AD 2022-17-05 Requires Either Doing Recurring Visual Inspections, Borescope Inspections, And Non-Destructive Inspections

The FAA is superseding Airworthiness Directive (AD) 2002-14-28, which applied to all de Havilland Inc. (type certificate currently held by Viking Air Limited) Model DHC-2 Mk. I, DHC-2 Mk. II, and DHC-2 Mk. III airplanes.

AD 2002-14-28 established a life limit for the front fuselage struts and required repetitively replacing the front fuselage struts every 15 years or repetitively inspecting the struts for corrosion or fatigue damage and replacing when the damage exceeded a certain level. Since the FAA issued AD 2002-14-28, Transport Canada superseded its mandatory continuing airworthiness information (MCAI) to correct this unsafe condition on these products. This AD requires either doing recurring visual inspections, borescope inspections, and non-destructive inspections (NDIs) of the struts and airframe lugs with corrective action as necessary or replacing the struts every 15 years and doing recurring NDIs of the airframe lugs with corrective action as necessary. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective September 30, 2022.

Supplementary Information: The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to supersede AD 2002-14-28, Amendment 39-12828 (67 FR 47684, July 22, 2002) (AD 2002-14-28). AD 2002-14-28 applied to all de Havilland Inc. (type certificate currently held by Viking Air Limited) Model DHC-2 Mk. I, DHC-2 Mk. II, and DHC-2 Mk. III airplanes. AD 2002-14-28 established a life limit for the front fuselage struts and required repetitively replacing the front fuselage struts every 15 years or repetitively inspecting the struts for corrosion or fatigue damage and replacing when the damage exceeded a certain level. The FAA issued AD 2002-14-28 to prevent structural failure of the front fuselage caused by corrosion or fatigue damage to the struts that develops over time, which could result in reduced or loss of airplane control.

The NPRM published in the Federal Register on June 7, 2022 (87 FR 34591). The NPRM was prompted by AD CF-2020-22, dated June 5, 2020 (referred to after this as “the MCAI”), issued by Transport Canada, which is the aviation authority for Canada, which superseded its prior AD on this unsafe condition, AD CF-98-37R1, dated August 20, 1999. Transport Canada issued the MCAI to introduce a revised inspection schedule for the front fuselage struts from previously published schedules to alleviate the burden of mandatory replacement every 15 years or ultrasonic inspections every 5 years. The MCAI states:

Operators have reported incidents of corrosion of the DHC-2 front fuselage struts which are installed on each side of the flight compartment windshield. Deterioration of the airframe lugs to which the struts are attached has also been reported. The actions specified by this [Transport Canada] AD are intended to prevent structural failure of the front fuselage caused by damage to the fuselage struts and airframe lugs that develops over time, which could result in the loss of airframe structural integrity.

AD CF-98-37 issued 29 September 1998 mandated a 15-year life limit on the strut. It also prohibited installation of part numbers (P/Ns) C2FS209 and C2FS210.

Revision 1, CF-98-37R1, introduced repetitive inspection as an alternative to replacement of the strut. Detailed visual inspection was required to begin within 12 months from the effective date of the [Transport Canada] AD and be repeated every 12 months regardless of the age of the strut. Ultrasonic thickness measurements were required to begin within 24 months from the effective date of the [Transport Canada] AD and be repeated every 5 years regardless of the age of the strut.

After AD CF-98-37R1 was issued, it was determined that the repetitive inspections are not required to be started until the strut has accumulated 15 years since installation. As a result, Transport Canada (TC) approved several AMOCs [alternative methods of compliance] to authorize starting the inspections at that time.

Since the issuance of AD CF-98-37R1, TC has received several Service Difficulty Reports (SDRs) indicating that the corrective actions of that [Transport Canada] AD have not been effective at controlling damage of the fuselage struts to an acceptable level.

Viking Air Ltd. (Viking) has determined that a modified program of recurring visual inspection, borescope inspection and non-destructive inspection (NDI) of the struts and airframe lugs would be more effective than the existing inspection program. This program modifies affected parts by introducing a hole to permit a borescope inspection if that hole does not already exist in the parts.

To implement the modified inspection program, Viking has published Service Bulletin (SB) V2/0010 and Technical Bulletin (TB) V2/00002 that provide specific instructions for performing the modification, inspections and measurements required by this [Transport Canada] AD. The SB and TB also define the follow-on actions associated with those inspections and measurements.

Viking has also developed a version of the front fuselage strut with improved resistance to corrosion and with provisions for borescope inspection. The improved struts have been assigned P/Ns C2FS3281A-9 (left strut) and C2FS3282A-9 (right strut).

The corrective actions of this [Transport Canada] AD differ from those of AD CF-98-37R1 in the following ways:

• AD CF-98-37R1 included the details for all of the corrective actions, it did not require reference to other documents. For this [Transport Canada] AD, the details of the corrective actions are now specified in a SB and a TB.
• AD CF-98-37R1 required repetitive detailed visual inspection (DVI) of the airframe lugs. This [Transport Canada] AD requires repetitive DVI and NDI of the airframe lugs.
• AD CF-98-37R1 only permitted installation of P/Ns C2FS3281A and C2FS3282A. This [Transport Canada] AD permits installation of those parts, the superseding Viking P/Ns, parts installed by TC-issued or -accepted Supplemental Type Certificate (STC) or Part Manufacturing Approval (PMA) and Part Design Approval (PDA) parts that are approved for installation in DHC-2 as replacements for P/Ns C2FS3281A and C2FS3282A. Those are all approved parts.
• AD CF-98-37R1 did not specify to remove parts from the aeroplane to perform inspections. This [Transport Canada] AD requires repetitive removal of the struts from the aeroplane followed by a NDI of the airframe lugs. This requirement applies to DHC-2 where the struts are being replaced when they reach 15 years since installation. It also applies to DHC-2 where the struts are kept in service and inspected as required by the SB and TB.
• AD CF-98-37R1 required the visual inspection to start within 12 months from the [Transport Canada] AD effective date and the NDI to start within 24 months from the [Transport Canada] AD effective date. This [Transport Canada] AD requires the repetitive inspections to start no later than when the struts have accumulated 15 years since initial installation.
• AD CF-98-37R1 required repetitive ultrasonic thickness measurement for all parts. This [Transport Canada] AD only requires that measurement if corrosion is detected during an inspection.
• AD CF-98-37R1 required visual inspection of the exterior surfaces of the strut with the strut installed in the aeroplane. For struts that have accumulated more than 15 years since first installation, this [Transport Canada] AD continues to require visual inspection of the accessible exterior surfaces of the strut with the strut installed. This [Transport Canada] AD also includes repetitive requirements for:
  • Inspection of the fillet sealant;
  • Borescope inspection of the interior of the strut; and
  • Removal of the strut from the aeroplane followed by visual inspection of the entire strut and NDI of the strut end fittings.

All TC-issued or -accepted AMOCs with AD CF-98-37R1 are cancelled on the effective date of this [Transport Canada] AD. Parts in service must be replaced or modified, inspected and maintained in accordance with the requirements of this [Transport Canada] AD unless TC approves AMOCs with the requirements of this [Transport Canada] AD.

You may examine the MCAI in the AD docket at www.regulations.gov under Docket No. FAA-2022-0602.

In the NPRM, the FAA proposed to require either doing recurring visual inspections, borescope inspections, and NDIs of the struts and airframe lugs with corrective action as necessary or replacing the struts every 15 years and doing recurring NDIs of the airframe lugs with corrective action as necessary. The FAA is issuing this AD to address the unsafe condition on these products.

FMI: www.regulations.gov