Some authorities use a type of check, known as a 3C check or Intermediate Layover (IL), which typically includes light structural maintenance, including checks for corrosion, or on specific high-load parts of the airframe.[7] The 3C check may also be used as the opportunity for cabin upgrades, e.g. new seats, entertainment systems, carpeting. This shortens the time the aircraft is out of service, by performing two distinct tasks simultaneously. As component reliability has improved, some MROs now spread the workload across several C checks, or incorporate this 3C check into D checks instead.[2]