Airworthiness DirectiveEASA AD US-2020-02-11

Electrical Power - Static Inverters - Replacement

Published: Feb 17, 2020
Effective: Mar 17, 2020
Deadline: Mar 17, 2020
Replaces: 2015-04-04

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What to do

Operators must replace affected static inverters with the improved inverter or retrofit kits within 25 hours time-in-service after the effective date of March 17, 2020. They should verify inverter serial numbers to confirm applicability and follow Bell Helicopter Textron service instructions for installation. Compliance with this AD terminates previous flight restrictions and ensures continued safe operation of the helicopters.

Summary

Airworthiness Directive 2020-02-11 is a final rule issued by the Federal Aviation Administration addressing Bell Helicopter Textron Inc. Model 412 and 412EP helicopters. It mandates the replacement of certain static inverters with improved versions to correct unsafe conditions caused by inverter failures. The directive applies specifically to static inverters with part numbers 412-375-079-101 or 412-375-079-103 having serial numbers 29145 or higher.

What changed

This AD supersedes AD 2015-04-04 by requiring the replacement of affected static inverters with a new improved inverter, part number 412-375-079-105, or retrofit kits. It removes previous flight limitations such as restricting operations to visual flight rules and prohibiting night flights by addressing the root causes of inverter failures. The compliance time is set to within 25 hours time-in-service, and the AD clarifies applicability to specific serial-numbered inverters.

Why it matters

This directive is critical for aviation professionals as it addresses a known unsafe condition that could lead to inverter failures, potentially compromising electrical power systems on Bell Model 412 and 412EP helicopters. Compliance ensures continued airworthiness and safety, allowing operators to resume normal flight operations including night and instrument flight rules with two pilots. Maintenance and compliance teams must update procedures to reflect the new inverter replacement requirements and deadlines.

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