AUMAN JL T-51 near Dekalb, IL — 2012-12-11

Probable cause

The improper engine overhaul by the airplane kit manufacturer, which resulted in a catastrophic engine failure.

NTSB narrative

The experimental amateur-built airplane experienced a total loss of engine power during a phase one test flight. The pilot performed a forced landing on a field where airplane nosed-over due to the rough condition of the field that precluded a normal landing rollout. Before the phase 1 test flight, the pilot had returned the engine to the kit manufacturer for repair due to leaking engine coolant. Postaccident examination of the engine revealed catastrophic damage; the engine head bolt had been tighten above the engine manufacturer's torque values, which indicated that the kit manufacturer used excessive torque on the head bolts in an attempt to repair coolant leakage through the engine head. The postaccident examination showed that the engine was assembled with cast and not forged pistons, which should be used in high performance applications. The bending and thread damage on the intact connecting rod bolt for the forward right cylinder and the mating thread damage in the connecting rod were consistent with the bolt backing out until it sheared the remaining threads. Another bolt that backed out of position was also present on the connecting rod in the middle right position. Measurements of cylinder wall carbon lines showed a variance in size, which may have been due to hydraulic lock related bending of the connecting rods.

Analysis

Primary failure mode

Engine power loss

First missed decision gate

Properly torquing the engine head bolts before installation could have prevented failure.

NTSB coding

• Powerplant sys/comp malf/fail · Enroute-climb to cruise
• Maintenance

Evidence available

• 6 docket documents

Docket documents6

• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1form
• Record of Conversation - Pilotother
• Record of Conversation 1 - Titan Presidentother
• Record of Conversation 2 - Titan Presidentother
• Record of Examinationother
• Materials Laboratory 15 - Factual Report 13-106report

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