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.

@ Last Ditch,

the question raised was about a total loss of electrical power, not hydraulic power.

@I-2021
Ooops sorry.
For some reason I was assuming we had lost both engines as well, as at Hudson.

What in my mind demonstrates Captain Sullenberger's professionalism aside from his flying of the aircraft is that he knew, from studying and knowing his aircraft, that the correct ditching attitude was 11 degrees. A very small note in the QRH states this. Any more than that and the aircraft would have slammed down on the water, any less and the engines would have "bit" into the water and caused a break-up.

For those who start waffling on about Alpha floor look at Fatflyers post.

You may read the report first as well ...
The 11 degrees attitude was refused to the pilot even if adequate margin in the AoA before attaining alpha max was available ...
He could not pull more than 9.5 degrees attitude in the flare due to obscure system restriction.

Dear conf iture, where can I find the full report and all the actions the pilot did during their descent and ditching?

thanks in advance

Sully could have landed any airliner in the Hudson that day. He was an excellent pilot. He was restricted on how much he could pull up but he still planned the glide to a picture perfect ditching. His speed control kept the computer from screwing up his flare otherwise the computer would have put him in the Hudson at a high sink rate breaking up the airplane and costing many lives. If you can not flare beyond a certain AOA you can not break your descent rate.

NTSB report ...
 

Just here, earlier in the thread.

Thanks for the correction CONF but my point was he knew what body angle he was after. Not sure if you are familiar with the Airbus QRH but the 11 degrees is a very small note in the ditching checklist. The main reason all survived was because of the experience and professionalism of the crew.

Are we reading the same report ???

The computer didn't stop him flaring, or restrict him - his difficulty maintaining airspeed did that. He didn't have enough enegry to flare when he needed it.


Note: before deciding I or NTSB are criticising the crew: Could it have been done better ? Sure - if flying an armchair with plenty of time to read up on it and a few goes to practice (and BA38 could have made the runway too...). On the day - excellent decision making, CRM and airmanship and the right result. Hampered by a checklist designed for use at 20000ft, he got the speeds a bit wrong and bent the airframe a bit more than he might have. I'll take that any day given those circumstances.

Lets stop eulogising shall we, and call it 50/50 ... sure the crew did well, particularly making the right decision very quickly and not losing focus.

I hate to break up the mutual back slapping party, but just what were Sully's options?

- Slam into a skyscraper
- Do a 180 Glide back to the airport
- Make a left turn and land on miles of calm water.

He's not the first guy to ditch a plane, nor will he be the last, nor is he the first guy to have only one option and not be so stupid as to not take it.

Sure, Sully did not go by the book when he speed was below Vls. However, he was smart enough to start the APU out of sequence. I think that was the single key event which most influenced the outcome as it kept the aircraft in normal law for the flare. (The NTSB has since recommended revamping the checklists and introducing ditching training with dual-engine failure.)

The computer did restrict him, absolutely.
He did have enough energy, not a ton, but enough to improve the touchdown. The system had decided otherwise.

The 11 degrees attitude as mentioned by Lookleft was refused to the pilot.

From the NTSB report pages 97/98

The A320 alpha-protection mode incorporates features that can attenuate pilot sidestick pitch inputs. Because of these features, the airplane could not reach the maximum AOA attainable in pitch normal law for the airplane weight and configuration; however, the airplane did provide maximum performance for the weight and configuration at that time.

So the aircraft gave Sully the max performance that it could. A very different picture to the one presented if you only refer to the aircraft limiting AOA.

F speed for Config 2 was around 150kts and IAS was 125kts when he ditched (NTSB). So he was very close to the stall and was in fact in Alpha Protection from 150' rad alt. So far from the aircraft being at fault I would say that it perhaps saved them at this stage. Sully pulled full aft stick (in order to flare) close to the stall, had it been a Boeing it may well have stalled with disasterous consequences. Of course had it been a Boeing Sully may well have chosen not to pull full aft stick.

The key was his decision to start the APU which kept the aircraft in Normal Law. The aircraft looked after him and gave him the maximum performance it could while preventing a stall. Well done Sully and well done Airbus in my view.

So we can say Sully could have done better with his airspeed and that Airbus could have done better with their checklist but the end result was the best that could be hoped for. Sully looked after the jet and it looked after him.

Absolutely.
It did performed as designed, but that’s not necessarily the performance the pilot was after for working the flare.

... as per its design … but that’s not necessarily the performance the pilot was after for improving the touchdown.

What is a flare Ashling ?


Oh such comment rings a bell, doesn't it ?
Please, would you address it directly to Sully, I think he might put its politically correct discourse aside for the reply …

The good for starting the APU was to assure full hydraulic + electric but certainly not to maintain Normal Law. Direct Law was all what needed to FLARE properly ... without interference.

Where published figures say otherwise … ?

Conf

Sully, and his crew, did a great job on the day. No one, least of all me, wants to take away from that. However that does not mean they did everything perfectly and so it is perfectly reasonable to look at the report and draw lessons from it. That does not amount to a personal attack on Sully. It is the NTSB that draw our attention to the issue of speed control and the effect it had. They also qualify their comments by explaining the effects of task saturation etc.

You quoted my comments re Sully rather selectively. Here is what I said

"So far from the aircraft being at fault I would say that it perhaps saved them at this stage. Sully pulled full aft stick (in order to flare) close to the stall, had it been a Boeing it may well have stalled with disasterous consequences. Of course had it been a Boeing Sully may well have chosen not to pull full aft stick."

I said "perhaps saved them" which is very different to saying did save them. It is fact that Sully pulled full aft stick close to the stall. He was trying to cushion the impact perhaps in the knowledge that he could not stall the aircraft in Normal Law. I went on to say that had it been in a Boeing he might have flown it differently.

Sully's 2 key decisions, to start the APU and to Ditch allied to his leadership and the teamwork of his crew is why they all survived. No one can take that away. However there were issues. A few quotes from the NTSB report.

Despite not reaching this portion of the Engine Dual Failure checklist, the captain stated during postaccident interviews that he thought that he had obtained green dot speed immediately after the bird strike, maintained that speed until the airplane was configured for landing, and, after deploying the flaps, maintained a speed “safely above VLS,” which is the lowest selectable airspeed providing an appropriate margin to the stall speed. However, FDR data indicated that the airplane was below green dot speed and at VLS or slightly less for most of the descent, and about 15 to 19 knots below VLS during the last 200 feet.

The NTSB concludes that the captain’s difficulty maintaining his intended airspeed during the final approach resulted in high AOAs, which contributed to the difficulties in flaring the airplane, the high descent rate at touchdown, and the fuselage damage. (See additional discussion in section 2.7.1.)

The NTSB concludes the captain’s difficulty maintaining his intended airspeed during the final approach resulted, in part, from high workload, stress, and task saturation.

The airplane’s airspeed in the last 150 feet of the descent was low enough to activate the alpha-protection mode of the airplane’s fly-by-wire envelope protection features. The captain progressively pulled aft on the sidestick as the airplane descended below 100 feet, and he pulled the sidestick to its aft stop in the last 50 feet, indicating that he was attempting to raise the airplane nose to flare and soften the touchdown on the water. The A320 alpha-protection mode incorporates features that can attenuate pilot sidestick pitch inputs. Because of these features, the airplane could not reach the maximum AOA attainable in pitch normal law for the airplane weight and configuration; however, the airplane did provide maximum performance for the weight and configuration at that time.The Airbus simulation indicated that the captain’s aft sidestick inputs in the last 50 feet of the flight were attenuated, limiting the ANU response of the airplane even though about 3.5° of margin existed between the airplane’s AOA at touchdown (between 13° and 14°) and the maximum AOA for this airplane weight and configuration (17.5°). Airbus’ training curricula does not contain information on the effects of alpha-protection mode features that might affect the airplane’s response to pilot sidestick pitch inputs. The flight envelope protections allowed the captain to pull full aft on the sidestick without the risk of stalling the airplane.

14. Despite being unable to complete the Engine Dual Failure checklist, the captain started the auxiliary power unit, which improved the outcome of the ditching by ensuring that a primary source of electrical power was available to the airplane and that the airplane remained in normal law and maintained the flight envelope protections, one of which protects against a stall.

16. The captain’s difficulty maintaining his intended airspeed during the final approach resulted in high angles-of-attack, which contributed to the difficulties in flaring the airplane, the high descent rate at touchdown, and the fuselage damage.

17. The captain’s difficulty maintaining his intended airspeed during the final approach resulted, in part, from high workload, stress, and task saturation.

So airspeed control was an issue.

Starting the APU played a key part in the successfull outcome

The aircraft Max Performed when asked to. Had it given him more alpha the performance wouldn't have changed and they would have been closer to the stall. Note that Airbus are only told to highlight this more in training. No where does it say that they need to change the control logic or that the aircraft failed to give maximum performance when asked. You should know that you can raise the nose more to no effect.

Had Sully been able to carry more speed into the flare, F speed or at least VLS he would have found the flare much easier in any control law.

Sorry for all the quotes but you did ask.

Once again, what is a flare, Ashling ?
It is not something you sustain in the time.
It is only a transitory phase very limited in the time.

The potential to improve the touchdown was in the aerodynamics.
The electronic prevented the pilot to get it.

Where published figures say otherwise ?

Conf

I've in excess of 12,000 hrs, flown Mil Fast Jet, instructed, and flown civil Boeing and Airbus. I think I know what a flare is by now. Thank you very much.

The aircraft max performed, there was nothing more it could do aerodynamically. You need to appreciate that more backstick does not always mean less rate of descent or a gentler touchdown. In fact it may mean the opposite. The aircraft certainly knew this hence why it attentuated the inputs to give max performance.

We won't agree so I'll leave it there except to say that Sully, his crew and the Jet did a fine job that day.

Having viewed the landing on the water many times, I can say that the AoA looked highly appropriate, and the "Rollout" proceeded quite well. Again, in viewing the Ditch, I couldn't see much to criticize.

Absent deployed landing gear, she flew somewhat "different", I would say, than in an ordinary TouchDown.

Nose High, what if the Tail Holed? Nose High, what if the Nose planted, instead of skipped? Fatalities, perhaps many. Perhaps all.

You know, data can be a fluffy pillow for those who weren't there, but make a living crunching others' work.

Flare? On a water Landing? Hmm......

In 11 of the 12 runs, the touchdown flightpath angle ranged between -1.5° and -3.6° (the touchdown flightpath angle achieved on the accident flight was -3.4°). In 1 of these 12 runs, a -0.2° touchdown flightpath angle was achieved by an Airbus test pilot who used a technique that involved approaching the water at a high speed, leveling the airplane a few feet above the water with the help of the radar altimeter, and then bleeding off airspeed in ground effect until the airplane settled into the water.

Interesting technique and not one I would have thought of before reading it.