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Comment by smileysteve | Hacker News Reader

Re Delta

It's not so much a severity as "hard"; but with the hub and spoke model that Delta uses, scheduling being down (at all on Friday), combined with FAA hour limits. It becomes exponentially difficult to reschedule flights.

Put more plainly, on Friday, your scheduling software is down for 4 hours in the morning, so you "borrow" any replacements you need for employees that are late or sick. This ruins the availability for the next flights, at which time you hope the system is up again; but if it's not, you borrow from the evening flights. Combine this with each flight that was late/cancelled as you were hoping to fill now affects the hours available for the employees that were available. Finally, as you've cascaded this, you head into a weekend trying to catalog how many hours each crew member did or did not log, and you're not sure how to get them back in time.

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Except for Southwest the other legacy airlines (United, American) also use a hub and spoke model. So does jetBlue.

Funny you should mention WN. Delta's meltdown is the exact same scenario as Southwest. Crew scheduling is messed up, they don't have a way of tracking where employees are, if the employee is legal, etc and so the operation grinds to a halt

To clarify, Southwest's meltdown last year, which was all about the difficulties of crew scheduling and the knock-on effects of same.

wouldn't this imply either an upper bound on down time (airline simply folds as it never catches up) or an upper bound on the duration of the impact ?

Worst case, with good weather, you can stop service for a few days: day 1 mandatory rest; day 2 fly crews to where they need to be to start service; day 3 mandatory rest; day 4 return to service. Then start rebooking passengers and picking up the pieces. Carriers with long haul international may need longer, and maybe you need more rest days to ensure everyone is ready for their normal shift, but that's a reasonable napkin estimate.

Otoh, Delta seemed to have recovered after about a week, and canceled about 1,000 out of about 4,000 flights for several days. It's way better to fly 75% of the daily flights than not. There's less wiggle room in a summer schedule for weather, but there's still some wiggle room.

There probably is an upper bound on down time, by which point the business has suffered some irreparable harm. It might not result in the business simply folding, but might result in significant expense or legal complications, long-term reputational damage, etc. In business continuity speak, that's the "maximum tolerable downtime," and while I don't know how Delta defines it for the impacted systems... I imagine they're not happy with how long they were down.

They did a "reset." Cancel enough flights to reduce load, then manually recalibrate the crew tracking software to figure out where everyone is and their hours. Then start operations again.

It's like stopping your in-place manual software recovery efforts and restoring from backup. You KNOW it's going to take a massive amount of time, but at least you know how much time it's expected to take, and what the expected result is, rather than "2 more hours... 2 more hours.... 2 more hours.." for a week.

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