Why are the minima for Cat A higher than for other categories at KSEA ILS 16L? I was looking at the KSEA ILS 16L approach (depicted below) and was wondering just why the minima are bumped up for Cat A aircraft (64 feet on both DA and HAT, as well as 200 feet of RVR).  Thing is, I've already checked Chapter 10 of the TERPS, and nothing in there says anything about approach-category-specific adjustments to ILS minima, nor does the Form 8260 for this approach say anything about the cause.  (This also makes the SA CAT I and CAT II/III procedures Cat A NA, which matters for aircraft that have a small aircraft CAT II ILS authorization IAW FSIMS 4.2.3.)  Furthermore, neither 16C nor 16R's ILS approaches have this feature, which is even stranger because you'd think that 16L and 16C are close enough together that their ILS OCSes would overlap, and they also use highly similar MAPs (climb to 900 on a heading, then intercept the SEA 161 radial, then proceed to TEBNE along that radial -- the only difference is the initial heading of 160 for 16C vs 165 for 16L).



What is doing this? Is there an obstacle there that is doing this only to small aircraft?  Is there some vagary of the TERPS I'm not finding? Is this an error?
The minima's are usually decided based on the Missed Approach procedure, which one of the criteria being obstacle clearance. I believe the answer lies in your question, its due to the heading course and altitude restriction on the MAP point. RWY 16L needs to climb straight 165 deg which puts you through the obstacle , whereas 16R Missed approach procedure heading can clear the '464' obstacle. . In either case Obstacle driving the change, Having CAT A with the lower speed in the heading of 165 deg it won't get you clear the obstacle. The PBN approaches are even marked higher for all aircraft type which can be inferred from other terminal charts.