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Multi engine helicopters - Governor failure procedure

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Multi engine helicopters - Governor failure procedure

Old 7th Jun 2021, 05:21
  #41 (permalink)  
 
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As others have said - the clue is what the Nr is doing. If the Nr is lower than you would expect for that power setting, the low Tq engine is the problem - if the Nr is higher than you would expect, it is the high Tq engine.

Contain the Nr within limits using collective - this will also help you confirm your diagnosis.

If you can, establish safe single flight speed before doing anything with the engine controls.

When you do select and engine to turn off, only select it to idle to check you have A. correctly diagnosed the fault and B. actually selected the correct engine.

In the E Timor accident linked above - the Nr was higher than normal in the middle of a transition to forward flight - that immediately tells you high side runaway if the Nr goes up at a high power setting.
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Old 7th Jun 2021, 11:17
  #42 (permalink)  
 
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I have not flown the 214ST but have been at operations where they were flown....and my understanding is they will fly at max weight with only a single engine operating. (Someone might correct me if that perception is incorrect).

If that is the case...there should be no hurry to carry out any immediate acton beyond fly the machine and accelerate and climb away.

Analysis of the failure has to be done with the Power Setting at the time of the. failure....as altering the Collective Setting then checking Nr will only add to the difficulty of assessing what kind of failure you have.

In the linked Accident Report we see that happen.....moving the Collective.

The Co-Pilot did not correctly state the problem....which also added some confusion into the situation.

Neither Pilot got it right and fortunately no one got hurt but an aircraft got written off as a result.

What is shown is proper training (which the pilots had not had) is the key to success.

The decision to not send Pilots for Sim Training in the United States was based upon cost.....and I have to wonder how many trips to the States could have been done for the cost of replacing the damaged aircraft?

Was this another example of false economy?

We saw something similar in the Koby Bryant Crash.....the absence of Sim Training.
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Old 7th Jun 2021, 15:27
  #43 (permalink)  
 
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High side failures in a twin engined machine have always been a challenge as described. Hopefully, the new dual Fadec designs will eliminate all but the fuel valve failing open. Perhaps someone from an engine manufacturer can address the news on that area.

Last edited by JohnDixson; 7th Jun 2021 at 15:28. Reason: additional thought
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Old 7th Jun 2021, 23:37
  #44 (permalink)  
 
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The fuel valve failing open AND a high side governor failure? Glad you were never my sim instructor.
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Old 8th Jun 2021, 00:44
  #45 (permalink)  
 
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Gulli....in your time teaching in the Sim....how many well experienced Pilots were unable to cope with a High Governor Failure that did not respond to Throttle movement?

Never mind the added thrill of a failed fuel valve to boot!
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Old 8th Jun 2021, 05:25
  #46 (permalink)  
 
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Casting my eye over my training session notes, "DECU Hi" appears time and time again as problematic for many pilots to deal with. I see one note here where the pilot lowered the collective three times in a row in response to DECU Hi and the NR went off the dial. After being told that was the wrong thing to do, and why, and what he should have done, and then to be told we were going to repeat the exercise, and he did the same thing again. Unfortunately there just isn't enough time allocated to keep repeating the exercise until they get it right.
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Old 9th Jun 2021, 01:37
  #47 (permalink)  
 
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GB, I wasn’t suggesting a dual simultaneous failure. I was merely explaining that once dual fadecs are on a given machine, the redundancy of sensors and processing eliminates all of the failure modes that could cause a high side governor ( I’mm pretty sure-but never say never in aviation ) except for the failure of the final metering valve. And again, the engine manufacturers may.may have introduced changes in that area to further mitigate aginst a high side/max fuel failure.
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Old 9th Jun 2021, 02:47
  #48 (permalink)  
 
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Yes, the redundancy is so redundant with dual digital electronic engine controls that the high side governor failure is extremely unlikely. I've never heard of it happening, but it is still in the RFM for the S76C++. However I am aware of real life DECU MAJOR malfunction where the fuel flow is fixed (in the position the fuel metering valve was in when the malfunction was sensed by the DECU). This is a more realistic training exercise in the simulator than doing the DECU hi-side. In recurrent training I would bring it on during the take-off roll before CDP (i.e. when the engines were at a high power setting). Crew response went one of two ways. More often than not the malfunction was not noticed by either pilot and they continued the take-off and climb out, despite a big blue warning light being on right in front of their eyes. The malfunction only being noticed when power was reduced when establishing cruise flight and the torque split becoming apparent. As long as the good engine is still delivering torque the NR will not increase. On the rare occasion the malfunction was noticed early the take-off would be rejected and land back on the runway, which is exactly the wrong thing to do. Because they lower the collective all the way at touch-down and the NR goes off the dial and there you have a needless $1M repair bill. When I hear a crew departure brief "any malfunction before CDP I'll reject back on to the runway" I will give them that malfunction and they will see why it is not a good idea to reject the take-off with a fixed high power setting. You need to keep flying, get a safe altitude, PNF get out the ECL and deal with the issue as written. It is a very easy malfunction to deal with, and an expensive one if you act in haste and mess it up.
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Old 9th Jun 2021, 06:59
  #49 (permalink)  

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I will give them that malfunction and they will see why it is not a good idea to reject the take-off with a fixed high power setting. You need to keep flying, get a safe altitude, PNF get out the ECL and deal with the issue as written. It is a very easy malfunction to deal with, and an expensive one if you act in haste and mess it up.
Departing into a low overcast and encountering a high side failure....really not your day.
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Old 9th Jun 2021, 07:34
  #50 (permalink)  
 
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The venerable Wessex had electric fuel computers which would freeze the throttle actuator in the event of loss of signals (NF, N1 etc) but also if the battery voltage dropped below 18V if memory serves.

The problem was that once frozen, you could only recover the engine from it's frozen power level by bringing it back to idle.

Due to a series of electrical problems and a lack of a voltmeter, it was possible for a bad generator to drag the good one off line as well and result in rapidly falling battery voltage.

This led to a number of double computer freezes in tricky conditions.

We used to pull to just under max twin Tq on the first transition of the day and at that point, with a moderately low cloudbase, a colleague discovered that both had frozen and he was zooming skywards.

Fortunately he managed to get one back to idle and avoided IIMC but was till left with the other stuck at a high power setting.
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Old 9th Jun 2021, 07:45
  #51 (permalink)  
 
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Originally Posted by ShyTorque View Post
Departing into a low overcast and encountering a high side failure....really not your day.
Departing into a low overcast even with everything working properly....regrettably the outcome can be ruinous of one's day. Fortunately the reset button can recover the ruins.
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Old 9th Jun 2021, 19:40
  #52 (permalink)  

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gulliBell, unfortunately that reset button only works in the simulator!
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Old 9th Jun 2021, 21:18
  #53 (permalink)  
 
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Had that bit of fun....and whizzed through a layer like a rocket headed to Mars.....no sooner had looked in to get on instruments and we were back into the sunshine....pulling G's going UP!
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