Sun, Sep 12, 2004
AD/BELL 407/25, Amdt 1,
Tail Rotor Drive Shaft Bearings 11/2004 DM
Applicability: Bell Helicopter Textron Canada
(BHTC) Model 407 helicopters.
Requirement:
- 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.
- 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.
- 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.
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