CO Levels

[Nstarbf]

Hello All,

I went up with my CFI for some crosswind training a couple of weeks ago and he brought along a new gadget he had recently bought, an electronic CO meter.

To our surprise, the device was reading high levels while we were on the ground but almost negligent when we're up in the air.  The highest reading we received was on the ground, just before shutdown with the nose pointed into the wind.  I'm just over a year into the plane, i bought it from my CFI (so all of this was a surprise and unnerving to him as well) and during the purchase process a new exhaust pipe was put in.  We went up again last weekend and the same thing, high levels on the ground but negligent levels in the air.  

Any thoughts.

 

[ragedracer1977]

What are high levels?

[Stephen]

Same behavior mine shows. Think that (depending on the numbers) higher on ground and less in cruise jives with the slipstream getting the exhaust away from the aircraft in flight , whereas you are "sitting in" the exhaust fumes on the ground and the find their way in via the side window, firewall holes , vents etc.  What type of CO monitor do you have and what are your High and low numbers?

[slowflyin]

What were the levels?   My CO monitor is so sensitive it indicates when I run my power tow.  While on the ramp, particularly with the door open, levels rise when the wind is blowing certain directions.  A quick google of OSHA guidelines should provide what’s acceptable.   I can’t remember the values but they where much higher than I expected. 

[slowflyin]

OSHA Limit-  50 ppm average over an 8 hour period.   Disclaimer- quick google search.  I’m sure there is more detailed info available.   

[Mooneymite]

Various possible reasons for CO to penetrate the cabin on the ground, but not airborne:

●Nose gear doors open on the ground: check for air leaks in the nose wheel well.

●Airflow pattern on the ground.

●Cabin door or hurricane window open on the ground.

●Less airflow to sweep exhaust away from cabin.

●Less airflow in engine compartment could allow exhaust to find it's way through firewall openings.

[moontownMooney]

Ive seen the same using the Sensorcon. I cant remember exactly, but ballpark 15-30 ppm on the ground, less than 5 ppm in the air.

Sent from my LM-V405 using Tapatalk

[Nstarbf]

The Co monitor is and Ensorcon Inspector Industrial PRO.

there was a few moments where it popped up over 50 if i remember correctly.  enough to set off the alarm on the thing.  

[moontownMooney]

50 ppm is the OSHA continual 8 hr continual exposure limit. Meaning it is acceptable for persons to work in an environment full time with CO levels that high (up to 8 continuous hours per day). Doesnt sound pleasant, but not unsafe.

Sent from my LM-V405 using Tapatalk

[Skates97]

I have the sensorcon and often see 10-30 on the ground during run up, especially if the door is open. It will sometimes jump higher than that on climb out but ends up at zero in cruise. Sometimes see it come up on descent as I'm slowing into the pattern. I'll see it around 5-10 just after shutdown. 

I'm not too concerned about a few minutes with the readings on the ground and various phases of flight. If I saw the number move, even 1-2 points, when using cabin heat I would be very concerned and have everything checked before any further flying. In fact anytime I use cabin heat I make note of the reading on the sensorcon before and watch to make sure it doesn't go up. 

[0TreeLemur]

Any time I smell exhaust, my Sensorcon shows CO.   Worst is taxiing downwind in the summer on a hot day with the door open.  The Sensorcon starts to beep at some concentration (50 ppm?).   I've had it do that a time or two.    After takeoff it takes a few minutes for the sensor to unload its CO and show 0.  That happens maybe 10 minutes after I stop smelling exhaust.

[MikeOH]

I have the FORENSICS CO detector ($100 on Amazon) and occasionally see 10-50 ppm during run-up, depending upon wind direction.  It's always read zero in flight even with the heater on.  I've never worried about it.

[DXB]

My monitor has a threshold of 50ppm to yellow alarm and 80ppm to red alarm and beep loudly.  The fuel truck has started up upwind of me will make it flash red and alarm wildly, completely breaking my checklist flow 

[carusoam]

Good news...

Sensorcon makes a very sensitive CO monitor...

Bad news...

Our engines continuously produce CO...

 

Also good to know...

It takes some practice with the device to see when and why the alarm goes off...

While on the ground... you are sitting in a pool of your own exhaust... or down-wind from somebody else...

Sometimes in the climb... the numbers may be a touch higher than in cruise...

In cruise they should be about zero...

 

Most often, dangerous levels of CO are coming into the cabin through the heater system... 

Put the monitor in different places to see if the numbers change... in front of the heater outlet would be a smart place to check...

 

If CO is coming from the heater... this is an important sign.... something to fix now...

PP thoughts only, not a mechanic...

 

inviting @DanM20C to the conversation... Dan has some really good experience with CO monitors and things...

Best regards,

-a-

[exM20K]

5 hours ago, carusoam said:

Our engines continuously produce CO

Not when operated LOP ;-)

Bravo and acclaim  guzzle tons of fuel in the climb, and there is plenty of leftover, unburnt fuel to make CO in that flight regimen. Both my Mooney’s have shown 30 ish levels of CO in taxi and climb.  No biggy for me.

-dan

Edited January 26, 2020 by exM20K

[whiskytango]

My Sensorcon shows 7 ppm at all time in flight.  The good news is that operating the heat doesn't change the reading.

[carusoam]

Nstar,

You get a feel for all the detail... as you can see, the other MSers have added additional valid data...

Best regards,

-a-

[flyer338]

exM20K mentioned mixture in relation to CO. This is critically important. Those talking about CO while on the ground, do you lean for ground operation and how much? The leaner the mixture, the less the percentage of CO in the exhaust gas. Leaning for ground operation, when there is less airflow to dissipate CO is a great way to mitigate CO effects on the ground. In flight, and running lean of peak there is less CO as a percentage of exhaust gas. If it goes up, even a little, when using the heater, that is cause for concern.

Just an old smog technician, among other things.

[daytonabch04]

I’ve had readings from 50-200 ppm from my Sentry in climb...

[Yetti]

Something to do is pull up all the duct tape that seals the floor from the outside.   Replace with aluminum tape.

[carusoam]

The oddest place somebody found CO entering the cabin...

There is a cabin seal at the back of the cabin where cables traverse from the tail cone to the inside...

Somebody had removed the seal to bring new antenna wires in...

The mild vacuum that gets induced into the cockpit, is also a driving force to bring air in through odd places...

Small missing fasteners downstream from the exhaust pipe are also a potential entry point...

PP thoughts only, stuff I have read around MS...

Best regards,

-a-

[Nstarbf]

Thanks much everyone.  I did a quick google search and see that .2 ppm is the normal level in the air.

the levels are negligent in flight so it sounds like the CO is creeping in when the gear doors are down. 

I'll keep monitoring it with the suggestions here and get back

[cliffy]

Might be interesting to take a CO monitor along on your next big airline ride and read what the numbers say and you taxi out, one jet behind another, each smelling the exhaust of the one in front. I've had to shut down all the a/c packs a time or two because the exhaust fumes were so bad inside the cockpit and cabin. 

The CO monitors are a great safety feature to have  (I have one) but then again airplane shaven't been falling out of the sky every year because of CO poisoning. Thankfully, most of the time, we are warned that the muffler is bad by the smell or good maintenance. A pressure check should be done at every annual to look for leaks (using soapy water spray). Its easy to do with just a shop vac blowing up into the exhaust pipe. I found a cracked end plate on my muffler that way just this year. You couldn't see it visually but the soap bubbles showed it just fine. 

Stay ahead on maintenance (get rid of those deferred items) and increase your safety margin. 

[ArtVandelay]

Looks like my muffler has sprung a leak, CO levels pop up for first time, turn heat off and it drops to single digits.
My muffler is 6 years old with about 800 hours on it...would this be considered average lifespan?


Tom

[carusoam]

Keep in mind the heat cycles that the muffler parts go through... once a crack starts, it can grow in length during a flight... essentially tearing open to deliver exhaust to the cabin...

Dan Bass noticed something regarding exhaust in the cabin on the flight out... including a headache...

On the flight back he was passed out in the climb...

Aside from being a very good Mooney CFII, he is also a machine savvy guy from working with factory type machinery...

+1 on being on top of muffler maintenance...

+1 using a good CO monitor...

+1 getting to know where all that CO comes from, and how it gets in...

 

Letting Dan know I’m talking about him...    @DanM20C

Best regards,

-a-