A320 and the Miracle on the Hudson
 

I'm sitting here watching a Discovery program on the Miracle on the Hudson. The program seemed to hint at something I found very interesting, and I wanted to turn to the experts.

The program suggests that during the final flare, before touchdown in the water, that the A320 actually controls the pitch attitude of the aircraft - not the pilot. That not matter what input the pilot gives to the side stick, the aircraft will deliver a perfect touchdown attitude (approx 7 degrees.)

As I am not familiar with Airbus, fly by wire, etc, I wonder...is this true?

Hi Rtrhead,

short version: no way
long version:
In normal circumstances, the FBW will switch into a so-called flare mode as you approach the ground (or water...) and will introduce a nose-down elevator input, forcing the pilot to actively input up-elevator to maintain attitude. So without pilot input, the aircraft would actually lower the nose and make contact at a higher rate of descent.
But this is only for normal OPS. If the FBW system switches into an alternative mode due to power loss, the handling changes (to a point where the sidestick deflection is proportional to evelator deflection) - but at no point will the FBW system automatically pitch up to a specific attitude in either modes.
I'm not sure in which mode the hudson bus was in, shortly before contact. Even if both generators tripped offline (due to low engine RPM), there is still the RAT (a small turbine which drops into the airstream to deliver electrical/hydraulic power to key systems) plus I think the FO started the APU as part of the drill - but not sure if it was online at that point. If so, the FBW system would have been in normal law the entire way down.

@RtrHead

Yeah, the busses are fully automatic. Even with all engines out. Just press the "ditching" button and get a cup of coffee.

If you are in a deep stall, don't worry. You and your fellow will not know anyway and the BEA or whoever will take care to cover AB asses.

In Flare Mode, is Alpha Floor still active?

I'm wondering if what the program is alluding to is Sully going for minimum speed, holding the stick full back and letting the FBW maintain attitude for Maximum Alpha?

Absofreakingly not true.

The Hudson ditching was made in normal law, speed got so low that alpha protection was activated. It's not active during normal landing, not because it's deactivated but because excessive AoA is not approached.

Before this thread gets clogged by the contributions of "FBW is dangerous!" brigade, I would suggest that we use NTSB report as the beginning point of our discussion.

On the contrary, it displayed all the best aspects of FBW.

BUT, if Alpha Floor WAS active, it is KINDA right that at that stage the FBW was controlling the attitude, as the pilot was (probably deliberatly and with good reason) holding back stick in order for the FBW to deliver minimum speed at touch (splash?) down.

Do you really think, Chesley Sullenberger and his F/O could it manage only by FBW?

On a 737 they wouldn't?
:ugh:

NTSB already answered that, far, far, far better than I ever could.

Did they?

And did they leak it to the press first?

:cool:

Sully could have landed any Boeing in the Hudson as well as the Airbus. Don't give credit for his skillfull landing to a machine because Sully did it with his skill and nothing else. Airbus has a lot of automatic features but none of those helped him that day. His talent as a pilot saved all of those people, nothing else. We are all very proud of him.

Just curious, full electrical failure, no batt or gen power...can the Airbus be flown?

Nope. Ditto with all Hyds gone.

Neither can the B777 or B787, for that matter. All hydraulics out, just about everything in the last 30 years for transport category planes.

GF

Yes, the airplane will fly in mechanical backup, that is mechanical control of THS via the trim wheel, mechanical control of the rudder and finally the thrust via the normal thrust lever control. It is a very very unlikely situation, because you need so many failures to end up in this situation that it is really unlikely to happen, but still you can get yourself out of it.

Cheers.

Hi,

Just to be pedantic, alpha Floor protection is an autothrust function which adds TOGA(full) power and locks the thrust at this when the angle of attack reaches a certain figure. It is not a flight control function. They would not have had this as the engines had failed! it is also not available below a certain rad alt height.
The flight control protections, alpha prot and alpha max may have been available( if still in normal law) This would have allowed the aircraft to sink at just above the stall speed (as in habsheim crash) but would not maintain a pitch angle at touchdown(splashdown) it would however maintain an angle of attack if the stick was held full aft.

I think that "miracle on the Hudson" needs to be left where it belongs .. in typical media gross hyperbole.

The crew did a fine job - no-one doubts that - and underlying that was their ability to assess the situation and make a workable decision in a short timeframe.

Without taking away from their performance on the day, is it not reasonable to presume that a majority of experienced, competent crews probably would have gone for the same gameplan ?

What impressed me - from an NTSB interview transcript (which I linked in another thread) .. it was the F/O's first flight post endorsement training.

The crew necessarily had to ad lib a bit and, with the benefit of hindsight, possibly would have done the odd thing a little differently .. but a mighty fine performance overall in this observer's view.

I would also dispute the title. This was not a miracle. It was professional pilots doing a professional job. That is not to be seen as taking anything away from their achievement on that day.

It also clearly highlights the difference in outcomes when you have a crew in tune with their aircraft.

FULL RESPECT TO THEM

@ I-2021

We still need Hyd actuators to move the surfaces (G/Y for THS and G/Y/B for Rudders). This is unlikely in this scenario. However, if you have Hyds going, the Bus can be flown. I actually managed to "get her down" on one of the two occasions attempted during sims.

Fly By Wire
 

Read the book.... Fly By Wire, The Geese, The Glide, The Miracle on the Hudson by William Langewiesche.

It explains in detail the capabilities of the aircraft and the events which occurred. It by no means expresses that either Sully or FBW were the dominant contributing factor to being "the miracle" that we all know of. It does however allow you to decide on your own what was happening that day.

Also a very intersting read into FBW systems.