C210 landed gear up; mistaking gear warning horn for alarm indicating excessive carbon monoxide.

Attributes
ACN	741705
Time
Date	200706
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 0
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : bdr.tower
Operator	general aviation : personal
Make Model Name	Cessna 210 Centurion / Turbo Centurion 210C 210D
Operating Under FAR Part	Part 91
Flight Phase	descent : approach landing : roll
Route In Use	approach : visual
Flight Plan	None
Person 1
Affiliation	other
Qualification	pilot : cfi
Experience	flight time last 90 days : 40 flight time total : 890 flight time type : 70
ASRS Report	741705
Person 2
Affiliation	other
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 10 flight time total : 800 flight time type : 380
ASRS Report	742115
Events
Anomaly	ground encounters : gear up landing
Independent Detector	other flight crewa other flight crewb
Resolutory Action	none taken : detected after the fact
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

We were flying a VFR flight from bjc to cys with the plan to practice a diversion to ZZZ by pilotage and dead reckoning. We decided to practice some short and soft field takeoff's and lndgs at ZZZ. On our descent into ZZZ and while in the traffic pattern we noted the carbon monoxide monitor alarm went off. This was an intermittent problem and has on occasion; though not often; been noted before. (I had addressed this issue with our a&P in the past who thought it may be due to turbulent exhaust entering the gear wells and cabin.) while we were practicing in the pattern (left closed traffic on runway 16) I noted the alarm appeared to be sounding again on final approach. This became a distraction for us; and we became fixated on the co monitor as the problem when in fact the gear had not been lowered and the sound we were hearing was; in fact; the gear warning horn. Mistaking the gear warning horn for the co monitor alarm; we both failed to do the final checklist and verify landing gear down (green light). I know that had the co monitor alarm not been in the aircraft; the only sound I would have idented was the gearing warning horn; but obviously this was not the case. I had become fixated on the co alarm sounding to the exclusion of basic responsibilities involved with landing. We are usually vigilant about checking for a 'tire' and checking the mirror for the nosewheel and verifying the gear indicator light 'on;' especially since we have had a problem this past yr with the gear either not extending or the gear up indicator light not lighting up after retraction. We have had the plane worked on for this problem and our a&P can verify this; but this is not an excuse for our mistake. In addition; to verifying gear down with the checklist and gumps check in the pattern as well as a final check on final approach; the verification must be verbally acknowledged by both pilots; just as when positive xfer of control of aircraft is performed. If alone; it would be best to verbally acknowledge aloud to oneself that the checklist and gumps have been completed. In addition; if any warning horn is heard again; it will from this event; be acknowledged that the sound may in fact be from the gear warning horn.

Original NASA ASRS Text

Title: C210 LANDED GEAR UP; MISTAKING GEAR WARNING HORN FOR ALARM INDICATING EXCESSIVE CARBON MONOXIDE.

Narrative: WE WERE FLYING A VFR FLT FROM BJC TO CYS WITH THE PLAN TO PRACTICE A DIVERSION TO ZZZ BY PILOTAGE AND DEAD RECKONING. WE DECIDED TO PRACTICE SOME SHORT AND SOFT FIELD TKOF'S AND LNDGS AT ZZZ. ON OUR DSCNT INTO ZZZ AND WHILE IN THE TFC PATTERN WE NOTED THE CARBON MONOXIDE MONITOR ALARM WENT OFF. THIS WAS AN INTERMITTENT PROB AND HAS ON OCCASION; THOUGH NOT OFTEN; BEEN NOTED BEFORE. (I HAD ADDRESSED THIS ISSUE WITH OUR A&P IN THE PAST WHO THOUGHT IT MAY BE DUE TO TURBULENT EXHAUST ENTERING THE GEAR WELLS AND CABIN.) WHILE WE WERE PRACTICING IN THE PATTERN (L CLOSED TFC ON RWY 16) I NOTED THE ALARM APPEARED TO BE SOUNDING AGAIN ON FINAL APCH. THIS BECAME A DISTR FOR US; AND WE BECAME FIXATED ON THE CO MONITOR AS THE PROB WHEN IN FACT THE GEAR HAD NOT BEEN LOWERED AND THE SOUND WE WERE HEARING WAS; IN FACT; THE GEAR WARNING HORN. MISTAKING THE GEAR WARNING HORN FOR THE CO MONITOR ALARM; WE BOTH FAILED TO DO THE FINAL CHKLIST AND VERIFY LNDG GEAR DOWN (GREEN LIGHT). I KNOW THAT HAD THE CO MONITOR ALARM NOT BEEN IN THE ACFT; THE ONLY SOUND I WOULD HAVE IDENTED WAS THE GEARING WARNING HORN; BUT OBVIOUSLY THIS WAS NOT THE CASE. I HAD BECOME FIXATED ON THE CO ALARM SOUNDING TO THE EXCLUSION OF BASIC RESPONSIBILITIES INVOLVED WITH LNDG. WE ARE USUALLY VIGILANT ABOUT CHKING FOR A 'TIRE' AND CHKING THE MIRROR FOR THE NOSEWHEEL AND VERIFYING THE GEAR INDICATOR LIGHT 'ON;' ESPECIALLY SINCE WE HAVE HAD A PROB THIS PAST YR WITH THE GEAR EITHER NOT EXTENDING OR THE GEAR UP INDICATOR LIGHT NOT LIGHTING UP AFTER RETRACTION. WE HAVE HAD THE PLANE WORKED ON FOR THIS PROB AND OUR A&P CAN VERIFY THIS; BUT THIS IS NOT AN EXCUSE FOR OUR MISTAKE. IN ADDITION; TO VERIFYING GEAR DOWN WITH THE CHKLIST AND GUMPS CHK IN THE PATTERN AS WELL AS A FINAL CHK ON FINAL APCH; THE VERIFICATION MUST BE VERBALLY ACKNOWLEDGED BY BOTH PLTS; JUST AS WHEN POSITIVE XFER OF CTL OF ACFT IS PERFORMED. IF ALONE; IT WOULD BE BEST TO VERBALLY ACKNOWLEDGE ALOUD TO ONESELF THAT THE CHKLIST AND GUMPS HAVE BEEN COMPLETED. IN ADDITION; IF ANY WARNING HORN IS HEARD AGAIN; IT WILL FROM THIS EVENT; BE ACKNOWLEDGED THAT THE SOUND MAY IN FACT BE FROM THE GEAR WARNING HORN.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.