Update On The Crash In Brazil
As you may know, pilots -- like anxious passengers -- can be 'control freaks'. Of course that works to everyones benefit if being so focused on control ensures everything is done right.
So when pilots intentionally do something wrong, other pilots find that hard to understand. We don't yet know if the pilots of the Long Island-based business jet intentionally did something wrong or not. But that is what Brazilian authorities say may have happened. An investigation is underway to determine whether the device which both causes an airplane to be seen by radar and by anti-collision devices was turned off intentionally or simply failed.
The Transponder
The device which allows an airliner to be seen by radar and by other airliner's anti-collision equipment is called a 'transponder'. You may even have one in your car. Here in the New York area, we have EZ-Pass for paying tolls on bridges and the New Jersey Turnpike. The EZ-Pass device that is attached to your car is a transponder which sends a coded signal which identifies your car as you go through a toll booth.
Similarly, the transponder on an airplane sends a coded signal which is seen by both air traffic control and by the collision avoidance system on other airliners. Part of the information transmitted by the transponder is the plane's altitude.
With A Transponder Failure, The TCAS Should Still Work
If the transponder on the business jet had simply failed, the pilots would still have been able to see the transponder of the 737 on their radar scope, and their own anti-collision device would have warmed them automatically, in time to act, about being on a collision course with the 737.
Transponder And TCAS Are On The Same Switch
But if the transponder on the business jet had been intentionally turned off, the same switch that turns off the transponder also turns off the anti-collision device that would have allowed the pilots of the business jet to see the 737.
Brazilian authorities say the business jet's transponder was not operating. But had it simply been a failure of their transponder, their TCAS would have still seen the transponder signal from the 737, and alerted them of the impending collision with the 737.
Both Intentionally Turned Off?
It is because the business jet's pilots transponder was off AND their TCAS did not warm them about the 737 that leads the Brazilian authorities to believe the transponder of the business jet was off -- not due to an equipment failure -- but due to a deliberate act. If the transponder switch was turned off to hide the airplane's altitude from the air traffic control system, the TCAS would also have to be turned off.
Or, Dual Equipment Failure?
On the other hand, it is possible that the pilots did have the switch in the proper position (in which the transponder and the TCAS would be in the on position) but that both -- not just one -- failed.
So the investigation will attempt to determine whether this was a dual failure or an intentional act of switching both off.
But, Dual Failure, Plus Failure To Change Altitude?
The fact that the pilots continued to fly at 37,000 feet even though they were instructed to change to 36,000 feet makes it appear they deliberately disobeyed air traffic control instructions and turned off their transponder to keep it from giving information on their altitude to air traffic control (which it does automatically when operating).
If this is true, this is not just a matter of pilots making a mistake, but a criminal act.
There is a recent report at: http://www.cbsnews.com/stories/2006/10/04/world/main2061814.shtml.