Spanair accident at Madrid

[justme69]

This post is for those recent posters who favor mechanical error with flaps deployment. The rest can just skip it.

I'm not an aviation expert of any sort nor an MD-82 pilot. I have only travelled as a passenger in those or any other airplanes. Some experienced pilot should help me out with the correct explanations.

But, as I understand it, NOBODY, let me repeat, nobody is ignoring the possibility of some sort of mechanical malfunction with the flaps/slats. But, as those that know can explain much better than I could, there is a 99.9 to 0.1 chance that it was human error rather than mechanical.

First: over 60% of all aviation accidents are due to human error as the main cause. This an statistical fact, whether you like it or not. Only less than 30% are due to mechanical/electric failure as the main cause. About 10% are due to climate and other reasons. This is the way it is. Therefore, when there is an accident, chances are it was human error. You should not "dismiss" human error as the least likely cause. On the contrary, (some studies say as much as 80%) is usually the real cause. It's the same with car traffic accidents. Cars usually don't "break" and cause accidents. It's usually the drivers doing something wrong.

Second: An MD-82 pilot could say this more clearly and more authoritatevily. An MD-82 should NOT take off without the flaps extended. They can be extended as little as a few degrees or, in situations with heavy weight and short runaways, much more (i.e. 11º). Of course, a more powerfull MD-83 or one without much weight or a long runaway could take off w/o flaps, but it is NOT recommended to do that.

Think about it. First: the flight plan that the pilots had for this takeoff called for flaps 11º. Second: their first line up for take off (before the return to gate for the probe heater problem) had the flaps correclty selected to 11º according to the investigation (as recorded on the FDR). Third: the recommended configuration for the airplane is flaps 11º on those circunstances. Are you trying to tell me that they tried to take off w/o flaps on purpose or that they were trying to takeoff with flaps 11º but they (perhaps) FORGOT to set the flaps? If you agree that they SHOULD and probably TRIED TO deploy the flaps 11º, then trying to argue that an MD-82 routinely takes off without them (0º) is pointless (besides not being the truth). The speed calculations are different for flaps 0º and 11º if you want to avoid getting too close to stall.

An MD-82 does NOT usually take off with flaps at 0º. It is not designed not recommended that it does so. Ever. It COULD take off under some circunstances, though, but this doesn't seem to be the case.

So the conclusion is: The crew either forgot to deploy the flaps or the flaps failed to deploy. Those that say that this flight SHOULD have taken off with flaps 0º, don't know what they are saying.

Now, on to the slats.

The slats are "mechanically linked" to the flaps controls. I do not know if the MD-82 can deploy the slats with the flaps still at 0º. But I do know that this is not "normal" and that usually, on the MD-82, one would deploy the slats are part of the same operation as setting flaps. If you forgot to set the flaps, i.e., you probably didn't set the slats either. The investigation will probably be able to find if the slats were set or not. But the investigation is pretty sure the flaps weren't set. Therefore, we must now assume the slats weren't set either, until proven wrong.

Trying to take off without flaps 11º probably reduced the speed needed to enter a stall situation by some amount (say 10 knots), but the slats retracted added some other amount to that (say another 25 knots).

So if the flaps weren't down, the slats weren't probably down either. If the flight was planned for flaps 11º, and the flaps were incorrectly set to 0º, then the speed calculation were X (i.e. 10 knots) too short for a take off or even much more (i.e. 35 knots) if the slats were also not out.

Now let's analyze the mechanical against human probability of this error. The way the flaps are set on the MD-82 has been explained in this thread before. It's a very simple mechanical system which is extemely reliable. Unlikely that it would fail. Also, even if it failed, the pilots should've noticed when they read (they are required to do it) the indicator that reads back the settings of the flaps. So even if the flaps mechanically failed to deploy, the pilots STILL made the error of not reading the indicators correctly.

So in the "pilots forgot to lower flaps/slats" against the "flaps and slats malfunctioned" theories we have:

-A 60% pure statistical chance of human error against a 30% chance of mechanical.
-A previous take off and planning for flaps 11º and a manufacturer recommendation of T/O with flaps over 4º for most situation and never (recommended) at 0º. It looks to me like a high chance that the flaps SHOULD have been deployed.
-A very simple flaps mechanical system that has been proven reliable "always" before. Chances of flaps being selected to 11º and the flaps not coming out at all are very low. Even if they did fail, the pilots should've noticed reading the analog dial.
-A slats system linked to the flaps deployment. They lower from the same set of handles (please, correct me if wrong). If you forget or incorrectly set the flaps, chances are you didn't correctly deployed the slats either (could happen, but unlikely).
-An airplane that fell down for what symptons are consistent with attempting to takeoff without flaps and/or slats.
-Other instances were accidents have happened on MD-82 (DC-9-82) when taking off after the crew forgot to deploy the flaps/slats (Northwest, Detroit). Also, it has happened to others as well (LAPA, MAPJET). So "forgetting" to deploy the flaps/slats is not "impossible and less likely than a flaps mechanical failure". On the contrary.
-Even if the flaps failed, the crew should've read the dial indicator. Even if the slats also failed, the crew should've read the colored bar indicator.

And we know the investigation, at this point, concludes the flaps were at 0º.

Now, about the "prior days" AUTOslats failures on the airplane maintenance log. Again, I have NO IDEA how an MD-82 is "made", but from what has been explained here before by those that do, the flaps have 3 setting:
-Retracted ("off")
-Mid (Deployed to a certain angle "mid-way" that roughly corresponds to the right setting for flaps up to 11º)
-Autoslat (An autoslat computer sets the correct angle ABOVE MID-WAY depending on the circunstances for flaps from about 13º and more).

The "retracted" and "mid" settings are MECHANICALLY set. As a result, the slats are either "off" or "deployed to some degree" MECHANICALLY and this can be seen by the pilots on the indicators that MECHANICALLY link the correct position to the indicator. If the pilot sees that the indicator color is set for the slat, the slats are at least set to the mid possition.

So that is enough for take off. The AUTOslat is NOT necessary or normally used for take off.

And it was the AUTOSLAT fail warning light that turned on a couple of times before. While I'm not 100% sure what the autoslat warning light signals (i.e. correct settings can not be figured by the autoslat computer or assymetrical wing settings), those are usually only used during LANDING anyway with flaps set over 13º or so.

Besides, an occasional AUOTSLAT (don't confuse with plain, mid "slat" extension) fail light is a KNOWN "glitch" with the MD-82 and often can be dealt with just retracting the flaps/slats and re-deploying them. If the light remains on, then I'm assuming new LANDING must be calculated for flaps 11º (flaps less than 13º) and mid-slats (thus, turning off autoslats), as that's the "safe" setting that "can not fail", as it is fully mechanically linked and fedbacked. Of course, if the analog dials still show the incorrect settings, then I guess one must plan and calculate a high speed landing w/o flaps and/or slats.

Again, I'm not sure that's the way it works, just the way I understood it. Some MD-82 expert could probably correct any mistakes I'm sure I must have made.

Also, it is not the "authorities" not speaking of "human error" (yet). It's most of the press, specially the newspaper "el pais", which has QUOTED ME very extensively without permission (copied-paste) on one article and changed every occurrance of "pilot error" with "flap deployment failure". Some other newspapers (about 1/3), openly speak of human error.

Again, NOBODY denies the possibility of the pilots setting the flaps and the slats correcly and those failing to deploy. The pilots probably still "screwed up" since they didn't notice the dials indicating the WRONG settings, though. And also, the chances of both the flaps and slats failing to come out when the handles were activated are, in all reality, very very very small.

On the good news, only 8 survivors remain hospitalised. 5 with significant medical issues still. Only 2 of those in serious condition, one of which is still in intensive care in very serious condition. But both doing better. All, in fact, doing better.