CO Alarm Help

A

AA5Bman

Line Up and Wait
Joined
Jun 14, 2009
Messages
831
Display Name
Display name:
He who ironically no longer flies an AA5B
Hey everyone - we’re getting a “high” CO alarm in our Cessna using a CO Experts monitor. Can’t find any leaks. Is it normal to have some CO values at idle? I am away from home so some urgency. We were getting a value of 35 PPM taxiing around the airport. There are a ton of other planes and we were kind of sitting in some jet blast when the alarm started going off.

Would it be normal to have some non-zero value on the minitor? Would it be so sensitive as to alarm due to jet blast?
 
Last edited:
I don't fly with one regularly but have flown a few planes that do have them and have seen that it can be normal to see higher readings on the ground. The owners typically make sure they keep a window or door cracked open when that happens. You may even find that the direction if the wind may affect it. If it is normal in normal flight I wouldn't worry much about it. I seem to recall seeing the reading go up during slow flight and stall demonstrations in some airplanes.

Brian
CFIIG/ASEL
 
Yeah I remember some of that discussion about CO and slow flight. I would say that this seems more dramatic than that - “high” reading, beeping, etc. the monitor appears to be working in that it does go back down to 0 when the engine is shut down.

No exhaust leaks, no muff leaks, no firewall penetrations that are new or obviously open, checked the steering boots. We’re now in “chasing” mode - the best mode to be in when not at your home airport :facepalm:

Any other thoughts appreciated.
 
May not help much but thought I'd mention that on the particular airframe I fly that CO can get inside the cockpit from openings near the tail. Also known to seep in around the wing roots.

FWIW ...
 
AA5Bman said:
we were kind of sitting in some jet blast when the alarm started going off.
Click to expand...
So, high CO in the exhaust of a turbine? Not a turbine expert, but somehow I am not surprised.
Went away when you got out of the exhaust?

Non-zero number on the ground? Happens - there is a reason the exhaust pipe in your car runs all the way to the back. And, I assume you are running rich - more likely to happen.
 
AA5Bman said:
Hey everyone - we’re getting a “high” CO alarm on a 205 using a CO Experts monitor. Can’t find any leaks. Is it normal to have some CO values at idle? I am away from home so some urgency. We were getting a value of 35 PPM taxiing around the airport. There are a ton of other planes and we were kind of sitting in some jet blast when the alarm started going off.

Would it be normal to have some non-zero value on the minitor? Would it be so sensitive as to alarm due to jet blast?
Click to expand...


50 ppm is really a big concern. 35 ppm with a jet blast over you would just cause me to taxi out of the blast and open the windows. I assume it went back to 0 on takeoff?
 
We didn’t fly it. Taxied back to the hangar, shut down, fired up again, now out of jet blast. The monitor went back to zero when shut down, high again on idle.
 
I think on he ground the readings are inaccurate, my mooney sometimes goes over 50, but I think it has a lot to do with which way the prevailing wind is. In level flight it is 0 or 1, sometimes in the climb goes to 7 and that depends if I do a fast climb or slow climb. Sometimes it is 1 or 2 in the climb. And I realize that doesn’t answer your question. Just some thoughts.
 
Getonit said:
I think on he ground the readings are inaccurate, my mooney sometimes goes over 50, but I think it has a lot to do with which way the prevailing wind is. In level flight it is 0 or 1, sometimes in the climb goes to 7 and that depends if I do a fast climb or slow climb. Sometimes it is 1 or 2 in the climb. And I realize that doesn’t answer your question. Just some thoughts.
Click to expand...
I don't think it is inaccurate. The Navion will trip off on CO on the ground in some conditions, but the exhaust is being drawn into the cockpit. This goes away once there is a little airspeed in play.
 
If you're not already, lean aggressively while you're on the ground. Mine ticks up a bit on the ground and in the climb but then drops way down in cruise.
 
Getonit said:
I think on he ground the readings are inaccurate, my mooney sometimes goes over 50, but I think it has a lot to do with which way the prevailing wind is. In level flight it is 0 or 1, sometimes in the climb goes to 7 and that depends if I do a fast climb or slow climb. Sometimes it is 1 or 2 in the climb. And I realize that doesn’t answer your question. Just some thoughts.
Click to expand...

A Mooney is what I recall seeing the high readings on the ground in. I think there are just enough leaks in the cabin that when the wind is blowing the right direction some gets in, probably has since the plane was new, we just never measured it before. Now that we know it is there, we can do thing to mitigate it, turn a different direction into the wind. Keep the window/Canopy/door open or closed which ever works best.

Brian
 
I don't think I'd worry about it much as long as it drops down once taxiing at a moderate pace and goes away once you're in the air. Getting some chirps when sitting still at idle or in a conga line waiting for takeoff wouldn't be surprising at all depending on what the wind is doing and what is being pumped out of the other aircraft ahead of you.
 
Mine goes off on the ground after startup with the right wind direction. It never goes off in the air. I open my pilot side window to keep some fresh air in and then just get off the ground.
 
Mine starts to register in slow flight but not on the ground. Never saw 35 ppm, though.
 
I started getting 75ppm in my 182 last fall. I though perhaps the high concentration of smoke from our numerous forest fires. When I had my annual done in October I mentioned it to the shop. They did a very detailed inspection & found two nuts missing on one of my exhaust outlets on my manifold. I never have had another CO reading.
Another reason I'm glad I purchased a Sentry.
 
Throughout the years I have had multiple co experts units. I trust them 100%. I
get an alarm on the ground depending on wind direction in reference to my exhaust pipe but is always below 10pm.

One time in the past I had a somewhat higher reading on takeoff, hard to remember but I’m thinking 20ppm. At my destination I examined the exhaust system and risers but didn’t find a problem. After returning to home base using a mirror I found the cracked riser that was causing the alarm. I was very happy to have the co monitor and would never fly without it.

If this alarm and level is new I would look very closely for any issues with the exhaust system. If it’s always this low level alarm I would consider it normal. Good luck..
 
It is common to see low CO levels during taxi with the canopy open. Propwash (or tubine blast) can certainly circulate CO into the cockpit area if conditions are right. As long as those levels decline when buttoned up prior to takeoff and remain that way, I would not be concerned. Sustained levels of CO in flight IS a concern.
 
Getonit said:
I think on he ground the readings are inaccurate, my mooney sometimes goes over 50, but I think it has a lot to do with which way the prevailing wind is. In level flight it is 0 or 1, sometimes in the climb goes to 7 and that depends if I do a fast climb or slow climb. Sometimes it is 1 or 2 in the climb. And I realize that doesn’t answer your question. Just some thoughts.
Click to expand...

Thanks for this, is this with a CO Experts monitor by chance?

iflyatiger said:
Throughout the years I have had multiple co experts units. I trust them 100%. I get an alarm on the ground depending on wind direction in reference to my exhaust pipe but is always below 10pm.

One time in the past I had a somewhat higher reading on takeoff, hard to remember but I’m thinking 20ppm. At my destination I examined the exhaust system and risers but didn’t find a problem. After returning to home base using a mirror I found the cracked riser that was causing the alarm. I was very happy to have the co monitor and would never fly without it.

If this alarm and level is new I would look very closely for any issues with the exhaust system. If it’s always this low level alarm I would consider it normal. Good luck..
Click to expand...

Yeah, I think you nailed it - the CO Experts alarm was right on and it should definitely be trusted if something is new or abnormal. In this case I had been using it for a little while, but it had always read dead zero, so it was strange that it started alerting at all - I had started to wonder if it wasn’t reading anything at all.

As a general update, I think we have it figured out. I don't really want to go into details to protect the innocent, but all I would offer is that yesterday was a really good lesson in trusting your instruments (in this case the monitor), being conservative in decisions, being super careful post-maintenance, and not just forging ahead when something seems off. In our case, the problem was not at all the normal CO issues - exhaust leaks , firewall penetrations, etc - but was a symptom of a bigger problem introduced after maintenance. It is interesting that the CO alarm was the first thing that alerted us to the problem, and I’m really happy it did - had we pushed ahead with our planned flight, it could have been really bad.
 
Why not tell people what happened. Keeping safety issues hidden is bad practice.
 
I use a sensorcon CO detector. I was getting 10-15ppm at cruise. Climbout less than 5. On ground 5-10 maybe. Open air 0. Worse numbers always in back seats.
At annual a year ago was get to be secondary to bad door seals. They replaced the seals meh. Not really better. Then one flight I noticed they jumped to 30 in cruise. I am the only guy in club that uses the CO monitor. So its going into annual recently and exhaust muffler had a bunch of cracks in it. Replaced that $$. And now less then 10 all times.
 
I had this issue as well in my 182.
Took it in for an exhaust inspection, they found nothing. So I started looking around. I even bought a secondary CO monitor because the readings seemed strange.

I can’t recall where I found it, but someone pointed out that during taxi and flight, the exhaust can seep through the passenger door seal.

What temporarily solved this was keeping the air vent in the open position until I can get the seal replaced.
I even tested this a few times. If I close the air vent, it rises to 9ppm in just a few minutes.
With the air vent open. I never get a reading on either monitor unless I’m in a prolonged taxi around other aircraft in funky wind conditions.
 
You must log in or register to reply here.
Back
Top