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question for 412 pilots and or mechanics

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question for 412 pilots and or mechanics

Old 26th Aug 2012, 01:20
  #1 (permalink)  
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Join Date: Aug 2012
Location: Oregon
Age: 35
Posts: 2
question for 412 pilots and or mechanics

I am a mechanic myself working on Sikorsky helicopters for the last 6+ years.

I have worked around the world in a few different place's.

Currently I am working somewhere that requires me to take occasional flights in a bell 412ep. I am not familiar with these helicopters and something is alarming me.

On start up every morning these guys go through some checks and while doing those checks is sounds as if they are having compressor stalls. This happens on both of their 412ep's they have in camp.

one time when after picking up some passengers when rotor rpm started to increase as they were preparing to lift off the engine let out a much louder *bang* they continued on as if all was normal.

the mechanics informed me that this is normal on these helicopters to do this, and that it happens when switching from auto to manual governor
I did some reading and found and info letter directed at some 212 and 412s about engine manual fuel control operation procedures with helicopters using the PT6T engine. Not sure if that is what the 412ep has in it


What i am getting to is, is this safe? Would your ride in that machine? Is it normal? Should I bring this up with my company that the company we are contracting for is asking us to ride in a different contractors unsafe equipment?

thanks for any help
Tim
tim4g63fast is offline  
Old 26th Aug 2012, 04:15
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Join Date: Jun 2012
Location: Canada
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What is the field altitude where these checks are being done, and what are the engines flight idle stops set to? If the flight idles are set too high you can get a "pop" on change over. If I recall correctly a higher field altitude causes more of a drop in N1 on change over. I wouldn't say that is normal though, however I am not all that familiar with PT6T-3D's just -3B's.

Are you sure the noise you are hearing isn't just the extra noise from the hydraulic tests? When either system is switched off (especially number 2) they make a lot of noise, hydraulics off checks are part of the start-up procedure. I don't think that sounds like compressor stall though.

Last edited by cbox chip; 26th Aug 2012 at 04:27.
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Old 26th Aug 2012, 07:03
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Join Date: Feb 2011
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This is normal when going from auto to manual governor during pre-flight checks with the PT6T-3D or 3DF engines in the 412EP. There will be some differences in how much noise you hear depending on atmospheric conditions, altitude, etc.
HueyDog is offline  
Old 26th Aug 2012, 08:31
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Join Date: Apr 2008
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412 EP Auto Manual Governor Check

The popping noise tends to be louder on the 3D series than on the 3B.

The noise is also more likely to occur on reselecting Auto after gently winding up to 70% N1 in Manual to check normal response then closing the throttle prior to reselecting Auto.

The popping can be minimised by reselecting Auto 2% - 3% N1 above the normal Idle setting - i.e. around 64% N1 decreasing (normal Idle 61% N1 + or - 1%)


Trog
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Old 26th Aug 2012, 09:02
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Join Date: Jul 2003
Location: UK
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I used to fly as crew on the B412EP in the UK and yes the noise is quite normal when completing the governor manual checks during the start up functional checks. I understand that it was not a problem as when completing these checks as the power loading was light (other engine driving the rotors and the engine being checked is at idle at the time of changing from manual to auto or vice-versa)

The only time I've heard the noise in flight ( and only on a couple of rare occasions) whilst the engine is in auto governor mode was at the bottom of a PFL (autorotation) when recovering to S&L flight whilst pulling in power (going from power on auto to power on flight). We were informed that this was "pop surge" and the a/c were to be landed on and shut down (I believe this was an instruction from Bell) and then subject to engineering inspections. Exactly what inspections, I dont know as I'm not an engineer but I suspect it is something to do with transient torque spikes as both engines are under load at this time.

Our a/c were equipped with the PT6T twin packs.

Hope this helps
WASALOADIE is offline  
Old 26th Aug 2012, 14:36
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Join Date: Aug 2012
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thanks for the help guys. Helps me out a lot with decision making, on the helicopter i work on this wouldn't be considered normal so I was a bit nervous.

cbox chip- the altitude is 1000 ft or so. of course the DA is like 1500-5000 depending on the temp.
tim4g63fast is offline  
Old 27th Aug 2012, 02:16
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Join Date: Sep 2008
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Wink

If the Auto / manual changeover is rigged correctly, and the bleed valve serviceable loud stall like sounds shouldn't be heard at all through the flight.Also on pick up -if you hear a more mechanical repetitive knocking -its the main rotor droop restraints catching.
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