Flightlover, I wanted to reply in a bit more structured way, which was not possible from my cell phone, so here we go...
flightlover wrote:A: wasn't track 27A used by the old 'amsterdammer' before they dug a tunnel from Anterp central station? At least after the detour he made between Berchem and Antwerp central?
Before the works at the Central Station started and the train still called there, the Amsterdammer used line 12 (the one close to the city centre).
During the works, when it didn't call there, they used line 27A (the one away from the city) upto Antwerpen Oost and switched there to line 12. Maybe sometimes they switched even further.
Line 27 A starts already in Mortsel, at Y Liersesteenweg, where it splits from line 27. Line 15 terminates there as well.
As already posted: 27 goes to Berchem and the Central Station (pax traffic from 27 and 15) and line 27A goes to Berchem, Antwerpen Oost and the harbor (freight traffic from 27 and 15).
flightlover wrote:B: There are a whole series of switches in between mortsel -> Berchem and Berchem -> Antwerp central. So, although it migh take a bit longer, it must be perfectly feasible to create a path to Antwerp central.
Crossing tracks in railway world is like intersecting runways in aviation world: it greatly reduces capacity and leads to delays. But in railway world there's a solution: a flyover!
A flyover has been foreseen so that Northbound train from line 15 can go to line 27A without crossing the Southbound track of line 27A. But nothing extra has been foreseen at Berchem, so chances that trains will call at the airport on line 27A are very limited. And as already posted: politically it'll be very difficult as long as the CRL railway station hasn't been built.
Cheers,
Stij