Service Difficulty Advisory

AV 2002-03
17 June 2002

Voltage Regulators Installed on Cessna Single Engine Aircraft With 14-Volt Electrical Systems

Numerous Parts Manufacture Approval (PMA) parts are available and eligible for installation on many aircraft operated in Canada (see AWM 571.07 for specific criteria regarding the installation of these types of parts).

During recent maintenance on a Cessna 172, an AME noticed the installation instructions for a PMA Electrosystems VR600A voltage regulator, called for removal of the OEM (Cessna) installed over-voltage protection device. The removal of this device is required because the PMA Electrosystems voltage regulator has its own internal over-voltage protection circuit.

The VR600A voltage regulator is authorized under Electrosystems' PMA as an approved replacement part for some Cessna and Beech voltage regulators. Therefore its installation and coincident modification of the OEM installed over-voltage protection, does not require an STC. As a result, aircraft technical records respecting the installation of an Electrosystems VR600A voltage regulator may not contain details regarding the modification of the OEM over-voltage protection system. If this modification is not evident to maintenance personnel who later replace these VR600A regulators with OEM, or with other PMA'd regulators, they may unwittingly, not reinstall the OEM over-voltage protection. Consequently, some aircraft could end up being operated with no over-voltage protection.

Note: "other PMA'd regulators" may include, but are not limited to: the Electrosystems VR600 and the Lamar DGR6.

Maintenance personnel involved in the replacement of the Electrosystems VR600A voltage regulators, with other than a VR600A regulator, should ensure that the over-voltage protection is reinstalled or reconnected to the appropriate aircraft circuit.

It is also recommended that owners or operators of single engine Cessna and Beech aircraft, fitted with 14-volt electrical systems, verify the integrity of their over-voltage protection system(s). Aircraft that have had any voltage regulator replaced since April 1997 (the date of the PMA supplement granting authority to manufacture these parts), should be inspected to ensure a VR600A has not been replaced with another style of voltage regulator without having the OEM over-voltage protection reinstalled or reconnected.

Any defects or further occurrences should be reported by sending a Service Difficulty Report to Transport Canada, Continuing Airworthiness, Ottawa.

For further information, contact a Transport Canada Centre, or Mr. Steve Dudka, Continuing Airworthiness, Ottawa, telephone (613) 952-4361, facsimile (613) 996-9178 or e-mail

For Director, Aircraft Certification

B. Goyaniuk
Chief, Continuing Airworthiness