What retirements? IBT site shows 31 for this year. More than covered by the class of 18 followed, by the class of 24, 24, 24... Not to mention all the hiring before that.
As for attrition, I suppose it depends on your reference point. Hiring in 2012 to Apr 13 was pretty steady then it dried up with only 2 small classes the rest of the year after Apr 22nd, Until Feb 14 and it's been pretty steady since. When I started in Feb 14 we had around 1000 +/- a few so we have gained a little since then. The company's annual report lists 959 pilots as of 31 Dec 13. So in their eyes I guess the company is a net 85 since that point. So I guess it depends on your point of reference as to gains/losses.
Annual report reference, pg. 11...
Employees
Our business depends on highly qualified management, operations and flight personnel. As a percentage of our consolidated operating expenses, salaries, wages and benefits accounted for approximately 20.3% in 2013, 20.7% in 2012 and 21.0% in 2011. As of December 31, 2013, we had 1,792 employees, 959 of whom were pilots. We maintain a comprehensive training program for our pilots in compliance with FAA requirements, in which each pilot regularly attends recurrent training programs.