Radio Management Unit (RMU)
Transponder Status Indication
Primary Flight Display (PFD) TCAS FAIL Indication
The single item that could most likely be determined as a primary cause of this accident was the fact the transponder was not operating at the time of the collision. As a result, the Traffic Alert and Collision Avoidance Systems (TCAS II) with which both aircraft were equipped was not able to alert either crew of a possible collision.
There are several conspicuous indications of the TCAS/Transponder status in the aircraft instrument panel – eight visible indications in all, with two in the RMUs, two in the PFDs and another two in the MFDs (when the MFD was set to display TCAS), and the blinking amber transponder reply light in the “ATC window” boxes on both RMUs.
The Brazilian Crash investigation was unable to discover why it was not turned on even though considerable resources were expended. A special ergonomics committee was established to see if there was the possibility of a leg or foot movement that could accidentally turn off the transponder.
One positive result of that study discovered that not enough consideration had been spent to make the on/off status of the transponder clearly displayed to the crew under all lighting conditions.
The authors of the Brazilian Air Force Accident Report, a 268 page .pdf document failed to even mention two very important points. The first one they missed was the failure of either crew to apply the principle of randomness in their aircraft's track.
The concept of randomness is recognized in the form of the Strategic Lateral Offset Procedure (SLOP). SLOP is in use today and much of the world's airspace, especially the non-radar coverage oceanic airspace as well as in Africa and in China while in radar contact with ATC's approval.
See this Blog's post entitled "Randomness is good!" posted in January of 2010.
They also failed to mention the value of a third cockpit crew member. Without a doubt, the ideal size of an aircraft's crew is three. (I recognize I may be beating a "dead horse" when bringing up the subject of minimum cockpit crew size of three. Today's trend of automating and remotely controlling aircraft is a move to decrease the size of the crew to one and even to completely eliminating the crew.)
If a third crew member had been on board each aircraft, there is increased opportunity for enhanced safety in operations. The richness of the intellectual results of three pilots working together far exceed the results of just two pilots working together.
Since the advent of two man crews in the early seventies, this consideration has been dropped and not ever mentioned in National Transportation Safety Board (NTSB) accident investigation reports. The subject of possible three man crews is a taboo subject.