The cost to change one line of code on a piece of avionics equipment is #1 Million , and it takes a year to implement.

The cost to change one line of code on a piece of avionics equipment is $1 million, and it takes a year to implement. For Southwest Airlines, whose fleet is based on Boeing’s 737, it would “bankrupt” them if a cyber vulnerability was specific to systems on board 737s, he said, adding that other airlines that fly 737s would also see their earnings hurt. Hickey said newer models of 737s and other aircraft, like Boeing’s 787 and the Airbus Group A350, have been designed with security in mind, but that legacy aircraft, which make up more than 90% of the commercial planes in the sky, don’t have these protections.


For More:
http://www.aviationtoday.com/2017/11/08/boeing-757-testing-shows-airplanes-vulnerable-hacking-dhs-says/