table of contents other areas in which we do business . depending on the scope of such regulation , certain of our facilities and operations , or the operations of our suppliers , may be subject to additional operating and other permit requirements , potentially resulting in increased operating costs . future regulatory developments future regulatory developments and actions could affect operations and increase operating costs for the airline industry , including our airline subsidiaries . see part i , item 1a . risk factors 2013 201cif we are unable to obtain and maintain adequate facilities and infrastructure throughout our system and , at some airports , adequate slots , we may be unable to operate our existing flight schedule and to expand or change our route network in the future , which may have a material adverse impact on our operations , 201d 201cour business is subject to extensive government regulation , which may result in increases in our costs , disruptions to our operations , limits on our operating flexibility , reductions in the demand for air travel , and competitive disadvantages 201d and 201cwe are subject to many forms of environmental regulation and may incur substantial costs as a result 201d for additional information . employees and labor relations the airline business is labor intensive . in 2015 , salaries , wages and benefits were our largest expenses and represented approximately 31% ( 31 % ) of our operating expenses . the table below presents our approximate number of active full-time equivalent employees as of december 31 , 2015 . mainline operations wholly-owned regional carriers total .
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Mainline  Operations Wholly-owned  Regional Carriers Total
Pilots and Flight Crew Training Instructors 13,100 3,200 16,300
Flight Attendants 24,100 1,900 26,000
Maintenance personnel 14,400 1,800 16,200
Fleet Service personnel 16,100 3,200 19,300
Passenger Service personnel 16,500 7,100 23,600
Administrative and other 14,700 2,400 17,100
Total 98,900 19,600 118,500
mainline operations wholly-owned regional carriers total
pilots and flight crew training instructors 13100 3200 16300
flight attendants 24100 1900 26000
maintenance personnel 14400 1800 16200
fleet service personnel 16100 3200 19300
passenger service personnel 16500 7100 23600
administrative and other 14700 2400 17100
total 98900 19600 118500