7 July 1999
Silver plating fuel pumps
All Rolls-Royce (RR) Dart and certain Spey engine models originally incorporated Lucas fuel pumps that had silver plating on the rotor port faces and the piston 'slipper tops'. This silver plating served as an aid to lubrication in these two key areas. Conversely, high levels of reactive sulphur in the fuel can attack the silver in a corrosive-like manner called 'sulphidization', resulting in the silver plated surface flaking away and exposing the base material. The most commonly associated engine symptoms are poor starting, low power and slow acceleration caused primarily by pump performance loss, but also by wear debris contaminating the fuel control system. In some cases, the sulphiding attack was severe enough to cause the fuel pump to seize and lead to an engine shutdown.
Aviation fuel manufacturers have assured an acceptable reactive sulphur content by performing a 'silver strip' test on each batch of fuel and any fuel that exceeded the reactive sulphur limit was recycled back to the refinery; this need to recycle was a rare occurrence in Canada. Consequently, because of the guaranteed low level of reactive sulphur in Canadian aviation fuels and adherence to the manufacturer's recommendations addressing overhaul frequencies, sulphidization has not been a problem for affected aircraft operating in Canada.
Transport Canada has been advised by the Aviation Fuels Committee (AFC) of the Canadian General Standards Board that the petroleum industry will be phasing out the silver strip test in the near future as very few engines worldwide are affected by reactive sulphur levels that occasionally exceed the limits of the silver strip test. This should have no effect on Canadian-based operations when the RR/Lucas maintenance recommendations are followed.
For Canadian operators deploying their aircraft to parts of the world where the quality of the fuel could be questionable or the fuel is manufactured from crude oil having an inherently high reactive sulphur content, Transport Canada recommends that such aircraft incorporate fuel pump modifications that have replaced the silver plating with alternative surface coatings. These modifications are introduced by Rolls-Royce Service Bulletins 73-36, 73-53 and 73-74 for Dart engines and 73-22, 73-127 and 73-212 for certain Spey engine models.
Any defects or occurrences related to fuel pump sulphidization should be reported by sending a Service Difficulty Report to Transport Canada, Continuing Airworthiness, Ottawa.
For further information, contact a Transport Canada Centre, or Mr. Robin Lau, Continuing Airworthiness, Ottawa, telephone (613) 952-4461, facsimile (613) 996-9178 or e-mail firstname.lastname@example.org.
For Director, National Aircraft Certification
Chief, Continuing Airworthiness