Delta currently has 2 A350-900's sitting at MSP (now for over 2 weeks). These are the first 2 that were delivered to DL (N501DN and N502DN). These were delivered in 2019-June/July time-frame (almost exactly 3 years ago). I looked at a few sites about this type of aircraft to determine when "checks" are to occur - "C-checks" are from 18 to 36 months apart (depending upon the airline company). Based on these criteria, am I way off base on this is what is going on with these 2 aircraft at MSP? My original thinking was that they were having C+ seats added (which will need to happen eventually to all 13) and / or installing additional fuel tank(s) to handle the ATL-JNB (via CPT on the west bound trip) for the extended distance: the current 13 DL A359's cannot make this leg. This round-trip is scheduled to be converted on 2020-October 24 (according to the companies current online schedule). For the daily service, there needs to be 2 frames, 1 would be able to do the route 3 times a week. But what I have read in this and other blogs, is that ATL-JNB is a very popular route and most of the times it goes each way 100% full. The current A359 DL online schedule works for the remainder of the year without having any additional A359's being delivered. But as the B777-200's get retired within this year, DL will need to readjust some of the upcoming A359 schedule or at least 4 additional frames will need to be delivered: (current online schedule shows 777 to 359 swaps on 2021-January-01 {place-holders, I know}: LAX-HND, ATL-PVG, LAX-PVG, LAX-SYD, and JFK-BOM). JFK-BOM continues to show B777-200LR through 2021-May-15.