Uncontained Engine Failure Leads to Damage on Learjet 35A

Casualties unknown • Rendsburg, DE

An uncontained failure of the left engine during climb resulted in turbine components exiting the engine casing and striking the aircraft fuselage.

What happened

On January 16, 2023, a Learjet 35A was performing a target presentation flight departing from Hohn Airfield. Shortly after takeoff, while climbing through approximately 7,000 feet AMSL, the aircraft experienced a sudden vibration and a significant loss of thrust from the left engine. Engine parameters indicated a drop in N1 to 0% and N2 to 11%.

The crew declared an emergency and initiated procedures to secure the engine. Due to the uncertain extent of the damage, the crew decided to perform a visual approach back to Hohn as quickly as possible. The aircraft landed at Hohn with a landing mass of 16,800 lbs, which exceeded the maximum landing weight of 16,000 lbs. There were no injuries to the crew, though the aircraft sustained significant damage.

The investigation

The BFU examined the aircraft and the Honeywell TFE 713-2C-2B engine. Inspection of the left engine revealed that the cowling was partially torn open and the combustion plenum flange had ruptured, with only 29 of the original 144 bolts remaining. Notably, the first and second-stage rotor assemblies of the low-pressure turbine (LPT) and the second-stage stator were missing from the engine.

The investigation also focused on the aircraft's fuselage, which showed multiple impact holes and scratches on the left side, particularly around frame 25A. While some damage was caused by smaller fragments hitting the fuselage, the most energetic components of the turbine rotor were found to have exited the engine casing entirely, avoiding direct contact with the airframe but causing damage to the cowling and horizontal stabilizer.

An extensive search for the missing turbine components was conducted in the Rendsburg area, involving police and local authorities, but the parts were not recovered.

Findings

  • The engine failure was caused by a disconnection of the 1st and 2nd LPT rotor stages.
  • The specific mechanism that triggered this separation—whether a failure of the tie-rod, a rotor disc fracture, or another mechanical issue—could not be determined because the critical components were lost in flight.
  • The tie-rod connecting the N1 shaft components was found bent and damaged, showing evidence of overload.
  • Maintenance records, including oil analysis and engine trend monitoring, showed no prior indications of impending failure.
  • The engine's electronic control system (N1 DEEC) showed that all operational limits had been respected prior to the event.

Probable cause

The exact cause of the engine failure remains undetermined due to the loss of the primary failed components during flight; however, the failure was characterized by the separation of the first and second-stage low-pressure turbine rotor assemblies.

Frequently asked questions

What happened in the 2023-01-16 Learjet Corporation Learjet 35 A accident near Rendsburg, DE?

An uncontained failure of the left engine during climb resulted in turbine components exiting the engine casing and striking the aircraft fuselage.

What aircraft was involved and where did it happen?

The accident on 2023-01-16 involved a Learjet Corporation Learjet 35 A, at Rendsburg, DE.

What was the probable cause of the accident?

The exact cause of the engine failure remains undetermined due to the loss of the primary failed components during flight; however, the failure was characterized by the separation of the first and second-stage low-pressure turbine rotor assemblies.

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