KL691/YYZ, but also KL605/SFO, are currently some of the most delay-sensitive flights. The reason is that these flights are operated by the full passenger B744, of which KLM is only operating 5 units, and which are all very heavily scheduled during the current peak season. The smallest technical problem can, as such have very serious consequences for the on time performance of B744 operated flights because there is virtually no spare capacity available in the system.

Yesterday KL691 had yet another long delay, and the only reason that the flight is operating on time today is that it has been downgraded to a B74E combi aircraft (resulting in massive overbookings). Because of yesterday's delay, today's KL605/SFO is still running almost 4 hours behind schedule. Meanwhile, another B744 broke down in KUL, which will undoubtedly impact tomorrow's B744 operation.