As350 B2 Vemd Problems

[logon]

we are having problems with our VEMD giving false over limit indications. Gong is going off numerous times before screen indicates overlimit in either NG or NR. Does anyone have a solution to this problem?

[Coastal]

we are having problems with our VEMD giving false over limit indications. Gong is going off numerous times before screen indicates overlimit in either NG or NR. Does anyone have a solution to this problem?

 

Oh boy, this is a can of worms. I'm just a pilot and can't explain it properly, but something about the VEMD taking analog signals from the a/c systems (eg: NR counter) and turning it into a digital signal for the VEMD may be at the root of your problem. We have a B2 that used to give multiple FLI error messages in flight that you could 'ignore' by pressing 'reset' on the VEMD. Then we had a more serious hiccup when, similar to your problem, the VEMD gave a false NR overlimit. The pilot was coming in with a sling load and the gong went and after the initial pucker he realized it was a glitch. Upon landing the recorded overlimit was something like 475 rpm on the NR. Obviously this did not happen and it was a false alarm. I believe the wise ones looked into the actual NR counter and unfortunately I can't remember if they actually found anything wrong with it. That a/c has since moved on so I can't tell you for sure if that false NR overlimit was due to the analog/digital interface problem, the NR counting mechanism, or both.

 

I can see all you wrenches that know better rolling your eyes at this muddled post, but that's what I recall. Don't know if this helps you or makes you scratch your head even more, so take it with a grain of salt...the beauty of the internet!

 

C

[whirlygig]

we are having problems with our VEMD giving false over limit indications. Gong is going off numerous times before screen indicates overlimit in either NG or NR. Does anyone have a solution to this problem?

 

Hello,

 

The B2 with VEMD has a known issue with monitoring those parameters.

 

The VEMD in the B2 should not be used for keeping track of NG/ NP cycles automatically.

 

The example the poster above me and you described is a "Zero time failure". That is to say when you look up the over limit in the VEMD, you will see a valid parameter excedance, ie. 470 RPM, but the 'time' value will be "0" seconds. This means that the Rotor was at 470 RPM for 0 seconds. Obviously that allows you to sign off that is was a VEMD error and not an actual occurance.

 

I believe that the issue lies within the "ARINC link", a communication bus within the helicopters wiring. Last I heard from Eurocopter it was a known issue and they were working on it.

 

There were some wiring improvements to be made to help (don't think it solved it) with this issue. I will try to find the documentation.

[whirlygig]

I was recalling a couple of EC120 SB's,

 

63-009. changing the value in a resistor (10k to 2.4k) found within the NR wiring to prevent false indications of overspeeds.

 

63- 016. Replacing a module within the NR circuit because poor crimping of one of the contacts creates false overspeed indications.

 

These still show you the types of things that can cause the false overspeed in the AS350.

 

If the solution ends up being new VEMD software (and you are out of the warranty period) you will be faced with a VEMD exchange, which the last time I was invloved with that was $10,000 USD. That is (was) the standard exchange price.

 

The current standard for the VEMD is V05 for the AS350.

[Gui]

I had several Nr overlimit detected few weeks ago(Nr indication ont the gauge was correct). There is no issued flight time for this overlimit, but the pilot had several ''gong song''. The troubleshooting revealed a defective Nr sensor and it's a known issue by ECL and they published a service letter for that.

 

The problem is that the magnetic core of the sensor is coming out of their casing and pulling on the wire, causing false indication/Nr overlimit. It also can cause rubbing on phonic wheel. There's is an SB on the AMM about Nr sensor replacement by a superseded one, but you have to do some modification of the wiring, to put a new canon plug.

 

But in you're case, you say that you have also Ng overlimit, so I'm not sure that this is the same problem, it's not suppose to cause Ng false indication...

 

I know that you had this snag few weeks ago, I hope that you had already solve it.

 

Gui

[whirlygig]

the NR sensor SL was due to obselescence, not due to an issue. They don't make the old ones anymore, so if you need to replace an old one you have to modify the wiring.