Friday, July 20, 2007

Analysis of the crash...

I've been looking at the video now in step-mode. It's poor quality, but I can derive a couple of things that question the statement that the reverse thrusters had been in operation the whole time. Looking at the video and taking some screenshots however, I'm not so convinced this was the case.

(click on the pictures to see them larger)

Here are some considerations of mine that suggest a different sequence of events that seems to be a closer account:

Here we see the approach of the aircraft, right, where the plane sees the camera at an angle of about 300 degrees, head-up:

This image shows how the aircraft is passing the camera. The rain should be an indication of full-thrust working. The speed of the air at thrust surpasses the speed of the airplane by far. I see no waterspray being pushed in front of the airplane. Also, the size of the spray and its shape seem to indicate that the jet being pushed backwards is solely attributable to the wheels. There isn't even, as far as I can see, a buildup around the wings that indicate any kind of reverse-thrust to stop the plane at this point. Note that at this point the plane is probably around half the length of the runway. The Airbus A320 requires at least 300-500 meters of runway beyond the 1.9km that this runway has:

Here we see another camera recording the event. The plane is in view lower right and is just entering the camera frustrum:

Camera 10 has a detail view. Now we do see a waterspray being pushed forward even beyond the forward wheel. The buildup of spray around the body of the aircraft as a whole is noticeable. This is what you'd probably have to see in the first image (albeit the shape of the water spray would be longer due to higher speed), but at least the water should move higher and around the body of the aircraft if reverse-thrust is to be engaged. See that white cloud in this picture? I didn't see that in the previous pictures. Common sense tells me that if reverse thrust was working earlier, we should at least see a visible deceleration and similar upward-moving waterspray in the previous pictures.

Here we see another image a second later. In the overall movement of things, I don't see the aircraft noticeably slowing down, but it's as if it suddenly starts rolling out ( no thrust applied whatsoever ) and it's as if the spray of the reverse thrust is suddenly diminishing significantly. Has the pilot just decided to abort the landing at this point in an attempt to take off again with the remaining speed? This is probably about 3/4 down the runway or so:

This image here shows another camera about 3 seconds later. There seems to be a short flash at the left turbine, which may indicate the thruster reversing again into forward mode. I am not sure whether reversing the thrusters at this point, when still rotating reverse, would ignite a flash of some kind (maybe someone can comment?). The length of the runway in front must definitely be very limited.

Even though the news indicates that the right reversor was defective, I'm not sure whether this is truly the cause. It's very well possible that it was not operating and the aircraft logic prohibiting the operation of the left reverse thruster. However, there are other accounts of disabled reverse thrust or braking due to failure of the sensors or conditions prohibiting proper sensing of ground conditions (the A320 does not allow pilots to engage reverse-thrust in "flight" condition).

Plus... we see that the reverse thrust does kick in at some point (picture 4), albeit much too late. If there was a full defect, this wouldn't have happened.

There seems to be quite some confusion with engineers as to how the actual braking operation works, as the manual is not very clear at this point:

I can imagine that when one engine does not allow reverse thrust, the other should not apply it as this would spin the airplane around. There should be a safety mechanism in an aircraft that guarantees (more or less?) equal thrust being applied to both engines. Steering in an aircraft is not done through thrusters, but through wing action and ailerons.

Personally, if this is what happened, I can understand the stress of the pilot. There is only just enough length to land in dry weather conditions. The runway is wet. The pilot with 20 years of experience must have landed here before and know about the length of the runway. The pilot must have known about the pending maintenance action for the right turbine. The grooving has not yet been done (pending for September) due to "commercial pressure" to open the airport ( the losses would be too great ). The aircraft on touchdown does not respond to any braking commands (see potential similarity with other reports on other A320 crashes). More than halfway down the runway, the aircraft finally responds, but the length in front of the plane simply doesn't cut it. The pilots probably both decide to pull back up. The reverse-thrust is aborted and the thruster is set to forward thrust again. The speed of the aircraft at this point is far from favourable with only very little runway left. Is it possible that another 300-500m would have saved their lives? The A320 takes off and lands at around 160knots. This is 82m per second. The landing speed was above 160 knots at the time of touchdown.

Besides this plane having probably suffered a technical problem, we cannot ignore the other factors that have contributed to this. The pilots get informed that they better circle around for another landing attempt if they do not manage to land at the first 300m on the runway. Imagine the consequences if the braking system doesn't work and you're halfway down the runway (that is 8-10 seconds down). The decision you are forced to take in the next 10 seconds is crucial and every second is very, very crucial. Braking the airplane at more or less full-speed having only half of the runway left, a runway without grooves in wet conditions? This probably went through the pilot's minds at the last point of decision.

A couple of people in Brazil just put a value on the price of human life. For a jet full of people to crash in a busy airport, the monetary equivalent is the money that was made from February 2007 until now.

My expectation for any airport wherever in the world is that all international and safety norms are met, if not exceeded. THEN we can talk about weighing off extra security and safety measures versus economic benefit.

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