Paper 012 Ageing Aircraft Programme Working Group (AAPWG) Paper 012 Understanding the Corrosion Threat to Ageing Aircraft Dennis Taylor Final December 2015 1 DISTRIBUTION Task Sponsor Dr Steve Reed, Dstl Mrs Mandy Cox, MAA-Cert-Structures4-Gen Mr Matt Sheppard DES DAT-AEM 2 EXECUTIVE SUMMARY With many military aircraft platforms being required to operate past their original out of service date, there is increasing concern that structures and systems may be experiencing an increased airworthiness risks from corrosion. This Paper has been commissioned to capture the full extent of corrosion issues in the long-term Ministry Of Defence air fleets. It is suggested that the information presented in this Paper should be used to assist in focusing the MOD’s Research and Development Corrosion Programme onto key remedial requirements. All current in-service platform PTs were contacted to arrange meetings to discuss their current Environmental Damage Prevention and Control (EDPC) problems and how they applied the requirements of RA 4507. Prior to these meetings the PTs were requested to provide current EDPC or Structural and/or Systems Integrity Working Group (SIWG/SyIWG) meeting minutes so an appreciation of current corrosion issues (if any) could be gained. PTs were also requested to provide any policy documents that supported EDPC management of the platform such as the Support Policy Statement from the Platform Topic 2(N/A/R)1 and the Structural Integrity Strategy Document. To enable generic issues that affected a particular type of operation or aircraft platform category the air platforms were divided into three groups: Heavy Aircraft and Communications (HA&C) Fast Jet and Training Aircraft (FJ&T) Rotary Wing (RW) Examples of some of the significant issues identified are as follows: The poor availability and serviceability of aircraft washing equipment and base washing facilities and an increase in reports of corrosion damage occurring to armament equipment Widespread cadmium corrosion on electrical wiring connectors The effect of runway de-icer fluid on landing gear and carbon brake packs on both FJ&T and HA&C aircraft A lack of preparation for the impact that the Regulation, Evaluation and Authorisation of CHemicals) (REACH) will have on the supply of materials for EDPC protection on both FJ&T and HA&C aircraft fleets 3 It was found that there was a generally poor adherence by the PTs to the acceptable means of compliance for EDPC management contained in RA 4507. Three particular issues were identified: A lack of Environmental Damage Control Plans The meaning and intent “of the recovery procedure following an “exposure incident”” A lack of clarity as to the PT’s responsibility with regard to training requirements There is also an underlying problem with RA 4507 and potentially many other Regulatory Articles, bought about by the introduction of the Continuing Airworthiness Management Organisation (CAMO) role. There are many extant acceptable means of compliances where the responsibility is stated as being the PTs that are now likely to be in conflict with those of the CAMO. 32 recommendations have been made; some of the more significant are given below: The problems with aircraft washing equipment and facilities should be investigated The current concerns of the possible damage caused to undercarriages and associated equipment, particularly carbon brake packs, by Clearway 3TM runway de-icing fluid is formally addressed by each platform PT. It is recommended that a method to address the REACH regulations be carried out by cross-platform discussion to ensure a consistent cost effective solution There were several examples of “beneficial practice” observed, such as: A specific post identified within the Typhoon PT responsible for EDPC The Chinook PT Environmental Damage Control Plan The Tornado PT 2(R)1 Leaflet for the handling of cadmium corrosion on electrical connectors These have been identified as methods and procedures that other PTs might consider adopting to address similar issues or requirements on their particular platform. 4 AUTHORSHIP Principal Author: Dennis Taylor 5 TABLE OF CONTENTS Distribution ............................................................................................................................................................................................. 2 Executive Summary ............................................................................................................................................................................. 3 Authorship ............................................................................................................................................................................................... 5 Table of Contents .................................................................................................................................................................................. 6 Abbreviation ........................................................................................................................................................................................ 13 1 INTRODUCTION ........................................................................................................................... 15 2 INFORMATION GATHERING .................................................................................................... 18 3 THE NATURE OF CORROSION ................................................................................................. 20 3.1 INTRODUCTION ........................................................................................................................................ 20 3.2 IDENTIFICATION OF CORROSION .......................................................................................................... 21 3.3 SURFACE CORROSION ............................................................................................................................. 21 3.4 PITTING CORROSION .............................................................................................................................. 22 3.5 INTERGRANULAR CORROSION ............................................................................................................... 22 3.6 EXFOLIATION CORROSION ..................................................................................................................... 23 3.7 GALVANIC, DISSIMILAR METAL OR ELECTROLYTIC CORROSION .................................................... 23 3.8 CREVICE CORROSION .............................................................................................................................. 24 3.9 FILIFORM CORROSION ............................................................................................................................ 24 3.10 FRETTING CORROSION ........................................................................................................................ 24 3.11 CORROSION FATIGUE ........................................................................................................................... 25 3.12 MICROBIOLOGICAL CONTAMINATION ............................................................................................... 25 3.13 STRESS CORROSION CRACKING (SCC)............................................................................................... 26 3.14 TECHNICAL INFORMATION .................................................................................................................. 26 4 FINDINGS: HEAVY AIRCRAFT & COMMUNICATION ........................................................ 27 4.1 HEAVY AIRCRAFT AND COMMUNICATION PLATFORMS ..................................................................... 27 4.2 ISLANDER/DEFENDER ........................................................................................................................... 27 4.3 SENTRY ..................................................................................................................................................... 28 4.3.1 Keel beam corrosion to electrical earth bonding points ................................................... 28 4.3.2 Front spar cracking............................................................................................................................ 29 4.3.3 Wing plank corrosion on beaver tail ......................................................................................... 29 4.3.4 Magnesium alloy flying controls .................................................................................................. 29 6 4.3.5 Aircraft wash facilities ..................................................................................................................... 30 4.3.6 Bleed air duct corrosion .................................................................................................................. 30 4.3.7 Hydraulic reservoir corrosion ....................................................................................................... 30 4.3.8 Electrical connectors ......................................................................................................................... 31 4.3.9 Repair Assessment Programme (RAP) ...................................................................................... 31 4.3.10 ZH105 Ageing Aircraft Programme Laboratory (AAPL) (Sentry) ............................ 31 The AAPL programme remains in progress. .........................................................................................