The Class 66's brake flow indicator does not work like it does in real life-it seems to measure the rate of change in the front brake pipe reading, rather than measuring how much air is flowing in/out of the brake pipe. Now, usually that would not be too obvious. The brake flow goes up when you apply, goes up when you release-makes sense. BUT when you tell the brakes to hold position, the brake flow drops to 0...even if the brake pipe is still emptying out/filling up in the back of the train: On drag line (because an HST is the only way to see EOT brake pressure) I applied the brakes to full service, waited for the brake flow to drop to 0, then checked the HST cab (awkwardly so but oh well). As you can see, the HST end has not hit 3.5 bar yet, and the brake cylinders are only at 2 bar, not 4.5. Waiting a bit longer, the brake pipe at the end continues to empty. Now, if the brake flow indicator was reading brake flow, and not change in brake pipe, it would still be showing positive airflow as the air in the HST is flowing forward to the front to be released. It's definitely not doing that. And this does actually matter, because there is usually no way to see the rear brake pipe pressure in the UK, and the brake flow would be the only thing telling you if the brakes were still releasing/applying across the whole train [fun fact-that's why brake flow indicators were included on early US diesel locomotives. Once FREDs and HOTDs were invented, brake flow became redundant but still is often included in instruments] but...right now it only tells you if brakes are applying/releasing at the front-which makes it useless.
