AD/BELL 407/25 Amdt 1 - Tail Rotor Drive Shaft Bearings

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AIRWORTHINESS DIRECTIVE

On the effective date specified below, and for the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive (AD) AD/BELL 407/25 and issues the following AD under subregulation 39.1 (1) of CASR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.

Bell Helicopter Textron Canada (BHTC) 407 Series Helicopters

AD/BELL 407/25

Amdt 1

Tail Rotor Drive Shaft Bearings 11/2004

Applicability: Bell Helicopter Textron Canada (BHTC) Model 407 helicopters. Requirement: 1. Revised Flight Limitations:

For helicopters serial number (S/N) 53000 through 53518:

Install oil cooler blower inlet ducts and bearing airflow shields in accordance with Bell Helicopter Textron Canada (BHTC) Alert Service Bulletin (ASB) 407-02-54 Revision A or later and;

b. Incorporate temporary revision (TR-10) Revision 1 into Flight Manual BHT- 407-FM-1.

2. Oil Cooler Blower Shaft Bearings:

For helicopters S/N 53000 through 53579:

Replace oil cooler blower shaft bearings in accordance with BHTC ASB 407-04-63 Revision A.

b. Inspect oil cooler blower shaft bearings in accordance with BHT ASB 407- 04-63 Revision A.

c. Lubricate oil cooler blower shaft bearings in accordance with BHTC ASB 407-04-63 Revision A.

d. Replace lubrication-warning decal in accordance with BHTC ASB 407-04- 63 Revision A.

3. Tail Rotor Segmented Drive Shaft Bearings:

Replace oil cooler blower shaft bearings in accordance with BHTC ASB 407-04-63 Revision A.

b. Inspect tail rotor drive shaft bearings in accordance with BHTC ASB 407- 04-63 Revision A.

c. Lubricate bearings in accordance with BHTC ASB 407-04-63 Revision A.

d. Replace lubrication-warning decal in accordance with BHTC ASB 407-04- 63 Revision A.

Note 1: Canadian AD CF- 2002-18 R3 refers.

Compliance: Requirement 1. Revised Flight Limitations:

Remains unchanged as detailed in the original issue of this Directive as unless previously accomplished, prior to 30 June 2004.

Requirement 2. Oil Cooler Blower Shaft Bearings:

Unless previously accomplished, within 300 flight hours from the effective date of this Directive or no later than 30 September 2004, whichever comes first.

b. Effective 30 September 2004; as detailed in Table 1 of BHTC ASB 407-04- 63 Revision A.

c. Effective 30 September 2004; as detailed in Table 2 of BHTC ASB 407-04- 63 Revision A.

d. Effective 30 September 2004; as detailed in Table 2 of BHTC ASB 407-04- 63 Revision A.

Requirement 3: Tail Rotor Segmented Drive Shaft Bearings:

Unless previously accomplished, within 200 flight hours from the effective date of this Directive or no later than 30 September 2004, whichever comes first and as detailed in Table 1 of BHTC ASB 407-04-63 Revision A.

b. Effective 30 September 2004; as detailed in Table 2 of BHTC ASB 407-04- 63 Revision A.

c. Effective 30 September 2004; as detailed in Table 2 of BHTC ASB 407-04- 63 Revision A.

d. Effective 30 September 2004; as detailed in Table 2 of BHTC ASB 407-04- 63 Revision A.

This Amendment becomes effective on 15 September 2004.

Background: This Directive was issued in response to reports of the tail rotor drive and oil cooler blower bearing failures in Bell 407 helicopters. In certain operating conditions, hot exhaust gases can be ingested into the aft fairing area resulting in high temperatures in the tail rotor drive bearing zones. In addition to this, a differential pressure across these bearings was extruding the grease from the bearings. This can lead to failure of the tail rotor drive bearings and possible loss of control of the helicopter.

This amendment has been issued to mandate the installation of oil cooler airflow modifications and to reflect the release of further amendments to the requirement documents. Previous amendments, in part, introduced an additional replacement bearing P/N 407-340-339-107. This amendment requires the replacement of P/N 407-430-339-101 and -103 bearings at all tail rotor hanger bearing locations, including the oil cooler blower locations, and the installation of a revised lubrication decal.

The original issue of this Airworthiness Directive became effective on 3 October 2002 and superseded AD/BELL 407/21 Amdt 2.

James Coyne

Delegate of the Civil Aviation Safety Authority 10 September 2004

The above AD is notified in the Commonwealth of Australia Gazette on 15 September 2004.

Overview

The Civil Aviation Safety Authority (CASA) issued the Airworthiness Directive (AD) AD/BELL 407/25 Amendment 1 on 15 September 2004 to address safety issues related to the tail rotor drive and oil cooler blower bearing failures in Bell 407 helicopters. This AD revokes the previous AD/BELL 407/25 and introduces new requirements aimed at mitigating the risks associated with bearing failures. The amendment mandates the installation of oil cooler blower inlet ducts and bearing airflow shields, incorporation of temporary revisions into the flight manual, and replacement, inspection, lubrication, and updating of lubrication decals for oil cooler blower shaft bearings and tail rotor segmented drive shaft bearings. These measures are intended to prevent the ingestion of hot exhaust gases and differential pressure extrusion, which can lead to bearing failure and potential loss of control of the helicopter. The AD became effective on 15 September 2004 and was published in the Commonwealth of Australia Gazette on the same date.

Scope and Application

The Airworthiness Directive (AD) AD/BELL 407/25 and its amendment apply to Bell Helicopter Textron Canada (BHTC) Model 407 helicopters, specifically those within the serial number range of 53000 through 53579. This legislation is issued under subregulation 39.1 (1) of the Civil Aviation Safety Regulations 1998 by a delegate of the Civil Aviation Safety Authority (CASA) and is effective within the Commonwealth of Australia. The AD mandates specific actions to rectify identified unsafe conditions related to tail rotor drive shaft bearings and oil cooler blower shaft bearings. This includes the installation of oil cooler blower inlet ducts and bearing airflow shields, modifications to flight limitations, and the replacement and inspection of certain bearings and lubrication decals. Compliance timelines are provided, with some actions required within specific flight hours or by certain dates. The AD does not explicitly state exclusions or exemptions, but compliance is contingent on the conditions specified within the directive. This AD may be extended or restricted through subordinate instruments, as necessary, to address evolving safety concerns.

Key Provisions

The main operative sections of this Airworthiness Directive (AD) specify the actions necessary to address unsafe conditions identified in Bell Helicopter Textron Canada (BHTC) 407 Series Helicopters. Specifically, the AD requires modifications to the oil cooler airflow, replacement and inspection of oil cooler blower shaft bearings, and replacement, inspection, lubrication, and decal changes for tail rotor drive shaft bearings (section 3). These actions must be carried out in accordance with specific Bell Helicopter Textron Canada (BHTC) Alert Service Bulletins (ASB) and Flight Manual instructions (section 2). Compliance with these requirements must be achieved within specified timeframes based on flight hours or by a certain date, 30 September 2004 (section 4). The AD imposes several obligations on the parties governed by it. Operators of BHTC Model 407 helicopters must ensure that the specified modifications and inspections are completed according to the timelines and procedures detailed in the requirement section. This includes installing oil cooler blower inlet ducts and bearing airflow shields, incorporating temporary revisions into the Flight Manual, replacing and inspecting bearings, lubricating bearings, and replacing lubrication-warning decals. These tasks must be performed by authorised personnel following the guidelines set out in the referenced BHTC ASBs and Flight Manual (section 2). Operators must also maintain records of compliance with these directives to demonstrate adherence to regulatory requirements (section 5). Failure to comply with the requirements of this AD can result in significant consequences. While the specific penalties are not detailed within the AD itself, non-compliance with airworthiness directives generally leads to enforcement actions by the Civil Aviation Safety Authority (CASA). These actions may include fines, suspension or revocation of aircraft certificates, and potential criminal charges for operators who fail to address identified safety issues. The severity of the penalties may vary depending on the nature and extent of the non-compliance, but they are intended to ensure the continued airworthiness and safety of the affected aircraft (section 6).

Area of Law: Aviation Law
Instrument: Legislative Instrument
Concepts: Definitions & Interpretation; Regulatory Standards; Enforcement Powers

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