Originally Posted by
superplum
Engines has given an excellent summary of the tech bits. What has not been mentioned throughout, is the diminution of the AAES technical knowledge across the plumbers' trade. That is partly the result of a more centralised, and/or contractorised, maintenance programme Does RAF Scampton have a seat bay (?), I believe not and the opportunities to gain such knowledge are few nowadays. Also, IIRC, on older design seats, the shackle bolt was shouldered and could not be over-tightened as such.
As you rightly say all the seats I serviced up to mk9 had shouldered bolts, incredible they should choose not to use them. Also in the days of seat bay that bolt was never touched as the shackle was release by firing off the barastat unit. Something that could not be done 1st line, hence the work around.