Several years ago a class C tower controller chided a student I was instructing for mistakenly squawking altitude while taxing, remarking that doing so "cluttered up" his screen. Recently an astute reader pointed out a change to transponder operation procedure contained in the February 2012 Aeronautical Information Manual 4-1-20, to wit:
Civil and military transponders should be turned to the “on" or normal altitude reporting position prior to moving on the airport surface to ensure the aircraft is visible to ATC surveillance systems.This is a significant change from the previous procedure of keeping the transponder in "stand by" mode and squawking "altitude" just before departure. If you're operating an aircraft with a transponder that provides a "gnd" or "ground" mode, my understanding is that mode meets the new requirement.
The motivation for this change would seem to be to prepare pilots and controllers for the deployment of ground surveillance systems, current and future (NextGen/ADS-B). But there might be some problems and here's why.
ATC Not up to Speed
After learning this change had taken effect, I queried two different ground controller (one class C in northern CA and on class D in southern CA). I was startled to hear that neither controller had heard anything about the change nor had they been briefed on it. This leaves dilligent pilots and instructors in an odd position: Should they adopt and teach the new procedure or not? I'd be interested in hearing from other tower or ground controllers on their experiences.
Traffic System Conflicts
The other issue has to do with TIS and other traffic alerting systems (TAS) installed in aircraft. For instance, my initial experience in Cirrus aircraft several year ago revealed an annoying problem: All it took was a pilot holding short with their transponder turned on and the cockpit would be flooded with enough aural traffic alerts to drown out all other radio communications. Thank goodness newer aircraft with TAS have a mute function. TIS-equipped aircraft can suffer from the same issue, barking "TRAFFIC" at inoportune times. G1000 aircraft provide a means to turn off traffic, but this isn't the best use of time in single-pilot operations.
Being a tech nerd who's had my share of close encounters during ground operations, I'm all for technological solutions. What should a pilot do if instructed to taxi before being assigned a squawk code? In these cases I'm planning to set the transponder code to 1200 set the mode to "on." It may take some time to work out the wrinkles and get the FAA, ATC, pilots, and aircraft equipment working toward the same goal.