Today's aircraft possess higher levels of performance and capability than their predecessors because of the force multiplier of technology. Advanced communications, guidance and navigation played key roles in the victory of the United Nations coalition forces in the Gulf War. Along with the successes came important lessons learned where additional capability could have been used. The use of advanced technology is essential to meeting the mission requirements of present as well as future aircraft. Modular avionics are being introduced into next generation aircraft, such as the Air Force F-22 Advanced Tactical Fighter (ATF), the Navy Advanced Medium Attack Aircraft (AX) and the Army Light Helicopter (LH), as the means of achieving higher levels of performance, including reduced volume and improved adaptability, maintainability, and expandability. The reduction in military spending may result in a stretch out of these programs, delaying their availability. This will require that aircraft presently in inventory remain in service beyond their original design lifetime. These platforms must also continue to improve their capability if they are to cope with the threats of the 21st century. Therefore, it is important to apply technology improvements like modular avionics to existing aircraft. The government has started this effort through the establishment of the Modular Avionics System Architecture (MASA) program, created to promote the retrofit application of modular concepts to government program managers and industry avionics suppliers through study programs, sponsorship of public forums and establishment of a Modular Avionics Handbook.The purpose of this paper is to aid the application of modular avionics to today's aircraft. It discusses the status of present modular avionics standards and identifies several areas throughout the equipment life cycle where traditional approaches must be reexamined.