ARINC 653 (Avionics Application Software Standard Interface) is a software specification for space and time partitioning in safety-critical avionics real-time operating systems (RTOS). It allows the hosting of multiple applications of different software levels on the same hardware in the context of an integrated modular avionics architecture.

It is part of ARINC 600-Series Standards for Digital Aircraft & Flight Simulators.

In order to decouple the real-time operating system platform from the application software, ARINC 653 defines an API called APplication EXecutive (APEX).

Each application software is called a partition and has its own memory space. It also has a dedicated time slot allocated by the APEX API. Within each partition, multitasking is allowed. The APEX API provides services to manage partitions, processes and timing, as well as partition/process communication and error handling. The partitioning environment can be implemented by using a hypervisor to map partitions to virtual machines, but this is not required.

The standard is overseen by the AEEC APEX Subcommittee[1], which is co-chaired by representatives from Airbus and Boeing. Gordon Putsche was the Boeing chair from 2002 until 2023. Steven H. VanderLeest is the current Boeing chair. Pierre Gabrilot is the current Airbus chair.

The initial version of ARINC 653 was published on October 10, 1996.

Supplement 1 was published in January 1997 and introduced the concepts of APEX and Time and Space partitioning.

Supplement 2 was published in 3 parts between March 2006 and January 2007: