The official word is down 23 airframes for some portion of 2017. Most likely the draw down of -300's would take place after the busy summer schedule and then flexed back up before summer 2018. They are adding 67 aircraft in 2017 and currently there are 78 -300's in the fleet which are now scheduled for retirement by third quarter 2017.

Long story short, there most likely will be a steady need for pilots to compensate for retirements and attrition. A short term loss of 23 airframes most likely will not deter hiring because the staffing model is predicated on flying the busy summer schedule and that schedule will most likely not be effected by the short term drop in fleet totals. The fleet is reported to be at 730 to 750 in 2018.







"This year and next, the Dallas-based carrier plans to boost deliveries, in part to compensate for the previously announced early retirement of about 50 older-version 737s by 2017. It will add 67 planes in 2017, compared with the previously envisioned 61. Some of the additional planes are used 737-700s Southwest has found on the market at good prices. Others are new 737-800s it had on firm order and the third tranche, starting next year, are Boeing’s new-engined version of the 737, the Max-8."

"The deferral of 67 firm deliveries over the next several years supports the goal of 2% annual net fleet growth."

"Southwest, which flies only variants of Boeing 737s, expects to end this year with 723 planes in its fleet, a number that will dip to 700 in 2017 before rising again to between 730 and 750 aircraft in 2018."

Southwest Airlines Revamps Aircraft Order Book - WSJ