AD/F50/92 Engine Mounting Frame Welds (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.

Fokker F50 (F27 Mk 50) Series Aeroplanes

AD/F50/92 Engine Mounting Frame Welds 9/2005

Applicability:

Model F27 Mk.050, 0502, and 0604 aircraft, all serial numbers.

Requirement:

a.    Inspect the engine mounting frames, including units held as spares, in accordance with Part 3, Accomplishment Instructions of Fokker Service Bulletin (SB)
F50-71-048 or Component Service Bulletin (CSB) F8200-035-71-10, as applicable, both documents dated 30 May 2005; or later CAA-NL approved revisions.

b.    When deviations are found between 0 and 2mm, no further action is required on that frame and the aircraft may be returned to service.  Any spare frame similarly inspected and identified may be used as a replacement part.

c.    When deviations are found between 2 and 5mm, the aircraft may be returned to service.  However, within 2 weeks after the inspection, report the inspection findings to Fokker Services.  These welds must be NDT-inspected in accordance with Fokker SB F50-71-049.  Any spare frame similarly inspected and identified must be NDT-inspected in accordance with CSB F8200-035-71-11.  In the meantime, these frames may be used as a replacement part.

d.    When deviations are found exceeding 5 mm, before further flight, report the inspection findings to Fokker Services and request detailed instructions which must be adhered to before further flight, because affected frame may need to be replaced.  Any spare frame similarly inspected and identified may only be used as a replacement part after written consent of Fokker Services.

e.    As of the effective date of this Directive, no person shall install an Engine Mounting Frame having part number F8200-035-427/-441/-451/-463 (forward frames); F8200-035-425/-443 (A-frames); or F8200-035-403/-439/-449/-461 (rear frames) as a replacement part, unless it has been inspected and identified in accordance with Requirement paragraphs a. and b.

Note:  CAA-NL AD NL-2005-007 refers.

Compliance:

For the Requirement a. Inspection:  Within 2 calendar months after 1 September 2005.

This Airworthiness Directive becomes effective on 1 September 2005.

Background: Welding defects were discovered during recent scheduled X-ray inspections of F50 engine mounting frames.  Investigation revealed that during manufacture of the frames, when tubes were welded to the end fittings, movement of the electric arc resulted in some welds running beside the borderline for a part of the tube circumference.  The defective welding process appears to have occurred at some of the welds in an unknown number of engine mounting frames.  This condition, if not corrected, could lead to failure of an affected engine mounting frame.

David Villiers
Delegate of the Civil Aviation Safety Authority

20 July 2005