Limited carry out line maintenance. Line maintenance services include routine servicing of aircraft performed during normal turnaround periods and regularly scheduled layover periods. Base maintenance covers all airframe maintenance services and for this HAECO has a three-bay hangar, which can accommodate up to three Boeing 747-400 aircraft and two Airbus A320 aircraft, and an adjoining support workshop. HAECO also has the world's largest mobile hangar, weighing over 400 tons. It can be used to enclose half of a wide-body aeroplane so that the whole facility can fully enclose four 747s when the mobile hangar is used. On 29 May 2009, CASL opened its first aircraft maintenance hangar in the maintenance area of the airport. The new hangar occupies an area of about and can accommodate one wide-body and one narrow-body aircraft at the same time; the hangar also has an about area in its annexe building. CASL specialises in Airbus A320 family and Boeing 737 Next Generation series heavy maintenance. Airport based ground services The Air Traffic Control Complex (ATCX), located at the centre of the airfield, is the nerve centre of the entire air traffic control system. Some 370 air traffic controllers and supporting staff work around the clock to provide air traffic control services for the Hong Kong Flight Information Region (FIR). At the Air Traffic Control Tower, controllers provide 24-hour aerodrome control services to aircraft operating at the airport. A backup Air Traffic Control Centre/Tower constructed to the north of the ATCX is available for operational use in the event normal services provided in the ATCX are disrupted by unforeseen circumstances. Apart from serving as an operational backup, the facilities are also used for air traffic control training. The Airport Meteorological Office (AMO) of the Hong Kong Observatory (HKO) provides weather services for the aviation community. The AMO issues alerts of low-level windshear and turbulence. Windshear detection is made using traditional doppler weather radars as well as the more effective doppler LIDAR, of which Hong Kong International Airport was the first to introduce. Doppler LIDAR systems use lasers to detect windshear and wind direction even when atmospheric conditions are too dry for Doppler radar to work. Fire and rescue services Rescue and fire fighting services within the airport are covered by the Airport Fire Contingent of the Hong Kong Fire Services Department. The contingent has 282 members, operating three fire stations and two rescue berths for 24-hour