What are the technical details of how airline seats are installed on an airliner? The step by step. Not made how they are installed.
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Economy seats are removed (and installed) row by row. The row of seats (typically 2 - 5 individual seats) are bolted to a track on the airframe floor. You can see them being removed in this video (~18:30) during a D-Check. The rows are usually held in place with bolts, often in the corners and where seats meet. You can see an example bolt pattern here.
Modern First class seats (the more sophisticated individual ones) will be removed one at a time often with the whole entertainment center around them. The above linked video also shows this.
And, of course, installation is the reverse of removal.
On most western jets, there are seat-tracks where the seats are fitted. The tracks are fixed to the floor beams and while the seats are fixed to this track, they are not rigidly fixed. This is to allow slight movement when the aircraft flexes. If they were rigidly fixed they would cause localized stress which is undesirable. In fact most of the stuff in the aircraft is not fixed rigidly to the airframe .. Overhead racks and bulkheads included.
The part on of the seat which interfaces with the rack has a circular part which corresponds to a cut-out in the seat-track. You fit this part in and then slide it so that its in between two cutouts. A bolt is then used to prevent further movement.
Similar tracks are used on aircraft ULDs (containers and pallets).