Malaysia Airlines Loses Contact With 777 en Route to Beijing

[pacoperez]

A constant descent at green-dot speed (best lift-to-drag = best glide angle) will take the plane farther.

Something like this?



At the time of impact: 6600 fpm descent rate; 225 knots

[Evan]

Speaking of engines and fuel, if one runs out of fuel before the other...does the 77 autopilot have the authority to keep the plane in the air until the other exausts? thanks.

Joe, I think you are speaking of thrust asymmetry. This is actually a very interesting aspect of the 777 FBW. With the Airbus A320/330/340 FBW, if you lose an engine the PFD will display a sideslip target for guidance but will not do anything to correct the sideslip itself. The pilot has to make those rudder inputs manually. The 777 FBW, however, has something called TAC (Thrust Asymmetry Compensation). TAC engages when the system detects a thrust asymmetry exceeding 10% between engines and adds necessary rudder trim or rudder inputs up to 60% of the total rudder availability to keep the aircraft out of sideslip. It does not have any inertial guidance input; it works solely on thrust calculations coming from the engines.

Now there are several failure scenarios to TAC. One is that it can be simply switched off in the cockpit (if we are talking about a suicidal pilot for instance). Another is that the data coming from the engine could be considered invalid (usually during a catastrophic engine failure where the engine is physically damaged). A third is, of course, when the other engine fails and there is no longer any thrust to compare.

So in a scenario where both engines are running at FL near 100% N1 and one begins to falter due to fuel exhaustion, the TAC is going to automatically compensate with rudder trim to avoid an upset. When the other engine fails shortly therafter, there will no longer be any TAC inputs and the rudder trim will be recentered.

How this plays out in such a scenario, where there is no pilot flying, is beyond me but it is reasonable to say that the 777 FBW will minimize the effects of asymmetric thrust without pilot intervention and that the scenario I've seen described in the media about the plane entering a fatal in-flight upset due to the first engine failure is highly unlikely due to the FBW protections.

[TheKiecker]

From what we know today, if we believe the core of the the official information (what I do), the ACARS was turned off but not the SATCOM. It would be the equivalent to not make cell phone calls and not answering when it rings, but the phone is kept on. There will be no information to/from the user but the cell network operator will know that the phone was turned on and on what cell it was logged. The "cell" in this case is the satelllite, the phone is the SATCOM and the user making and answering calls (or refraining from doing so) would be the ACARS.

In short: Bullshit.

Gabriel ,
As you know you are my favorite poster here. Can you please further explain ?

Thank you.

TK

PS Evan is #2 . Great post above .

[Evan]

Hi Peter, thanks for the comment. The train of my question is to eliminate, at least in my mind, a structurally intact water landing such that the debris might be more contained by the intact fuselage and carried down as opposed to a breakup that would lay down far more floating stuff. My uneducated thinking was that maybe the wind-turbine could power the autopilot in such a way that after the 2nd flameout there might be a possibility of a fuselage intact water impact (ie...non tumbling).

One problem is configuration (flap setting): To successfully ditch a 777 (if that is even possible) you must float it in a high-lift configuration until it settles into the water with the lowest possible vertical speed and ground speed. The A320 that ditched in the Hudson was, according to a number of experts, not configured optimally for ditching and therefore hit the water at too high of a vertical speed, thus causing extensive damage to the lower fuselage and the water ingress that eventually sank it. Yes, it was a successful ditching because it was still configured for landing, just not optimally. A wide-body ditching would require optimal everything.

A 777 on autopilot alone, with no pilot flying, is going to be in clean configuration (no flaps) all the way down. That means it is going to need a higher groundspeed to remain in flight and will impact at a higher speed and a higher vertical rate. That scenario is not going to be successful at all.

[TheKiecker]

One problem is configuration (flap setting): To successfully ditch a 777 (if that is even possible) you must float it in a high-lift configuration until it settles into the water with the lowest possible vertical speed and ground speed. The A320 that ditched in the Hudson was, according to a number of experts, not configured optimally for ditching and therefore hit the water at too high of a vertical speed, thus causing extensive damage to the lower fuselage and the water ingress that eventually sank it. Yes, it was a successful ditching because it was still configured for landing, just not optimally. A wide-body ditching would require optimal everything.

A 777 on autopilot alone, with no pilot flying is going to be in clean configuration (no flaps) all the way down. That means it is going to need a higher groundspeed to remain in flight and will impact at a higher speed and a higher vertical rate. That scenario is not going to be successful at all.

Evan,
So if the 777 ran out of fuel would the AP be " pulling up the whole time " ( couldnt resist ) or would it just stay trimmed like it was at FL350 level flight even though it would be pointing down.

[guamainiac]

EconomyClass, that's not necessarily true evidence the "Gimli Glider", Air Canada 153, a Boeing 767. It doesn't need power but it does rely on the "stored" energy that it has acquired in the attained altitude.

You need forward motion to develop (degrading lift), and that is the "formula" BoeingBobby refered to.

It depends on how the plane was trimmed regarding how far it would be able to travel regarding winds and air speed.

If it was slaved to an altitude it will come down in a series of porpoise like "hunting" motions, if trimmed to an airspeed, it would for the most part maintain that, and it's constant decline.

[Evan]

Gabriel, What is your feeling about this uninterrupted auto-pilot thing floating around?

What is that?

[guamainiac]

Regarding the condition of the aircraft, in a smooth glass like sea, perhaps some parts intact but conditions weren't reported as good. That may equal hitting a brick wall.

[Evan]

Evan,
So if the 777 ran out of fuel would the AP be " pulling up the whole time " ( couldnt resist ) or would it just stay trimmed like it was at FL350 level flight even though it would be pointing down.

Like the Airbus FBW, Boeing FBW has envelope protections that will keep the a/c from reaching stall AoA. (The difference is in philosophy: Boeing pilots can always override this with breakout force, something that becomes irrelevant when there is no pilot flying). Therefore it will not relentlessly pull up into a stall. Eventually, as the airspeed decays, the FBW would have to accept a loss of altitude over a stall-regime AoA. I believe the AP would have disconnected when it could no longer hold flight level (at least in pitch modes).

The phugoid thing is interesting and I wonder how it all fits together with AP and FBW protections.

[BoeingBobby]

BoeingBobby...yes. Recovery of flotsam improves chances of the recovery of aircraft, black boxes, evidence of wrongdoing...So if my goal were to have minimum floating stuff...wouldn't I try to keep as much of the cushions, bags, floating parts contained inside an intact as possible in a sunken fuselage?

As the aircraft sunk into 400+ atmospheres of water, the fuselage will break up anyway. Eventually anything that will float will make it to the surface. If I was trying to make the FDR and CVR as hard to find as possible, I would plant it in at the highest rate of speed possible.

[BoeingBobby]

Something like this?



At the time of impact: 6600 fpm descent rate; 225 knots

If the aircraft impacted the water at 6600 fpm decent rate, and 225 knots, good luck with an intact airframe!

[Evan]

Something like this?



At the time of impact: 6600 fpm descent rate; 225 knots

I suppose this has to do with the 777 FBW C*U flight control law speed stability function:

The ‘‘U” term in C* refers to the feature in the control law which will, for any change in the airspeed away from a referenced trim speed, cause a pitch change to return to that referenced airspeed. For a increase in airspeed, the control law will command the airplane nose up, which tends to slow the airplane down. For a decrease in airspeed, the control law causes a corresponding speed increase by commanding nose down pitch.

[BoeingBobby]

What is that?

Evan, I have never heard of this before the other day. And I have never seen any trace of it in any of our 74's. But here is the (Bull Shit in my opinion) story.

http://www.homelandsecuritynewswire.com/boeing-wins-patent-uninterruptible-autopilot-system

[Evan]

Evan, I have never heard of this before the other day. And I have never seen any trace of it in any of our 74's. But here is the (Bull Shit in my opinion) story.

http://www.homelandsecuritynewswire....topilot-system

That has to be total BS. Maybe a patent was applied for but I doubt that it's going to get certified if it can't be isolated and shut down by the crew. Also, as you know BB, autoland is not really autoland. Someone still has to configure the flaps and lower the gear. Would tha CAA's really allow an automated (therefore fault capable) system to do that in flight? And as for the system's 'total independence', that system isn't going to be of any use if the FBW computers are manually shut down. Hijackers could still force pilots to bellcrank it around the sky (or try to).

ANd what is being implied anyway, that the ship was being remotely hijacked? If so, how do they explain the radio silence? It's nonsense.

[Peter Kesternich]

Evan, I have never heard of this before the other day. And I have never seen any trace of it in any of our 74's. But here is the (Bull Shit in my opinion) story.

http://www.homelandsecuritynewswire....topilot-system

It looks as if this has also been reported by Flight International, quite a reputable source, linked here through Flight Global:

http://www.flightglobal.com/news/articles/boeing-autopilot-would-seize-back-control-from-hijackers-210923/

HOWEVER, just because someone holds a patent on something doesn't mean it's deployed or even practicable. This kind of system may work theoretically, but unless it's deployed, it doesn't add anything to the discussion of MH370.

BoeingBobby - I think we should put that to rest