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january

AirBus Ditching on the Hudson

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Any experts out there who can comment on how AirBus A320 Fly by Wire control apparently continued to function after total engine loss?One would assume that all Generators and Hydraulic Pumps ceased function as the engines shut down from bird ingestion.What servos then, were available to actuate control surfaces?Presumably there would be battery power sufficient to send control signals from flight deck to the servos- but what powered the servos? Does the Airbus have an external generator turbine similar to the Boeing 767?Does the A320 have a backup cable control system to substitute for Fly by Wire in the event of total power loss? Alex Reid

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Likely battery power initially, followed by either the deployment of the Ram Air Turbine, or the automatic startup of the APU to supply juice to the electrical hydraulic pumps. There are several possibilities...-Greg

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Not an expert by any means but...When both engines failed the RAT (Ram Air Turbine) would have dropped and after 30 seconds or so started providing hydraulic pressure (to the blue system) and electrical power to the essential buses.Fly-by-wire wise it would have dropped out of normal law and into alternate law (without protections). It would fly very similar, if a little twitchy, to usual. If they had put the gear down it would have gone into Direct law which can be a little unfamiliar but not overly difficult.They would have had control over most of the control surfaces, the only exception being the flaps, they would have had slats only. They wouldn't have had that many spoilers either but it would fly and be controllable.The Airbus uses a mechanical backup for the rudder and trim only, the idea being that you can keep the aircraft flying with those until you can get something else back and get into another law, in this case it was unnecessary.Overall they did a great job, you can't argue with no fatalities. Also goes to show the Airbus is perfectly safe in an emergency situation, FBW Luddites notwithstanding. Also proves that ditching procedures and training are all spot on, text book ditching, aircraft behaved exactly as designed, Crew did everything they were trained to and ... no one died. Gold stars all round then, so hopefully we can get people to shut up and watch the safety demo now ... I live in hope.Hope this helps,Ian

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Not an expert by any means but...When both engines failed the RAT (Ram Air Turbine) would have dropped and after 30 seconds or so started providing hydraulic pressure (to the blue system) and electrical power to the essential buses.------Ian
-----------------------------So the A320 DOES have a RAT? All AirBus versions?(My recollection of the Boeing 767 RAT is that it provides electric power sufficient to power instruments but not hydraulics. In the case of the Air Canada 767 "Gimli Glider" which ran out of fuel at cruise, there was no hydraulic power- including to the gear, resulting in the nose gear dropping but not locking and collapsing upon "dead stick" landing.) Alex Reid

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the rudder receives mechanical input from the rudder pedals. This input is sent to 3 servomotors which operate in parallel, on blue, yellow, and green hydraulic systems.the stabilizer receives mechanical input from the trim wheels. this input is sent to a single jackscrew powered by 2 hydraulic motors on the yellow and green hydraulic systems. The aircraft has a 5kVA emergency generator driven by the RAT hydraulic system. 2 separate DC batteries are installed. the emergency generator will supply the DC ESS bus though its rectifier, and the AC ESS bus. ELAC 1 and SEC 1 are powered in this configuration providing alternative law.the RAT provides hydraulic power on the Blue system. It deploys when power is lost on AC Bus 1 and 2 and airspeed > 100 kts, or via a switch on the overhead.scott s..

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the rudder receives mechanical input from the rudder pedals. This input is sent to 3 servomotors which operate in parallel, on blue, yellow, and green hydraulic systems.the stabilizer receives mechanical input from the trim wheels. this input is sent to a single jackscrew powered by 2 hydraulic motors on the yellow and green hydraulic systems. The aircraft has a 5kVA emergency generator driven by the RAT hydraulic system. 2 separate DC batteries are installed. the emergency generator will supply the DC ESS bus though its rectifier, and the AC ESS bus. ELAC 1 and SEC 1 are powered in this configuration providing alternative law.the RAT provides hydraulic power on the Blue system. It deploys when power is lost on AC Bus 1 and 2 and airspeed > 100 kts, or via a switch on the overhead.scott s..
Thanks Scott for the explanation. Do you suppose the crew exclaimed "Oh rats!" as the engines shut down? (or other words to that effect!)Alex Reid

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Check out this all engine flame out QRH, from smart cockpit.com, http://www.smartcockpit.com/pdf/plane/airb...nstructor/0036/ In alternate law. you only have the left aileron,the right floats up, like the inboards on the DC-10 at Sioux City. Also the captain has to reset FAC 1 in order to get rudder trim recovery. I wonder what US Air's procedures are,and what the APU usage policy will be from now?

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In alternate law. you only have the left aileron,the right floats up, like the inboards on the DC-10 at Sioux City.
Not according to my documentation but I reserve the right to be wrong :( Alternate law feels very similar to normal law, slightly more twitchy in roll but barely noticeable.
Also the captain has to reset FAC 1 in order to get rudder trim recovery.
True, but in the few minutes they had before hitting the deck I can't imagine they would have been overly concerned about recovering the rudder trim. It would have flown just fine without it.
I wonder what US Air's procedures are,and what the APU usage policy will be from now?
Unchanged would be my guess, they've proved (in the hardest and most stressful way possible) that their procedures allow for a double engine failure at low level and low speed over a built up area and everyone still walks off the aircraft alive. Sounds like pretty good procedures to me, I would have thought it would be every other airline that would say "woah! would our procedures result in the same outcome?".QRH and ECAM drills are all well and good but let's not forget they had very limited time, I'm sure they went through some kind of procedure to get things together but the pair of them would have had to make some very difficult decisions very quickly, time was of the essence, they wouldn't have wasted any going through an unwieldy QRH drill or nonsensical ECAM drill. They would have had to prioritise flying the aircraft and ditching safely well before worrying about drills, procedures and backside covering histrionics, they're pilots you know, not politicians :( that's why everyone lived. Normally summed up with that one, oft overlooked little word ... airmanship.Hope this helps,Ian

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