sailon Posted March 5, 2020 Report Share Posted March 5, 2020 (edited) Had a weird issue with prop control on descent. Shortly after beginning my descent into KMLB, I lost power, followed by an extremely loud buzzing coming from the engine. Tach showed immediate rise to 2550, so I followed the prop overspeed checklist. Nursing the throttle, I found a sweet spot where I could barely hold altitude at around 100 kts. I was close enough to KMLB that I was able to declare emergency and safely land directly onto the runway. This buzz was loud enough that it was difficult to understand the tower over an ANR headset. Upon landing, checked airplane over, no oil anywhere on the bird, or dripping onto the ground, no grease on the propeller blades, and no loss of oil as I checked the oil quantity the next day. In fact the oil was freshly changed, and it still had the sweet honey color of fresh oil. I pulled the engine monitor data, and correlated it to the flight path. Here is what the engine monitor data showed. Oil Pressure- nominal, no change through the entire flight. Close look at the tach data showed variation in tack readings from 2480 to 2510 regularly over this leg. I don't really see any standouts when I review the engine data. When the incident occurred, there was a significant spike in revolutions to over 2550 rpms, but then returned to 2410. Going to the mechanic tomorrow. Suspect a leaking propeller piston, or flat spot in governor? Thoughts welcome. Especially the source of the loud buzz!! Edited March 5, 2020 by sailon Add thought to the buzz Quote Link to comment Share on other sites More sharing options...
Oldguy Posted March 5, 2020 Report Share Posted March 5, 2020 You might want to add the engine monitor data to your post. Also, maybe @Cody Stallings can check in with some insight. 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted March 6, 2020 Report Share Posted March 6, 2020 glad you are still with us, Sailon... great description of emergency procedures... and getting down... When you say you lost power... do you mean you lost some power? Or the engine died...!?!? Load your engine data up to savvy.com enable the sharing feature... post link here... We all get to see what actually happened... more people involved, better idea of what happened... and next steps... Typically rpm changing by itself... has something to do with the govenor... its internal gear pump, or oil, or its actuating ability... Rpm increasing is usually caused by the oil pressure in the prop no longer there... pressure can leak internally so it won’t leave a trace... Confusing, because rpm increasing doesn’t usually feel like a power loss... We’re you able to use the prop control to increase or decrease rpm? wait a minute... see if this describes what happened... 1) Govenor decides to go off line... 2) Oil pressure in the prop drops... 3) Rpm increases towards redline.... May even exceed until it hits the stops... 4) pilot pulls the MP back to control the rpm to avoid over speeding.... 5) So much power gets removed there is barely enough to stay aloft... hence the 100mph 6) why not fly around using max rpm 2700? (Red line) still will be low on power to avoid over speeding... 7) or 2400 rpm was good enough, not trying to cause other issues... 8) Experience I had with my O360... a lost seal in the crank behind the prop allowed oil pressure to drain back into the sump... but no sound came with that ... having the stops set properly can help avoid this situation... So... engine buzzing + rpm control loss.... how many hours are on your govenor? What govenor do you have? When your mechanic looks at it see if the governor is asking for help... Are the controls working properly? any additional descriptions of the buzzing still occurring on the ground? PP thoughts only, not a mechanic... Good luck with the next steps... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
sailon Posted March 7, 2020 Author Report Share Posted March 7, 2020 Boy was I surprised when I looked at the engine data. Link is: https://apps.savvyaviation.com/my-flights/22682/3bcc1c70-6349-4aa2-8ae3-e48a7fcc5f31. So attention is diverting away from the propeller and towards the engine. What is interesting is the impulse loss of manifold pressure down to 14 in Hg. All other engine parameters including oil pressure, and prop governor appear nominal. Cannot explain loud buzz in the cockpit, nor the loss of power. Could I have done more trouble shooting? Perhaps, but between the loss of power and noise, I wanted to get on the ground and fast. You will see that the loss and recovery of MAP was quick enough to be outside of the capture range of the prop governor, there is a spike to 2553 rpm. Then there is a second unexplained drop in MAP. The mechanic and I took a look at the filter, and it may be coming apart. Filter is around a year old. Starting to suspect something obstructing engine inlet. 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted March 7, 2020 Report Share Posted March 7, 2020 Get behind the filter to see what may have come apart and blocked the air flow... Rubber parts of the air hose have been known to delaminate... Check the throttle plate to see if it is still attached... Oscillations in power can be ‘interesting’ as in something gets suck in by the high airflow... then falls back out as the power declines... and may start to get blocked again in cycles... Same thing for things blocking the exhaust... if the muffler collapsed blocking the exit... the engine can’t run very well until it clears... The FF and MP both indicate the engine operating around idle... the anomaly last 7 minutes... It comes back to life at full throttle and matching full fuel flow... The rpm is a mechanical system that will lag the power being delivered by the engine... Great data post! Great thought process while under stress... great decision making... With that little MP available... it would depend on how much weight you are carrying to know if sustained flight is possible... really helps to know your best glide speed for that... Great job. Thanks for sharing the data so well so quickly! Good luck with your next steps. PP thoughts only, not a mechanic or CFI... Best regards, -a- upon further review of the data... compare the fuel pressure data on this flight to other flights... there may be some bumps in the road... that might not belong there... The fuel Pressure being recorded is hanging around 25psi... and spikes up to 75psi a lot... ask your mechanic about this too... it may be normal... but as a PP, I would think it would be more stable... is that real? Or an instrument error? The buzzing sound may have been a fuel pump, or fuel pressure regulator making noises? 1 Quote Link to comment Share on other sites More sharing options...
takair Posted March 7, 2020 Report Share Posted March 7, 2020 12 hours ago, sailon said: Boy was I surprised when I looked at the engine data. Link is: https://apps.savvyaviation.com/my-flights/22682/3bcc1c70-6349-4aa2-8ae3-e48a7fcc5f31. So attention is diverting away from the propeller and towards the engine. What is interesting is the impulse loss of manifold pressure down to 14 in Hg. All other engine parameters including oil pressure, and prop governor appear nominal. Cannot explain loud buzz in the cockpit, nor the loss of power. Could I have done more trouble shooting? Perhaps, but between the loss of power and noise, I wanted to get on the ground and fast. You will see that the loss and recovery of MAP was quick enough to be outside of the capture range of the prop governor, there is a spike to 2553 rpm. Then there is a second unexplained drop in MAP. The mechanic and I took a look at the filter, and it may be coming apart. Filter is around a year old. Starting to suspect something obstructing engine inlet. I had a baffle crack a few years ago. The buzzing noise was so severe that I thought I was having an engine failure. I instinctively pulled power as I turned around to head for the airport. With the power and speed reduction the buzzing went away. Even after pulling the cowl, it was not immediately obvious because the baffle returned to its normal position. I would not have believed that the crack could make so much noise, but a temporary repair resolved it..... 1 Quote Link to comment Share on other sites More sharing options...
Jim Peace Posted March 8, 2020 Report Share Posted March 8, 2020 On 3/6/2020 at 7:40 PM, sailon said: Boy was I surprised when I looked at the engine data. Link is: https://apps.savvyaviation.com/my-flights/22682/3bcc1c70-6349-4aa2-8ae3-e48a7fcc5f31. Not sure if this is a factor unless FlightAware is wrong but does your plane frequently go a month or sometimes two without flying while living in coastal Florida? Could something be gummed up someplace? Curious what oil you use and if you use camguard or not........only because I live in the same area and at times have gone a month or so without flying...... Quote Link to comment Share on other sites More sharing options...
sailon Posted March 8, 2020 Author Report Share Posted March 8, 2020 No, it not usually a factor, but our WX this spring has been terrible. Using Aeroshell 100+ oil, which I understand makes Camguard redundant. If 100+ not available, I use Camguard. Quote Link to comment Share on other sites More sharing options...
sailon Posted March 8, 2020 Author Report Share Posted March 8, 2020 On 3/6/2020 at 9:46 PM, carusoam said: Get behind the filter to see what may have come apart and blocked the air flow... Rubber parts of the air hose have been known to delaminate... Check the throttle plate to see if it is still attached... Oscillations in power can be ‘interesting’ as in something gets suck in by the high airflow... then falls back out as the power declines... and may start to get blocked again in cycles... Same thing for things blocking the exhaust... if the muffler collapsed blocking the exit... the engine can’t run very well until it clears... The FF and MP both indicate the engine operating around idle... the anomaly last 7 minutes... It comes back to life at full throttle and matching full fuel flow... The rpm is a mechanical system that will lag the power being delivered by the engine... Great data post! Great thought process while under stress... great decision making... With that little MP available... it would depend on how much weight you are carrying to know if sustained flight is possible... really helps to know your best glide speed for that... Great job. Thanks for sharing the data so well so quickly! Good luck with your next steps. PP thoughts only, not a mechanic or CFI... Best regards, -a- upon further review of the data... compare the fuel pressure data on this flight to other flights... there may be some bumps in the road... that might not belong there... The fuel Pressure being recorded is hanging around 25psi... and spikes up to 75psi a lot... ask your mechanic about this too... it may be normal... but as a PP, I would think it would be more stable... is that real? Or an instrument error? The buzzing sound may have been a fuel pump, or fuel pressure regulator making noises? As to the fuel pressure data, yes that is a known instrument error. I have the original fuel pressure gauge, and it is stable between 25-29 PSI. 1 Quote Link to comment Share on other sites More sharing options...
sailon Posted April 22, 2020 Author Report Share Posted April 22, 2020 (edited) UPDATE: Annual wrapping up, turns out the issue was caused by foam from the air filter injected into the throttle body. Mechanic very happy that I stayed easy on the power, as could have damaged the servo. Lesson learned, new air filter EVERY ANNUAL! Wrap up the annual, then pitot static, and will be back in the air. Still need to discuss source of buzz. Edited April 22, 2020 by sailon 2 Quote Link to comment Share on other sites More sharing options...
carusoam Posted April 22, 2020 Report Share Posted April 22, 2020 Great follow-up Sail! The whole idea behind the air filter... is to keep things from entering the intake... Not to be the supply of the things going into the intake... Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
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