In the case of UPS Airlines Flight 6, they did send a message out to air traffic control, but only by relaying messages via nearby aircraft.
> The thick smoke required the pilots to communicate with nearby planes over VHF to relay messages to Bahrain ATC, as Bell was unable to see the radio through the smoke.
Given that whatever happened to MH370 occurred during an ATC handover (similar to UPS Airlines Flight 6), it's not hard to believe that the following scenario occurred:
* Shortly after the handover from Kuala Lumpur ATC to Ho Chi Minh ATC the crew realise there is a fire on the aircraft
* The pilot-in-command focuses on navigating to the alternate, while the pilot-observing runs through the fire checklist
* As they transit away from Ho Chi Minh ATC they lose range of the signal
* They don't prioritise switching ATC because they're still quite far away from their alternate and they are busily trying to get the fire under control
* Smoke enters the cockpit at this time and hinders their ability to operate the radio equipment
* They either lose track of the alternate because they are distracted by the fire or determine they can't land till the fire is under control (possibly because they cannot contact ATC), so they end up flying across Malaysia
* They eventually realise their error and attempt to turn back, but by this point oxygen in the cabin has depleted and they are unable to complete the maneuver
These sorts of things can happen, the three-person crew of Eastern Air Lines Flight 401 were so distracted debugging a faulty light bulb that they didn't notice the autopilot disengaging and their plane slowly losing altitude before crashing. I imagine had the CVR not survived, people might be speculating that a member of that crew may have purposely crashed it.
> The thick smoke required the pilots to communicate with nearby planes over VHF to relay messages to Bahrain ATC, as Bell was unable to see the radio through the smoke.
https://en.wikipedia.org/wiki/UPS_Airlines_Flight_6
Given that whatever happened to MH370 occurred during an ATC handover (similar to UPS Airlines Flight 6), it's not hard to believe that the following scenario occurred:
* Shortly after the handover from Kuala Lumpur ATC to Ho Chi Minh ATC the crew realise there is a fire on the aircraft
* The pilot-in-command focuses on navigating to the alternate, while the pilot-observing runs through the fire checklist
* As they transit away from Ho Chi Minh ATC they lose range of the signal
* They don't prioritise switching ATC because they're still quite far away from their alternate and they are busily trying to get the fire under control
* Smoke enters the cockpit at this time and hinders their ability to operate the radio equipment
* They either lose track of the alternate because they are distracted by the fire or determine they can't land till the fire is under control (possibly because they cannot contact ATC), so they end up flying across Malaysia
* They eventually realise their error and attempt to turn back, but by this point oxygen in the cabin has depleted and they are unable to complete the maneuver
These sorts of things can happen, the three-person crew of Eastern Air Lines Flight 401 were so distracted debugging a faulty light bulb that they didn't notice the autopilot disengaging and their plane slowly losing altitude before crashing. I imagine had the CVR not survived, people might be speculating that a member of that crew may have purposely crashed it.