What happened
During a descent, the pilot of a Piper PA-32R-301T observed smoke emanating from beneath the left side of the instrument panel. Following this, the primary flight display (PFD) became blank and the 10-amp PFD circuit breaker tripped. The pilot declared an emergency and diverted to the nearest airport, where the aircraft landed uneventfully. At the time of the incident, the aircraft had a total of 526 hours of operation.
The investigation
An examination of the aircraft revealed that a Transient Voltage Suppressor (TVS) had failed. Subsequent investigations by the National Transportation Safety Board identified similar TVS failures in other aircraft, including one with only 132.5 total hours of operation and others with approximately 20 total hours.
Testing of the failed components showed several types of electrical malfunctions, including shorting, reverse leakage, breakdown voltage, and excessive leakage. Physical examination of the failed units revealed damaged dies that had separated from the base disc, holes in the center of the die or silicon, molten solder, and physical damage to individual sub-assemblies.
Findings
While manufacturer information indicated that the maximum ratings and electrical characteristics were compatible with the affected systems, the TVS components were prone to internal failure. In response, the manufacturer implemented high-temperature reverse bias testing for all units prior to delivery and advised customers to remove units with matching date codes from service. Furthermore, aircraft manufacturers and the FAA took corrective actions to replace the faulty components.