Comment by vdqtp3

The vast majority (or at least a very significant portion) of GA aircraft are from the 60s-70s. Plenty of 135 and even some 121 aircraft are old also (90s, 2000s, etc). The Lear that crashed in Philly was from 1982.

Upgrading to the latest avionics costs tens of thousands of dollars in the cheapest case. Multiply that times the number of aircraft, and the weeks or months it takes for the upgrade to be completed and you're talking about a staggering economic impact.