It's a problem on high spec knitting as well. At high speeds the first pantograph will set a wave in motion in the contact wire and that means the second panto may struggle to stay in contact with the wire. TGVs on high speed lines will only have the rear power car's pantograph raised, the front being fed by the rooftop bus line. Eurostars are long enough for the initial wave to dissipate but you'll still see a lot of sparking from the rear powercar. 395s in multiple will use the Front on the leading unit and Rear on the trailing to put as much space as possible between them...
What happens with Pendolinos then ? do they only raise one pantograph as well ?, if not - what has changed since APT ?
Are such limitations common, as in many EMUs have two pantographs, especially when operating in multiple (e.g. Thameslink, Electrostars and Desiros) - and I'm sure I've seen them running with both up ?
Couple of questions;
a) Why was ATP 12 cars (2 central power plus 2 end driving/passenger and 8 other passenger) ?, given that it is only literally now that we are seeing that length of train & capacity on the WCML ?
b) Could an ATP with a single power/driving car (as per ECML 225 arrangement) have pulled that many trailers ?, or sufficient for a WCML service replacing 8X and Mk2s as was.
It strikes me that these High Speed BR plans suffered from the classic British overstretch, 155mph for instance, on infrastructure that despite vast sums of money and technological progress, 30 years later still limits trains to 125mph, suggesting that whatever a view of the management/efficiency of the spend, there are underlying issues about trying to raise speeds to such levels. Was there a disconnection between the idealists who were specifying the trains (and what the technology could deliver in pure train speed) - and the reality of actually operating them ? The reference to the Operating Authorities not permitting ATP to run at full speed with limits on paths suggests that such speeds weren't able to sensibly be accommodated within the network.
HST seems a much more evolutionary approach, building on top/tail and push/pull concepts that long pre-dated it, hence perhaps it's success rather than the revolutionary ATP.
Very interesting to read about the changes from ATP as we know it to what would have been a production version.