MS804

[Catfish]

There was that Air France Flight from South America. Ice had rendered all tachometer devices useless, and the autopilot tried to counter with the data it received. When the jet lost altitude it gave positive elevator control and the nose went up until stalling.
The pilots did not know what was going on and were not able to switch from automatic to manual steering. A stall, drop and circling could be a hint for a similar technical failure.
Just saying.

[Von Due]

Until they find some hard evidence, it might be a good idea, like been posted above, to think of all the things that can lead to something like this.

Deliberate actions by crew: A flight engineer attacked both pilots of Federal Express flight 705 with hammer and speargun in murder/suicide attempt. The pilots did successfully return though and the guy was arrested, tried and sentenced. Germanwings Flight 9525 saw the pilot commit murder/suicide.

Malfunctions. It is possible albeit extremely unlikely that the plane lost all electric power/radio/communications for some bizarre reason. Ice can cause sudden crashes. Ground maintenance errors like forgetting to remove duct tape covering the pitot tubes.

Structural: Airliners have disintegrated for no immediate apparent reason while in the air before. Comet, the first jet airliner (design flaw), China Airlines flight 611 (improper, previous repairs) and more.

Terrorism: Is a candidate too.

[Oberon]

A good summary there Von Due, hopefully now that they've located some of the wreckage from the flight they'll be able to narrow down the search area and locate the FDR.

[Jimbuna]

EgyptAir crash: Debris found from flight MS804

Debris from the missing EgyptAir flight has been found floating in the Mediterranean, Egyptian officials say.
Flight MS804 was en route from Paris to Cairo with 66 passengers and crew when it vanished early on Thursday.
Egypt's army spokesman said wreckage and passenger belongings were found 290km (180 miles) from Alexandria.
Greek Defence Minister Panos Kammenos said a body part, two seats and at least one suitcase had been found.
The items were found slightly to the south of the area where the plane disappeared from radars on Thursday, Mr Kammenos said.
The search is now focused on finding the plane's flight recorders, the Associated Press news agency reports.

http://www.bbc.co.uk/news/world-middle-east-36339614

[Aktungbby]

With Von Due's summary in mind, I'm thinking massive tail/rudder failure a with AirAsia in 2014 and a rudder loss-combined with off-auto manual flying of the aircraft by the desperate pilot in extreme circumstances. Inasmuch as the 'dog is not barking'; no organization is taking 'credit' for a terrorist operation. That is not their usual modus operendi. http://blogs.crikey.com.au/planetalking/2015/12/01/harsh-truths-about-crash-of-airasia-qz8501-come-out/ Also:

March 2005: Air Transat Flight 961, an Airbus A310-308, en route from Cuba to Quebec City with nine crew and 261 passengers on board, experienced a structural failure in which the rudder detached in flight. The aircraft returned to Varadero, Cuba, where they made a safe landing. The crew made no unusual rudder inputs during the flight nor was the rudder being manipulated when it failed; there was no obvious fault in the rudder or yaw-damper system. Subsequent investigation determined that Airbus' inspection procedure for the composite rudder was inadequate; inspection procedures for composite structures on airliners were changed following this accident.

https://en.wikipedia.org/wiki/Airbus_A310

[Aktungbby]

Originally Posted by Aktungbby

Inasmuch as the 'dog is not barking'; no organization is taking 'credit' for a terrorist operation. That is not their usual modus operendi.

“received information from three independent channels”, that ACARS (Aircraft Communications Addressing and Reporting System) received the following messages from the aircraft: 00:26Z 3044 ANTI ICE R WINDOW
00:26Z 561200 R SLIDING WINDOW SENSOR
00:26Z 2600 SMOKE LAVATORY SMOKE
00:27Z 2600 AVIONICS SMOKE
00:28Z 561100 R FIXED WINDOW SENSOR
00:29Z 2200 AUTO FLT FCU 2 FAULT
00:29Z 2700 F/CTL SEC 3 FAULT
The timestamps refer to GMT and point to the alerts being received in the minutes before the flight dropped off radar screens.

Still no claim by a terrorist group "in contrast to a quick claim by Isis after a Russian plane exploded over Egypt in November." Avionics fire appears likeliest at present....

[kraznyi_oktjabr]

Originally Posted by Catfish

There was that Air France Flight from South America. Ice had rendered all tachometer devices useless, and the autopilot tried to counter with the data it received. When the jet lost altitude it gave positive elevator control and the nose went up until stalling.
The pilots did not know what was going on and were not able to switch from automatic to manual steering. A stall, drop and circling could be a hint for a similar technical failure.
Just saying.

There are three major errors in your narrative:
1) When autopilot does not get sufficient data to fly safely it disconnects. That happened on Air France Flight 447.

2) Change between flight control laws is automated process not manual one. However ff person knows what he or she is doing it can be intentionally triggered by shutting down some of flight control computers.

3) At time of the accident plane's captain was off duty. First officer was in captain's seat with second officer in FO's. When troubles started first officer tried to correct situation. However second officer was applying constant nost up command in his side stick which caused the orignal stall situation and as it overrode all first officer's control inputs also ensured first officer could not correct situation. However I do not know if first officer's intended actions were appropriate or not.

Air France Flight 447 crash was due pilot error with mechanical malfunction (frozen pitot tubes) and user interface design (presentation of information and lack of feedback via side stick controllers) playing secondary role. Procedures exist for flying aircraft without accurate speed information but those were not followed.

(Air France 447 and Air Transat 236 were used as examples in user interface design course when speaking about user interface design in safety critical applications.)

[Skybird]

The probabilities seem to shift in favour of a cable fire or something like that as an explanation scenario. Board systems should have rang alarm over problems with the heating system on the toilets.

[Von Due]

According to BBC, there are unconfirmed (officially, that is) reports of smoke detection coming from, among other areas, the avionics bay. Fire is seriously bad news. Fire in the avionics bay ups the bad bit by a lot.

Pure speculations here: If there was a fire in the avionics bay, that could possibly explain why no mayday call was heard as monitoring systems, radio and transponders could be affected by this. A fire seems like a very likely candidate at this point but still, nothing is for sure yet. As for possible causes, that is a complete unknown at this point.

[Jimbuna]

Images of some of the debris:

http://www.bbc.co.uk/news/world-middle-east-36349882

[Von Due]

Update

Black box signal detected
http://www.bbc.com/news/world-middle-east-36427053

Now as soon as they can recover it, theories can give way for answers.

[Oberon]

The Egyptian investigation committee has said that the Cockpit Voice Recorder has been recovered from the sea.

https://twitter.com/AP/status/743430423192141824