Date: 201501
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: M-20 K (231) / Encore
Flight plan: None
Mission: Test Flight / Demonstration
Flight phase: Initial Climb
Airspace: Class E ZZZ
Aircraft component: Engine Exhaust System
Component problem: Malfunctioning
Reporter organization: Other Remote Sensing
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Commercial; Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Communication Breakdown
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Aircraft Damaged; Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Procedure; Human Factors
Primary problem: Human Factors

Narrative: The exhaust system on our Mooney M20K-305 had been repaired and this was the first flight post maintenance. Shortly after takeoff; climbing through approx. 500 feet AGL; the engine monitor alarm indicated a high and rapidly rising Cylinder Head Temperature (CHT). Suspecting detonation/pre-ignition; power was reduced to minimum needed for level flight and a left turn to enter a downwind for runway 27 was started. At this point I noticed a hot/burning smell. A tight pattern was flown and the aircraft promptly landed. Exiting the aircraft; smoke was seen rising from the engine cowling near the air inlet. This was extinguished with a fire extinguisher and the cowling removed. The inside of the cowling was visibly damaged due to melting/extreme heating from what appeared to be the exhaust manifold. Post inspection revealed that the exhaust system had been improperly assembled. The exhaust manifold from the cylinders was not fully fitted into the slip joint of the exhaust Y-tube transition pipe. It was approximately one inch out of place. This reduced the clearance between the exhaust and cowling causing the melting and smoking. Additionally; because the manifold was out of place; there was a small gap between the cylinder head and the exhaust manifold flanges. Exhaust leaks from this area potentially caused the high CHT indication. In the future; a much more in-depth post maintenance inspection is necessary to prevent a recurrence.

Callback: Reporter stated the exhaust manifold was previously sent out for repair after a small hole was noticed in the manifold during an Annual Inspection. When mechanics reinstalled the exhaust manifold they were apparently hoping the attaching nuts would help pull-in and seat the manifold against the engine. But that did not happen. Instead; the small gap that still existed between the exhaust manifold and the engine allowed hot gases to blow near the Cylinder Head Temperature (CHT) sensor causing a high temp indication. The smoke and heat damage to the engine cowling was caused by the same exhaust manifold not being properly fitted into the slip joint of the exhaust Y-tube transition pipe.



Synopsis: A single pilot reports that on the first flight after Maintenance repaired the Exhaust System on their Mooney M20K-305 aircraft; they noticed a hot/burning smell and the engine monitor alarm indicated a high and rapidly rising Cylinder Head Temperature (CHT). Exhaust manifold from cylinders was not fully fitted into the slip joint of the exhaust Y-tube transition pipe causing smoke; extreme heating and melting of an engine cowling.