Ross Aimer, a retired United Airlines pilot and former 777 instructor, said it is possible that one pilot could reach up and turn off the transponder without the other pilot seeing it, say if one was looking away or distracted.
If the plane was in contact with an air traffic controller, the controller would alert the pilots that the transponder signal had been lost. But, Aimer — now head of Aero Consulting Experts — said, if they were not in contact with an air traffic controller, a pilot might miss it if the other shut down the transponder.
In the case of the missing Malaysian plane, even pilots are a bit puzzled by somebody turning off the transponder.
John Gadzinski, a Boeing 737 captain, said that among fellow pilots “there is a raised eyebrow like Spock on ‘Star Trek’ — you just sit there and go, ‘why would anybody do that?’”