Questo l'articolo, secondo me abbastanza interessante, del WSJ
http://www.wsj.com/articles/smoke-alerts-like-that-on-flight-804-have-raised-questions-in-the-past-1464390994Long before EgyptAir Flight 804’s pilots received an alert signaling smoke in a vital electronics compartment, U.S. safety watchdogs documented that
such warnings on that airliner model were frequently erroneous and sometimes prompted unnecessary and risky cockpit responses.According to people familiar with the probe into this month’s crash of the Airbus Group SE A320,
such warnings on that airliner model were frequently erroneous and sometimes prompted unnecessary and risky cockpit responses.Possible pitfalls of that procedure emerged vividly in an April 2011 incident. Shortly after United Airlines Flight 497 took off from New Orleans, the pilots of the A320 plane received a smoke alert from the hub of its avionics system, but investigators from the National Transportation Safety Board later said they found “no evidence of fire or overheated components.”
The pilots told investigators that “after they began to respond to the smoke warning, electrically powered items in the airplane ceased to function,” according to National Transportation Safety Board documents.
The crew lost some radios and a transponder, and needed air-traffic controllers to direct the jet back to the runway, where it landed with impaired steering and its nose wheel veered into grass beside the runway. Nobody was injured.
Ten days later, United sent pilots a bulletin saying its “Airbus fleet has experienced cases of spurious avionics smoke warnings” and stressing that emergency electric shutdowns are required only in the event of “perceptible smoke.”
It isn’t known if the EgyptAir alert was false, or what actions the crew took. The newer-model, optical smoke sensors installed on the 13-year-old jet have been deemed more reliable than older technology like that on the United plane. But the more recent variants continued to issue false warnings—though at significantly lower rates than the older ones—and were “still sensitive to dust and some aerosols,” Airbus told U.S. crash investigators in 2011.
Recovery of the black-box voice and data recorders is expected to reveal whether the aviators got the warning and began the prescribed series of complex, computer-aided steps intended to isolate the problem by shedding electrical load from the main circuits.
Going back to 2011, that procedure, designed by Airbus, was controversial among critics who said it could be confusing and overly complicated.The prospects that the EgyptAir crew inadvertently cut off power to some essential systems or otherwise failed to react appropriately during the checklist procedure are among the investigative strands being pursued by the international team of experts involved in the EgyptAir probe, people familiar with the issue said. The effort includes running ground-based simulator sessions to re-create possible sequences of events.
Given the scant information now available, it isn’t clear which of the scenarios examined so far—ranging from aircraft malfunctions and pilot missteps to a terrorist act—can be considered the most likely, these people said.
Airbus has been working on the problem of erroneous avionics smoke alerts since the late 1990s. An Airbus spokesman on Friday declined to comment, citing the continuing investigation. EgyptAir officials couldn’t be reached to comment.
Theories about what might have occurred in the avionics bay of Flight 804—an under-floor compartment near the cockpit that houses the jet’s electrical brains—don’t seem to fit with the relatively few system-failure messages the aircraft automatically transmitted before it stopped communicating with the ground, safety experts said.
In addition to the avionics smoke warning, the six other messages included malfunctions of cockpit-window systems and of a flight-control system.
The avionics smoke checklist rarely pops up during recurrent training, according to several pilots who fly the workhorse A320, one of the world’s most widely used jetliners.
“We only get to practice the procedure once or twice in the simulator every couple of years,” said Ben Riecken, who flies A320s for a U.S. carrier.In the past, information compiled by the manufacturer and U.S. accident investigators showed avionics smoke detectors were plagued by systemic problems. According to data Airbus supplied to the NTSB as part of an earlier A320 investigation, the manufacturer collected 63 reports of avionics smoke warnings between 1996 and 2011. Forty-two of them were false. At the time, more than 1,400 older planes were still due to be retrofitted with improved sensors.
But in the probe into the 2011 United Airlines incident, Airbus experts tried to play down the significance of smoke-warning hardware altogether. They told NTSB investigators that the “primary method of smoke detection” from the avionics compartment was “visual and smell on the part of the flight crew and that the avionics smoke detector is secondary,” according to a summary of interviews posted on the board’s website.
Around the 2011 probe, United Airlines told the safety board that only one of 19 reports related to avionics smoke warnings ended up with pilots actually sensing smoke. Still, 15 of those flights either returned to their departure airport or were diverted to an en-route alternate. A spokesman for the carrier on Friday said it “made procedural changes in coordination with Airbus” in the wake of the incident, but declined to elaborate.
Barely hours after the EgyptAir crash killed all 66 people on board, Egyptian officials appeared to jump on the idea of terrorism. But since then, with President Abdel Fattah Al Sisi saying nothing has been ruled out, public attention has shifted to other potential causes spanning an array of airplane malfunctions and cockpit errors.
In the case of EgyptAir Flight 804, safety experts said turning off both generators could account for the sudden loss of automated transmission of system updates as well as dropping off air-traffic control radar screens. But they cautioned that other combinations of problems also could lead to such communication loss.Investigators are also looking into terrorism, including checks of those on board and others who may have accessed the plane at Charles de Gaulle airport before it left Paris.
—Robert Wall contributed to this article.
P.s: la cosa assai strana dell'incidente UA del 2011 é che a distanza di 5 anni l'NTSB non ha ancora rilasciato alcun rapporto preliminare sull'accaduto. Il che é piuttosto inquietante considerato che l'aereo e tutta la sua strumentazione erano integri e immediatamente ispezionabili. Io non sono un complottista, ma che qualcosa di poco chiaro e trasparente, pure per gli esperti del settore, ci sia attorno alla complessa avionica computerizzata di questi apparecchi, a me sembra per lo meno probabile.
P.s2: l'attivazione di un rilevatore di fumo nel compartimento dell'avionica produce immediatamente una serie di ECAM tra i quali, oltre alla chiusura del circuito di ventilazione del comparto avionico al fine di impedire all'eventuale incendio di propagarsi, proprio la "ELEC EMERGENCY CONFIGURATION". Procedura che potrebbe, secondo questa ipotesi e come provato dal caso UA, tradursi in un disastro in determinate circostanze che evidentemente non sono ancora riusciti a replicare e isolare, oltre che per l'erronea esecuzione della procedura stessa (considerata rischiosa, complessa e per la quale gli equipaggi non sono nemmeno addestrati a sufficienza).
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