AD/Bell 412/55 Tail Rotor Blades 2 (Cth)

AIRWORTHINESS DIRECTIVE

For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.001(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 412 Series Helicopters

AD/BELL 412/55 Tail Rotor Blades - 2 7/2008 DM

Applicability:

Model 412, 412CF, and 412EP helicopters, equipped with tail rotor blade part number 212-010-750- (all dash numbers).

Requirement:

1.    Visually check both sides of each tail rotor blade for a crack.

2.    Accomplish the following:

a.     Clean each tail rotor by hand using a mild degreaser and water to remove soot and grime on both sides of the blade using a coarse, loosely woven cotton cloth in a spanwise direction.  Use a cloth with a colour that contrasts with the colour of the tail rotor blade so that a snag will be visible.

b.    Using a 3-power or higher magnifying glass and a bright light, visually inspect the tail rotor blade skins, leading edge spar, doublers, grip plates, and trailing edge for a crack, corrosion (may be indicated by blistering, peeling, flaking, bubbling, or cracked paint) and any other damage (including a nick, scratch, or dent).  See Figure 1 of this Directive.  Pay particular attention to both sides of the tail rotor blade in the area located 16 to 20-inches from the tail rotor blade tip (blade station 25 to 35; the blade tip is located at blade station 51) and to the inboard blade butt area near the attachment of the external balance weights and screws.  Also pay particular attention to any blade surface that was snagged by the cloth, as that may be an indication of a crack or paint chip that could lead to corrosion.

Figure 1

c.     If any blistering, peeling, flaking, bubbling, or cracked paint is detected, remove the paint from the affected area and visually inspect the affected area for corrosion or a crack using a 10-power or higher magnifying glass.  If any corrosion is found, measure the depth of the corrosion (a digital optical micrometer is one tool that can be used for this measurement).

d.    If a nick, scratch, or dent is found, visually inspect for a crack using a 10-power or higher magnifying glass and measure the depth of the damage (a digital optical micrometer is one tool that can be used for this measurement).

If a crack is detected during any inspection, before further flight, replace the blade with a serviceable blade.

If any corrosion, nick, scratch, dent or other damage is detected during any inspection that exceeds any maximum repair limit, before further flight, replace the blade with a serviceable blade.

Note 1:  The maximum repair limits are specified in the applicable maintenance manual.

Repair or replace with a serviceable blade any tail rotor blade that has any corrosion, nick, scratch, dent, or other damage that is within the maximum repair limits.

Note 2:  The repair procedures are specified in the applicable maintenance manual and component repair and overhaul manuals.

Note 3:  FAA AD 2008-10-03 Amdt 39-15509 refers.

Compliance:

1.    Before each start of the engines.

2.    Within 25 hours time in service or 30 days after 21 May 2008, whichever occurs first, unless already accomplished; and thereafter at intervals not to exceed 25 hours time in service or 30 days, whichever occurs first.

This Directive shall be entered on the Maintenance Release as maintenance required. The Requirement 1 inspection may be performed and certified by a Pilot in Command who has been trained by an appropriately qualified person.  In this case, a copy of this Directive is to be carried in the aircraft.

This Airworthiness Directive becomes effective on 21 May 2008.

Background:

The FAA received reports of three in-flight failures of tail rotor blades, and a recent incident of a cracked tail rotor blade detected during a scheduled visual inspection. Undetected damage to a tail rotor blade could lead to cracking of the blade and subsequent loss of control of the helicopter.

David Villiers
Delegate of the Civil Aviation Safety Authority

8 May 2008