Singapore Airport Terminal Services is a company that provides ground services, such as passenger check in, meal catering, aircraft cleaning, etc, for various airlines, mainly at the Singapore airport but also at other locations through subsidiary companies it invested in. A somewhat outdated map is given below - there have been additional units acquired recently

SATS used to be a subsidiary of Singapore Airlines, which is also SATS's biggest customer; in 2005 Lee Kuan Yew himself suggested that SIA should divest SATS and SIA Engineering, which provides aircraft engineering maintenance, again with SIA as the largest customer but also to other airlines in Singapore and other locations. This is presumably to free SIA from certain issues of conflict of interest, as well as to allow the three companies to undertake international expansions without being constrained by group planning. In 2010 SIA finally took the step of distributing its SATS shares to its own shareholders, who now own SATS directly rather than through SIA; there however have been no announcement regarding SIA Engineering.

However, in a new twist, SIA Engineering has put in a bid to enter the ground servicing business too, by bidding for a third ground handling license being offered by the Singapore Airport Authority. This license was originally awarded to a swiss operator (the second license is held by CIAS Changi International Airport Services, which started as a government owned corporation but was divested to owners from middle east some years ago) which however decided to withdraw after finding profitability elusive. If SIA Engineering succeeds in getting the license and then starts getting some of the SIA business (from SIA itself, subsidiary Silk Air, partially owned Tiger Airways, etc) then we are back to the situation of SIA having its ground servicing and aircraft maintenance done by its own subsidiaries. It shows how difficult it is to change one's familiar practice.