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.

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.

whitav8r
".. a minor bank angle..." (if stable) will cause a certain radius of turn, now beyond my arithmetic, with decreasing T.A.S. as well !

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.

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)

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.

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?

Shadoko, you are thinking along the same lines as I am.

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.

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.

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?

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.

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.

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.

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.

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 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 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.

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.

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.

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.

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.

Please tell us how that's done.

(Without rolling the plane inverted)