On Oct 18 I flew AC 837 from MAD to YYZ. As we were taxiing towards take-off, the SD announced that ALL the toilets on the left side of the plane would be inoperative, and to please use those on the right-hand side.

Normally 31C/H involve the tradeoff of being the only economy seats with decent legroom on the 787, but having people line-up for the toilet in front of you. 31C lucked out on this flight. I, seated in 31H, spent the entire 8 hours looking at other passengers' butts planted not two inches from my nose. Not my idea of in-flight entertainment. The poor sods in 31 DEF had to put up with a steady stream of people crossing from the left to the right side of the plane and back. Needless to say, after a couple of hours all toilets were a stinky mess.

Clearly the situation was known before takeoff, and a decision was made to fly anyways. And I appreciate that we got to YYZ on time. But at what point must the airline call a flight off? Is there an equation of flight length / number of operative toilets / load that must be followed? Nothing extreme happened on this particular flight, but it would only have taken one or two passengers with GI issues (I have been that passenger) for things to quickly become unmanageable.