As I mentioned in another thread - the issue is with the ongoing back and forth with the pilot group. Basically, both the pilots and the company are exercising contractual loopholes that have crippled the company's ability to staff trips that become open with less than 18 hours to departure.

Ironically, it started when the company introduced some new software to try and improve the situation. Several years back, the company introduced a 3rd party crew staffing app (ARCOS) to help automate some crew scheduling processes. Prior to this software, the last minute overtime coverage ("Green Slips" / double pay) was done manually by a crew scheduler and if they got the pilot on the phone, the trip was theirs. With this software, the company could contact pilots in groups ("batch sizes") instead of 1 at a time. This created situations where pilots would be woken in the middle of the night to acknowledge a trip that they in fact would not be given because 10 pilots had been called, but only the senior pilot who acknowledges gets the trip. So, they negotiated an option to "auto-accept" a trip which would then give them a 12 minute window to contact the company and acknowledge the trip. Eventually the company decided that they didn't want batch sizes and ALPA essentially gave away batch size limits for free (a controversial move). Now that the company could call everyone at once, this created more nuisance calls in the night which drove up the use of the auto-accept feature. More recently, they negotiated to also have this same app be used for normal last minute pickups ("White Slips" / standard pay).

Because of the increase in auto-accept and reduced staffing in crew scheduling, the company found they were having trouble staffing flights. So, they turned to a previously obscure and little used function in the contract called 23M7 which allows them to skip all of the coverage steps (the app) and simply award a trip to anyone they can get on the phone ("Inverse Assignment"). In order to do this, they pay the pilot who flies the trip 2x pay and then they have to identify a "harmed" pilot who was skipped over (since they skipped the app) and pay them 1x pay. It costs Delta 3x to staff trips this way, but it eliminates all the steps that are normally followed - making it much easier for a crew scheduler to get the trip covered. The proliferation of this method of staffing has created an even greater use of the "auto-accept" feature of the app because a pilot has to have this feature turned on in order to potentially become the 23M7 "harmed pilot" and get 1x pay without having to fly.

So, let's say a trip needs a new captain 12 hours before departure. They will begin to ask pilots through the app if they want the trip, but imagine in a large base (ATL 320) that 200 pilots have "auto-accept" turned on. That means that each of them has 12 minutes successively to acknowledge the trip. As you can see, the math doesn't math and they then have to go into the emergency coverage step / 23M7. All of that is a manual process though and they have staffed the department at a level that expected / anticipated automation.

Weather may be the initial cause of why a flight needs new pilots, but make no mistake - the reason they are cancelling like this is because of this contractual catch-22 they find themselves in. There is of course a great amount of finger pointing behind the scenes about who's fault it is - good arguments on both sides.

In the end though, it is the passengers who suffer.