CHI99FA163 · Cessna 421B
Cessna 421B · Accident: partial loss of engine power (mechanical failure) on approach
From Poplar Bluff Municipal Airport (POF) to Jefferson City Memorial Airport (JEF)
Event
- NTSB case
- CHI99FA163
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 4 · all aircraft and ground
- Ground fatalities
- 0
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Cessna 421B
- Aircraft type
- Cessna 421
- Category
- Airplane
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N34TM
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Poplar Bluff Municipal Airport (POF), Poplar Bluff, MOTo Jefferson City Memorial Airport (JEF)
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 91: General Aviation
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- Approach · VFR pattern final
- First occurrenceThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Partial loss of engine power (mechanical failure)
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Destroyed
Cause areas
- Pilot in command › Aircraft control, not maintained
Approximate · Estimated position: the centre of Jefferson City, MO, the place the record names. Not the accident site.
NTSB narrative
The airplane impacted the ground in a nose low, inverted attitude. The pilot reported, 'Jeff Tower, N34TM, I've just lost power on the right engine, eh, left engine.' The airplane's altitude was approximately 200 to 400 feet when the airplane's wings wobbled back and forth. The airplane's wings banked approximately 90 degrees to the left, and then the airplane nosed over and impacted the ground. White smoke was seen coming from the belly of the airplane for 1 to 2 seconds about 20 seconds prior to it impacting the ground. The terrain was a flat, hard packed field used for growing grass sod. Both the left and right propellers were found 12 to 18 inches under the hard packed soil. Rotational paint transfer patterns from the propeller blades onto the hard packed soil were evident. The left and right propeller blades exhibited chordwise scratching and leading edge polishing. The #2 cylinder piston was broken and the piston pin was still attached to the piston rod. The NTSB Materials Laboratory examination revealed the fracture face of the #2 exhaust valve stem was consistent with a bending fatigue separation. Both #2 and #6 exhaust valve guides showed heavy wear that ovalized the bores. The annual inspection conducted on March 15, 1999, indicated the compression on the left engine was 80/64, 50, 67, 70, 69, and 62.
Probable cause
the pilot failed to maintain control of the airplane. A factor was the partial loss of power due to the exhaust valve fatigue failure.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record CHI99FA163
- Event ID
- 20001212X18707
- Case number
- CHI99FA163
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: 63ba414c23143b35eaf503577f7f76f48d83c702a8b9080ddd31fce51d5fbf07; retrieved 2026-09-20T22:05:18.996Z.