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Malaysian Airlines MH370 contact lost

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Malaysian Airlines MH370 contact lost

Old 7th Jul 2014, 01:52
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sky9: from what I read (I don't know about that), I understand that RAT extends (and APU starts) if both AC transfer buses lose power in flight (even with engines running). That could be from failures or if both general switches (and both backup generators switches?) are switch off.

Propduffer: the log-on sequence could not be from power failure. It could only happen from power recovering (if the lost was from an electrical "problem"). Nobody knows for how long the SATCOM was unpowered (or not functional) because there was no communication at all between 17:07 and 18:25. The non-response to a request at 18:03 proves that the link was not functional around this time. This doesn't prove that the link was out of order all the time between 17:07 and 18:25.

Could someone confirm that the cockpit door cam is on the same electrical bus that the IFE?
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Old 7th Jul 2014, 02:06
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If the log-on sequence of 18:25:xx was the result of a power loss and come back, was not the RAT to be extended at this time?
Not necessarily. Three things will cause the RAT to deploy automatically:

1. Loss of AC power to both AC transfer busses in-flight.

2. Both engines failed and centre system hydraulic pressure low.

3. All three hydraulic system pressures are low.

Given that the aircraft flew on for a number of hours after the log-on attempt at 1825, it seems unlikely that any of the above events occurred at that time.

As Propduffer said above, the log-on at 1825 could have been caused by a power interruption to the satcom system. Possibilities include the tripping and resetting of the satcom circuit breakers, or some other short-term interruption of power to the AC bus that supplies the satellite data unit.
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Old 7th Jul 2014, 02:15
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The fact that the transponder was turned off just before 1:21:13 and no ACARS message was generated to report that fact seems to tell us that ACARS was shut down not long after the 1:07:48 report.
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Old 7th Jul 2014, 02:37
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Possibilities include the tripping and resetting of the satcom circuit breaker
These CB's (there are three of them for the sat xmit system) are located in the electronics bay. The only way to turn off the satellite transmitter/modem from the flight deck is to drop the left AC bus.
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Old 7th Jul 2014, 03:37
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The only way to turn off the satellite transmitter/modem from the flight deck is to drop the left AC bus.
Agreed. However, deliberately shutting down half the aircraft's AC electrics, even for a short time, would be a major step to take, with serious repercussions. I'd be very surprised if a pilot would do that just to interrupt the satcom system. There are far easier ways of disabling the ACARS & satcom if that was the intent.

The satellite log-on at 1825 may have been caused by a power interruption on the aircraft, or it may have been caused by something else. In my experience, aircraft occasionally 'lose' the satcom for a short time time in-flight and subsequently log-on again automatically.

If the log-on was caused by a power interruption, then possible causes include a malfunction in the L Main AC Bus, causing the system to isolate itself automatically; or deliberate actions taken by the flight crew to achieve the same result. That's not something the flight crew would normally contemplate, except perhaps in the case of an electrical fire where they might attempt to isolate part of the system. As I said above, I think it is highly unlikely they would isolate half the aircraft's AC electrics just to turn off the satcom.
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Old 7th Jul 2014, 04:01
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Shutting down half the aircraft's AC electrics, even for a short time, would be a major step to take, with serious repurcussions
In light of the actions taking place aboard 9M-MRO at that time, I wouldn't think repercussions from de-powering the left Bus and the left FMS would be of much consequence to a person in the act of diverting the plane from its scheduled flight path.
I'd be very surprised if a pilot would do that deliberately just to interrupt the satcom system.
I don't think it was done to disable the sat system - in fact I believe that was an unknown and unintended consequence of de-powering the left AC Bus. IMO the bus was taken down to de-power the left FMS which would allow direct pilot control of the aircraft without interference from the FMS. The FMS would provide physical resistance to control column movements which are outside those Boeing expects an airliner to experience in "normal operation."
There are far easier ways of disabling the ACARS & satcom if that was the intent
There is no other way to disable the satellite transmitter/modem from the flight deck other than to de-power the left AC Bus. The CB's for this are in the EE Bay.
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Old 7th Jul 2014, 05:26
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IMO the bus was taken down to de-power the left FMS which would allow direct pilot control of the aircraft without interference from the FMS.
Surely there are easier ways to take 'direct pilot control of the aircraft without interference from the FMS'. Why not just use other autopilot modes such as HDG or TRK? Failing that, why not just disconnect the autopilot and fly manually? Far easier than taking down half the aircraft's electrics.

There is no other way to disable the satellite transmitter/modem from the flight deck other than to de-power the left AC Bus. The CB's for this are in the EE Bay.
I beg to disagree. The CBs for the satcom may be in the EE bay (I can't remember to be honest), but on the 777s I flew there was definitely a way for the flight crew to force the system to log-off.
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Old 7th Jul 2014, 06:55
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In over 5,000 hours flying the 777 I never found the need to de-power an entire AC bus in order to take 'direct pilot control of the aircraft without interference from the FMS'.
And presumably you've never had the need to turn off the transponder either, yet these are things that happened aboard MH-370 that night.

We have to address the facts as they present themselves. One fact that won't go away is that there was a satellite communications blackout from 9M-MRO which began at 17:07:48.9 and lasted until 18:25:27.4 when the sat modem initiated a cold login to the satellite. A cold login would only be caused by restoration of power unless you prefer to think that this sat modem which had performed flawlessly since the plane was delivered from Boeing, all at once developed a bug the same night the plane was diverted to the southern ocean.

The sat receiver/transmitter/modem receives its power from the left AC Bus in the EE Bay. Down there there are three circuit breakers which provide the only way to turn power off to the sat equipment. There is no way to power off the sat equipment from the flight deck other than to bring the left AC Bus down. Your "on the 777s I flew there was definitely another way of disabling the system from the flight deck" reeks of the kind of stuff that comes out of the Malaysian transport/defense ministry. It appears that you parsed your words to give yourself as many outs as possible.

Let me state it clearly: there is no way to remove power from the satellite modem/transmitter from the flight deck on a 777 without powering off the left AC bus.

You can use your knowledge of the Boeing 777 to shed light on what happened aboard MH-370, or you can use your knowledge of the aircraft to obfuscate the issue. Your choice.

But I suggest that you give some thought to what you are doing.
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Old 7th Jul 2014, 07:19
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...presumably you've never had the need to turn off the transponder either, yet these are things that happened aboard MH-370 that night.
Turned off, or failed, who knows for sure? I certainly don't. The suggestion that it was deliberately turned off is pure speculation at this point. The only known fact is that it stopped transmitting.

It is certainly possible that the left AC bus was de-powered for a time, I never said that it wasn't. However, your suggestion that it was deliberately de-powered in order to 'take direct pilot control of the aircraft' is, frankly, preposterous.

Further, it IS possible to force the satcom to log off a satellite from the flight deck, WITHOUT de-powering the system.
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Old 7th Jul 2014, 07:55
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it IS possible to force the satcom to log off a satellite from the flight deck, WITHOUT de-powering the system
Please tell us how that's done.

(Without rolling the plane inverted)
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Old 7th Jul 2014, 08:21
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Who do you think you're fooling?
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Old 7th Jul 2014, 08:29
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Gentlemen, may I recall this thread is about resolving the Inmarsat data. Speculations should go to ""Rumors and News".


Someone suggested that the satcom re-logon at 18:25 may have been caused by power interruption. This is not by far the only possible technical explanation of this event.


Propduffer, you appear entirely focused on finding ways everyting was done intentionnally. That just reflects a lack of imagination or knowledge about all that could go wrong aboard an airplane.
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Old 7th Jul 2014, 08:36
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Someone suggested that the satcom re-logon at 18:25 may have been caused by power interruption. This is not by far the only possible technical explanation of this event.
Other than a power failure or the modem coincidentally developing a bug that very same night, what other "technical explanation" do you have that would cause a modem to initiate a login?
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Old 7th Jul 2014, 09:41
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Gentlemen,

Whether or not this is the proper thread for this particular discussion (though it seems appropriate enough considering it's mostly technical aspects), I dare interject nevertheless.

Propduffer is correct in this instance.

Buzzbox, with due respect, you first agree that the only way to turn off the satellite transmitter/modem from the flight deck is by dropping the left AC bus.

Then, seemingly out of thin air, you disagree all of the sudden and provide no basis for this change of mind, other than to claim that this is 'sensitive information'.

DJ177, with due respect, I feel it unfair to accuse Produffer of a lack of imagination. He has clearly stayed solidly grounded in fact, and the burden is on you or others to factually discredit his claims, which you have failed to do.
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Old 7th Jul 2014, 10:15
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@DJ77

I asked about the "log on" at 18.25
It was suggested it was likely a power interruption.

The T7 has a high level of redundancy so I was trying to discover "intentional" and "non intentional" reasons for this from (limited) OFFICIALLY RELEASED information (and where the location of the a/c was).

...and what a "thankless task" that is !

1. After 1.21am MYT (around IGARI) there is nothing.
2. There is no "relevant" data gleamed from the 2.03am MYT/2.05am MYT Inmarsat transmission.
3. There is no "officially released" Primary Radar data. The ATSB Report is "not recognised" by Malaysia, although the "last contact" given by the Malaysians as 2.22am MYT is noted
4. A "new log on" is given at 2.25am MYT, which places the a/c in the Banda Aceh area.
5. There follows a number of "handshakes" recorded by Inmarsat along with 2 "telephone calls", which correspond to the activities MAS undertook.

Like it or not, they are the facts. There is NO overlap in events.
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Old 7th Jul 2014, 11:10
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Tawnybird:

I did not disagree with the suggestion 'that the only way to turn off the satellite transmitter/modem from the flight deck is by dropping the left AC bus'. I said that 'it is possible to force the satcom to log off a satellite from the flight deck, WITHOUT de-powering the system'. There is a difference.

The basis for that statement? A few thousand hours flying 777s in airline operations.

The satcom is not completely autonomous from the flight deck. Honeywell was kind enough to provide the flight crew with some control. Most of those functions are not normally used by the flight crew, but they are available.
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Old 7th Jul 2014, 13:52
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@BuzzBox

As a way of "resolving" this "log off and Log on" issue which is believed to have occurred at "some time prior to 1825 UTC" and "at 1825 UTC", you are saying with your time on T7's it is possible to "force" a "log off" without de-powering the system...and without leaving the flight deck.

Assuming you did this. The system has power but is "off line", how would you "log on" again ? Would this be something that would be "automatic" ? Or a "manual" function ?
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Old 7th Jul 2014, 13:58
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@ tawnybird
At least, by saying that there is no need to "de-power" the left FMC in order to take control of the T7, BuzzBox has a more solidly grounded point than Propduffer.


@JamesGV
Formally, the log on at 2.25am-MYT is on the relevant Inmarsat-computed ping arc. It is assumed close to Banda Aceh only due to the existence of the radar track of an UFO believed to be MH370. I mean this has never been a certainty.
As I understand the works of RichardC10, Gysbrecht or Hyperveloce, when the 2.25 log on is assumed close to Banda Aceh it appears impossible reconcile the Inmarsat data and possible trajectories without large variations of ground speed. According to the end of flight analysis in ATSB report of June 26th, the unresponsive crew scenario appear more probable (given available evidence). I am vainly trying to figure out how this could add-up with large speed variations an neither can I find any logic for intentionally fiddling with speed.
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Old 7th Jul 2014, 14:38
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@DJ77

Taking your first point....

"It (the "log on" and therefore what we believe was MH370) is assumed close to Banda Aceh only due to the existence of the radar track".

Are you saying that IN CONJUNCTION WITH the "last/lost conatct" Primary Radar data is it possible to establish that a plot for the "first arc" is possible ?

As in, it is IMPOSSIBLE to establish a plot for this "start point" using Inmarsat data/BFO/Doppler Effect alone ?
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Old 7th Jul 2014, 20:05
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Search radars operate at frequencies above 1 gHz, where atmospheric refraction is less of a factor. The Butterworth radar track data photo that was posted some time ago went out to 200 miles, with a gap from around 100 to 130 miles. Using an online radar horizon calculator it looks like flying at 5000', then climbing thru 10000' at 130 miles would produce a gap like that. That would jibe with the claim that MH370 flew "as low as 4500'". However, the radar horizon at 200 nautical miles is about 23000', which does not jibe with the reported last altitude data of 29500'. In my experience, a huge target like an airliner is easily detectable at max range if it is above the radar horizon. Max range of a search radar is typically around 250 nautical miles, and it is a hard limit, determined by the pulse repetition frequency.
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