What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
On April 2, 2024, about 1056 central daylight time, a Mooney M20E airplane, sustained substantial damage when the pilot attempted an off-airport landing in a field near Alpine, Arkansas. The pilot was not injured. The airplane was enroute from heber springs Arkansas to tyler Texas operated as a title 14 code of federal regulations part 91 personal flight.
According to the pilot, while in cruise flight, the airplane’s two carbon monoxide (co) detectors began alerting and he felt symptoms of carbon monoxide poisoning. The pilot closed the cabin vents, opened the cockpit window, and attempted (unsuccessfully) to open the door. The pilot decided to not continue the flight to the nearest airport. He shut down the engine and performed a forced landing in a field. During the forced landing, the airplane sustained substantial damage to the forward fuselage.
On 3 April 2024, FAA inspector dispatched to the scene to commence investigation. Due to weather conditions and the nature of aircraft damage, on-scene inspection was limited to a visual inspection.
On 02 may 2024, FAA and NTSB conducted inspection of exhaust and cabin air ventilation system. Exhaust tailpipe had a preexisting weld that encompassed the circumference of the exhaust pipe and appeared to be non-aviation quality. The weld had mounds of metal exhibiting ununiform heating, significant variation in weld pattern, excessive splatter, and poor penetration. Close examination of the weld revealed several areas that looked like cracks and pinholes.
The scat air duct that supplied heated air to the cabin ventilation system was compromised in two areas immediately adjacent to this unapproved weld. The scat air duct connects the heat muff with the cabin ventilation air box located on the firewall. Within the airbox, a manually operated flapper-style valve allows hot air into the cabin. The pilot has a push/pull lever to open or close the valve. In the closed position, air is diverted back into the engine compartment. In the open position, air is allowed to flow to a distribution airbox that diverts the air to the front and backseat areas and to the defroster.
Inspection of the cabin ventilation air box located on the firewall revealed the manually operated valve which controls the supply of heated air to the cockpit was completely detached from its actuating arm. With this break, the pilot had no control of the cabin heat. A closer inspection of the break revealed significant corrosion indicative of a long-preexisting break. Aircraft records show on 11/23/2021, “seal for heater / air box allows exhaust air into cabin when in use. Found crack in exhaust tail pipe. Sent out exhaust pipe and reinstalled.”
Based on our inspection, the faulty and unapproved exhaust weld allowed high-pressure super-heated exhaust gas to concentrate on one area of the scat duct which eventually scorched and burnt a hole in the duct. This allowed carbon monoxide gas to infiltrate the cabin air system. A faulty cabin air valve gave the carbon monoxide free and unobstructed access into the cockpit. This gas infiltration was recognized by the carbon monoxide alarms.
The direct cause of the high carbon monoxide level was this faulty cabin air valve. If the valve were operating as designed, the pilot would have stopped the carbon monoxide infiltration by manually shutting the cabin heat valve.
Two parts involved:
1. Exhaust manifold. Manufactured by privacy data omitted. Part number: 637-35. Jasc code: 7800
2. Cabin junction inlet. Manufactured by Mooney aircraft. Part number: 640047-1. Jasc code: 2120
As the FAA filed it
ON APRIL 2, 2024, ABOUT 1056 CENTRAL DAYLIGHT TIME, A MOONEY M20E AIRPLANE, SUSTAINED SUBSTANTIAL DAMAGE WHEN THE PILOT ATTEMPTED AN OFF-AIRPORT LANDING IN A FIELD NEAR ALPINE, ARKANSAS. THE PILOT WAS NOT INJURED. THE AIRPLANE WAS ENROUTE FROM HEBER SPRINGS ARKANSAS TO TYLER TEXAS OPERATED AS A TITLE 14 CODE OF FEDERAL REGULATIONS PART 91 PERSONAL FLIGHT.
ACCORDING TO THE PILOT, WHILE IN CRUISE FLIGHT, THE AIRPLANE’S TWO CARBON MONOXIDE (CO) DETECTORS BEGAN ALERTING AND HE FELT SYMPTOMS OF CARBON MONOXIDE POISONING. THE PILOT CLOSED THE CABIN VENTS, OPENED THE COCKPIT WINDOW, AND ATTEMPTED (UNSUCCESSFULLY) TO OPEN THE DOOR. THE PILOT DECIDED TO NOT CONTINUE THE FLIGHT TO THE NEAREST AIRPORT. HE SHUT DOWN THE ENGINE AND PERFORMED A FORCED LANDING IN A FIELD. DURING THE FORCED LANDING, THE AIRPLANE SUSTAINED SUBSTANTIAL DAMAGE TO THE FORWARD FUSELAGE.
ON 3 APRIL 2024, FAA INSPECTOR DISPATCHED TO THE SCENE TO COMMENCE INVESTIGATION. DUE TO WEATHER CONDITIONS AND THE NATURE OF AIRCRAFT DAMAGE, ON-SCENE INSPECTION WAS LIMITED TO A VISUAL INSPECTION.
ON 02 MAY 2024, FAA AND NTSB CONDUCTED INSPECTION OF EXHAUST AND CABIN AIR VENTILATION SYSTEM. EXHAUST TAILPIPE HAD A PREEXISTING WELD THAT ENCOMPASSED THE CIRCUMFERENCE OF THE EXHAUST PIPE AND APPEARED TO BE NON-AVIATION QUALITY. THE WELD HAD MOUNDS OF METAL EXHIBITING UNUNIFORM HEATING, SIGNIFICANT VARIATION IN WELD PATTERN, EXCESSIVE SPLATTER, AND POOR PENETRATION. CLOSE EXAMINATION OF THE WELD REVEALED SEVERAL AREAS THAT LOOKED LIKE CRACKS AND PINHOLES.
THE SCAT AIR DUCT THAT SUPPLIED HEATED AIR TO THE CABIN VENTILATION SYSTEM WAS COMPROMISED IN TWO AREAS IMMEDIATELY ADJACENT TO THIS UNAPPROVED WELD. THE SCAT AIR DUCT CONNECTS THE HEAT MUFF WITH THE CABIN VENTILATION AIR BOX LOCATED ON THE FIREWALL. WITHIN THE AIRBOX, A MANUALLY OPERATED FLAPPER-STYLE VALVE ALLOWS HOT AIR INTO THE CABIN. THE PILOT HAS A PUSH/PULL LEVER TO OPEN OR CLOSE THE VALVE. IN THE CLOSED POSITION, AIR IS DIVERTED BACK INTO THE ENGINE COMPARTMENT. IN THE OPEN POSITION, AIR IS ALLOWED TO FLOW TO A DISTRIBUTION AIRBOX THAT DIVERTS THE AIR TO THE FRONT AND BACKSEAT AREAS AND TO THE DEFROSTER.
INSPECTION OF THE CABIN VENTILATION AIR BOX LOCATED ON THE FIREWALL REVEALED THE MANUALLY OPERATED VALVE WHICH CONTROLS THE SUPPLY OF HEATED AIR TO THE COCKPIT WAS COMPLETELY DETACHED FROM ITS ACTUATING ARM. WITH THIS BREAK, THE PILOT HAD NO CONTROL OF THE CABIN HEAT. A CLOSER INSPECTION OF THE BREAK REVEALED SIGNIFICANT CORROSION INDICATIVE OF A LONG-PREEXISTING BREAK. AIRCRAFT RECORDS SHOW ON 11/23/2021, “SEAL FOR HEATER / AIR BOX ALLOWS EXHAUST AIR INTO CABIN WHEN IN USE. FOUND CRACK IN EXHAUST TAIL PIPE. SENT OUT EXHAUST PIPE AND REINSTALLED.”
BASED ON OUR INSPECTION, THE FAULTY AND UNAPPROVED EXHAUST WELD ALLOWED HIGH-PRESSURE SUPER-HEATED EXHAUST GAS TO CONCENTRATE ON ONE AREA OF THE SCAT DUCT WHICH EVENTUALLY SCORCHED AND BURNT A HOLE IN THE DUCT. THIS ALLOWED CARBON MONOXIDE GAS TO INFILTRATE THE CABIN AIR SYSTEM. A FAULTY CABIN AIR VALVE GAVE THE CARBON MONOXIDE FREE AND UNOBSTRUCTED ACCESS INTO THE COCKPIT. THIS GAS INFILTRATION WAS RECOGNIZED BY THE CARBON MONOXIDE ALARMS.
THE DIRECT CAUSE OF THE HIGH CARBON MONOXIDE LEVEL WAS THIS FAULTY CABIN AIR VALVE. IF THE VALVE WERE OPERATING AS DESIGNED, THE PILOT WOULD HAVE STOPPED THE CARBON MONOXIDE INFILTRATION BY MANUALLY SHUTTING THE CABIN HEAT VALVE.
TWO PARTS INVOLVED:
1. EXHAUST MANIFOLD. MANUFACTURED BY ^PRIVACY DATA OMITTED^. PART NUMBER: 637-35. JASC CODE: 7800
2. CABIN JUNCTION INLET. MANUFACTURED BY MOONEY AIRCRAFT. PART NUMBER: 640047-1. JASC CODE: 2120
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.