AD/F50/96 Amdt 1 Bottom Skin Chine Line (Cth)

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/F50/96 and issues the following 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/F50/96 Amdt 1 Bottom Skin Chine Line 12/2006

Applicability:

Model F27 Mark 050 aircraft, serial numbers 20103 through 20172.

Requirement:

1.    Visually inspect the Fuselage Bottom Skin Chine Line between Fuselage Station (STA) 6675 and STA 15375 in accordance with Part 3, Steps A and B of the Accomplishment Instructions of Fokker Services Service Bulletin
SBF50-53-058, dated 30 June 2006, or later EASA approved revision.

a.     When cracks are found appearing through the paint layer, proceed in accordance with the instructions in SBF50-53-058 and within the following time limits:

If the crack length is more than 50 mm, before further flight, remove the paint in accordance with AMM Chapter 51-24-00 and reinspect.

If the crack length is between 10 and 50 mm, within 50 flight cycles, remove the paint in accordance with AMM Chapter 51-24-00, and reinspect.

If the crack length is less than 10 mm, within 1,000 flight cycles, eddy-current inspect in accordance with Fokker SBF50-53-059. dated
24 August 2006, or later EASA approved revision.

b.    When cracks are found after the removal of paint as instructed by Requirement 1.a., proceed in accordance with the instructions in
SBF50-53-058, and within the following time limits:

If the crack length is more than 100 mm, before further flight, repair in accordance with SRM Chapter 53-00-02 Repair No. 10.

If the crack length is between 50 mm and 100 mm, within 50 flight cycles, repair in accordance with SRM Chapter 53-00-02 Repair No. 10.

If the crack length is between 10 mm and 50 mm, repeat the visual inspection in accordance with SBF50-53-058 within 100 flight cycles after the initial inspection, and thereafter at intervals not to exceed 100 flight cycles; until accomplishment of SBF50-53-059.

If the crack length is less than 10 mm, within 1,000 flight cycles, eddy-current inspect in accordance with Fokker SBF50-53-059.

2.    Visually inspect the Fuselage Bottom Skin Chine Line between STA 1320 and STA 3100, in accordance with Part 3, Steps C and D of the Accomplishment Instructions of SBF50-53-058, dated 30 June 2006, or later EASA approved revision.

When cracks are found appearing through the paint layer, proceed in accordance with the instructions in SBF50-53-058 and within the time limits provided in Requirement 1.a.

When cracks are found after the removal of paint, proceed in accordance with the instructions in SBF50-53-058 and within the time limits provided in Requirement 1.b.

3.    In all cases, whether or not cracks were found and repaired in accordance with Requirements 1 and 2 of this Directive, eddy-current inspect the Fuselage Bottom Skin Chine Line (between the same fuselage stations as covered by the visual inspection) in accordance with Part 3, Accomplishment Instructions of
SBF50-53-059 dated 24 August 2006, or later EASA approved revision.

When cracks are found during the eddy-current inspection, proceed in accordance with the instructions in SBF50-53-059 and the following time limits:

If the crack length is more than 100 mm, before further flight, repair in accordance with SRM Chapter 53-00-02 Repair No. 10.

If the crack length is between 50 mm and 100 mm, within 50 flight cycles, repair in accordance with SRM Chapter 53-00-02 Repair No. 10.

If the crack length is less than 50 mm, within 100 flight cycles after the initial inspection, accomplish the eddy-current inspection in accordance with SBF50-53-059, and repeat thereafter at intervals not to exceed 100 flight cycles; until the repair is accomplished.

When cracks are found as a result of the inspection requirements of this Directive, within 7 days after the inspection, report all findings to Fokker Services B.V.

Note:  CAA-NL AD NL-2006-009 R1 refers.

Compliance:

1.    Upon accumulating 20,000 total flight cycles or within 3 weeks after
31 August 2006, whichever occurs later.

2.    Upon accumulating 45,000 total flight cycles or with 3 weeks after
31 August 2006, whichever occurs later.

3.    Within 1,000 flight cycles after the visual inspection in accordance with
SBF50-53-058.

The compliance times for Requirements 1 and 2 remain unchanged by this issue of this Directive.

This Amendment becomes effective on 23 November 2006.

Background:

The inspection procedure as described by Fokker 50 Non-Destructive Testing Manual (NDTM), Part 6, Chapter 53-30-02, which is referenced by Fokker 50 Maintenance Review Board (MRB) Tasks 530000-00-04 and 530000-00-08 does not show the correct inspection areas.  In addition to the existing procedure, the area at the kink in the bottom fuselage skin, the actual chine line, must be inspected.  Investigation revealed that a number of aircraft have already passed the relevant inspection thresholds by a considerable margin.  As a result, it may be possible that cracks have developed and remained undetected.  This condition, if not corrected, could result in failure of the fuselage bottom skin.

Amendment 1 is issued in response a revision of the related CAA-NL AD, which introduces additional eddy-current inspections.

David Villiers
Delegate of the Civil Aviation Safety Authority

12 October 2006