What aircraft was involved and where did it happen?

The accident on 2007-06-23 involved a Piper PA-28-161,, registration I-APCE, at Aeroporto di Brescia Montichiari, IT.

What was the probable cause of the accident?

The failure was caused by the structural breakdown of a welded T-shaped control bar, resulting from hydrogen embrittlement introduced during the original manufacturing process.

Control Column Failure in Piper Cadet During Training Flight

A structural failure of a T-shaped control bar during a training flight near Lake Garda led to a loss of control effectiveness, though the aircraft landed safely.

What happened

On June 23, 2007, a Piper PA-28-161 Cadet, registration I-APCE, was conducting a local flight training mission from Brescia Montichiari Airport. The flight, part of a private pilot license training program, included an instructor and a student on board.

While performing maneuvers at approximately 5,000 feet over Lake Garda, the instructor noticed significant difficulties managing the ailerons and elevators. After verifying the aircraft's controllability, the instructor notified Garda Approach and decided to return to the departure airport. The flight crew alerted the Brescia Montichiari tower, and emergency fire services were placed on standby for the landing.

Upon landing on runway 32, a misalignment of the control wheels was observed. A subsequent inspection beneath the cockpit revealed that the T-shaped control bar had fractured.

The investigation

The ANSV investigation, supported by metallurgical analysis from the Italian Air Force Experimental Flight Center, focused on the fractured component. The investigation established that the T-bar was an original part of the aircraft, having accumulated 8,996 flight hours since installation.

Laboratory examinations revealed an intergranular fracture pattern at the weld zone. Technical analysis identified the failure mechanism as hydrogen embrittlement. The investigation found that the welding process used during manufacturing was flawed, likely due to excessively high temperatures or rapid post-process cooling, which allowed atomic hydrogen to enter the crystalline lattice of the AISI 4130 high-strength steel. The presence of numerous blowholes and subsurface cracks further supported the conclusion of a substandard welding process.

Findings

The primary cause of the failure was the fracture of the T-bar weld zone due to pre-existing hydrogen embrittlement caused by improper original manufacturing welding procedures.
The component's high-strength steel (AISI 4130) was particularly susceptible to this type of degradation.
While the flight maneuvers (specifically a nose-down input) applied the stress necessary to trigger the break, the failure would not have occurred without the pre-existing metallurgical defects.
The timing of the failure after 9,000 hours of service was considered incidental.