Last week, a KLM Boeing 777-200 plane performing flight KL-702 from Buenos Aires to Amsterdam experienced transponder problems mid-flight. The plane landed safely in Amsterdam and was grounded for five hours. However, it then departed to perform the return flight to Costa Rica but was forced to return to Amsterdam when the same issue occurred within minutes of departure.
The first incident took place mid-flight, just southwest of Cape Verde. The crew found the transponder suddenly stopped transmitting altitude information. According to reports, both Mode-S and Mode-C stopped working while everything else appeared to be functioning normally. However, the plane continued on its route and landed in Amsterdam on time, six hours after the transponder stopped functioning properly.
The plane, registration PH-BQE, was grounded for around five hours before returning to service for a flight from Amsterdam to San Jose, Costa Rica.
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A second incident
According to the Aviation Herald, the crew on the return flight were not aware of the transponder’s previous issues. The crew performed the standard checks during departure when they found the transponder was not transmitting altitude information. However, as with the previous issue, the transponder was transmitting other information.
While the crew performed additional checks to solve the issue, the plane continued to climb out of Amsterdam airport. However, air traffic controllers advised the crew that the plane could not continue on its current flight path as it would pass through UK airspace; the UK authorities would not allow any plane without a functioning transponder. Consequently, the plane returned to Amsterdam after an hour in the sky.
KLM then secured a second Boeing 777-200, registration PH-BQC, which took all passengers on to San Jose. The delay was just under three and a half hours. It is still unclear why the crew on the second flight were not aware of the issues before departing.
Transponder failures
In these incidents, both Mode-C and Mode-S failed. These are both common transponder failures with the other most common type of failure is Mode-A, which is the aircraft identifier code. While a transponder failure isn’t as immediately life-threatening as other situations, it can cause Air Traffic Control problems.
Air traffic Control uses transponders’ information to keep track of all aircraft in the sky and on the ground. It’s also how websites such as FlightRadar24.com generate their maps.
Skybrary.aero reports that the main problem resulting from transponder failure relates to collision avoidance and aircraft separation. Additionally, aircraft misidentification can result in clearances being given to the wrong aircraft or infringement on airspaces. In some cases, it can also result in a loss of radio contact if the crew does not request a change of frequency.
Aircraft must have a functioning Mode-C or Mode-S transponder when entering busy airspace or passing close to a busy airport. The EU also requires that all general air traffic have Mode-S transponders.
Communicating with Air Traffic control on the ground is vital for ensuring safety and proper procedure, which is why a functioning transponder is legally required. The fact that KLM managed to fly for six hours without a properly functioning transponder is remarkable.
What do you think of the two incidents? We’d love to hear your opinions in the comments.
