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Alochrome and etch primer

We are manufacturing aircraft panels and the design calls several pre treatments. We are slightly confused about the following.
Is it appropriate to use an etch primer on top of an Alochrome 1200 treated panel, manufactured from a high strength, aluminium alloy L168 or L115-T651 or 6082-T6, or should we be using a filler primer? Either way we need to clear this up with the design department.

Alan Sinclair
Aircraft engineer - UK
2007

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Dear Alan,
Etch primer is a stand alone pretreatment and must be applied directly to the metal substrate. The phosphoric acid that is added in the form of the "catalyst", partially etches the metal and this is what improves the adhesion of the following primer or top coats. However, you should be made aware that although not banned by the UK H&S executive they do not like it because it contains chromates that are hazardous to the sprayers. I would suggest that you apply your coatings to the already Alochrome treated substrate.

Terry Hickling
Birmingham, United Kingdom
2007