AD/BELL 407/25, Amdt 1, Tail Rotor Drive Shaft Bearings 11/2004 DM

Applicability: Bell Helicopter Textron Canada (BHTC) Model 407 helicopters.

Requirement:

1. Revised Flight Limitations: For helicopters serial number (S/N) 53000 through 53518:
   
   a. 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:
   
   a. 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:
   
   a. 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:

a. 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:

a. 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 lower 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 407-340-339-10. 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.

FMI: http://casa.gov.au/avreg/aircraft/ad/ADfiles/Rotor/BELL407/BELL407-025.pdf