STUCK MIKE

STUCK MIKE AND OTHER STORIES
A popular story on TV and radio channels today is the accidental transmission of a vicious monolog by a Southwest pilot about his cabin crew.
This is not as unusual as one might think. In my 34 year flying career, I have often heard snippets of private conversation over the airwaves. All it takes is some inadvertent pressure by the pilot on the control column transmit trigger or leaning on one of the many radio selector boxes.
What is not asked in the media is why the controller was unable to successfully warn the gabby pilot he was on the air. The answer to that question has much more serious consequences than an anti gay rant.
In the main frequency range used for air traffic control (VHF), only one radio set can transmit at a time. All the other transmissions are blocked out until the first radio ceases to transmit. This is amazing when you realize dozens of aircraft may be controlled and need to respond on one frequency. If you listen to tapes of air traffic control at any busy airport, you can periodically hear a loud humming noise instead of speech. This is someone trying to talk while another radio is still transmitting. It is called a double transmission or someone is “stepped on” or “blocked” and the whole previous instruction will have to be repeated. Only a high level of radio discipline by ATC and pilots keeps the unwieldy system functioning.
Why does this matter to anyone? Because sometimes a vital instruction or clearance may be lost without anyone realizing a transmission was stepped on. This was the case in the Tenerife disaster where two Boeing 747’s collided on the runway in foggy conditions. There is evidence that vital information about one aircrafts position was lost in a dual transmission and was never repeated. This led the other pilots to believe the runway was clear and they began their take off roll while the first jet was still taxiing on the runway.
I have listened to the ATC tapes of the recent Egyptair / Lufthansa incident at JFK airport. Egyptair made an unauthorized runway incursion forcing the Lufthansa to reject their take off. The ultimate responsibility always rests with the pilots but the ATC instructions to the Egyptair were frequently blocked by other transmissions. This can cause pilots whose first language might not be English to misunderstand or try to interpret their clearance and may have contributed to the near disaster.
There is technical equipment available which can solve the signal blocking problem but it is deemed an unnecessary expense as the system generally works well without it. I wonder if the passengers on the doomed Tenerife jumbos or the offended Southwest cabin staff would agree?