Airworthiness assessments involve the quality and quantity of post-accident information, the ability to assess the causes of failure(s), the risk involved in allowing the fleet to continue to operate and the cost/feasibility of the corrective action(s). This calculus has been the subject of international news; so, this less publicized case provides an opportunity to review the difficulty of exercising this airworthiness judgment.
To say this is one of the most complex discretionary government is a gross understatement. An odd consequence of this year of review is that now the mandatory repairs are more difficult to accomplish because of the COVID-19 social distancing (the AMTs cannot perform the AD inspections.
The AD prompts inspection and mitigation in a range of models.
“Effective March 9, 2020, the FAA has released an airworthiness directive calling for the inspection of Cessna 210s in a specific model range, to determine the presence of corrosion and evidence of fatigue in the carry-through spar lower cap and carrying out mitigating preventative maintenance.
The AD comes as the result of an in-flight breakup of a Cessna T210M in Queensland, Australia, on May 26, 2019, where fatigue cracking started at a corrosion pit. The fracture itself was located inboard of the wing attachment lugs, according to the Australian Transportation Safety Board and the manufacturer, now Textron Aviation as the type certificate holder, in determining the cause of the accident and solutions to prevent its recurrence.
In the AD, the process calls for both visual and eddy-current inspections of the spar cap, corrective action, if needed, and the application of protective coating and corrosion inhibiting compound. The FAA requires a report as to the conclusions of the inspection in order to inform future action. According to the AD, there have been “subsequent reports of other Model 210-series airplanes with widespread and severe corrosion.” The agency has solicited comments on the AD; these must be posted by April 6, 2020.
The models in question include: Cessna 210G, T210G, 210H, T210H, 210J, T210J, 210K, T210K, 210L, T210L, 210M, and T210M aircraft.”
As a result of the accident, the following safety action has been taken:
- On 31 May 2019, the ATSB notified the Civil Aviation Safety Authority (CASA), the United States National Transportation Safety Board, the aircraft manufacturer, and the operator of the initial finding of fatigue cracking within the wing spar carry-through structure.
- On 7 June 2019, the ATSB published a preliminary report containing the initial findings of the investigation.
- On 24 June 2019, the manufacturer released Service Letters SEL-57-06 for the C210 and SEL-57-07 for the C177. These Service Letters instructed a one-off inspection of the structure and communication of inspection findings to the manufacturer.
- On 25 June 2019, the United States Federal Aviation Administration (FAA) released an Airworthiness Concern sheet supporting the manufacturer’s Service Letters and requesting further information from aircraft operators.
- On 12 July 2019, CASA released an Airworthiness Bulletin providing additional information to assist in managing the airworthiness of C210 and C177 wing carry-though spar structures.
- On 4 November 2019, following the receipt and analysis of results from the previously released Service Letters, the manufacturer released updated Service Letters SEL-57-08 for the C210 and SEL-57-09 for the C177. On 19 November 2019, the manufacturer released further revisions to these updated Service Letters.
- 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 requires:
- 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.
This AD was prompted by both the in-flight break-up of VH-SUX and subsequent reports of other C210 aircraft with widespread and severe corrosion.
“Textron has issued a mandatory service letter covering the carry through spars of almost every Cessna 210 with cantilevered wings and most operators have only 20 hours to comply. The Nov. 1 edict requires inspection of and mitigation of corrosion on the spars, which run through the ceiling of the cockpit and hold the wings. It’s not clear what prompted the all-encompassing service letter but only early 210s with struts and strutless models that were inspected under an earlier service letter for aircraft with more than 4,000 hours or those deemed to have been operated in severe service with more than 1500 hours are exempt.
Later model N and R models must be inspected within 200 hours or at the next annual. Those spars were painted at the factory before installation. The spars have to be inspected with a 10X magnifier for evidence of cracks or corrosion. Cracks ground the airplane immediately. Light corrosion can be mitigated with sanding it away. Only a certain amount of material, which varies by the location on the spar, can be removed without triggering an eddy current inspection. The inspection requires removal of the headliner, oxygen plumbing and head protection foam pads from the spars and anything else in the way of an unobscured inspection of the full strut. Inspection reports must be submitted to Textron. “
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