This is an excellent article on interoperability issues for public safety and the creation of FirstNet.

On September 11, 2001, just a few minutes after the South Tower of the World Trade Cen­ter col­lapsed, a po­lice heli­copter pi­lot circ­ling the re­main­ing tower re­por­ted that the top 15 floors were “glow­ing red” and said he be­lieved the build­ing would soon im­plode. Four minutes later, an­oth­er heli­copter pi­lot also warned that he didn’t think the second tower could last much longer. Most of the po­lice of­ficers in the North Tower heard those warn­ings and were able to evac­u­ate. But that in­form­a­tion nev­er reached fire­fight­ers, for a simple reas­on: Ra­dio sys­tems for the Fire De­part­ment, the Po­lice De­part­ment, and the Port Au­thor­ity Po­lice were all in­com­pat­ible with each oth­er. 

http://www.routefifty.com/2015/09/police-firefighter-emergency-communications/121634/