Fatigue damage detection inspection requirements
Date issue released
Safety Issue Description

Following an assessment of historical data, the aircraft manufacturer, Textron Aviation, replaced a flight hour based repetitive eddy current inspection for cracking of the carry-through structure with a three-yearly visual corrosion inspection for all operation types. This significantly limited the opportunities to identify fatigue cracking within the carry-through structure of low-level survey aircraft prior to a crack reaching a critical size.

Issue number
AO-2019-026-SI-02
Issue Status
Open – Safety action pending
Transport Function
Aviation: General aviation
Issue Owner
Textron Aviation
Mode of Transport
Aviation
Proactive action
Action number
AO-2019-026-NSA-048
Organisation
Textron Aviation
Action date
Action Status
Closed
Action description

On 24 June 2019, Textron Aviation (Textron) released mandatory service letters SEL‑57‑06 and SEL‑57‑07 for the Cessna 210 (C210) and Cessna 177 (C177) aircraft. These service letters required a one-off inspection of the structure and communication of inspection findings to the manufacturer.

On 4 November 2019, following the receipt and analysis of results from the previously released service letters, Textron released updated service letters SEL-57-08 for the C210 and SEL-57-09 for the C177.

Textron subsequently advised the ATSB that it was undertaking a fatigue analysis of the C210 wing spar carry-through. This analysis included information from the VH-SUX accident and inspections of other aircraft and aimed to determine whether a modified inspection program or life limit was necessary. Textron also advised that work on a certification program to install a new spar in the C210 with an updated configuration and material was ongoing.

ATSB Response

The ATSB acknowledges the safety action taken by Textron and welcomes its ongoing efforts to address this safety issue. However, the ATSB remains concerned by the indefinite nature of the proposed analysis and certification program. As such, the ATSB issues the following safety recommendation to Textron to take further action to address this safety issue.

Safety recommendation
Action number
AO-2019-026-SR-01
Organisation
Textron Aviation
Action date
Action Status
Released
Action description

The Australian Transport Safety Bureau recommends that Textron Aviation takes further safety action to address the risk of fatigue cracking within the carry-through structure of Cessna 210 aircraft operating in low-level geophysical survey roles.

Organisation Response
Organisation
Textron Aviation
Response Text

In response to the ATSB recommendation, in February 2022, Textron Aviation advised that a full fatigue analysis was completed using data collected by the ATSB using an aircraft configured similarly to the accident aircraft and flying a similar mission profile as well as fatigue spectra data provided in United States Federal Aviation Administration Advisory Circular AC23.13A. The analysis found that there would be a very limited probability of finding a crack during the interval between the crack becoming detectable and it reaching critical flaw size. Based on this finding, Textron assessed that inspections to identify cracking would be impractical.

Textron Aviation advised that it was seeking guidance and project acceptance from the United States Federal Aviation Administration to add a recommended safe life limit to the Model 210 Supplemental Inspection Document (SID) for aircraft that operate 50% or more of their time on the ‘Pipeline/Survey’ mission as defined by AC 23.13A.

Textron Aviation also noted that the accident aircraft was highly modified and routinely flown in a manner that exceeded the design envelope of the aircraft’s anticipated mission profiles and, that this niche operating environment may require additional mitigating activities to prevent structural failure. Textron Aviation suggested that the responsibility for development of these mitigation programs and methodologies should rest with the operators and/or STC holders of this very limited number of specific aircraft.

ATSB Response

The ATSB acknowledges that the cyclic loads induced by the low-level survey flight profile probably increased the risk of a fatigue related structural failure in the aircraft. However, it was determined that the airframe and system modifications incorporated into the aircraft did not significantly increase the fatigue damage accumulated by the wing spar carry-through structure.

The ATSB also acknowledges the substantial efforts and actions undertaken by the FAA in collaboration with Textron in implementing airworthiness directives (AD) 2020-03-16 (AO-2019-026-NSA-50) and 2023-02-17 (AO-2019-026-PSA-01). The actions completed to date have identified and rectified instances of corrosion-initiated fatigue cracking within the carry-through structure of the Cessna 210 fleet, including aircraft operating in low-level geophysical survey roles. The ATSB welcomes the ongoing work to develop appropriate measures aimed at managing the future risk of fatigue cracking in the fleet and will assess the progress of this safety action as it is implemented. 

Proactive action
Action number
AO-2019-026-NSA-50
Organisation
United States Federal Aviation Administration
Action date
Action Status
Closed
Action description

On 21 February 2020, the FAA adopted airworthiness directive (AD) AD 2020-03-16 for all Cessna model 210G, T210G, 210H, T210H, 210J, T210J, 210K, T210K, 210L, T210L, 210M, and T210M aircraft. This AD required:

  • visual and eddy current inspections of the carry-through spar lower cap
  • corrective action if necessary
  • application of a protective coating and corrosion inhibiting compound
  • reporting the inspection results to the FAA.

On 11 May 2021, the FAA issued a notice of proposed rulemaking for a one-time inspection for 210N, 210R, P210N, P210R, T210N, T210R, 177, 177A, 177B, 177RG, and F177RG models. On 25 June 2021, the consultation period for the notice of proposed rulemaking closed. At the time of writing, the FAA was reviewing the received comments.

Safety action update

As of 29 September 2023, the following inspection results were received by the FAA in response to the AD 2020-03-16:

C210 models G to M

  • 969 inspection reports
  • 446 aircraft reporting corrosion
  • 62 carry-through spars removed from service due to cracking, corrosion, or other damage.
Proactive action
Action number
AO-2019-026-NSA-049
Organisation
Civil Aviation Safety Authority
Action date
Action Status
Closed
Action description

On 12 July 2019, the Civil Aviation Safety Authority (CASA) released Airworthiness Bulletin AWB 53-011 providing additional information to assist with managing the airworthiness of Cessna 210 (C210) and Cessna 177 (C177) wing carry-though spar structures.

This bulletin recommended that operators and maintainers of C177 and C210 aircraft with cantilevered (unstrutted) wings undertake actions including:

  • C210 service letter SEL-57-06 and C177 service letter SEL-57-07 or later revisions as appropriate which relate to one-time inspections of the lower surface of the carry-though lower cap. It is prudent to extend the enhanced inspection (10 x magnification and bright light source) to the upper surface of the lower cap and the carry-through web where visible using a mirror and/or borescope.

Note: CASA recognises that some maintenance programs already require compliance with these Cessna service letters.

  • For Cessna Models with skin attaching to the carry-through (C210 G-M models), the following is recommended in addition to carrying out the Cessna service letter procedure:

    • Visually inspect the serviceability of the fuselage cabin skin to carry-through forward and aft joints for the condition of the sealant, any signs of bulging of the skin and for any loose or missing solid rivets. If corrosion is suspected, disassemble the joint to allow for a detailed visual inspection for corrosion or cracking.
    • If the joint is opened, it is recommended that fay surface sealant is applied as per Cessna Service Manual 2A-30-01.
    • If the joint edge sealant is found deteriorated, clean up and reapply the edge seal as per Cessna Service Manual 2A-30-01.
Proactive action
Action number
AO-2019-026-PSA-01
Organisation
United States Federal Aviation Administration
Action Status
Closed
Action description

Since the release of recommendation AO-2019-026-SR-01, the United States Federal Aviation Administration has also implemented additional safety action related to the C210 wing spar carry-through structure. In addition to the AD issued on 4 March 2020, (AD 2020-03-16, ATSB proactive safety action AO-2019-026-NSA-050), FAA also adopted AD 2023-02-17 (ATSB proactive safety action AO-2019-026-PSA-01) on 20 March 2023. This AD is applicable for all Cessna model 210N, 210R, P210N, P210R, T210N, T210R, 177, 177A, 177B, 177RG, and F177RG aircraft. This AD required the following for applicable aircraft:

  • visual and eddy current inspections of the carry-through spar lower cap
  • corrective action if necessary
  • application of a protective coating and corrosion inhibiting compound
  • reporting the inspection results to the FAA.

As of 29 September 2023, the following inspection results were received by the FAA in response to AD 2023-02-17:

C210 models N and R

  • 343 inspection reports
  • 21 aircraft reporting corrosion
  • 2 carry-through spars removed from service due to damage other than cracking or corrosion.

C177 aircraft

  • 547 inspection reports
  • 242 aircraft reporting corrosion
  • 34 carry-through spars removed from service due to cracking, corrosion, or other damage.

The FAA advised that the ADs were interim actions, and that FAA analysis of the inspection results would determine the final actions necessary to ensure the ongoing airworthiness of the affected aircraft.

ATSB Response

The ATSB acknowledges the safety action taken and inspections conducted to date to identify and rectify instances of corrosion-initiated fatigue cracking within the carry-through structure of the Cessna 210 fleet, including aircraft operating in low-level geophysical survey roles. The ATSB welcomes the ongoing work to develop appropriate measures aimed at managing the future risk of fatigue cracking in the fleet and will assess the progress of this safety action as it is implemented.