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On August 15, 2007, about 0600 central daylight time, a Piper PA-32R-301T, N3120T, was not damaged following the failure of a transient voltage suppressor (TVS) while descending near Alton, Illinois. The certificated airline transport pilot was not injured. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed for the flight that departed Aurora Municipal Airport (ARR), Aurora, Illinois, destined for Spirit of St. Louis Airport (STL), St. Louis, Missouri. The personal flight was conducted under the provisions of 14 Code of Federal Regulations Part 91.
According to the pilot, after departing ARR, the flight was uneventful until approaching Alton. After initiating a descent from 10,000 feet above mean sea level (msl), smoke began to emanate from under the left side of the instrument panel as the airplane descended through approximately 5,000 feet msl. Almost simultaneously, the primary flight display (PFD) "blanked out" and the 10-amp PFD circuit breaker opened. The pilot then declared an emergency and diverted to St. Louis Regional Airport (ALN), Alton, Illinois, where he landed uneventfully.
According to Federal Aviation Administration (FAA) and pilot records, the pilot held an airline transport pilot certificate with ratings for airplane single-engine-land, airplane-multiengine-land, and instrument airplane. He reported a total flight time of 4,500 flight hours, with 3,500 hours in single-engine airplanes, 1,000 hours in multi-engine airplanes, and 650 hours in the incident airplane make and model. His most recent FAA first-class medical certificate was issued on March 1, 2007.
According to FAA records, the incident airplane was manufactured in 2006. According to maintenance records, the most recent annual inspection was completed on July 6, 2007. At the time of the incident, the airplane had accrued 526 total hours of operation.
WRECKAGE AND IMPACT INFORMATION
Examination of the airplane by an avionics technician revealed that a TVS had failed. The TVS that failed was manufactured by ProTek Devices, and was listed as P/N 704-15K36. After confirmation of the failure and part number by an FAA inspector and Piper Aircraft, the failed TVS was forwarded to the National Transportation Safety Board.
TESTS AND RESEARCH
Loss of Primary Flight Display
In the incident that occurred with N3120T, when the TVS failed, almost simultaneously, the PFD "blanked out," and the 10-amp PFD circuit breaker opened.
On September 5, 2007, the Safety Board was advised of another TVS failure, this time involving a PA-45-500TP. At the time of the failure, the airplane had accrued 132.5 total hours of operation. In this instance, smoke accumulated in the cockpit and the pilot declared an emergency. Unlike the incident with N3120T, when the 10-amp PFD circuit breaker opened, the PFD continued to function and the smoke "cleared."
Information requested from Piper aircraft confirmed that on their single engine, single alternator, Matrix, and twin models (PA-28, PA-32, PA-34, PA-44 and PA-46R-350T), failure of the TVS would result in loss of the Primary Flight Display (PFD).
On their single engine dual alternator airplanes (PA-46-350P and PA-46-500TP) failure of a TVS would not result in loss of the PFD. A circuit breaker would open, but since there were dual power inputs to the PFD it would continue to operate normally.
Other Airplane Manufacturers
Research conducted by Safety Board investigators indicated that failures of the same part number TVS were occurring on multiple makes and models of airplanes. With failures in some instances occurring at approximately 20 total hours of operation. It was also discovered that on some models, multiple TVS were installed. Further research revealed that on at least one model of airplane, a total of eight were installed.
Information requested by Safety Board investigators from multiple airplane manufacturers confirmed that multiple failures of the TVS had occurred. At the time of the request, Piper Aircraft reported that they had received 11 reports of TVS failures, Diamond Aircraft indicated that they had received 9 reports of TVS failures, Cirrus reported that they had received 12 reports of TVS failures, and Columbia Aircraft reported 1 failure.
Testing at Cirrus Design Corporation
On September 15, 2007, Cirrus notified the FAA and the Safety Board of the results of testing that was conducted at Cirrus to attempt to discover the cause of the TVS failures.
During the testing, which included several in-flight and ground examinations of the essential bus and main bus on their airplane models, Cirrus measured airplane bus voltage under a number of flight conditions but did not note any conditions that could lead to failures of the TVS.
According to the manufacturer, the TVS were used as a voltage suppressor for 28-volt power supplies, and for power bus protection. It was sold commercially for use in both aircraft and vehicles.
Review of manufacturer-supplied information revealed that the maximum ratings and electrical characteristics were compatible with the incident airplanes electrical systems.
As part of the investigation, the Safety Board retained multiple TVS. Testing of failed TVS by the manufacturer revealed instances of "shorting," "reverse leakage," "breakdown voltage," and "excessive leakage." X-rays also revealed that internal damage had occurred to the sub-assemblies.
De-potting of the units revealed instances of damaged dies with some separated from the base disc, holes in the center of the die, and/or in the silicon near the center of the die, molten solder internally, and/or physical damage to the individual sub assembly.
TVS Manufacturers Corrective Actions
The TVS manufacturer notified its customers of its test findings and implemented high temperature reverse bias testing of all newly built TVS, and of all TVS in inventory, to screen out "infant mortality" and reduce the probability of TVS failure.
Additionally, they advised their customers to remove any TVS from service that displayed date codes: 0502, 0539, 0548, 0610, 0611, 0617, and 0633 (the same date codes as the failed units).
Avionics Manufacturers Corrective Actions
On October 31, 2007, Garmin issued Mandatory Service Bulletin No. 0738 which contained instructions on how to identify and remove/replace suspected faulty TVS and required a one time inspection for all G1000 equipped Diamond DA 40/DA 40F airplanes.
Airplane Manufacturers Corrective Actions
On September 11, 2007, Cirrus Design Corporation issued Service Advisory SA07-17 to advise operators of the possibility and mode of TVS failure, provided guidance for handling the failure, and to inform operators of the efforts to correct the condition.
Cirrus also changed their quality inspection process of the TVS to reduce the likelihood of a component failure and as TVS have failed they have replaced them with the more rigorously screened units.
Their aircraft maintenance manual was also updated to check the inline fuse associated with most TVS installations in order to catch any TVS that may have failed silently (no outward indication to the pilot).
On October 23, 2007, Diamond Aircraft Industries issued Service Information No. SI 40-066, to advise owners that Garmin had issued a service bulletin, which contained information about replacement of failed TVS.
On February 8, 2008, Piper Aircraft Corporation issued Piper Service Bulletin No. 1187 to provide for the mandatory inspection (and, if necessary, replacement) of all voltage suppressors used in the affected aircraft.
FAA Corrective Actions
On February 27, 2008, the FAA issued a series of Special Airworthiness Information Bulletins (SAIB CE-08-12, SAIB CE-08-13, and SAIB CE-08-14), to advise owners and operators that failure of a TVS in effected Cirrus, Diamond, and Piper airplanes could result in an increased workload for a pilot.