There are many kinds of land-air communication means on the plane (note that communication is not communication), such as VHF, HF, satellite phone, ACARS (Aircraft Communication Addressing Reporting System), CPDLC (Controller Pilot Data Link), transponder, ADS-B (Automatic Correlation Monitoring-Broadcasting) and so on.
In case of emergency, any available equipment, including mobile phone, car wifi, etc., can be used as a means of communication.
On the other hand, 3u8633, due to the broken windshield, the wind noise is too loud, so I can't hear anything, and the speech is also noise, so the voice communication means are all invalid. So VHF, HF, satellite phones, including mobile phones, are not available.
The remaining means of communication, the A3 19 plane of Sichuan Airlines does not have on-board wifi, so it cannot access the Internet.
I'm not sure whether Sichuan Airlines can choose CPDLC. ACARS is definitely available, but both of these communication methods need pilot typing control or scheduling for communication, which is inefficient, time-tight, and there is not much energy to spare for this work.
ADS-B most aircraft only have the sending function (ADS-B-OUT) and no receiving function (ADS-B-IN), which means that the controller can see the data of the aircraft, but the aircraft can't receive the information, so this method is not available. Only the answering machine is left.
The crew will inform the controller of the current distress situation and set the answering machine code to 7700, which can inform the controller at the first time and the action is very simple. The controller can respond immediately after receiving the signal, just like in the movie.
Repeater coding
This code will be displayed on the auxiliary radar screen of the controller. By assigning the transponder code, the controller can distinguish the aircraft within the control range.
Among the answering machine codes of 0000-7777, some are of special significance, among which three are more important: 7500 hijacking, 7600 communication failure and 7700 emergency. In these three cases, the pilot is unable or inconvenient to communicate directly with the ground, and the crew informs the relevant information through special transponder codes. Answering machine coding can transmit limited information.
In the movie, Flight 7700 has achieved the purpose of the crew. Subsequent changes to the codes of other transceivers will be counterproductive.