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Spanair accident at Madrid

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Spanair accident at Madrid

Old 23rd Aug 2008, 17:34
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A few comments about weighing an airplane.
One issue is to be sure the airplane is levelled. Conceivably, that requirement may be relaxed if the only objective is to find out the total weight and the balance aspect (C of G) can be disregarded.
A second and maybe more problematic issue is that any wind affecting the airplane may introduce errors in the measurement. Wings produce lift, even at low airspeed. If the airplane happens to be parked head on to a breeze, the lifting force may be significant - and also dependent on the deck angle the airplane is sitting at. For this reason a proper weight & balance procedure (for GA aircraft anyway) takes place inside a hangar.
I don't know if these are real issues for transport airplanes in practical life, but they may be an additional reason why using estimated average passenger weights has been found a satisfactory method.
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Old 23rd Aug 2008, 17:44
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Originally Posted by FrequentSLF
Understood, however I do wonder if what you say is correct, why such topic is being discussed so widely in this thread. I have seen so many different figures of estimated weight.
that's because everyone in this thread is (unless they are privy to the investigation and breaking the rules by posting here) guessing. None of us know what Spanair's policy on weight calculations is. Or what the empty weight of that specific aircraft was (aircraft are weighed as part of maintenance every so often). Or what fuel load was on board. But it's safe to say that the crew had ONE figure for their takeoff weight, not a bunch of guesses. Was it precisely the weight of the aircraft - no. Was it close enough to be good enough - almost certainly.

You are confirming what I was thinking however I am still puzzled because the cost of load cell weighing system will be a few tens of thousand of Euro. The measured weight could be compared with the estimated weight adding an additional layer of safety. If the system is broken or in error the estimated weight could be used.
Why would I, as an airline, pay even that amount of money for a system which could only ever reduce my payload - since you're proposing using the estimated method as well. Such a system really only becomes attractive if I can add cargo or passengers when I use it. Yet by then it's too late, in all likelihood - once everyone is on board, I can't suddenly try to add more cargo without incurring delays.

snowfalcon has also noted a couple of the technical issues with such a system; they can be overcome, but its not simple.
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Old 23rd Aug 2008, 17:45
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I would like to ask the mods if they would make a sticky of the known facts of the investigation to save me wading through pages of conjecture.
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Old 23rd Aug 2008, 17:54
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The basic structure designed in the 1960's, when precision weight measurements with onboard sensors were not around, the plane was probably designed for MTOW to be [worst case scenario + 15% or more]. The engineer of "yesteryear" would not place a absolute maximum anywhere near the actual lift limit of the wings, or structural limit of the airframe. Carrying more to even more weight than published should not significantly endanger the flight.

The pilots forgetting to configure the wings for takeoff is a rare event, and having the takeoff configuration warnings disabled for whatever reason is a rare event as well. Having both happen on the same flight is extremely rare and two cheese holes that have to be almost forced to line up (seems highly unlikely).
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Old 23rd Aug 2008, 18:46
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What's more, unlikely earlier rumors, no evidence of any of the engines (visibly) failing exists.

New public accounts by politicians briefed by other politicians with access to the Aena tape speak of the pilot "eating up the runaway to the limit" (probably not so much so) and the airplane "noticeably not having enough power to take off" (basically, speed seemed to them too slow to successfully taking off). Again, no visual indication of any catastrophic failures until the airplane "hits the ground".

All these reports should be taken for what they are: non-experts explaining to the public what other non-experts have explained to them.

One of the survivors, the woman in critical condition, died recently. Thus 18 survivors, 154 victims (2 died while in hospital). Now only 8 survivors remains in serious condition, with only 3 of those severe.

Someone shot the press an estimation of 15 months for the investigations to complete. ¿?

Spanair had a technician explain the (minor) maintenance that caused the first return to gate today.
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Old 23rd Aug 2008, 18:48
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Greetings!

I am not going to comment on this particular event, but the issue of having sensors to measure actual aircraft weight.

This system has been tried out on several aircraft models over the years with little or no success. The problem is, as already has been pointed out, is to get an aircraft in a level position to get the weight right. This is virtually impossible on a ramp. The other issue is what type of sensors will be used...? Pressure transducers in the landing gear struts are most practical, but again level and friction in the struts will significantly affect the readings. We have the NLG pressure transducers on the B777 for "stab trim greenband" check, but are having trouble with this relatively simple system.

After all this; accurate OEW weigh jobs, pax and cargo weight estimates is still the best solution today and gets you within a safe range...

Dag
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Old 23rd Aug 2008, 18:57
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Newpapers report the pilot had some 7000 hours (10 years) of experience on MD-80's series and the plane had performed a Barcelona-Madrid flight previously to this one without incidents.

The oficial explanation on the maintenance performed prior to take off is:

"A malfunction of the heater of the probe that measures the outside temperature while on ground as well as flying". The failure was in the mechanism that allows the probe to be "on" during flight and automatically deactivate while on ground" (I know it's somewhat contradictory to say in the same sentence that the failure was thought to be with the heater to then say it was with the automatic on/off switch of the probe, but that's what the expert brought by Spanair said to the families).

The 41yo mechanic had 20 years of experience and decided to deactivate the *probe* (according to the ...ehhh... probably-not-too-reliable reporter writing the news piece), considering the weather conditions good enough to safely fly w/o said mechanism.

Again, freaking confusion, I think the reporters are saying the wrong thing and only the heater was de-activated due to some failure of the on/off autoswitch (to heat while in fly-mode and be off while grounded?)

Perhaps we should just assume the whole probe was innoperative.

So the "literal translation" of the news piece on the technical briefing is, once again, not-all-that-clear. Either the heater didn't work or the switch that turned it on/off on air/ground didn't work and was disconnected. Or something.

Last edited by justme69; 23rd Aug 2008 at 19:12.
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Old 23rd Aug 2008, 19:28
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weigh in

Just a side note....up thread it was noted that this flight was normally not holiday types but business and residents so that luggage should be less.

As background I find that an interesting conjecture as after 30 some years in the industry I have seen it exactly the other way....couple bathing suits and sandals do not weigh much for the tourist but island residents will bring everything including the kitchen sink in an attempt to get around paying duty and higher prices on the island for the same goods than on the mainland.....and in more than a few cases goods that cannot even be found on the island at any price. In fact I see island residents pool together and send one on a shopping trip to bring back for many.....the one traveling get's a free trip to be the 'buyer'.

One other note in regards to weight....fuel is always far more expensive at an island station that on the mainland so aircraft are routinely fueled heavily on the outbound to reduce both cost and turn time for the return to the mainland.

Yes...all luggage is weighed but for the reason of charging for bags over the allowed weight....not to fill out a weight manifest. However, in the US the FAA has mandated that bags over 50 lbs be counted differently and a higher average weight used...whether this European carrier has the same procedure I do not know.

Overall I would expect the piece count per pax to be higher than an average Euro domestic trip/Holiday trip and the weight per piece also higher.
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Old 23rd Aug 2008, 19:47
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More speculation.

Maybe the 'OAT' probe issue combined with the whole 'return to stand' issue and time pressure/ fatigue combined and caused them to miss something else.

To me it looks like they tried to fly an aeroplane that was not quite ready to fly.

Either it was too slow or not properly configured.

The 'deployed' TR was likely a product of an attempt to stop once they found themselves 'off piste'.

Having speculated- to no useful prurpose- I don't suppose it will take long for the truth to surface with this one.

There but for the Grace of God.......................
 
Old 23rd Aug 2008, 20:04
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Do I understand that
1) the aircraft lifted off and then landed again
2) prior to the flight something was wrong with and/or done to a probe and/or its controller
3) the data from said probe is only used in flight?
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Old 23rd Aug 2008, 20:15
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Unacceptable

From Post # 358:

The practical value of video runway surveillance at airports has been known for decades and has been (pretty sure about that) recommended by crash investigators. Even if it hasn't, the benefits are still pretty obvious. A few cameras on the control tower would do it, with infra-red for nighttime. It could be used by airlines to monitor landings, enable analysis of RTOs and go-arounds, minor collisions on the ramp, etc. etc. And that is before stating the obvious value in a crash investigation on or near the airport (about 70% IIRC of crashes are within a mile of the tower). And in the US there is a lot of worry about land and hold short, and about potentially disastrous on-ground collisions and runway incursions. Video would help analyse all that.

The reason they are not installed is because if any such images became public it would be bad PR for the airport and the airline.
(emphasis added)

* * * * * * * * * *

And THAT IS JUST PLAIN WRONG!!!

The various regulatory agencies (FAA here in the States) should have, as their top priorities, the advancement of safe operating practices, accident prevention, and a safe environment for passengers and crew. Instead, proposals such as this are permanently shelved because these agencies are, as you say, more concerned about bad PR for the airport and the airline.

I heard that, a few years ago, a very advanced version of the "black box" was being sabotaged by the Industry because the more information it could collect, the more likely it could pinpoint possible negligence by the Carrier. Heaven forbid. The corporate lawyers certainly can't have any of THAT!!!

The airlines call all the shots and the regulatory agencies just go along with it all. The tail wagging the dog.
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Old 23rd Aug 2008, 20:16
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So far, after all the posts wasted on the subject, it's not even confirmed whether it was the OAT or RAT/TAT probe that caused the problem.
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Old 23rd Aug 2008, 20:29
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Suggest we maintain the status quo!

This is my first (and last!) post since joining this forum. I would just like to say that even the 'clinically thick' are able to determine whether comments submitted to the PPRuNe are from individuals who are either CPL/ATPL and therefore know and understand the substance of matters they are talking about. I have long since been intrigued by the character of any individual who is able to sit at the front of a high powered tube and traverse long-distances over plains and oceans, where at any moment the dull and ordinary can rapidly move to the most terrifying of experiences.

It is clear (to me at least), those who truly understand what FADEC/EICAS/EGT/EPR/DME/ILS/AoA/BA/V1....etc means, and how these systems and processes are applied to control modern commercial flight. The quest for knowledge is liberating and the professionals on this forum should remain, so that those who do not know what they are talking about are clearly exposed.

As one of those SLF's who smells fear the moment the wings of any aeroplane moves a mm from the horizontal, my sincere respect to all those individuals who we rarely meet and equally less get to know, who are prepared to apply all their professionalism and skill to take us safely to any far flung part of this planet.

Finally, I would like to close with my deepest condolences to all those who have been affected by this most recent tragedy in Madrid.


sAx
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Old 23rd Aug 2008, 21:17
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Any guesses how many weeks/months before the official inquiry results are out?
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Old 23rd Aug 2008, 21:29
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sAx_R54,

Informed comments do not only come from "individuals who are either CPL or ATPL", who "truly understand what FADEC/EICAS/EGT/EPR/DME/ILS/AoA/BA/V1....etc means".

There are those individuals who design and/or maintain aircraft, who know equally well what that alphabetti-spaghetti refers to, and whose informed comments can be equally valuable.

CJ
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Old 23rd Aug 2008, 21:44
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Also the alphabettii - spaghetti can confuse the debate.

IF, and it is a big if, the evidence shows that this aeroplane left the ground at less than required aerodynamic flying speed or failed to maintain speed for more than a few seconds then it simply aerodynamically could not fly. Most student pilots who have studied the principles of flight could deduce that.

The reason for that could be down to the complex issues people are throwing into the ring here, or it may not. The only people who will truly know are those that decode the Flight Data Recorder.
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Old 23rd Aug 2008, 21:50
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Well, that's it. It seems the media has lost interest in the story and information has stopped to a trickle.

Information given is VAGUE and by non-experts, therefore conclusions as to what happened are somewhat speculative. But what was said before applies. Here are known facts coupled with my own free interpretation.

-Flight prepares for T/O but returns to gate after pilot warns PAX of a malfunction indicator (red light) he is unsure about and he wants checked by a technician. Plane returns to gate where technician and pilot agree it's a warning related to the outside temperature probe heating device (probably a faulty automatic on/off switch). Either the heating device (likely) or perhaps the whole probe (unlikely, just a few reports probably mistakenly speak of this) was tripped-off (or fuse removed). Pilot and technician agree no suspected wheather condition will make the heating device needed operative (no danger of ice to perhaps foil reading the outside air temperature). They both sign the plane fit-to-fly. Pilot informs PAX that the small problem with the "heating sensor" is fixed and they are now going to leave (after about 1h delay).

-Plane starts acceleration and rolls. Some account the plane as moving slow, rolling quite late in the strip (but at least +600m still available), perhaps having a "weird nose angle" (a bit too steep?) without any other visible indications of malfunctions. Politicians witnesses of the security tape insists on the plane looking like "it didn't have enough power to take off".

-Front wheels (and likely back wheels) leave the ground, only to have the airplane behave erratically and "fall" soon afterwards.

-Once on the ground, the plane suffers unspecified damage. Some official speaks of a wing briefly touching the ground. The plane, probably, tries to brake and briefly thereafter loses control and turns right, getting off the strip (when at least +300m, possibly +500m of flat surface was still available in front of them). It then crashes.

Information being insisted upon: No visible damage (i.e. fire) on the plane on the video recording of the accident until after it "came down and touched the ground". And "the plane looked like it lacked enough 'power' to take off", for unknown reasons. Fire or engine problems, from a visual point of view, only seemed to have hapenned as a RESULT of the inability to sustain flight (or fully take-off, as it can be interpreted also), and not as a CAUSE. Again, speaking visually from the outside of the airplane. There is definetly no "explosions" or obvious visual malfunctions of any kind with the engines at that point.

I have no idea how, in such a long runaway, the pilots couldn't notice on time a severe lack of thrust (presumably on both engines) and couldn't correct it (or abort) and instead tried to take off presumably below V2m and perhaps at a steep angle (or perhaps the angle was shallow and they were trying to compensate ... the angle is spoken of as only being "slightly weird" or "slightly unusual", but doesn't mention whether it was steep or shallow). No mention whatsoever of flaps/slats.

It seems reasonable that after hitting the ground (on the landing gear) and bouncing around a bit the pilots possibly decided to try to stop (i.e. deploy reversers, brake hard). Somehow control was lost and the airplane didn't continue (much longer) on a straight line, coming off the side and finally hitting terrain obtacles several hundred meters later at a very high speed (as plane damage and victim's injuries would suggest, where every single survivor spoken about had one or more fractures and reports of several hard to ID victims with limbs severed would suggest).

Unfortunately, the Flight Data Recorder suffered some damage, which would no doubt delay a better understanding of what happened and what could've caused it.

I have the feeling that unless some major startling discovery is made, the probable causes of this accident are a long time away. Those witnessing the tapes say things like "you can't see any problems on the plane from the footage" (perhaps the resolution is not good enough to calculate things like slats angles, etc, without heavy analysis)
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Old 23rd Aug 2008, 21:55
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I read a survivor account, as reported in the media today. She reported that the aircraft became airborne, abruptly dropped a wing, suffered roll oscillation and then landed heavily and broke up.
Having not read this thread before I have skimmed through and note:

1. Someone posted that the wing LE devices appear to be in the retracted position.( this from a photograph which I have not seen)
2. There is speculation that the pre departure rectification work could have disabled the takeoff configuration warning
3. It is reported by survivors that the Captain talked ( via PA?) of an unexplained warning light.

In my experience, it is essential, under conditions of disruption such as a return to the gate and/or maintenance rectification, that checklist discipline is strictly followed. Is is easy to overlook items, or falsely 'remember' that they have been completed, under the stress of a non normal situation.

From the survivor description sounds as if the aircraft entered a stalled condition after climbing out of ground effect. If the LE devices were not selected ( maybe the Captain saw a visual warning that they were not set, but was confused by not getting an aural warning?) and takeoff was commenced, rotation would start at the normal point, but the aircraft would not get airborne until a considerable distance afterwards. After a late lift off and climb to low altitude, the wings would stall as they came out of ground effect, leading to loss of lift and the observed roll oscillation.

Then assume the crew, having a fair distance of runway left, tried get it back down, touching the right wing as they do so. The priority would be to stop asap, so it would be natural to apply max brakes and reverse. That would explain the reverser deployment and runway skid marks. Loss of directional control would have lead to the break up and fire, in the drop off to the right of the runway.
This scenario would not have been helped by an engine failure or uncommanded reverser deployment in the air,of course.
This is, as are all these posts, speculation but appears to fit the facts as so far described.

A terrible accident which serves to remind us all how quickly the routine can turn to disaster, in a moment. Condolencies to all who lost family or friend in this.....
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Old 23rd Aug 2008, 22:02
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Rat,art,atr

In the MD,the RAT probe send temp data into Air Data Computers.These, in digital format feed both digital flight guidance computers.The DFGC compute the EPR for each flight phase and pilot seleccion through the TRP(thrust rating panel).The RAT probe is heated only in flight for anti ice purpose.If for some reason,the ground sensing relays ( energized in ground) change to flight condition,the Rat sensor is heated and the EPR is reduced. This change may be for a circuit breaker open or a ground sensor relay fail .This condition may afected the takeoff condition warning too.All of this is not too much evident for pilots.
The ART ( automatic reserve trhust) is used only in normal TO EPR. Not in flex. or max. Is activated when the DFGC sense diferences (30 % ) between both N1 .Not is autothrottle funtion but inside the fuel control unit. Increase about 700 lbs thrust or .05 EPR to the present thrust.
The ATR ( auto thrust restoration) with the last DFGCs (-972 and subsequent ) only is active in noise reduction cutback procedures.
Accept grammatical corrections
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Old 23rd Aug 2008, 22:34
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777Fly, I stated this in two lines approximately 100 posts ago and you are one of the few to even address this likely issue. Rushed Crew, failure to configure, loss of CAWS power. Would fit the picture. And I believe in the absence of any further information, the scenario that fits the accident most closely so far.
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