FAA History Lesson -- March 1

From the FAA Historical Chronology, 1926-1996...

”Oct 15, 1960-Mar 1, 1961: FAA successfully tested positive control on an area basis, as distinguished from a route basis (see May 28, 1958 and Apr 6, 1961), in Operation Pathfinder. As a result, area positive control was continued as a regular service in the location used for the test: airspace between the altitudes of 24,000 and 35,000 feet overlying 120,000 square miles surrounding FAA's air route traffic control centers at Chicago and Indianapolis. Any aircraft entering this airspace, whether on or off the airways, were required to be equipped with (1) a radio permitting direct communication with controllers at the centers, and (2) a radar beacon transponder for identifying the aircraft, independently of voice communications, on the controllers' radarscopes. In addition, such aircraft were required to fly on instruments regardless of weather, remaining under control of the centers while in the positive control area. Under these conditions of constant radar surveillance, aircraft required as little as half the standard separation interval.

The launching of Operation Pathfinder was preceded by more than a year of special preparations at the Chicago and Indianapolis centers--including intensive controller training, installation of additional radar and communications equipment, development of air traffic control procedures and phraseology, and an exhaustive analysis of the program through simulation studies. “

To this day, the most common altitude boundary for air traffic control sectors is 24,000 -- or Flight Level 240 (FL240) as controllers would say. From the ground to FL230 is the “low” altitude sectors, FL240 to FL340 is the “high” sectors and FL350 to FL600 is the “ultra-high” sectors.

(English majors feel free to comment)

And just to show how things change...

Regulations used to require 2,000 feet of separation above Flight Level 290 (29,000 feet.) The assignable altitudes above FL290 were: FL310, 330, 350, 370, etc. With the advent of RVSM (Reduced Vertical Separation Minima) the “even” altitudes (FL300, 320, 340,360, etc.) became usable. Because of the lack of guidance at the FAA, some facilities put FL340 in the “ultra-high” altitude stratum and some put FL340 in the “high” altitude stratum. Unfortunately, many Letters of Agreement (LOAs) between facilities designate coordination requirements by altitude stratums.

This problem hadn’t been addressed fully when I left the FAA and I wonder if it still exists. I’m sure someone will let me know.

Don Brown
March 1, 2008