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Mode Aviation
Reference No. AR201500098
Date reported 15 November 2015
Concern title Visible corrosion on the aircraft
Concern summary

The concern related to visible corrosion on an aircraft used for sight-seeing tours.

Industry / Operation affected Aviation: Air transport
Concern subject type Aviation: Maintenance

Reporter's concern

The reporter expressed a safety concern related to the visible corrosion on the aircraft operated by [operator].

The reporter advised that during their scenic flight from the beach at [location], they observed visible corrosion on the flap brackets. As the take-off technique was to accelerate and then apply flap, there is a possibility that the flap bracket may fail at this critical phase of flight.

The reporter also observed:

  • landing light crack that has been drilled then the crack extends
  • the engine cover screws and cracking around the cowling
  • staining behind the fuel drain – indicating it has been leaking for some time.

Operator's response (Operator 1)

Our aircraft are subjected to a severe maritime environment as part of the daily operating requirements. As a result of this, corrosion control is an item which forms an important part of our ongoing maintenance. Particularly vulnerable are the exposed steel components. These include the flap attach brackets mentioned in the report, attaching hardware, screws, undercarriage legs, brake discs, rod end bearings and wheel bearings. There is also an issue with dissimilar metal surface corrosion on flying controls. An example of this is highlighted in a service bulletin relating to flap and aileron arm corrosion.

To reduce the impact of direct exposure to salt water we have replaced, insofar as possible, attaching hardware with stainless steel, for example, AN526 cadmium plated steel screws, AN3 cadmium plated bolts, etc with AN526C and AN3C hardware. Also, the cadmium plated steel quick release fasteners on the cowl with the stainless version. In some areas, the use of cadmium plated hardware has left unsightly rust stains in the paint. The rust highlighting cracking of the gelcoat on the composite cowling as noted by the observer is an example of this.

To respond directly to the concern regarding the flap attach brackets, an inspection carried out on receipt of the report confirmed that the corrosion is surface corrosion, which has been previously addressed, with no structural concerns. However, we agree it is not a good look.

The fuel stains behind the fuel drain are the result of a minor leak in the seam of the tank which was addressed some time ago.

The aircraft is currently in for a periodic inspection and all the items mentioned in the report have been entered for rectification, including cowl refinishing, landing light cover replacement, corrosion treatment and surface refinishing as required.

Regulator's response (Regulator 1)

CASA has conducted a search of all reported equipment failures by this operator on the Service Difficulty Reporting (SDR) system. While four SDRs have been submitted involving a manufacturing fault of an undercarriage axle, the failure of an engine driven pump and two instances of cracks being detected as a result of regular maintenance inspection activities, there is no evidence of any systemic or problematic maintenance issues from any of these SDR reports.

The issues identified in the ATSB REPCON report appear to be satisfactorily addressed.

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Last update 17 June 2016