Tuesday, October 18, 2011

How Much Time Would You Let Pass After Loss of Communications Before Selecting Transponder Code 7600?

TWA Lockheed Constellation L-1049G with tip tanks

The subject of Loss of Communications Procedures is not an unusual one for discussion in the cockpit. In most discussions in which I took part, it was almost always related to and limited to total failure of the radio transceivers. In addition, it was assumed Instrument Meteorological Conditions were being experienced at the time of the failure.

In my more than 50 years of flying, I never gave any thought to the question of how long to wait until I select code 7600. This question was brought to mind by a story told by a fellow pilot. He was approaching Teterboro to land during a busy afternoon. ATC directed him to change frequencies to contact Teterboro Approach Control. Teterboro Approach was really busy and the he was unable to establish contact.

He said he just selected code 7600 on his transponder and was shortly thereafter in contact with a controller. I really liked this thoughtful approach and the initiative he used to solve the problem.

Loss of communications was an important factor in the mid-air collision in Brazil 4 years ago between an Embraer Legacy 600 and a GOL Airlines Boeing 737-800. (Both airplanes were brand new and had all the latest collision avoidance equipment installed. Both were in radar contact in Brazil's modern, up-to-date air traffic control system.) Yet, the collision occurred with the loss of 154 lives.

The loss of communications resulted from the pilots not receiving a correct change of frequency instruction. This is not an uncommon event for pilots. The Embraer pilots made numerous calls to re-establish radio contact over the next 57 minutes with no success . During this period of time the pilots did not change their transponder code to 7600. What period of time would you consider as a maximum before selecting code 7600?

Another significant factor in the Brazillian mid-air collision was the fact the Embraer pilots had turned off their transponder about and hour and fifteen minutes into their flight. As a result, the Traffic Alert and Collision Avoidance System (TCAS II) installed in both aircraft was not able to do its job. (TCAS II relies on an operating transponder to be installed and operating to function.) Had the Embraer pilots considered use of Loss of Communication Procedures earlier with the selection of code 7600, they probably would have recognized the transponder was turned off and turned it back on. This would than have permitted the TCAS II systems to provide Resolution Advisories to each pilot and prevent the accident from happening.

The main point of my post is to suggest to each of you to do some thinking about this aspect of Loss of Communications procedures. When are you going to select code 7600? After 3 minutes, 10 minutes or after 20 minutes have gone by?

Your comments are appreciated.

For additional information:


  1. Dick, first I would go through all checklists to ensure I can not fix the Communication Problem. If I can't, the I do the 7600. What's the right answer?


  2. I think each instance could be vastly different and therefore one cannot decide on a time-frame for a general application.


  3. Bo Giese

    I say that one cannot assign a universal time-frame. Each instance of communication loss could be vastly different, requiring different decisions.


  4. There is no way to put a universal time frame in place to activate code 7600. Each instance is usually vastly different and would influence a decision greatly.


  5. Having had the experience of radio failure. i did`nt think of anythink like a time period, was busy trying to solve the problem. Once I realised I could do nothing to rectify the problem, my next thoughts went to where could I land to have the radio checked. On going over my man chart to select the nearest alternate, i noticed a major Class "C' airport 40 miles approx from me, the class "D' where I was headed less than 15 and whom I was trying to contact , I decided to squak 7600. of course I made sure throuout the precess I kept the airplane under control, including scanning for any other traffic. Untill reading this article i did`nt put a time on the situation.