Quote:
Originally Posted by 300magman
I did read the article you copied and posted....however, that scenario and what happened on Helios 522 are not the same (no fire on the Helios flight which is entirely what your article is based on). I was simply stating that what happened on Helios 522 would not result in a transponder being off.
If your interested, there is plenty of reading on-line about the Helios incident.
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I agree, the Helios crash has little similarity to this crash.
It seems lots of people really don't understand much about the equipment on most of these large commercial aircraft.
The main piece of equipment used to track aircraft is a transponder. This device sends out a signal back to radar that gives more detail about the aircraft. Depending on the type of transponder, they give out varying amounts of information. Mode A just gives a code recognition of the aircraft. The most basic still used is mode C which gives out altitude information as well as the recognition code of the specific aircraft. All commercial aircraft must have Mode S and any commercial aircraft over 9 seats need a Mode S transponder. The Mode S gives out more information and is used in conjunction with TCAS or collision avoidance equipment.
TCAS uses Mode S transponder information to send signals out to other aircraft which then is used to determine direction heading and altitude information, and then is processed to be used to prevent inflight collisions.
This aircraft will have had at least one Mode S transponder, if not up to 3, however at least one must have been working for it to be legal to fly. It also would have had at least one TCAS system working.
This aircraft also had a working Aircraft Communications Addressing and Reporting System or ACARS system. This system sends out text message data between the aircraft and various other users such as the airline, engine and airframe manufacturer. We have reports that Rolls Royce had data from the ACARS detailing information about the engines.
Also the aircraft would have both a CVR (cockpit voice recorder) as well as a FDR (flight data recorder). Both these devices record information about the aircraft communications and flight data, and both have a ULB (underwater locator beacon). The ULB is what they were searching for and was sending out a ping that can be detected. This is water activated, and is just a battery and pinger that will turn on anytime it is immersed in water. It has a life of 30 days, and has since stopped working.
Also the aircraft would have a ELT (emergency locator transmitter). This device is not possible to shut off, and is not accessible to anyone as it is usually installed under a panel in the tail or vertical fin. It is set off under a high G load, and would have gone off in a crash. All modern ELTs are 406mhz and send much more information than the older ones. This device is monitored by satellites.
The TCAS, transponders, ACARS, FDR and CVR are possible to be shut off with either switches, or with circuit breakers. If a fire happened, it is possible that the crew may have pulled some CBs to shed loads and try to stop a fire. This happened with the Swiss Air MD11 that crashed off Halifax a few years ago.
From what I have read, it sounds like the crew had a problem, and turned back to land. Before they got to land, it is possible that they became incapacitated, and passed out. If they had the aircraft on auto pilot, it would be possible for the aircraft to continue to fly until it ran out of fuel. This could explain why it flew for so long. But it does not explain why the ELT didn't go off. If they crashed, this should have been set off, unless it crashed straight in and went directly to the bottom. However if this happened, you would expect to find debris floating, as many things on the aircraft would float.
The big problem I see is that if they do find the CVR and FDR, and if they are still in good condition, they may only get the last half hour of information from the flight, as the CVR is a continuous loop recorder, and records over it's self after a period of time. Many are 30minutes, however some are longer up to 2hrs. So if there was a problem picked up on the CVR and then the crew passed out and the aircraft flew on for many hours, the voice information will be lost. The FDR records between 17-25hrs, but may not be of much help as is only records information such as position of flight controls, engine parameters, and altitude and airspeed.
I was involved in searching for a B737-800 that crashed in Cameroon a few years ago. It took off in bad weather, and the crew failed to recover the aircraft after it went into a dive caused by a stall. It dove directly into a mangrove swamp, and disappeared without much of a trace. When we did find the location, all that was visible was a dark patch in the swamp. The aircraft was 50m deep.
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