A320 tailstrike after radalt failures
 

Incident: Jetblue A320 at Tampa on Sep 29th 2010, dual radar altimeter failure, tail strike on landing

Never flown an Airbus. Is it true that altimeter failure invokes direct law, or were the two (failure and strike) just coincidental ?

Double RA failure means you go from "normal law" to " direct law" when the gear is lowered. Usually the sequence is NORM-ALTN-DIRECT.

Get configured to F3, established on LOC/GS at final app speed(Vapp).... THEN lower the gear to reduced the amount of trimming required on the trim wheel.

You'd have to go some to hit the tail though. :eek:

A4

Just read the link and it says the failure occurred just before the flare. Ouch. If they were in Conf Full then direct law becomes a real handful and very difficult to control on a go around because of the trim change required. Nasty situation, it'll be interesting to read the actual sequence on events.

4

The Airbus A320, A330 and A340 are built with many protections in Normal Law. I suppose A380 as well of course.
Just fly the airplane? You can of course in all these aircraft! But you still have the protections! These protections have avoided crashes at different times!
I' m curious to see how the dual RA failure happened just at the flare? Was it really the case?

FBW 390

When an aeroplane scrapes it's arse on the ground there is only one culprit... the PILOT... but airbus takes away the ability of the pilot to FLY THE AEROPLANE... that is why I will NEVER fly them.... you can argue the point all day but the Airbus system is just wrong.. it has killed too many people...

Let's start with Habsheim.....

Going from Normal Law to Direct Law in the flare is quite likely to result in a tailstrike. For those not familiar with the Airbus, Direct Law is far more responsive and sensitive than Normal Law and requires great care in manouevring. A very unfortunate time to experience a double RA fault for the crew involved.

For what it's worth, when you have a dual rad alt failure, the bus dumps you into direct law. So essentially, you have manual control of the aircraft. The bus becomes a Boeing.... So i guess the moral of the story is, when the computer protections go away, it becomes next to impossible to fly the bus? Where has the airmanship gone? Why couldn't they control this bird in manual law? Every Boeing, MD,Lockheed, is flown in manual mode every day in the flare..... I'm not sure I understand the logic here....

alcan60283

Not as simple a that. Direct Law is far more sensitive than what the pilot is familiar with 99.9% of the time, and is expecting. Going into Direct Law on an approach is straightforward enough to land successfully, but it happening in the flare will definitely lead to overcontrolling. I've flown both Boeing and Airbus and you could liken it in a way to the artificial feel system failing in the flare. Nothing to do with airmanship and down to a very unlikely but unfortunate dual failure which happens to Boeing's and Airbuses.

I don't buy into this Boeing/Airbus/My Dad's bigger than your Dad tripe. All aeroplanes kill people if you want to look at it that way!! :ugh: The Airbus is an extremely safe aeroplane. The Boeing is an extremely safe aeroplane. And this is thread drift!

pilot?
 

Having some difficulty following your rhetoric...

1. are all "tailstrikes" which is the correct term for your vernacular "scrapes it's arse" the result of a single underlying causal factor? That factor is the pilot?
2. [A]irbus flight crew don't pilot the aeroplane?
3. it has killed too many people...

You may be right. Then again, this being aviation, which is somewhat dynamic, I doubt that the real root cause of a tailstrike is solely the poor sod who inputs the final control. In any aircraft. In this case, specifically, a change of control laws near the flare is going to be an interesting event. It is also one that is not trained specifically in the matrices I have to hand for various Airbus programs but perhaps someone is doing this, I just don't know who. As the control laws change affects gains and also changes the trim laws, then I would think it rather unreasonable to blame the pilot so emphatically without knowing what their training is, what the fault was and what actions the crew undertook in the event. All that will be assessed by the NTSB and JB's safety department with full understanding of the facts, without rhetoric or (hopefully)bias.

LRRA failures have occurred before, MAS in MEL for instance, and control law mis-matches have occurred previously as well, ie HDA323, USAir at Washington National etc... and of course LRRA failure has also been problematic in at least one B737 accident, at AMS. Late failures of the LRRA on the Airbus is problematic, as all failures that affect the control laws/gains of any aircraft are.

Airbus crews pilot the plane. The interface is somewhat different, but the crew still input to the system as a pilot does in a Boeing. In many respects the Boeing FBW lags well behind the Airbus system, IMHO in normal law, any Airbus is nicer to fly than the B777, considering control response loop alone (displays, ergonomics, procedures, documentation etc are another matter...). Where the Airbus becomes an issue is in degradation, where a sound knowledge of the systems is necessary, and procedures need to be very carefully followed. Where the failure is a new or novel one, then the pilot becomes a TP for the rest of the flight or until the condition is resolved at least. Mainly this is an education, knowledge and procedures issue, not a pilot skills issue.


"too many people..." What would be your basis for this statement? If it is any, then that is probably true, any fatality is arguably too many. If it per departure, pax flown, ASM's etc I doubt that to be the case, but would welcome your statistics that show the Airbus being more dangerous by any metric to other transport category aircraft.

What is notable in events where gains are affected, is that even with the AP engaged, there is oscillation of the flight path, so it is hardly surprising that a human without time to adapt to the gains may have a fun time acclimating to the changes of laws which are potentially predisposed to causing PIO.

How about getting off the back of the pilot and the manufacturer and awaiting the analysis of the data?

How can people criticize Airbus for it's behaviour with a radalt failure while a Boeing crashed because of it just recently :ugh:

But more importantly: how can you get a dual radalt failure in the flare?
Hope they isolate the failure and prevent it from happening during, let's say, CATIII no dh?:uhoh:

For non A/Bus people. Imagine doing an approach in CWS (not that you would) then as you start the flare the CWS drops out and the input (back stick) you have just made doubles or even trebles, that may give you an idea of why a double rad alt fail at a late stage can give control problems. The a/bus handles well in direct law, but the controls are very powfull.
(CWS=Control Wheel Steering)

I'm sure that if you drastically change the input feedback during flare on the above mentioned airplanes you will see quite a few botched landings...

We don't have all the details of what happened here but as mentioned by others it sounds very unusual to have dual failure in the flare.

Smudger,

A single rad alt failure caused a hull loss and fatalities on a Boeing 737 recently. A duel rad alt failure on this airbus resulted in some scratched paintwork.

Me thinks Airbus wins on this occasion.

Until these biased people start to realise that safety is just the sum of the aircraft design and the pilots flying it we'll continue to get this biased rubbish.

I have 7000 hours with an approximate 50:50 split Airbus narrow body and currently Boeing wide body and have thoroughly enjoyed flying both. They're just tools to do a job and the better you know them, the safer you are.

LD

Smudger:

Ok, I'm game, lets start with Habsheim.

A Pilot that did not now how the aircraft systems/protections work crashed a perfectly good airplane into the woods. The only reason he is alive and that all the passengers did not die is because of the same protections he and you do not understand. The sidestick input he had would have stalled a "regular" aircraft and it would have killed everyone. The aircraft flew into the forest at V Alfa MAX or minimum speed under normal law and thus saved a bunch of lives. Try that on a Boeing.

If he just left the A/Thrust on or would have advanced the Thrust Levers earlier he would have had a much better day.

Read the report and educate yourself!

Next.......

G

Smudger has a point does he not?
IF I have dual RA fail on Boeing,its a total non-event.I fly the plane.No this law or that law.Just me and the stick.Does poor smudge not indeed havea point or are we too stupid to follow this high tech bs.
Turkish crashed because pilot didnt monitor his instruments(read AS) on app..the RA subtle failure created an automation trap which he could have extricated himself from by FLYING THE PLANE.

I'm curious as to WHY, in the Airbus, a double radar altimeter failure causes the aircraft to change 'laws' ?!

And.....could someone point me to a link regarding the 737 crash because of a radar altimeter failure?

DC-ATE

RA fail: Schiphol, Turkish. (As I see it, the RA had little to do with the outcome!)

I agree, the Law "change" is not helpful, why does it do this? If visual (one hopes), the pilot can't land? If soupy, the last thing one wants is manual, full powered controls,imo.

First of all talking Airbus stuff always sounds 800 times more complicated than it actually is in reality leading to more of the 'classic' A/B talks. It's been awhile since I flew the 319/320, but as I recall it's primarily because Flare mode is RA dependent. Flare mode is a submode of Normal Law(see what I mean?). With a few exceptions that aren't really relevant here, the Airbus FBW airplanes are 1G aircraft in Normal Law because the aircraft always trims in pitch to maintain the attitude set. Apparently the designers were afraid that in the flare this would cause overcontrol as their wouldn't be that familar feeling in the flare as the plane slows and goes into ground effect. So they invented Flare mode as basically an artificial feel system that makes it feel like landing any other airplane(my opinion , I'm sure someone will disagree). I may have the details off a bit, but I think it takes a snapshot of the attitude at 50RA and then over the next 7 secs it slowly feeds in a couple degrees(3?) of down trim to force you pull back further and give you that normal feeling in the flare.

Clearly that won't work with a dual RA fault so the plane reverts to Direct Law when the gear goes down so that you get used to what the plane feels like before the landing. As someone already mentioned the normal technique is to get the airplane stabilized on approach at Flaps 3 before dropping the gear so as to minimize the trim changes needed. Like most people I've only seen it in the sim, but as I recall the plane wasn't that touchy in pitch, but was a lot more responsive in roll. So theoretically if the plane was in trim when the RA fault occurred it shouldn't have been that hard to land, but we all know how theories go no matter what plane you're flying old or new! Also I have zero idea what happens to the Flare mode if the RA faults below 50RA, ie I don't know if the downtrim command continues(maybe), is interrupted(probably), or returns to where it was (unlikely). Ultimately whatever the case I suspect it would have felt squirly as most 320 pilots I saw always flew on the autopilot and tended to disconnect it late. I flew it like everything else I've flown. Who knows if that would have helped, but I did notice that a lot of guys who flew it mostly automated were all over the place if they decided to hand fly it at 250 kts or greater. It's not touchy imo, but as always if you don't use it, you lose it.

A 320 FCOM;

"The flight mode changes to flare mode when the aircraft passes 50 feet RA as it descends to land.
The system memorizes the attitude at 50 feet and that attitude becomes the initial reference for pitch attitude control.
As the aircraft descends through 30 feet, the system begins to reduce the pitch attitude, reducing it 2 degrees nose down over a period of 8 seconds. This means that it takes gentle nose up action by the pilot to flare the aircraft."

So depending on where exactly the rad alts failed you suddenly lose the artifical input you are inputting against. Very easy I would have thought to over control on a short term basis. Just a pity that in the flare there is no long term basis!

Direct law control is not a problem, normal flight mode to flare mode not a problem. A sudden jump yes probably would be a problem.

Having flown 15000 hours in everything from 1-11's to 747's, from Boeing to MD to Airbus to Boeing and back to the Bus they all have problems and weaknesses.

It was not a simple failure but something more subtle called undetected erroneous RA height indication. In the circumstances, nothing indicates that an Airbus wouldn't have known the same ending ...

guiones,
Maybe you could also read the Habsheim report ...

And Qantas had the same failure in a 737 and it resulted in a normal landing because the pilots knew what they were doing and can actually hand fly an aeroplane. The issue at play here is the Airbus system and the change of flight laws in a very critical stage of flight.