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Spanair accident at Madrid

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Spanair accident at Madrid

Old 30th Aug 2008, 14:08
  #1301 (permalink)  
 
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Could the buckets simply open unassisted? Does it not take considerable force to insert a piece of steel into a 20000 lb thrust stream? It doesn't seem like the bucket would insert itself naturally at full thrust.
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Old 30th Aug 2008, 14:28
  #1302 (permalink)  
 
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Could the buckets simply open unassisted?
No.

Image from Onur Air Runway overrun after rejected take-off. MD-88, TC-ONP, at Groningen Airport Eelde on 17 June 2003

[IMG][/IMG]

Last edited by forget; 31st Aug 2008 at 10:51. Reason: Added details.
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Old 30th Aug 2008, 14:34
  #1303 (permalink)  
 
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Isn't it possible that the flaps/slats were extended in a recovery effort, but too late? That would explain finding the slats extended.
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Old 30th Aug 2008, 15:17
  #1304 (permalink)  
 
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pasoundman

This is really amazingly retrograde thinking. Modern electronics with accurate load cells could easily establish the REAL take-off weight. Any deviation from the load sheet could then be quickly investigated. Correcting for lift in wind isn't an insuperable problem.
Well, the aviation industry have tried and not found it worthwhile, according to earlier posts.
With a background of designing 24/7/365 reliable embedded systems, using the latest then-available electronics, I've noticed many similar, at first sight surprisingly "retrograde" places in aviation. However, looking deeper into the reliability and other design issues, it has become clearer why the aviation industry in general tends to be cautious introducing new solutions. Sadly, I've also followed several recent aviation projects aspiring to introduce radical new technology, which have failed with many million dollars of losses.
So I'm not dismissing the load cell idea as such, but just want to point out that the road to a solution which is sufficiently economical and robust to displace current practice, may not be near as easy as it looks initially.
The wind issue as an example: Probably not insuperable, but I doubt much research has been done to fully understand all conceivable situations and error sources - as there have been no commercial demand for it so far. So someone would have to pay for that research too.
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Old 30th Aug 2008, 15:25
  #1305 (permalink)  
 
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Whatever system logic you have on different types, shouldn´t a warning as essential as an uncommanded TR deployment always come on? I would find it rather strange if that annunciation wouldn´t come on until climbing through 1000' ?
It all depends on how a flight deck is designed, based on the interface between flightcrew and flight deck. Alert inhibition is to prevent alerts being presented during flight phases with a high workload (human factors). Only alerts generated in a specific phase will be inhibited, an alert already active prior to entering a next inhibit phase will not be inhibited. For example, if a TR unlock alert would be presented before reaching 80kt, the alert would remain active when accelerating beyond 80kt.

Depending on design, even with certain alerts inhibited at different phases, system design and aircraft behaviour/performance should give clues as to which problem the crew is confronted with. Based on cause, effect and probability of such an event, inhibition is chosen above presentation. These issues are all part of the certification process for a particular design. Once such criteria are established, it all comes down to training for such events.




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Old 30th Aug 2008, 15:32
  #1306 (permalink)  
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Green-dot;
I would think, the MD82 not being FADEC equipped, there would be a provision in the mechanical interlock to retard the thrust lever to idle in case of an uncommanded TR deployment. Apparently this is not the case on the MD82.

Also I understand there is a difference in operational philosophy between the type I have worked on (Fokker 70 and 100) which inhibit certain alerts- and the MD8x series which apparently do not inhibit certain alerts during some stages of the takeoff phase.
Re attribution...no worries - it's one big dialogue, out there on the table!

To my knowledge, there's no such mechanical interlock which would pull a throttle to IDLE should a reverser accidently deploy. The other side of such a "protection" is the accidental operation of such a system at an inappropriate time...the same logic (and thinking) which is being used in places to discuss an "accidental" deployment applies to all systems including one which is designed to retard a throttle to IDLE - in considering the design of such a system, would it be an actual mechanical link between reverser (which bucket?..top/bottom/both) to the throttles, (very difficult and not reliable), or sensor-driven (pressurization of the hydraulic cylinders which deploy either reverser)? While the problems aren't insurmountable, is the need there? Would the actuators within the pedestal or below the floor/pedestal be clutches (part of the MD80 autothrust system) or separate bell-cranks/cables? On the Airbus, FADEC simply commands IDLE, (not comparing types here, please) so should such a system be software-driven?

I'm not an engineer but I know the outcomes (error-tolerance) of both brittle (those which must work perfectly if they are to work at all) and resilient systems (those which tolerate hardware/software error but still respond successfully). Designing a reverser system that is both resilient and does it's job well without undue risk to the aircraft is a challenge for the engineers. The prevention of accidental deployment in such designs rather than designing a system with "the aftermath" of such deployment in mind, has been a decision of the industry. Accidental deployment is generally viewed, with justification, as a rare though not impossible event- the choice of the industry would be based upon experience, capabilities, weight, complexity, reliability and costs. The reverser systems on the MD80 fleet type are essentially the same as the B737 fleet type - they've been around a long, long time and they're successful systems as proven by the stats...(someone posted a list of such deployments a few pages back - remarkable record really, when one considers perhaps a billion flights in these types from the mid-60's to today with the same basic design). Likely the decision regarding throttles-to-idle was made in this context - rarity, need and cost.

Regarding inhibition of warnings, I can't speak to the MD80 type; the DC9 may have but I can't recall - it was a superb, but pretty basic airplane at the time as was the 737 design. The Airbus 320 type does inhibit non-emergency/non-essential messages according to flight regime. A reverser-unlocked message is inhibited until 1500' on the Airbus, likely because they consider the airplane controllable - also, it was certified this way, with the same assumptions. Again, in the sim it is something one would need to be aggressive with but yaw and roll are not uncontrollable. Again too, FADEC reduces engine thrust to IDLE immediately.

Re,
These issues are all part of the certification process for a particular design. Once such criteria are established, it all comes down to training for such events.
Precisely!

On that point, I would like to digress a moment.

Perhaps out of this thread, among many benefits for those who persist and read but who aren't in aviation, is a notion of how often the cost-benefit equation comes up.

Perhaps out of such (rare, thankfully) public dialogues, people who want a ticket for 20 bucks may come to realize that like their car, their house and perhaps their life, airplanes and their operation, through millions of decisions, are one huge compromise and not the perfect machines (nor the perfect systems) that people assume.

They might also begin to realize that their comfortable, warm seat in a machine that is doing almost a thousand feet per second doesn't come without a price and that "29 Euros, dollars, etc" simply can't sustain a viable, safe aviation enterprise for long.

The potential for some appreciation of this point is present in this and other threads - those who literally whine about the price of an airline ticket by bringing their sense of entitlement to low prices from the department store to an airline need to consider their complaints and perhaps even hypocritical commentary within this very important context.

The angry, innocent and, after an accident, entirely reasonable question, "why?", will always have several components where failure first manifests, and which, until the moment of the accident, may remain known but unaddressed by cost-conscious managers who are trying to do their "very best" for shareholders.

Flight safety departments and programs are increasingly expected, by new-age, MBA'd managers, to be "profit centers". Flight Safety departments, if they exist at all at an airline, are expensive and, to the bean-counters and flight operations managers who spend too much time flying a desk, produce "nothing" and are therefore difficult to justify in both good and bad times.

Flight Safety departments are not "profit centers" however, unless the protection of the shareholder investment and keeping people safe in airplanes is accepted as contributing to profit by not causing lossess.

Such departments are iintended to be an independant intervenor when the commercial aspect of an enterprise takes too high a priority over risk but too often, such departments are seen as backwaters - as career-ending dead-end paths in a corporate world, instead of sharing center-stage with those departments which must make sure that costs are controlled.

Airlines teach the public that they can do this cheaply; "lo-cost" can be done, and safely, but the principles of aviation do not go away; they cost money and it takes more than twenty Euros/dollars to do the work.

The "inventory" for an airline is time and an empty seat which are both ephemeral ! - THAT is all an airline has to sell, (service, of course, but who's travelled lately?!). Once the airplane door is shut, those two "commoditites" disappear forever, irrecoverable assets lost to time but which have had to be paid for nonetheless. Thus the squeeze. Thus the need to fill every seat and even then, a full flight may not be breaking even.

These are the economic realities of all airlines. The next time one complains about the price of a ticket, consider that you are not buying a ticket from A to B. You are paying thousands of people dedicated to your safe arrival, a few pennies each for their services.

Sorry for the diversion...

sevenstrokeroll;
Isn't it possible that the flaps/slats were extended in a recovery effort, but too late? That would explain finding the slats extended.
I think the times involved (seconds) and the circumstances faced by the crew (which, if the slats/flaps were retracted, would not be apparent until rotation/liftoff) would not permit such action, nor would the surfaces achieve their extended position as shown, in the time available.

Last edited by PJ2; 30th Aug 2008 at 16:06.
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Old 30th Aug 2008, 15:40
  #1307 (permalink)  
 
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To my knowledge, there's no such mechanical interlock which would pull a throttle to IDLE should a reverser accidently deploy. The other side of such a "protection" is the accidental operation of such a system at an inappropriate time...the same logic (and thinking) which is being used in places to discuss an "accidental" deployment applies to all systems including one which is designed to retard a throttle to IDLE - in considering the design of such a system, would it be an actual mechanical link between reverser (which bucket?..top/bottom/both) to the throttles, (very difficult and not reliable), or sensor-driven (pressurization of the hydraulic cylinders which deploy either reverser)? While the problems aren't insurmountable, is the need there? Would the actuators within the pedestal or below the floor/pedestal be clutches (part of the MD80 autothrust system) or separate bell-cranks/cables? On the Airbus, FADEC simply commands IDLE, (not comparing types here, please) so should such a system be software-driven?
PJ2 being canadian you should know the CRJ system. It can break your thumb if you have it around the thrust lever
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Old 30th Aug 2008, 16:10
  #1308 (permalink)  
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ppppilot;
PJ2 being canadian you should know the CRJ system. It can break your thumb if you have it around the thrust lever
Being Canadian means a lot of things but it may not always mean knowledge of an airplane, even if it's built in Montreal!.... I haven't flown the CRJ. Does it bring the throttle back, (to possibly break a thumb!), if a reverser deploys? Anyone? I think many would be interested in knowing this...
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Old 30th Aug 2008, 16:31
  #1309 (permalink)  
 
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Airbus factory is not too long from my house and I have visited it 3 times. Bombardier and CAE are very close together at Montreal. I was studying the CRJ type rate there. If you have the chance try a visit. It is really amazing. If I were canadian I would be proud of bombardier
I don't remember exactly the conditions needed, but the CRJ doesn't retard the throtle to idle... it throws back the lever like a canion. Therefore CRJ pilots are encouraged to put the whole hand over the levers at TO not leaving the thumb at the back of them. As sonn as a reverse is deployed during the TO the corresponding lever goes back to idle, mechanicaly. I guess conditions are >80knt <1500' and power>60%
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Old 30th Aug 2008, 16:51
  #1310 (permalink)  
 
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PJ 2

Being Canadian means a lot of things but it may not always mean knowledge of an airplane, even if it's built in Montreal!.... I haven't flown the CRJ. Does it bring the throttle back, (to possibly break a thumb!), if a reverser deploys? Anyone? I think many would be interested in knowing this... Today 16:40
Yes the CRJ has a TL retarder, that with significant force "slams" the TL to idle should a thrust reverser deploy.

CRJ 200 FCOM R58

An autoretarding thrust lever mechanism makes sure that the thrust levers are at idle whenever the thrust reverser assemblies are in transit. In flight, should a thrust reverser inadvertently deploy, the autoretarding mechanism will automatically retard the affected engine thrust lever to IDLE to minimize asymmetric thrust.
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Old 30th Aug 2008, 16:53
  #1311 (permalink)  
 
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Regarding inadvertent thrust reverser deployment.

Lots of considerations have been taken in both the design phase and the certification phase.

For aircraft where the reverser efflux can wash over the wing and destroy pilot commanded roll recovery capability, it is essential that the effulx be diminished ASAP, since it is likely that the aircraft will roll in-flight into the dragging engine. The upset sequence in some flight regimes (high speed climb) is faster than most pilots can interrupt thus the available FADEC instant electronic response steps in. Unfortunately the engine spool down rate and thrust loss can not be instant enough due to inertia and aero issues in the engine itself so only fast thinking and correct interpretation by the crew can easily recover.

An extra layer of safety was then added ,after Lauda by informing the pilots of this behavior and training them to anticipate an inadvertent deployment when one barrier to deployment is activated (reverser light unlock). Even then we have had at least one instance following Lauda where a crew only took temporary action to pull back the engine where upon they readvanced the throttle and the reverser deployed flipping the aircraft on its back (they continued the roll 360 deg.and recovered the flight)

However in the case of aft mounted engines this threat does not exist and much more time is available to recover the aircraft from an inadvertent deployment through normal stick-n-rudder skills.

Now considering warning lights inhibition on any aircraft after V1 and below 400-1000ft. This is done based on human factor learning where it was learned that even precautionary light activation, including electrical malfunctions, were likey to lead to quick but unnecessary actions by the crew to abort flights, overrun the airfield, and by themselves create the circumstances for an accident. Taking into account that most failures of engine symptoms at this flight regime are accomodated by normally skilled crews it was decided that we could save more lives by inhibiting warnings in this flight regime.

I realize that many SLF reading this thread will wring their hands and damm the engineers but I can assure you that this has passed the test of time and been validated by the certification authorities.

Now if you want to more closely examine the "what-ifs" of this specific accident in this regard have at it but don't try to redesign the certification in this thread (take it to another thread)
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Old 30th Aug 2008, 16:59
  #1312 (permalink)  
 
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I'd like to ask pilots familiar with similar airplanes to the MD82 to comment on the questions below. Please allow me to make a few premises:

-Flaps and slats were properly set for TO. Perhaps flaps setting was a bit smaller than it should've been due to miscalculation or some malfunction, but not much. Say they were a couple of degrees shorter than they should've been. They were symetrical.

-Engines (and engine fuel supply systems) don't fail for the duration of the TO.

-Weather and other conditions were like in the accident, except that actual real ones were understimated by 2% (i.e. wind was tail 9kt+2%, airplane weight was 64.263+2%, air temperature was 30º+2%)

-Reversers didn't deploy uncommanded for the duration of the maneuver.

What on earth could make such a plane take some 500m longer than it should to complete V1+rotation, and then roll left-right heavily while entering stall-like condition?

Again, this is not to fuel "speculation". It's just an attempt on my side to learn better how airplanes work and some of the actions involved in take-offs.

Of course replies such as: "on those conditions, it's virtually impossible to produce such an accident" are perfectly acceptable. I just wanna know if there is anything anyone can think of that would fit the picture.

Of course, on-air collision with something, wind shear or major control functions failure could also precipitate the airplane to the ground, but wouldn't likely explain the long roll/rotation time.

Would something like ailerons stuck in "up" position be something necessarily noticed by crew before reaching V1?

If flaps/slats were deployed say "late" in the TO maneuver (say close to V1 the pilot realizes the mistake and lowers them), and by the time they reach VR they are deployed ... then surely, as long as enough thrust is produced, there shouldn't have been any stall, right?

Also, some witnesses refer to the nose angle during rotation as "weird".

Could a cargo piece such as that 400kg refrigerated container have moved and create enough imbalance to "throw off" the nose angle to the extend of being so steep to produce stall but still have the tail not hit the ground? I'm guessing not, but then again I haven't touched a flight simulator in 20 years and have never piloted any kind of airplane.

Again, OBVIOUSLY I don't know what I'm talking about, but I would certainly appreciate for those that do know to please explain a bit what, if anything, they can think of scenarios like these.

And also,

-About how many seconds does it usually take for these planes to reach flaps 15º/slats down from 0 setting?

-If you are flying with the bare minimun V2 and thrust setting to mantain it, and you extend flaps "suddently" from 0 to 15 and activate slats (no thrrust increase)... would the drag lower the speed and produce a stall condition?

-How responsive are the engines in this airplane on 30º air? I.e. about roughly how many seconds it would take them to increase thrust from say 70% to 80%?

Sorry for asking so many questions and thank for bearing with me. I'm trying to get a better picture on how much margin for errors or problems there are in these types of planes during take-off.

TIA.
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Old 30th Aug 2008, 16:59
  #1313 (permalink)  
 
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Reply to 1310 "Is this not the wing"

No it is not the wing. it is a picture of the end of the elevator (or maybe the aileron)
If it is the outer end of the elevator it is the anti float tab and the geared tab you can see atached to the back of the elevator

The rods stikking out are links that control the tabs and attaches inside the stabilizer.


MiloDK
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Old 30th Aug 2008, 17:00
  #1314 (permalink)  
PJ2
 
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Very interesting ppppilot, thank you!...didn't know. So then - the CRJ design or subsequent certification requirements required that the potential for deployment be addressed, possibly due to control issues, (speculating) whereas the MD series did not... For the Airbus 320 series, weight and software design were likely easily-resolved issues. For the Embraer 175/190 series, FADEC commands IDLE thrust if an inadvertent reverser deployment is sensed.
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Old 30th Aug 2008, 17:00
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Reverser deploying in flight.

I'm now retired. I've flown both the DC-9 and MD-80, but it's been many years. I do not have any manuals at hand. Does the MD-80 have clam shell reversers or cascade vanes? I can't remember.

Around 1983 an Eastern Air Lines DC-9 had a reverser deploy in flight shortly / immediately after take off. The Captain observed a reverser light illuminated after his airplane was trying to roll upside down. There was no proceedure for this occurance, but he reached down and closed the fuel control lever for that engine. 999 times out of 1,000 fast hands in the cockpit are a very bad thing. In this isolated occurance, it was the correct course of action. Retarding the throttle may have accomplished the same result. The aircraft returned to the airport, all on board lived. After 5 years on the engineer panel, I was having a hard time coping with heavy weight V1 cuts on the DC-9-30. This model did not have much excess performance to spare. When they demonstrated the reverser deploying after take off to me unannounced in the simulator, I crashed. I did not have the excess mental capacity to notice the reverser light illuminated.

As I recall, maintence had done some work on the engine that went into reverse, and some components of the reverse system were not correctly installed.

It's amazing how accidents involving pilot error are etched in stone and remembered forever. Yet the many times pilots prevent accidents go unreported and are forgotten. I'm happily retired.

It seems to me, after looking at the tire tracks adjacent to the runway used for this accident, that this may have been an instance where a reverser had deployed after V1. The aircraft diverges off runway heading rapidly with both sets of landing gear in the dirt. If the aircraft had stalled, I would expect a wingtip to impact the ground. Power on stalls tend to be rather violent.

All that is learned about flying is not done in the classroom, in the simulator, or by reading the manuals. Much is learned by simply discussing incidents, accidents, and events with other flyers. You never should quit learning. Part of me feels that it is unprofessional to speculate, part of me wants to know what happened, and can't wait for the official report.

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Old 30th Aug 2008, 17:09
  #1316 (permalink)  
 
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PJ2,

Sorry for the diversion...
No need to be. I enjoyed reading your reflection on the subject matter, it was written down very well.


Green-dot

Last edited by Green-dot; 30th Aug 2008 at 22:07. Reason: Correction
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Old 30th Aug 2008, 17:20
  #1317 (permalink)  
 
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milodk.
Reply to 1310 "Is this not the wing". No it is not the wing. it is a picture of the end of the elevator (or maybe the aileron) If it is the outer end of the elevator it is the anti float tab and the geared tab you can see atached to the back of the elevator. The rods sticking out are links that control the tabs and attaches inside the stabilizer.
You say it's not the wing then mention ailerons.

All flying surfaces of the Horizontal Stab are still attached; so what's in the foreground can't be part of it. Below from same photograph.

[IMG][/IMG]
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Old 30th Aug 2008, 17:38
  #1318 (permalink)  
 
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If you look closely at the picture, on the right side you can see the control tab and the geared tab still on the elevator but not the antifloat tab.
on the left side you can only see the control tab but not the part of the elevator with the geared tab and the anti float tab.

the tabs are arenged like this

the control tab is mutch larger the the others

anti float - geared - control- center section - control - geared - anti float



MiloDK

Last edited by milodk; 30th Aug 2008 at 18:10.
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Old 30th Aug 2008, 18:00
  #1319 (permalink)  
 
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Photos: McDonnell Douglas MD-87 (DC-9-87) Aircraft Pictures | Airliners.net

in this picture you can see the 3 tabs

the geared tab is dificult to see, it goes down when the elevator goes up

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Old 30th Aug 2008, 18:34
  #1320 (permalink)  
 
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A picture that may be of interest:
From La Vanguardia: http://imagenes.lavanguardia.es/lava..._JR2908080.JPG

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