21 February 2002

our Ref 9/97/7/5

LETTER TO OWNERS/OPERATORS NO 2325
CONTROL CABLE END FITTINGS-CRACKING AND CORROSION

In November 2001, the CAA received a request from the FAA to investigate the usage of particular control cable end fittings on UK manufactured aircraft.  These end fittings are manufactured from high selenium content, free machining stainless steel.  The FAA request is associated with an NTSB recommendation arising from investigations into ten incidents of fracture or cracking of such fittings.  To date, none of the fractures has resulted in a serious accident, but four have occurred in flight, in primary control circuits.

A survey of UK Type Certificate holders and Type Design organisations revealed that the suspect end fittings are in wide usage on UK products.  This information has been provided to the FAA as they requested, however the extent of the usage on UK products has prompted an internal review of the issue by CAA specialists.

Having discovered that these fittings could be fitted extensively in UK products, the CAA is concerned that these fittings could also have been fitted by UK maintenance organisations as replacement parts during cable changes.  There is also a desire to establish what, if any, problems exist with in service fittings currently installed on UK registered or manufactured aircraft.  The generic part numbers of these items are MS21260, AN669 and NAS650.

The CAA would like to draw your attention to these fittings and the possible cracking/corrosion issues.  We would ask that when performing any inspections on these fittings particular attention be paid to their conditon and any findings be reported to the relevant manufacturer and a Mandatory Occurrence Report raised.  Degraded control cable fittings have surface corrosion pits and in most cases these pits have initiated stress corrosion cracks.  In latter stages the cracks become surface breaking, and extensive cracking surface discolouration may occur.  Where locking wire is used to lock the barrel/fitting assembly more severe pitting corrosion could be evident underneath the wire.

Enquiries regarding this LTO should be referred to Mr Justin Goatcher, Aircraft Certification Section (Telephone No. 01 293 573292) at the address below.

Yours faithfully

signed
Lynda Gillett
Applications and Certification Section

Civil Aviation Authority
1E Aviation House
Gatwick Airport South
West Sussex
England
RH6 0YR
www.caa.co.uk
direct line: +44 (0) 1293 573150
facsimile: +44 (0) 1293 573860
E-mail: ad.unit@srg.caa.co.uk
 

If you wish to download a copy of the original letter, please click here for a zip-file (983 Kb) or here for a word-format (1 MB) version.