Le magazine anglais "The caravan" consacre un long dossier à ce crash, réfutant les premières conclusions du bureau indien.
https://caravanmagazine.in/crime/air-in ... eing-pilotC'est dense, il y a beaucoup d'informations, voici quelques extraits les plus "techniques" :
Citation:
The experts pointed to a specific chain of events that brought the plane down. The Caravan has copies of the Airplane Health Management records of VT-ANB—real-time digital dossiers of maintenance analytics that Boeing’s planes send to the manufacturer and operator. VT-ANB’s AHM records show that on its previous flight, from Delhi to Ahmedabad, both the stabiliser’s position sensor and electrical motor control unit had faulted.
[...]
It points to a potential single point of failure in the airplane’s pitch control architecture. Regardless, the AHM records show the stabiliser’s motor and sensor were replaced in Ahmedabad before 12.10 pm, when the maintenance crew released the plane for flight on 12 June.
Citation:
But fifteen minutes before take-off, at 1.23 pm, the FCMs themselves started faulting. These faults were all being communicated to Air India and Boeing via the plane’s satellite link, called the Aircraft Communications Addressing and Reporting System. An FCM is a highly critical component, and such a fault is called a NO-GO fault, requiring the aircraft to not be cleared for flight. VT-ANB’s ACARS codes, copies of which The Caravan has, clearly show that six NO-GO faults existed on the plane, and it was still given clearance to take off.
Citation:
The codes, according to several engineers I spoke to, suggested that the plane suffered a massive electrical failure shortly into take-off. This was likely because of a failing inverter in the back of the plane, which caused a sustained electrical arc that ran through the 787’s highly centralised wiring.[...]
So yes, it would’ve made the flight computers reboot.” The reboot led to flight computers briefly entering “ground-mode,” which, several Air India engineers told me, led FADEC—Full Authority Digital Engine Control, the engine’s computer—to cut off fuel to the engines.
Citation:
he only other source of power for the aircraft to attempt a relight is the permanent magnet alternator generator, which relies on the smaller fan in each engine that remains spinning for a short while after engine cut-off. “But it can succeed if it is producing at full voltage—that is, five to eight seconds after the engine goes down,” an Air India engineer who worked on 787s, including VT-ANB, told me. “It certainly could not have happened ten to fourteen seconds later, as the AAIB implies.” The bureau’s timeline for the engine relight, they said, was “electrically impossible.”
Citation:
After it was released from maintenance, fifteen minutes before take-off, the aircraft’s ACARS logs started streaming fault after fault. At 1.23 pm, six sets of NO-GO warnings were sent. The ACARS told everyone in the loop that AI171’s left and right bus power control units—the computers that act as traffic controllers for electrical power—had entered fault mode, unable to keep the left and right 115-volt AC buses, or electrical junction points, in sync. It gave this warning three times. The aircraft’s two main power highways were falling out of phase, a condition that can cause surges, flickers or even short-circuits across systems. Next, all three FCMs began reporting operational errors, before two general processor modules, which perform calculations and control power supply, faulted.
Citation:
At 1.50 pm, a full eleven minutes after the crash, an operator from Air India’s Gurugram operation centre sent the crashed plane a message asking, “DEAR CAPT CFRM ALL OPS NORMAL.”
Citation:
Soon after the plane was airborne, a rapidly growing number of ACARS codes began beaming out strings of faults codes, indicating that major systems, including flight control computers, were going down, taking dozens of subsystems and sensors in their wake. Multiple engineers and pilots told me that so many different systems failing at once points to a cascading electrical failure.
Citation:
In the critical take-off phase, when both engines are at full power and the aircraft is still on the ground, there is almost no room or time to correct an error, before the plane hits the airport perimeter wall, nearby buildings or planes. When it comes to the question of how much engine power to command, it is not the pilots but the FADEC that calls the shots. The FADEC continuously compares the pilot’s commanded thrust with the engine’s actual output, and calculates whether the thrust is accelerating or decelerating as expected. If the system detects that the thrust is contradictory to commands, then the TCMA informs the FADEC of a thrust control malfunction and automatically shuts off fuel to the engine.
Et si je comprends bien, le reboot électrique permet d'être dans ces conditions ponctuellement :
Citation:
As per the TCMA’s patent document and Boeing’s literature, five parameters need to all be true for a TCMA event: the aircraft is on the ground, its speed is less than 200 knots, the altitude is less than 17,500 feet, thrust levers or thrust reverser levers are in “idle,” and the engine fan speed is more than the TCMA threshold. At 1.38.44 pm, all these would have been seen as true. The airplane read “on ground,” airspeed was less than 200 knots, altitude was low and the fan speed was likely high, given take-off thrust.
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Une des 5 conditions n'était pas remplie, non?