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Malaysian Airlines MH370 contact lost

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Malaysian Airlines MH370 contact lost

Old 2nd Jul 2014, 17:25
  #11241 (permalink)  

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Hyperveloce
I have tested this for great circles between waypoints (LNAV mode), between BEBIM (and a shifted version to the east) toward 3 destinations: the south pole, the Wilkins airport and NOBEY
I am a retired airline pilot rather than a boffin. It looks to me from the data published that if LNAV is used it is likely that Wilkins (YWKS) was the "destination" or somewhere in that region.

All tracks flown in LNAV however small are G/S not rhumb lines. It would be reasonable to assume that at least for the cruise the aircraft would have flown a constant Mach No. (but not G/S as that is dependent on the upper winds) and changing heading to maintain the G/C track. In which case if you could take the 7th ping arc (use the ATSB yellow arc) and compare the tracks from various waypoints in the north and compare the times to cross the earlier ping arcs. Likewise you should be able to take the last "fix" round about MEKAR and look at the what waypoint(s) tie in with it).

If I was "doing the flight planning" I would have concentrated on the FIR points as turning points as they are handovers between ATC units. Skyvector.com has a good flight planning facility to play around with.
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Old 2nd Jul 2014, 19:59
  #11242 (permalink)  
 
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My understanding of this is very weak but from what I have read there are four sources of navigation information that George might use to hold a course. They are Inertial, magnetic, radio and GPS. It seems that aircraft comms were impaired and the information we have consists of some satellite pings. With no comms, what information is still available to the auto pilot to maintain course?

Can anyone shed some light on the possibilities? My reason for asking about the rhumb lines is that even if all other systems are switched off, a magnetic compass might still provide a heading.
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Old 3rd Jul 2014, 00:44
  #11243 (permalink)  
 
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Ulric,


I'm not a T7 expert, but...


FWIW we used to fly much earlier aircraft between Kano and Jeddah using a single course (C) of 072 or 252 for some 7 hours, on Hadj flights. This was a "Modified Lamberdrome" route, ie. a straight line on a Lambert's projection, between the Standard Parrallels. This gave us a Base leg at Jeddah and very long Finals at Kano.


Following ONE then TWO engines shut down... Others may have more ideas for the 100 -ish mile descent's heading.


This flight from KL would have expected sunrise on the Starboard, ( right) side. NOT the Port ( left).


Something similar, with sunrise in the wrong direction, had happened to G-ALDN, the " Hermes in the Desert", 60 odd years ago.
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Old 3rd Jul 2014, 02:43
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Should thread be closed?

I should stress at beginning that I'm not a pilot, professional or otherwise (unless you count PPL 50 yrs ago in a Tiger Moth , open cockpit, no electrical system, no brakes and only air to ground comms a Verey Pistol!!)

However, I do see a reason to keep thread active. What I think I am seeing from authorities is that as finding the aircraft becomes less and less likely, they become more and more definite in attaching blame to the aircrew. This thread does keep things balanced and evidence based. As fellow pilots I think you have a role to protect your colleagues from a rush to judgement unless and until the evidence clearly supports such a judgement.
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Old 4th Jul 2014, 00:26
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Gysbreght,


That looks fairly logical, thank you.
My "100+ miles..." should be Track miles, to allow for the possibility of not maintaining a constant heading, when without engines. ( RAT might help, I suppose.)
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Old 4th Jul 2014, 21:48
  #11246 (permalink)  
 
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Unfortunately, 2nd engine out = short decent

I don't have specific knowledge of the T7 either, but perhaps this would happen:

Following one engine shutdown, the autopilot will maintain heading and altitude. The autothrust will increase thrust on the remaining engine as required to maintain airspeed. If max. climb/cruise thrust is not sufficient to maintain speed, the airplane will slow down, still maintaining altitude. The autopilot will disconnect either when the speed becomes too low, or at the second engine shutdown, if that occurs earlier. With two engines shut down and autopilot off, the airplane will descend at approximately constant airspeed, probably fluctuating around the trimmed speed in a phugoid fashion.
The report says "spiral descent", but the more sensation-hungry posters immediately translate that to "spiral dive".
Gysbreght,
(2nd hand info...)
The B777 simulation results from the last month show that the one engine out case is handled gracefully - TAC (Thrust Asymmetry Control) will keep the plane flying straight. At first airspeed will be sacrificed due to single engine thrust limits. Then, altitude will be sacrificed to maintain airspeed. Eventually, flight will stabilize at an altitude and airspeed combination appropriate for the single engine case. (There are specific max engine limits for single engine operation that 'can' be different from the limits for 2 engine opration.)
An article I found very informative on TAC (beyond reding the manual...)
Thrust Asymmetry Compensation

Things get uglier when the 2nd engine cuts out...
1) TAC will (would?) drop out when it detects that both engines are out.
2) When the engines stop supplying AC power and hydraulic pressure, the hydraulic flight controls (including the TAC-adjusted rudder) will remain locked in place.
3) The Autopilot will drop out (disengage) with the total loss of AC power.
>> This creates a race condition in which the exact sequence of events will determine the flight control settings locked in after power is lost.

The suggestion has been made that the Autopilot would drop out first, with the rudder trip from TAC still fully applied. This would lead to an unfavorable condition while power is out. And, when power returns, the autopilot remains disengaged, so these flight control positions will be maintained.
-- This is what leads to the expectation of a very short glide period. The the plane will begin turning right at 2nd engine flame out, and continue that turn even when power is restored from the APC and/or RAT.
This is most likely the 'spiral decent' mentioned in the June 26th ATSB report.
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Old 5th Jul 2014, 13:58
  #11247 (permalink)  
 
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Can anyone tell me how the "log on" at 18.25 UTC determines that "this" was MAS370 ?

I presume "user data" unique to the satcom equipment ?
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Old 5th Jul 2014, 20:37
  #11248 (permalink)  
 
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Gysbreght,
Three distinct dependencies-
1) Autopilot disengages when all AC power is lost

2) The flight control surfaces will (would) lock up on loss of hydraulic power (not on loss of electrical power - sorry, I left that vague). This is a different chain of events. If Hydraulic power is restored, before pressure in the lines drops, then there will be no lock up.

3) TAC drops out when neither engine is powered. Part of the race condition is that TAC would release the rudder back to a neutral (to the prior trim) position, unless the hydraulics have already locked.


Battery backup keeps the lowest level flight controls operational. But, the plane is no longer in Normal mode (Law 1), so many of the stability controls would no longer apply. That is what allows any remaining rudder to continue to turn the plane.
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Old 5th Jul 2014, 21:32
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Originally Posted by GobonaStick
There's no positive identification linking the last transponder transmission to the radar plot. But I suspect every other aircraft that appeared on the radar has been positively identified, leaving just a single unexplained line of plots which begins roughly where MH370 vanished.

Similarly, nothing positively links the final radar plot to the log-on. But I believe the satcom terminal identifies its origin, confirming it is transmitting from the missing aircraft, and the timing data from that log-on is consistent with a region very close to the last radar plot.

Therefore it's reasonable to suggest that the three separate points - transponder loss, radar plot, log-on arc - are connected by the track given.
The SATCOM logon has the equivalent of a hardware MAC Address that is specific to that airframe. The range ring for the logon passed through the last radar reponse location +/- 3 miinutes to the accuracy of these rings. This was verified by comparing the known and calculated position of other aircraft.
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Old 5th Jul 2014, 21:53
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Originally Posted by Ian W
The range ring for the logon passed through the last radar reponse location +/- 3 miinutes to the accuracy of these rings. This was verified by comparing the known and calculated position of other aircraft.
I suspect this is one of the reasons for believing the aircraft was intentionally disappeared, as it's consistent with someone turning the power back on shortly after they knew they'd be out of radar range. I believe someone mentioned a few thousand posts back that the SATCOM terminal is on the same power bus as some other communication equipment, so turning off the power to that bus would turn all that equipment off.
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Old 5th Jul 2014, 23:51
  #11251 (permalink)  
 
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Control Transient at Second Engine Shutdown

Second failed engine thrust would decay over several seconds - as the rudder is released from TAC offset, it would return to centerline just as the thrust from both engines approaches windmilling. I would expect a minor yaw wobble for a few seconds, but then the FBWire direct (alternate) mode would tend to keep the wings level and the pitch constant until airspeed decays severely, at which time (without pilot input), the pitch angle will drop in order to maintain a non-stall airspeed - maybe 180 or more knots. The FBW lateral law is mostly a rate system and assuming the yoke is centered, there should be only a minor bank angle. I also expect a phugoid pitch angle oscillation, but really not as severe as was reported by one 777 simulator user - perhaps only a variation from maybe 1500 to 3000 fpm down. This situation was probably not really flight tested and the simulators might be somewhat inaccurate.
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Old 6th Jul 2014, 00:51
  #11252 (permalink)  
 
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Originally Posted by MG23
I suspect this is one of the reasons for believing the aircraft was intentionally disappeared, as it's consistent with someone turning the power back on shortly after they knew they'd be out of radar range. I believe someone mentioned a few thousand posts back that the SATCOM terminal is on the same power bus as some other communication equipment, so turning off the power to that bus would turn all that equipment off.
This is the kind of statement that bothers me. If the purposed individual turned off the power bus to make the aircraft invisible (as much as theoretically possible), why bother turning it back on at all ? What's the point ?

Was there something else that they needed active that required turning it back on, or was someone on flight deck randomly reseting CBs trying to get things back on and working.

Also, how would a pilot who normally flies with ADS enabled (for SSR) even know the precise range of that PSR ? Did enabling the power bus cause the ADS to become active again as well ?

Various drawings suggest that that the T7 has dual pairs of SATCOM antennas, mounted on either side of the hull (but near the top). I'm more inclined to wonder if changing course caused the re-establishment of SATCOM, than power being restored.
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Old 6th Jul 2014, 01:01
  #11253 (permalink)  
 
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".. a minor bank angle..." (if stable) will cause a certain radius of turn, now beyond my arithmetic, with decreasing T.A.S. as well !
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Old 6th Jul 2014, 05:57
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Things get uglier when the 2nd engine cuts out...
1) TAC will (would?) drop out when it detects that both engines are out.
2) When the engines stop supplying AC power and hydraulic pressure, the hydraulic flight controls (including the TAC-adjusted rudder) will remain locked in place.
3) The Autopilot will drop out (disengage) with the total loss of AC power.
>> This creates a race condition in which the exact sequence of events will determine the flight control settings locked in after power is lost.

The suggestion has been made that the Autopilot would drop out first, with the rudder trip from TAC still fully applied. This would lead to an unfavorable condition while power is out. And, when power returns, the autopilot remains disengaged, so these flight control positions will be maintained.
-- This is what leads to the expectation of a very short glide period. The the plane will begin turning right at 2nd engine flame out, and continue that turn even when power is restored from the APC and/or RAT.
This is most likely the 'spiral decent' mentioned in the June 26th ATSB report.
That's not quite correct. The aircraft would have lost AC power when the second engine failed, triggering a series of events:

1. The flight control system would revert to secondary mode and the TAC would immediately drop out as a result of that reversion.

2. The RAT would immediately deploy and begin supplying electrical power via the standby electrical system and hydraulic power to the primary flight controls via the centre hydraulic system.

3. The APU would attempt to start automatically.

There would be several power transfers while all this was taking place, but the left and centre flight control power supply assemblies would remain powered throughout, via the main battery.

I don't believe the flight controls would remain 'locked in place' as you suggest. Some hydraulic power would be lost when both engines failed, but there would still be some hydraulic pressure and shortly thereafter the RAT would spin up and begin providing pressure to the centre system. With no further control inputs, the rudder would centre.

There is a theory that a spiral descent would be triggered by the extra drag from the RAT, which deploys from the RHS of the rear fuselage, behind the wing.
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Old 6th Jul 2014, 09:40
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With such a high level of redundancy on the T7, it is hard to think of anything that can account for this tragic episode, other than something of a "catastrophic" nature.

A SATCOM "reboot" in flight !
Only with a simultaneous dual IDG and APU failure would that happen.
(BUGs/PMG's don't power SATCOM or TCAS)
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Old 6th Jul 2014, 12:09
  #11256 (permalink)  
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It is easy to calculate the radar horizon given height above ground for antenna and target.

Obvious assumptions in this case at 37,000ft (FL370) and radar at 15ft. This gives a theoretical range of 236 nms.

These assumptions are probably incorrect and unless your perpetrator was sufficiently knowledgeable a 3 minute (23 mile) gap between leaving radar cover (225 miles) and restoring power would be too close or ineffective.

In reality FL370 would be nearer 39,000ft in the tropics. That gives a radar horizon of 241 nms.

Then there is a property known as anaprop or anomalous propagation where the radar bends and goes further over the horizon.

Now in this instance we know the last radar contact fell well below the theoretical ranges. Did this mean the aircraft was at 32,000 feet or that the radar performance was well below optimum?

I submit therefore that for there to be a deliberate masking until beyond the radar horizon and resumption of power 3 minutes later was unlikely the timing was too tight for the probable variations in range but just pure coincidence.
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Old 6th Jul 2014, 23:04
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About the RAT.
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?
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Old 6th Jul 2014, 23:13
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Shadoko, you are thinking along the same lines as I am.
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Old 6th Jul 2014, 23:19
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The RAT comes out when a double engine failure is sensed. The APU also automatically starts and provides power until that also runs out of fuel. The log on was probably caused by the APU starting with the fuel available in its fuel line which rapidly ran out.
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Old 6th Jul 2014, 23:29
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The 18:25 login is attributed to the removal of power from the left AC bus which powers the sat transmitter and modem. This "power failure" was a local event, only affecting items powered by that bus.

The power failure which brought about the 00:19 login attempt was a total failure as explained above.
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