Attention:
Owners, Operators and Maintainers of Bell Textron Canada Limited (BTCL) Model 407 Helicopters
| File Classification No.: | Z 5000-35 |
|---|---|
| RDIMS No.: | 20047803 |
| Document No.: | CASA 2025-02 |
| Issue No.: | 01 |
| Effective Date: | 2025-03-20 |
Purpose:
The purpose of this Civil Aviation Safety Alert (CASA) is to inform BTCL model 407 helicopter owners, operators and maintainers of the release of BTCL Technical Bulletin (TB) 407-23-140, which provides installation instructions for a new Collective Pitch Transducer (CPT) P/N 412-074-101-105. The -105 has design improvements incorporated to address the engine parameter oscillations and FADEC faults being induced by the P/N 412-074-101-103/-107 transducers.
Background:
The CPT is installed under the copilot seat. The transducer tells the FADEC system the rate of movement of the collective control stick. The transducer is an electrical potentiometer that is connected to the airframe at one end and connected to a clamp assembly installed on the collective jackshaft. When the collective stick is lifted or lowered, the transducer increases or decreases length, which changes the resistance output to the FADEC system. The output signal allows the FADEC to provide anticipation logic, which helps to reduce main rotor RPM droop and overshoot.
BTCL was made aware of a condition where engine parameter oscillations and FADEC faults, such as Nr droop, Nr lag and reduced maximum power capacity, could occur during flight operations of the 407 GXi variant of the model 407. BTCL investigated the condition and originally released Alert Service Bulletin (ASB) 407-21-125, dated 28 September 2021, which provided instructions to replace the P/N 412-074-101-103 CPT with a redesigned transducer P/N 412-074-101-107.
Despite the installation of P/N 412-074-101-107 CPTs, the 407 GXi variant continued to experience issues with engine parameter oscillations and FADEC faults requiring further investigation.
BTCL completed a full redesign of the CPT assembly, including flight testing of the new transducer P/N 412-074-101-105. Upon successful completion and validation of the design solution, BTCL released TB 407-23-140, dated 2 March 2023, which provides installation instructions for the new P/N 412-074-101-105 transducer.
Recommended action:
TCCA recommends that all owners, operators and maintainers of BTCL Model 407 helicopters replace the older P/N 412-074-101-103 and 412-074-101-107 CPTs at their earliest convenience.
Contact office:
For more information concerning this issue, contact a Transport Canada Centre; or contact Grant Walker, Continuing Airworthiness in Ottawa, by telephone at 1-888-663-3639 or by e-mail at TC.CAWWEBFEEDBACK-retroactionWebMDLN.TC@tc.gc.ca.
Original Signed By
Craig McAllister
Acting Chief, Continuing Airworthiness
National Aircraft Certification
The Transport Canada Civil Aviation Safety Alert (CASA) is used to convey important safety information and contains recommended action items. The CASA strives to assist the aviation industry's efforts to provide a service with the highest possible degree of safety. The information contained herein is often critical and must be conveyed to the appropriate office in a timely manner. The CASA may be changed or amended should new information become available.