CO alarm going off after takeoff and climb but not in cruise

[warrenehc]

Hello,

I have a sentry adsb with the CO monitor.

I use to have a F model and never had issues with CO.

My M model during climb the CO alarm goes off but when I level off the warning stops. 
 

It is mounted on the pilot window in the same place as it was in my F model.

I thought it could be the lower pilot side vent since the exhaust is on the pilot side. I closed that and still have the issue. 

I have checked the firewall and see nothing. 
 

Any help would be great.

[alextstone]

Pull out the back seats and the plastic "buckets" the seat bottoms ready in.  You should see Aluminum tape sealing ALL of the seams.  If any of that is missing, exhaust from the tail pipe can enter through the belt panel seams and into the cockpit. 

 

Alex

[dkkim73]

Same problem, comes and goes. A bit better but still intermittent and vexing for me. Generally comes up more at higher AOA (not just climb but slow flight and approach occasionally). 

Check the gear rod boots ("mouse boots") and give a think to penetration through the floor as noted above. I also had my exhaust system pressure-tested and checked the heater mixer box. Some have mentioned the door seals. 

Knowledgeable people say this can be a PITA to find. 

Good luck. 

 

[IvanP]

Cabin door seal can also play role in this. I had a bit of a gap on the top of my door and had the same issue with my CO monitor. In climb the monitor would show increased CO levels. Seems that he gap would create airflow from bottom up and brought some exhaust gases in the cabin. Closing the door gap and fully opening the top air vents for T/O and climb to direct airflow from top to bottom improved the situation. I still get a small increase on the CO monitor but not much.    

Edited Thursday at 08:03 PM by IvanP

[exM20K]

At what level is the alarm set?

as I’m sure you’re aware, you’re burning a lot more fuel in the Bravo, especially in the climb.  
I wouldn’t sweat a 30-50 ppm reading that clears in level flight.  
 

edit…. Also, I find that covering the bottom rear corner of the door with a piece of paper significantly reduces noise and the Venturi effect that draws CO into the cabin.
-dan

[Rick Junkin]

@warrenehc If you're getting an audible alarm from a Sentry then you have an issue that I would address sooner rather than later. According to the Foreflight web site, the audible alarm doesn't trigger until 200PPM.

The one time I saw over 200PPM on my Sensorcon during a departure I declared an emergency and landed. Turned out to be a prudent decision. We found an under-torqued v-band clamp.

From the Foreflight site:

What are the Sentry and Sentry Plus carbon monoxide (CO) alert thresholds?

Sentry and Sentry Plus alert users to elevated carbon monoxide (CO) levels with color-changing LEDs, a built-in audible alarm, and in-app alerts. The thresholds for these features are described below.

LED Color

• Red: When the detected CO level exceeds 200 PPM (All Sentry LEDs turn red).
• Yellow: When the detected CO level is between 75 and 200 PPM.
• Green: When the detected CO level is less than 75 PPM.

Alarm

• An audible alarm is triggered when the detected CO level exceeds 200 PPM.

In-App Alerts

• An in-app alert is provided when the detected CO level exceeds 200 PPM.
• A second in-app alert will be displayed after five minutes if the detected CO level continues to be greater than 200 PPM.

https://support.foreflight.com/hc/en-us/articles/13592147336599-What-are-the-Sentry-and-Sentry-Plus-carbon-monoxide-CO-alert-thresholds

 

[Rick Junkin]

I'm in the process of removing the carpeting and rear seat buckets to inspect/reseal all the floor gaps with aluminum tape. I'll take some pictures to show you where the gaps are located. Some of them are quite large.

The CO level in my Bravo can go as high as the low 40's during a full rich climb-out and then drops to zero or low single digits at LOP cruise. I'm convinced I can improve on that so I'm taking a look at everything. Follow the exhaust trail down the left side of the airplane and you'll see all of the places it can find a way into the cockpit, especially at lower airspeeds/higher angles of attack. It spreads well beyond the visible trail at higher AOA. The joints between the belly panels need attention too. Thin weather stripping is effective on those. And look for missing fasteners, especially along the left edge of the main belly panel. One empty fastener hole can suck in a lot of exhaust. The wheel wells were already mentioned, as was the door seal.

Remember that CO poisoning is cumulative. You've experienced high CO levels in climb, so the higher you climb the worse it gets for you. And if you're making multiple hops in a day those repeated exposures add up. That's what got Dan Bass @DanM20C.

Please let us know what you find.

[N201MKTurbo]

I wouldn’t use aluminum tape. It seems to come loose eventually. I would use fireproof fiberglass aircraft tape. I believe it will last longer.

https://aerotape.com/products/polyken-290fr-cargo-tape

 

[dkkim73]

1 hour ago, Rick Junkin said:

I'm in the process of removing the carpeting and rear seat buckets to inspect/reseal all the floor gaps with aluminum tape. I'll take some pictures to show you where the gaps are located. Some of them are quite large.

 

I'll look forward to those. I'm curious about the whole process of removing the coverings. 

[larryb]

How old is your detector? After 2 years they typically need a new battery and calibration. My Sensorcon started reading higher than normal after 2 years. I did get a couple of alerts in the 40 to 50 range. The airplane was inspected and no trouble found. I got a new battery but then decided to just get a new unit rather than deal with calibration. Magically my airplane was fixed with the new unit. 

Larry