What happened
On July 7, 1998, a Piper PA-34-200T, registration OH-PZL, was performing a training flight when the forward cargo compartment door opened at approximately 2,500 feet. The airflow caused the door to hinge upward, breaking its fiberglass reinforcements. Upon the door opening, the crew observed that the lock handle was in the vertical position, indicating the lock was unlocked.
During the subsequent return to Helsinki-Malmi airport, a piece of cockpit insulation material from the cargo compartment escaped the aircraft and became entangled in the left elevator. To prevent the fabric from striking the propeller, the pilot shut down the left engine and feathered the propeller. Despite the partially degraded elevator control, the crew managed a controlled descent and landing. The loose fabric eventually detached and fell into a residential area near the airport threshold.
The investigation
The investigation focused on the mechanical failure of the cargo door lock and the maintenance history of the aircraft. Investigators examined the lock mechanism, which had been replaced with an unapproved Abloy-brand lock. Physical inspection revealed that a critical spring within the locking mechanism had been broken for an extended period.
Furthermore, the investigation reviewed the maintenance logs and task cards used by various maintenance organizations. It was discovered that the maintenance personnel were using outdated task cards that lacked references to necessary inspections required by Service Bulletin 872. This omission meant that the specific, detailed inspection of the cargo door lock was not performed during recent maintenance intervals.
Findings
- The cargo door was improperly secured, a condition that went undetected during the pre-flight inspection.
- The aircraft was fitted with an unapproved lock mechanism (an Abloy lock) that did not meet aviation standards, rendering the aircraft technically unairworthy.
- The replacement lock featured a flawed design and significant wear, which allowed the key to be removed even when the door was not fully locked, misleading the crew.
- A critical spring in the locking device had been broken for a long time.
- Maintenance oversight occurred because technicians were using obsolete maintenance task cards that did not include the mandatory inspections required by Service Bulletin 872.
- Previous instances of the cargo door opening had occurred but were not recorded in the aircraft's technical log, preventing necessary repairs.