Quote:
Originally Posted by Woof
According to GCS, the pinging probably would have stopped soon after the engines were submersed.
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I'm not familiar with the Trent 800 engines, the 777's I work have the GE90's on them. But, it depends on where the signal originates to send the engine monitoring data. Admittedly, I've never heard of an engine being a standalone communication device that can send and receive data to its manufacturer and all be self-contained inside the engine. I'm not saying it's impossible, I had just never heard of it until this situation arose.
Generally speaking (I know I say that a lot but you never say "The way it is" in aviation because you'll be proven wrong), there is a computer on board the aircraft which is connected to the SatCom system (which is also on board the aircraft). The computer on the aircraft fetches data from the engine computer (there is a computer on the engine), compiles it, and then uplinks it to SatCom.
I'd be willing to bet that's the type of setup this 777 had. It's not so much that the engine is dialing 1-800-ROLLS-ROYCE to report on its activity, but that there is a computer inside the aircraft that is doing that FOR the engine.
If that is the case, and again I don't work the Rolls engines so I don't know for certain, then I can see a scenario where the engines were no longer spinning or even submerged, but the plane was not. Maybe some standby electrical system like the aircraft battery was still powered and the computer inside the aircraft was able to try and ping the satellite. It would be retrieving no data from the engines but it's still going to try and set up shop?
The other scenario I was thinking about would be the ping was sent the moment the first engine shut down. The 777 aircraft is an ETOPS (
Extended range
Twin
OPeration
S) aircraft or, what we mechanics refer to as "Engines Turn or People Swim."
Basically, the premise of ETOPS came about when technology enabled us to fly transoceanic and polar routes on aircraft with two engines. It used to be that aircraft like the 747 (with 4 engines) could feasibly lose an engine in flight and still have three left to get to where you needed to go. With aircraft like the 777, only having two engines, certain procedures have to be put in place to make sure the remaining engine is as reliable as possible. It's been a while but I believe the 777 was the first aircraft certified to be 180-minute ETOPS capable. Basically, this means that the aircraft could fly any route as long as it was within 180-minutes of a potential landing zone. That's pretty good when you think about it. You could lose an engine and still have three hours before you really even had to worry about anything - if at all.
Some of the basic premises of ETOPS are things like ensuring that the same mechanic does not perform the same procedure on both engines. These restrictions vary by various air carrier policies but they're generally pretty much the same. For example, I can't go replace the engine generator on the left engine and then go to the right engine and do the same thing. If I don't do it right... I don't replace a seal properly, lubricate this, install that, etc... Then it only affects ONE side - not both engines. That way, I don't make the same mistake twice.
Along with ETOPS, comes very strict monitoring of the engines. Oil consumption is measured after every single flight and ANY engine shutdowns are reported to the FAA and/or other agencies involved. Along with that, engine performance trends are also constantly monitored to look for the smallest signs of degradation or wear and tear with the engines (rising exhaust gas temperatures, for example, may indicate signs of fatigue).
To be ETOPS qualified, a company is only allowed so many in-flight engine shutdowns per year. It's a pretty big deal if one does shut down - whether it be on the Rolls or the GE90's, and that stuff gets reported immediately.
So, my thoughts are that the ping may have come when the engines shut down after running out of fuel. To my knowledge, for 7 hours there were no other engine parameters reporting (pinging) and then, for some reason, they decide to ping a satellite 7 hours later? It sounds to me like the plane flew that long, ran out of fuel, and then the engines began to drop off one by one. As soon as that first engine dropped off, I'd be willing to bet it was dialing 1-800-ROLLS-ROYCE to report it - or at least trying.
I HAVE been thinking about it trying to dial after it'd been floating for seven hours. I just can't imagine that happening. If you're in the water, your engines aren't running. Your APU isn't running either. So, the only source of power is a battery. The battery is good for 30 minutes in-flight (actually, I think it may be 60 for ETOPS aircraft). Now, granted, in case of an emergency, the plane will shed loads to ensure maximum electrical performance for critical systems but I just don't see it supporting things like SATCOM for 7 hours while it was in the water - and yet not have dialed to report an engine failure. Again, I guess it's possible but, wow, I'd find that amazing.
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