie until it does not fly anymore.
5Y-RAE ex ZS-OLX EX PH-RAE is s/n UE 18 is an aircraft that I spent many hrs mending.
True story:
the now defunct Aviation Assistance had a 1900 C with timex engines.They got permission from the Danish CAA to fly the a/c to altitude and 5,000 lbs of torque for one minute.The pilots reckoned that the a/c was rocking and rolling but the engines and the airframe stayed together.It says something for the a/c however I,m not too crazy about the tail feathers.
So , guys and girls if the torque fluctuates but the N2 stays normal ie 1700 rpm , in a perfect world , fly the a/c.
The other interesting thing that I experienced in Algeria was that on a very hot day the pilots reported that the prop could not reach 1700rpm.The m/m says that under those circumstances the prop will not achive 1700 rpm however the primary gorvernor can be adjusted to give you 1720 only, because as the oat gets colder and you guys set descent power the prop is going to over speed everytime, and that will put a lot of strain on the overspeed gorvernor.
The only engine failures ie -67D that I have heard of was the 2 1900,s from Rossair Europe , out of Hamburg with passengers.The cause was the failure of H.P. pumps on both a/c
5Y-RAE ex ZS-OLX EX PH-RAE is s/n UE 18 is an aircraft that I spent many hrs mending.
True story:
the now defunct Aviation Assistance had a 1900 C with timex engines.They got permission from the Danish CAA to fly the a/c to altitude and 5,000 lbs of torque for one minute.The pilots reckoned that the a/c was rocking and rolling but the engines and the airframe stayed together.It says something for the a/c however I,m not too crazy about the tail feathers.
So , guys and girls if the torque fluctuates but the N2 stays normal ie 1700 rpm , in a perfect world , fly the a/c.
The other interesting thing that I experienced in Algeria was that on a very hot day the pilots reported that the prop could not reach 1700rpm.The m/m says that under those circumstances the prop will not achive 1700 rpm however the primary gorvernor can be adjusted to give you 1720 only, because as the oat gets colder and you guys set descent power the prop is going to over speed everytime, and that will put a lot of strain on the overspeed gorvernor.
The only engine failures ie -67D that I have heard of was the 2 1900,s from Rossair Europe , out of Hamburg with passengers.The cause was the failure of H.P. pumps on both a/c
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V1... a good explanation.
I guess my understanding of the Fuel Topping governor differs a tad. Maybe you can straighten my thingking.
The FTG regulates fuel flow by sampling P3 air through the FCU. When the FTG senses a speed at or above 106% of selected RPM it opens the Py valve (at the FTG) which lowers the pressure of the p3 air being sampled by the FCU. The FCU in turn reduces fuel flow to match a fuel flow consistant with the 'new' P3 pressure created by the gas generator. After fuel flow reduces enough to slow the engine to a speed that will bring the props back below 106% of selected RPM (substancial decrease in N1) the Py valve will once again close. As N1 drops below 92% the P2.5 valve will then start to modulate open, which also effects the p3 being produced, further pronouncing the 'spiking' p3 pressure.
The Py valve only has two positions, open or closed. To modulate P3 pressure to a constant value the Py valve would have to find an intermediate position as P3 air is continuously being sampled by the FCU, which of course is happening whenver there is N1. So this yields an oscilation of P3 pressure, hence an oscilation of fuel flow, torque. RPM, ITT etc as the Py valve opens and closes due to the FTG being satisfied then not, then satisfied etc!
Unlike the pilot valve on the Primary and Overspeed governors, the Py valve does not supply almost instantaneous results. It acts through a long chain of events and is ultimately a very crued governor. When the RPM drops below 106% of selected RPM the Py valve closes at a time when N1 is in rapid decay. It then takes a few moments for P3 pressure to build back up, the FCU to sense this and then start delivering more fuel.
I can see that potentially the oscilations could get smaller and smaller...its just that my understanding is that the chain of events is just to slow and cumbersome for a stable prop speed to exist...its always playing catch up in other words....
Brinda
I guess my understanding of the Fuel Topping governor differs a tad. Maybe you can straighten my thingking.
The FTG regulates fuel flow by sampling P3 air through the FCU. When the FTG senses a speed at or above 106% of selected RPM it opens the Py valve (at the FTG) which lowers the pressure of the p3 air being sampled by the FCU. The FCU in turn reduces fuel flow to match a fuel flow consistant with the 'new' P3 pressure created by the gas generator. After fuel flow reduces enough to slow the engine to a speed that will bring the props back below 106% of selected RPM (substancial decrease in N1) the Py valve will once again close. As N1 drops below 92% the P2.5 valve will then start to modulate open, which also effects the p3 being produced, further pronouncing the 'spiking' p3 pressure.
The Py valve only has two positions, open or closed. To modulate P3 pressure to a constant value the Py valve would have to find an intermediate position as P3 air is continuously being sampled by the FCU, which of course is happening whenver there is N1. So this yields an oscilation of P3 pressure, hence an oscilation of fuel flow, torque. RPM, ITT etc as the Py valve opens and closes due to the FTG being satisfied then not, then satisfied etc!
Unlike the pilot valve on the Primary and Overspeed governors, the Py valve does not supply almost instantaneous results. It acts through a long chain of events and is ultimately a very crued governor. When the RPM drops below 106% of selected RPM the Py valve closes at a time when N1 is in rapid decay. It then takes a few moments for P3 pressure to build back up, the FCU to sense this and then start delivering more fuel.
I can see that potentially the oscilations could get smaller and smaller...its just that my understanding is that the chain of events is just to slow and cumbersome for a stable prop speed to exist...its always playing catch up in other words....
Brinda
Thread Starter
Hello Brinda:
Your understanding of Nf governor function, as you explained it above, is based on two incorrect assumptions. The first error is your assumption that the Nf governor operates at a fixed Np value, and your second error is your statement that the Py valve on the Nf governor only has two positions, open or closed.
The Nf governor on a PT6A engine, such as the -67D that is the subject of the discussion here, operates at a variable Np. In forward thrust, that is typically 6% above the speed that the pilot has selected using the propeller lever. For example, if the pilot has selected 100% Np using the propeller lever, the Nf governor will begin to restrict fuel flow when Np reaches 106%. If the pilot has selected 80% Np, the Nf governor will begin to restrict fuel flow when the Np reaches 86%.
In forward thrust, the Nf governor serves two functions: First, it provides a fallback method of regulating Np in the event of a failure of both the primary and overspeed governor, and second, it provides a method of regulating propeller speed by reducing Wf in the event of, for example, a high-speed dive during which airflow over the propeller causes the propeller speed to grossly exceed that which the pilot has selected using the propeller lever.
In reverse thrust, the Nf governor serves an entirely different purpose - it prevents actual Np from ever reaching the speed selected by the pilot with the propeller lever. In reverse thrust operations, the propeller must always be kept in an underspeed condition relative to the primary governor. If Np was allowed to reach the speed set with the propeller lever during application of reverse thrust, the primary governor would begin to govern - by restricting oil supply to the propeller - and the reduction in oil supply to the propeller would drive it from a negative blade angle (reverse thrust) to a positive blade angle (forward thrust) - not at all what you would want when you have the power levers yanked back to row 3 in an attempt to stop on a short surface.
To accomplish this function during reverse thrust, the teleflex arm that leads from the cam cluster at the rear of the engine (near the FCU) to the outboard end of the reversing lever at the front of the engine has a small attachment on it called a 'Nf reset arm'. When the pilot pulls the power lever aft of the idle position, the Nf reset arm lowers the actuating mechanism for the Nf governor and recalibrates the cut-in speed of the Nf governor, from +6% of selected Np in forward flight to -5% of selected Np in reverse operations. These figures are typical, and may vary slightly depending on the airframe the engine is installed in, but the theory is true for all PT6A engine that are equipped with single action reversing propellers.
Because the Nf governor is reset to 5% less than the propeller speed selected by the pilot using the propeller lever in the flight compartment, the reversing propeller is prevented from ever reaching the speed at which the primary governor would kick in and attempt to regulate propeller speed. This ensures that the propeller is always kept in an underspeeding condition during reverse thrust operations, and thus control of propeller blade angle during reverse thrust application always remains with the beta reverse valve - and, by extension, with the pilot, whose hand on the power lever is ultimately connected directly to the beta reverse valve, via the power lever linkage, the cam cluster, the teleflex cable, and finally the reversing lever itself.
This also explains why the limitation given for Np during reverse in most AFM's is typically 5% less than normal maximum propeller speed. This limitation has nothing to do with any inability of the propeller to cope with a higher speed in reverse thrust, instead, it has everything to do with keeping the propeller in an underspeed condition, and keeping the primary governor 'out of the loop' during reverse thrust operation.
From this, I think you can see that we have established that the speed that the Nf governor kicks in at is not a fixed integer, it is a percentage value either higher (forward flight) or lower (reverse thrust) than what the pilot has selected using the propeller lever. Now you can also comprehend why the propeller lever must always be placed in the maximum RPM position before you can select reverse thrust...
Respecting your second point, about the Py bleed valve (that being the part of the Nf governor that controls Wf, or fuel flow) being either open or closed, that is incorrect. Py air pressure bleed invoked by the Nf governor will be proportionate to the requirement to reduce propeller speed. You can easily check this for yourself - go to your aircraft, look up the limitation for Np in reverse and take note of it, then slowly bring one engine all the way back into reverse until you notice that Np begins to govern at the published limit. It will be governing because the Nf governor is bleeding off Py pressure, thus reducing Wf as needed - no more and no less than is needed.
If you hog the power lever roughly back to the stop, you will certainly encounter momentary oscillations before Np (and, eventually, Ng as well) stabilize. But, if you slowly pull the power lever back until the reverse Np speed limit is reached, you will see that the Nf governor will smoothly and gradually begin to govern Wf and by extension Np, and both values will stabilize.
We see surging in Wf and engine temperatures when the Nf governor kicks in during heavy reversing after we land our aircraft because of external variables - changing airspeed, unstabilized propeller blade angles, and dynamic (torsional) movement of the propeller blades themselves. In addition to that, during normal landing operations, we rarely leave the power in the full reverse position long enough to allow Np, Wf and Ng to stabilize. But, if you conduct the above experiment slowly, you will see that the Nf governor has the capability to very smoothly modulate Wf to achieve the Np limit it has been set to maintain.
I hope this clarifies operation of this commonly misunderstood control mechanism.
Your understanding of Nf governor function, as you explained it above, is based on two incorrect assumptions. The first error is your assumption that the Nf governor operates at a fixed Np value, and your second error is your statement that the Py valve on the Nf governor only has two positions, open or closed.
The Nf governor on a PT6A engine, such as the -67D that is the subject of the discussion here, operates at a variable Np. In forward thrust, that is typically 6% above the speed that the pilot has selected using the propeller lever. For example, if the pilot has selected 100% Np using the propeller lever, the Nf governor will begin to restrict fuel flow when Np reaches 106%. If the pilot has selected 80% Np, the Nf governor will begin to restrict fuel flow when the Np reaches 86%.
In forward thrust, the Nf governor serves two functions: First, it provides a fallback method of regulating Np in the event of a failure of both the primary and overspeed governor, and second, it provides a method of regulating propeller speed by reducing Wf in the event of, for example, a high-speed dive during which airflow over the propeller causes the propeller speed to grossly exceed that which the pilot has selected using the propeller lever.
In reverse thrust, the Nf governor serves an entirely different purpose - it prevents actual Np from ever reaching the speed selected by the pilot with the propeller lever. In reverse thrust operations, the propeller must always be kept in an underspeed condition relative to the primary governor. If Np was allowed to reach the speed set with the propeller lever during application of reverse thrust, the primary governor would begin to govern - by restricting oil supply to the propeller - and the reduction in oil supply to the propeller would drive it from a negative blade angle (reverse thrust) to a positive blade angle (forward thrust) - not at all what you would want when you have the power levers yanked back to row 3 in an attempt to stop on a short surface.
To accomplish this function during reverse thrust, the teleflex arm that leads from the cam cluster at the rear of the engine (near the FCU) to the outboard end of the reversing lever at the front of the engine has a small attachment on it called a 'Nf reset arm'. When the pilot pulls the power lever aft of the idle position, the Nf reset arm lowers the actuating mechanism for the Nf governor and recalibrates the cut-in speed of the Nf governor, from +6% of selected Np in forward flight to -5% of selected Np in reverse operations. These figures are typical, and may vary slightly depending on the airframe the engine is installed in, but the theory is true for all PT6A engine that are equipped with single action reversing propellers.
Because the Nf governor is reset to 5% less than the propeller speed selected by the pilot using the propeller lever in the flight compartment, the reversing propeller is prevented from ever reaching the speed at which the primary governor would kick in and attempt to regulate propeller speed. This ensures that the propeller is always kept in an underspeeding condition during reverse thrust operations, and thus control of propeller blade angle during reverse thrust application always remains with the beta reverse valve - and, by extension, with the pilot, whose hand on the power lever is ultimately connected directly to the beta reverse valve, via the power lever linkage, the cam cluster, the teleflex cable, and finally the reversing lever itself.
This also explains why the limitation given for Np during reverse in most AFM's is typically 5% less than normal maximum propeller speed. This limitation has nothing to do with any inability of the propeller to cope with a higher speed in reverse thrust, instead, it has everything to do with keeping the propeller in an underspeed condition, and keeping the primary governor 'out of the loop' during reverse thrust operation.
From this, I think you can see that we have established that the speed that the Nf governor kicks in at is not a fixed integer, it is a percentage value either higher (forward flight) or lower (reverse thrust) than what the pilot has selected using the propeller lever. Now you can also comprehend why the propeller lever must always be placed in the maximum RPM position before you can select reverse thrust...
Respecting your second point, about the Py bleed valve (that being the part of the Nf governor that controls Wf, or fuel flow) being either open or closed, that is incorrect. Py air pressure bleed invoked by the Nf governor will be proportionate to the requirement to reduce propeller speed. You can easily check this for yourself - go to your aircraft, look up the limitation for Np in reverse and take note of it, then slowly bring one engine all the way back into reverse until you notice that Np begins to govern at the published limit. It will be governing because the Nf governor is bleeding off Py pressure, thus reducing Wf as needed - no more and no less than is needed.
If you hog the power lever roughly back to the stop, you will certainly encounter momentary oscillations before Np (and, eventually, Ng as well) stabilize. But, if you slowly pull the power lever back until the reverse Np speed limit is reached, you will see that the Nf governor will smoothly and gradually begin to govern Wf and by extension Np, and both values will stabilize.
We see surging in Wf and engine temperatures when the Nf governor kicks in during heavy reversing after we land our aircraft because of external variables - changing airspeed, unstabilized propeller blade angles, and dynamic (torsional) movement of the propeller blades themselves. In addition to that, during normal landing operations, we rarely leave the power in the full reverse position long enough to allow Np, Wf and Ng to stabilize. But, if you conduct the above experiment slowly, you will see that the Nf governor has the capability to very smoothly modulate Wf to achieve the Np limit it has been set to maintain.
I hope this clarifies operation of this commonly misunderstood control mechanism.
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V1...thanks for that, you have also clarified my thinking on the operation of the Py valve.
I think if you read Brinda's post again he/she sees the Nf governor as a variable value also.
"106% of "SELECTED RPM.
Selected RPM could be anything within the governing range!! Where as O'speed is 106% of MAX...
Cheers MJB
I think if you read Brinda's post again he/she sees the Nf governor as a variable value also.
"106% of "SELECTED RPM.
Selected RPM could be anything within the governing range!! Where as O'speed is 106% of MAX...
Cheers MJB
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I don't wan't to get into a long explanation here but something needs to be clarified.
If the Primary gov fails ----- the fuel topping gov is rendered useless as it shares a common shaft and fly weights with the primary gov.
Lead Training Captain
Beech 1900
If the Primary gov fails ----- the fuel topping gov is rendered useless as it shares a common shaft and fly weights with the primary gov.
Lead Training Captain
Beech 1900
Thread Starter
Your observation is correct, in certain cases. For example, if the primary governor failure resulted from any failure in the components that drive the hollow gear-shaft and turn the flyweights, that will also take out the Nf governor.
However, if the failure of the primary governor to regulate oil supply to the propeller arises from any form of impaired movement or breakage of the pilot valve - the pilot valve being the shaft that moves vertically within the rotating hollow gearshaft - then the Nf governor will still be functional. The Nf governor will continue to function as long as the hollow gearshaft and the two flyweights are still turning in correct proportion to Np.
The cut-in Np of the Nf governor is determined by the preload pressure exerted on the coil spring in the top of the primary governor assembly (not the spring you see on top of the exterior of the assembly, but another spring inside the very top of the dome). This is the spring that we, as pilots, adjust preload on when we operate the propeller lever. The pilot valve itself is physically independent of this coil spring, although its range of movement is directly affected by spring preload.
However, if the failure of the primary governor to regulate oil supply to the propeller arises from any form of impaired movement or breakage of the pilot valve - the pilot valve being the shaft that moves vertically within the rotating hollow gearshaft - then the Nf governor will still be functional. The Nf governor will continue to function as long as the hollow gearshaft and the two flyweights are still turning in correct proportion to Np.
The cut-in Np of the Nf governor is determined by the preload pressure exerted on the coil spring in the top of the primary governor assembly (not the spring you see on top of the exterior of the assembly, but another spring inside the very top of the dome). This is the spring that we, as pilots, adjust preload on when we operate the propeller lever. The pilot valve itself is physically independent of this coil spring, although its range of movement is directly affected by spring preload.
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To all the people that have contributed to this posting, I want to say thank you.
A lot of worthwhile information have come out of this for all of us to learn from.
Now is'nt that what makes a discussion forum like this worthwhile?
A lot of worthwhile information have come out of this for all of us to learn from.
Now is'nt that what makes a discussion forum like this worthwhile?
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Nf Governor
I might be mistaken but some of the info on this subject is not quite correct-as I understood,the Nf governor is only active in the beta/reverse range.how does it govern any forward trust? This governor is a integral part of the Primary Governor,it consists of a reset arm,bleed link(which could be a rigid or lostmotion tube).The reset arm is connected to the reverse/beta cable,which is directly contolled by the beta valve activation.This is motion is controlled through a cambox arrangement activated by the input arm connetced to the Cockpit contol.Once the reset arm is moved from the min. stop it bleeds modified Py pressure off,this then resets the fuel flow on the FCU. and actually not controlled by oil pressure.The oil pressure has only and effect on the parameters once fuel schedules have been adapted.Is this correct?
Thread Starter
Traveltech:
I'm not really sure what information you are questioning, or what information you don't understand.
I explained quite clearly how the Nf governor will function in the forward thrust range of propeller operation, thus your statement ...as I understood, the Nf governor is only active in the beta/reverse range... is not correct. The last two sentences in your post are confusing, it is not clear if you are making a statement or asking a question.
Best suggestion I can give (and please appreciate that I am NOT trying to be sarcastic here) is that you print out this thread, then review the discussion and explanations carefully on the printed pages. It is often very difficult to follow the something like this just by looking at it on the computer screen. If you then want to make any specific follow-up questions about points you don't understand, or think are not correct, post specific questions or a specific hypothesis.
I'm not really sure what information you are questioning, or what information you don't understand.
I explained quite clearly how the Nf governor will function in the forward thrust range of propeller operation, thus your statement ...as I understood, the Nf governor is only active in the beta/reverse range... is not correct. The last two sentences in your post are confusing, it is not clear if you are making a statement or asking a question.
Best suggestion I can give (and please appreciate that I am NOT trying to be sarcastic here) is that you print out this thread, then review the discussion and explanations carefully on the printed pages. It is often very difficult to follow the something like this just by looking at it on the computer screen. If you then want to make any specific follow-up questions about points you don't understand, or think are not correct, post specific questions or a specific hypothesis.
