News Air Asia flight QZ8501 missing

[Spacethingy]

Tragically, it appears 2014 has claimed another airliner around Malaysia and Indonesia:

http://www.bbc.co.uk/news/live/world-asia-30615089

Contact was lost around midnight UTC.

 

[Eccentrus]

The Plane is still brand new and the authorities are blaming the bad weather condition that have been the norm in these islands for the last 3 weeks or so. Through what I know from the once in a blue moon flights I take around my country, I can say that the fog is pretty bad in the inter-insular seas whenever the rainy season comes in, and visibility is almost never perfect below certain altitudes, so that might be a contributing factor as well.

What I gather from social media here is there's 1 Malaysian, 1 Singaporean, 1 British, 3 Koreans, and 149 Indonesians on board.

My thoughts and prayers goes to those affected in this incident, I sincerely hope that this is just a case of communication problem.

 

[Urwumpe]

Seems like it really went missing in bad weather over the ocean. Possibly another AF447 like event.

Radio contact broke off 5 minutes after a request by the pilot to turn to the left and ascent from FL320 to FL340. one minute after radio contact broke off, the ADS-B signal died. There had been multiple other planes on the same route that day, could be possible that some more witnesses of the conditions that night are around.

 

[Alfastar]

Its unconfined, but there are reports the plane crashed in the water, near Belitung timur.

http://www.themalaysianinsider.com/...rash-in-belitung-timur-says-indonesian-portal

 

[garyw]

Seems like it really went missing in bad weather over the ocean. Possibly another AF447 like event.

It does seem to be a lot like that doesn't it. Whilst we shouldn't rush to judgement here, if this is a second AF447 then the airline industry will have a lot of hard questions to answer.

 

[Urwumpe]

It does seem to be a lot like that doesn't it. Whilst we shouldn't rush to judgement here, if this is a second AF447 then the airline industry will have a lot of hard questions to answer.

Well, also even if it is like that: We are talking about really tough conditions that no technology can really make harmless. Events like that can happen.

While we are writing here, a ferry near Greece is in flames and the 300 passengers can't be evacuated because there is a storm in the Mediterrenean Sea right now (They are now trying to use helicopters to rescue as many as possible). Thats the nature of the oceans. They are maybe not as hostile as space, but still hostile.

 

[boogabooga]

Not a good year for flights about the Malay Peninsula.

 

[kamaz]

Possibly another AF447 like event.

Radio contact broke off 5 minutes after a request by the pilot to turn to the left and ascent from FL320 to FL340. one minute after radio contact broke off, the ADS-B signal died.

Please, no. Not another AF447. That would mean another pilot relying on Alpha Floor to increase thrust for him and stalling. Alpha Floor is a safety feature for God's sake, it's still the pilot's job to fly the plane!

 

[Urwumpe]

Please, no. Not another AF447. That would mean another pilot relying on Alpha Floor to increase thrust for him and stalling. Alpha Floor is a safety feature for God's sake, it's still the pilot's job to fly the plane!

Sorry - but the cause was a completely frozen pitot system. of course it didn't help that the pilots also failed badly in very bad weather conditions.

But it would really be a rather new Airbus (first flight in 2008) failing during tropical thunderstorm conditions.

 

[kamaz]

Sorry - but the cause was a completely frozen pitot system. of course it didn't help that the pilots also failed badly in very bad weather conditions.

The cause was pilot's incorrect reaction to stall warning.

But then there is FAA advisory from 10th December:

An occurrence was reported where an Airbus A321 aeroplane encountered
a blockage of two Angle of Attack (AoA) probes during climb, leading to
activation of the Alpha Protection (Alpha Prot) while the Mach number
increased. The flightcrew managed to regain full control and the flight
landed uneventfully.

When Alpha Prot is activated due to blocked AoA probes, the flight
control laws order a continuous nose down pitch rate that, in a worst case
scenario, cannot be stopped with backward sidestick inputs, even in the
full backward position. If the Mach number increases during a nose down
order, the AoA value of the Alpha Prot will continue to decrease. As a
result, the flight control laws will continue to order a nose down pitch rate,
even if the speed is above minimum selectable speed, known as VLS.
This condition, if not corrected, could result in loss of control of the
aeroplane.

To address this unsafe condition, Airbus *** [has] developed a specific
Aircraft Flight Manual (AFM) procedure, which has been published in
AFM Temporary Revision (TR) No. 502.

Ouch.

---------- Post added at 09:09 PM ---------- Previous post was at 08:57 PM ----------

Meanwhile on reddit:

Chilling.

 

[Kyle]

Search has resumed for missing airliner.

 

[Thunder Chicken]

But then there is FAA advisory from 10th December:
Ouch.

I understand that the Airbus software is trying to automatically get the aircraft out of an potentially unsafe predicament, but it seems that all sorts of nasty logic corner cases crop up when there is a pitot-static system failure.

Just when an emergency hits, the plane starts doing uncommanded things, quickly leading to a stressed and baffled flight crew that has completely lost situational awareness. It's really hard to fly the plane when you don't have good visual or instrument cues and the plane is trying to do something else.

 

[Urwumpe]

I understand that the Airbus software is trying to automatically get the aircraft out of an potentially unsafe predicament, but it seems that all sorts of nasty logic corner cases crop up when there is a pitot-static system failure.

Actually all that Normal law, alternate law and direct law stuff is the consequence of such failures like a pitot-static system freezing up. But yes, there are situations where the software does fail.

But I am not yet convinced, that the software fails easier than pilots in the worst case - if pilots also fail to put additional information into consideration, such a sensor failure can also cause big problems.

 

[Thunder Chicken]

Is the Airbus inherently stable i.e. if power and trim are set and controls are neutral, can the Airbus eventually recover level flight without input, even if it stalls completely?

If so, at altitude in turbulent weather and icing conditions, that would seem to be a sensible 'default' condition with a corresponding alert to the pilot that AOA / sinkrate / whatever are out of bounds (for whatever reason) and require the pilot's attention. It doesn't help to have the computer or the pilot to fly out of a situation they don't understand; this condition might buy some time for the crew to sort things out.

A pitot-static failure is not necessarily fatal if the pilots recognize the condition. As I understand it, AF447 was caused by an unrecognized pitot-static failure, and the control inputs (backpressure on the stick, which under normal conditions would have caused the computer to advance the throttles if the airspeed indicators were indeed functional) actually exacerbated the problem. I'm wondering if in such a situation the 'default' condition (either pilot or computer implemented) of neutralizing the controls, setting the trim and throttles would have remedied the situation.

 

[garyw]

Is the Airbus inherently stable i.e. if power and trim are set and controls are neutral, can the Airbus eventually recover level flight without input, even if it stalls completely?

In Normal Law, an airbus will not stall. Close the throttles and the airbus will go nose up and SIT there, just below stall speed. It'll spend all day like that if no other inputs are made.

In ANYTHING other than normal law, an airbus can stall, will stall if it's mishandled and it'll fall out of the sky.

So, Yes, the Airbus is inherently stable. As long as the aircraft is in normal law, quite often the correct response to any issues with the flight controls is to do nothing but monitor. The plane will fly itself.

If it's in alternate law then most of the protections are gone. At this point the PF earns his or her money. There are procedures for handling most upsets, for example, if the plane loses all speed reference data so there is no way to tell how fast or slow it's going then it'll go to alternate law because the autopilot doesn't have enough data to fly the plane.

At this point, the normal response is to leave the throttles where they are and watch the artificial horizon until the speed data comes back.

Another option is to pitch up the nose to 2.5 degress and set the N1 to 85% - both will keep the plane in the air until the speed sensors recover.

which under normal conditions would have caused the computer to advance the throttles

This is one problem with the airbus, if you close the throttles the autopilot will correct the speed but it does not move the throttles, therefore, in some situations, the position of the throttle levers does not correspond with engine power.

 

[Thunder Chicken]

That was something I noticed in the AF447 reconstruction - the pilot and copilot can enter separate (and conflicting) inputs on the side controllers. Add the fact that the throttle position doesn't necessarily correspond to power level (I didn't know that previously), it seems that there is great potential to confuse the flight crew about what inputs are being ordered (and whether it is the computer or the pilot actually flying).

Can the computer detect a plugged pitot? If the pitot is plugged, that can give you erroneous airspeed and AOA information, but would that necessarily kick the system out of Normal law? If the plane doesn't know it is stalled and is still in Normal law, what then?

 

[Eccentrus]

There have been reports of plumes from Long Island southeast of Belitung island, a Singaporean Frigate and an Indonesian Aircraft is due to be sent there today to scan the area for debris. It is understood that the frigate employed have a sonar capability beyond 200m so it will be able to scan deeper than the previous ones.

 

[garyw]

That was something I noticed in the AF447 reconstruction - the pilot and copilot can enter separate (and conflicting) inputs on the side controllers. Add the fact that the throttle position doesn't necessarily correspond to power level (I didn't know that previously), it seems that there is great potential to confuse the flight crew about what inputs are being ordered (and whether it is the computer or the pilot actually flying).

Yes, they changed the code after this so that the phrase "DUAL INPUT" is actually said rather than just displayed on the screen.

Can the computer detect a plugged pitot? If the pitot is plugged, that can give you erroneous airspeed and AOA information, but would that necessarily kick the system out of Normal law? If the plane doesn't know it is stalled and is still in Normal law, what then?

No, what it can detect is different readings from the different pitots. So, if one pitot disagrees with others then it's input is discarded. If all three (I think it's three) give wildly different readings then all three are discarded and the computer drops to alternate law and hands the plane to the flight crew.

 

[Urwumpe]

Yes, they changed the code after this so that the phrase "DUAL INPUT" is actually said rather than just displayed on the screen.

I think the message "DUAL INPUT" is already older than AF447. See also here, from 2006:

http://www.ukfsc.co.uk/files/Safety Briefings _ Presentations/Airbus Safety First Mag - Dec 2006.pdf

Important is just the small line "Note: This audio has the lowest priority among the synthetic voice audio alerts" - the stall message would like have overridden the dual input.

 

[garyw]

You're right Urwumpe but Airbus has changed things as I think dual input has more priority is certain circumstances, certainly it isn't heard once during AF-447's stall.

Aural Indication
After the visual indication has been triggered, a synthetic voice “DUAL INPUT” comes up every 5 sec, as long as the dual input condition persists.
The synthetic voice is a WARNING of a dual input situation
Note: This audio has the lowest priority among the synthetic
voice audio alerts.