|Quoting SKAirbus (Reply 179):|
sounds possible that the pilots were drifting in and out of consciousness.
This would not cause the a/c to stop sending transponder signals.
|Quoting anstar (Reply 182):|
I think most airlines have procedures in place to have communications with the flight crew at regular intervals to prevent this sort of thing happening again.
Irrelevant - the a/c would not stop sending transponder signals.
The ringing phones theory is a distraction. The cellular network can return several rings to the "caller" for a phone that is off or not in contact.
You do NOT need to ring a cellular phone to identify if it is on the network. They 'check in' with the network regularly.
So - if passengers cell phones were on and in contact with the network - we would know and we would have a tower location.
Hypoxia theories - unless you think a hypoxic crew would turn off the transponder(s) (unlikely) - then hypoxia of the crew would NOT cause loss of the transponder signals.
Again - we know very little.
We do know
- The a/c is missing. We don't even know if it crashed, ditches or landed. All we know is it would have run out of fuel long ago.
- We can surmise that, because the transponders went off line that one off 2 things happened
- They were turned off
- They failed due to a failure of the transponders or the a/c systems that power them.
Many may not know what "Secondary Radar" really means.
There are 2 types of radar returns possible.
- Primary. This is the 'traditional' type of military detection radar and what stealth a/c are intended to defeat. A radio signal is sent from the transmitter, some part of the signal reflects back from an aircraft and is picked up by a receiver (co-located or near the transmitter). The return is the "primary return." The system uses time of flight information to identify a distance and direction.
Note: All primary radar can tell you is "the a/c is on this bearing (including both a horizontal and vertical component) and is this far away."
Add multiple returns over time and you can measure and changes in bearing and distance.
Add multiple transmitter/receiver pairs and you can start to triangulate better data.
Back in the "day" primary radar was used for ATC in local areas - to day it is rarely used.
For primary radar to be effective over a distance, it takes a lot of power - smokin' amount of power. The Aegis system can run up to 6 Megawatts. Do not stand in front of it - you will be cooked....
- Secondary: Secondary radar does not depend on the primary return - it depends on the fact that when the aircraft 'sees" the interrogating beam - it responds (transmits) with a signal from the transponder. Depending on what class transponder, more information will be sent. The most basic ones will return the assigned transponder code. The most sophisticated will return GPS
location, flight information, etc.
Note: If the transponder fails or is turned off - secondary radar is ineffective.
Basically, it is sending out a directional signal that says "tell me about yourself" and the airplane returns with "here I am."
If the transponder fails to respond - secondary systems 'may' display a primary return - but 'may' is key.
Essentially - secondary radar is not radar in the sense of the term "RAdio Detection And Ranging". It is more like a 'directional radio conversation".
For MH370, secondary or transponder signals were lost. This is what "loosing contact with the a/c..." means. If there were no primary radar systems looking at it - then it would simply "disappear". Note - I believe modern ATC systems will continue to show a predicted track and information for a time - I don't know how long (minutes or seconds I would expect). This prevents the a/c from appearing and disappearing all the time due to momentary signal loss.
So - fro MH370 - either the transponders failed, or were turned off.