Notes from an airfield design perspective
In the interest of brevity, I'll minimize mention of how I became involved to some degree in airfield design work; and likewise minimize the detailed derivation of some conclusions which may be of interest (based on personal experience). At this point I've read over 2000 posts on three sites, on this matter. Since I am familiar with runways, you'll notice that I tend to see their less desirable features; and lean toward a philosophy that they should be made forgiving if at all possible. That said, our own DCA illustrates some of the economic difficulties of always achieving this.
Runway length - Mention was made somewhere that this runway was a long as DCA. It is true that DCA operated jet ACFT at about 6300 feet for a rather long time (10-15 years), but it's now been 20-25 years since it was extended to 7000 feet (US concensus minimum for any jet operations at all at the time) with added overrun as well, to perhaps 600 feet IIRC. The adverse turn at the north is well known; less well known is the problem caused to approach from south by a 6 or 7 foot levee against Potomac River flooding.
The runway here at Sao Paulo remains short (6362 feet?), although it may be said to be marked off such that there is a 400-foot paved overrun on the accident end. However, the elevated approach end terminated in a steep embankment tends to make planes land consistently at the long end of the landing zone (see vertical photo). This could be called an awkward detail.
New paving - Asphalt paving overlay obviously has advantages in minimizing out-of-service time in an operating airport. A disadvantage is the difficulty of controlling the mix such that the desired surface friction is obtained-- on occasion problems can occur, and the investigation should look at this. Some asphalt work is very demanding.
Missing grooving - As for grooving, this should be thought of more as performing the same function as the grooving of the tires. It is hydraulically most effective if crosswise; a picture of the older surface shows it lengthwise, as well as showing the typical ruts formed by gear weight over time (the ruts will fill with water, is the problem). It is OK to think the grooves will store a little water and buy time (1 minute?) in a downpour, but I question whether they much aid the removal of water to the side (due perimeter drag of the small cross-section).
Hydroplaning - As there is a 1 percent downgrade, the water path to the side may reach 100 feet on a diagonal. At approaching a minute to go this far, that's how long it will take a heavy downpour burst to create a depth of water that's a problem (typically deeper than the tire grooves) particularly off the runway centerline, increasing to the edges. There is some thought that the depth of pavement grooves adds effectively to that of the tire grooves. So the lack of trouble to the preceeding plane is not indicative that the accident plane did not encounter sudden hydroplaning conditions.
Bright flash artifacts in the surveillence videos - I had occasion to write the section on runway/taxiway lighting and signing in the late 60's airfield design standards/details manual for one of the military services (US). Although modified for military types of course, it was based on civil aviation practices at the time, per extensive interviews including controllers and pilots. It may have been the first time a complete set of required practice for facilities in the jet age was ever set down on paper. It was still in use nearly two decades later. I can say with some confidence that so long as the gear remained on the paved runway, the engines did not strike any lighting or signing, assuming that US practice guided these details. In the video of the preceeding plane touching down, there is also a bright flash. This occurs when the plane uncovers a bright background light. It appears the imaging system removes the flare (=flash) caused by the sudden appearance of such lights, but does not do so instantly.
Perimeter "wall" - this is actually a standard roadway curb and gutter section poured as one piece of unreinforced concrete. The curb could be 6, 8, or 10 inches high in US practice. Ten inches is called a barrier curb and will generally prevent a vehicle with car-sized tires (small service vans) from going over the edge of the embankment, as well as preventing erosion of the slope. The ACFT gear broke a piece of this in half. Allowing 50 percent impact loading, indicated weight on main gear at 94 knots departure speed was roughly at least 20 percent of the parked weight.
Vertical trajectory upon runway exit - from a vertical photo, it is about 400 feet to a possible point location for the taxi, assuming this taxi over the hood of which the gear passed to be in the far lane (of four). Then the vertical drop would indicate a weight on main gear leaving the field of about 15 percent of parked weight. As other indicators of this weight indicate rather more, we can assume the taxi perhaps a lane closer or more. I don't recall the position of the taxi being given in detail. The ACFT falls in a path combining the 1% downgrade of the runway/field and that of a parabola due to the action of the proper percentage of gravity-- this latter being determined by the percentage of ACFT weight on gear. I estimate 30-foot embankment height at this corner; the reported 50 feet has to be on the other (right) corner, from the vertical photo. Obviously, better data, better results.
Other indicators of lift - assuming configuration somewhat similar to takeoff, and lift increasing as square of speed, it is hard to see how the weight on gear at 94 kts field departure (158 feet per second) could be less than 25 percent of the parked weight. Of course, with FDR data, this can be better known. I've not seen manufacturer data, although it must exist; and runway centers (away from the ends) are often designed for only half the weight of aircraft. The ruts indented into the grassed area are typical in depth of a semi-trailer (9000 lbs per each 2-wheel pair (US limit)) and so, consistent with 15-25 percent weight on gear, given soil strength known only generally without tests.
My opinion on spoilers - based on the preceeding two paragraphs, IMHO it is unlikely that the spoilers were fully deployed at the field end. As has been pointed out, the effect of this on manual (or other) braking is a serious reduction, at least down to the percentage of weight on gear.
My opinion on statistics - with rare events in reliability studies, one needs to look at the failure events, not the success events. It is significant that now almost a third of AB320 hull losses seem to involve the control sequence being discussed re landing with 1-RT U/S. Until now, there was no great loss of life from this cause (I'd have to recheck this), due apparently to more forgiving runways or good luck. But in my mind, it does point up the need for a forgiving runway. I think TAM has taken a step in the right direction by ruling out such landings (RT U/S) here.
Bottom line - We used to say in the engineering office, that death is too great a penalty for so small a mistake (if that is the case). In many cases, we really do need better airfields. Its worth noting that the 7000-foot minimum grew up in an era before fly by wire, and the preconceived notion that FBW would make such fields safer in operation might better be replaced by an evaluation of exactly what the idiosyncracies of FBW require.
OE