Today, Indonesian officials announced that the preliminary report, due by the end of the month, will not be made public.
The accident investigators have had a few days to look at the flight recorder. Thus, I assume they now know what happened. Why then today's announcement? On one hand it may be claimed that to release information prematurely would be a mistake that could cause problems. That's true. But the announcement may also be to allow time to pass so the public loses interest, and the media moves on to other matters. Then, perhaps in a couple of years, the official results will be made known and, because of the dalay, there will be no public outcry.
I have been searching the web for info about the pitot tubes and I ran across a remarkably interesting discussion on a law web site. See: http://nolan-law.com/latest-air-france-crash-update-bereft-of-analysis/
It suggests that, in the case of AF 447, as the pitot tubes began to be blocked, the lower pressure in the pitot system signaled the fly-by-wire computer (and informed the pilots in the cockpit) that the plane was flying too slow, and so the fly-by-wire system added power. That caused the plane to fly faster, and thus faster than it should fly. As the blockage continued to build up, plane continued to appear to be slowing, and the fly-by-wire system added even more power, causing the plane to fly much too fast.
As a plane speeds up, more air across the wing would, if the nose is not lowered, cause the plane to climb. So, to keep the plane as the assigned altitude, the nose needed to be move down slightly to maintain altitude. This process continued: the plane speeding up and the nose being moved down.
At some point - according to his analysis - the fly-by-wire system’s authority to hold the nose down reached its limits, and the autopilot disconnected. Now, with the fly-by-wire autopilot no longer holding the nose down, the nose abruptly went up. Since the speed was already far too high, the plane zoomed rapidly up. As it did, with the nose so steeply up, he speed quickly decayed. As the speed sharply decayed, with the nose far too high up, the "angle of attack" - the angle at which the wing meets the oncoming air - became too extreme for the wing to work, and the plane descended, even though the nose was up.
In the case of AirAsia, the plane zoomed up at an extremely high rate, and stalled. Sounds like a replay, indeed, or AF447.
Though Airbus recommended back in 2006 that the original Thales pitot tubes (model - AA) be changed, either to a later version (model - BA). This was only a recommendation, not directive. Nevertheless, changing from original Thales - AA tubes to the - BA tubes would have made little or no difference, as a later assessment by Airbus said it had been determined that the - BA tubes were not better than the - AA.
The tubes built by Goodrich, however, were said by Airbus to have been better than the either the - AA or the - BA Thales tubes.
In 2009, following the AF 447 crash, the Air France pilots union demanded pitot tubes be changed, saying they would not fly the A330 unless the tubes were changed. According to http://www.segurancaaerea.coppe.ufrj.br/docs/aviation_week.pdf the pitot tubes where changed on all Air France Airbus planes.
Shortly thereafter, Airbus recommended all A330s and A340 have either three Goodrich tubes or two Goodrich tubes and one Thales tube in a specified third position. The Airbus recommendation did not extend to the A320.
At about the same time, the FAA required tube replacement on all A330s and A340. A pilot's message board says the pitot tubes have been replaced on all Delta A320s. See http://www.airliners.net/aviation-forums/general_aviation/read.main/4470008/
The accident investigators have had a few days to look at the flight recorder. Thus, I assume they now know what happened. Why then today's announcement? On one hand it may be claimed that to release information prematurely would be a mistake that could cause problems. That's true. But the announcement may also be to allow time to pass so the public loses interest, and the media moves on to other matters. Then, perhaps in a couple of years, the official results will be made known and, because of the dalay, there will be no public outcry.
I have been searching the web for info about the pitot tubes and I ran across a remarkably interesting discussion on a law web site. See: http://nolan-law.com/latest-air-france-crash-update-bereft-of-analysis/
It suggests that, in the case of AF 447, as the pitot tubes began to be blocked, the lower pressure in the pitot system signaled the fly-by-wire computer (and informed the pilots in the cockpit) that the plane was flying too slow, and so the fly-by-wire system added power. That caused the plane to fly faster, and thus faster than it should fly. As the blockage continued to build up, plane continued to appear to be slowing, and the fly-by-wire system added even more power, causing the plane to fly much too fast.
As a plane speeds up, more air across the wing would, if the nose is not lowered, cause the plane to climb. So, to keep the plane as the assigned altitude, the nose needed to be move down slightly to maintain altitude. This process continued: the plane speeding up and the nose being moved down.
At some point - according to his analysis - the fly-by-wire system’s authority to hold the nose down reached its limits, and the autopilot disconnected. Now, with the fly-by-wire autopilot no longer holding the nose down, the nose abruptly went up. Since the speed was already far too high, the plane zoomed rapidly up. As it did, with the nose so steeply up, he speed quickly decayed. As the speed sharply decayed, with the nose far too high up, the "angle of attack" - the angle at which the wing meets the oncoming air - became too extreme for the wing to work, and the plane descended, even though the nose was up.
In the case of AirAsia, the plane zoomed up at an extremely high rate, and stalled. Sounds like a replay, indeed, or AF447.
Though Airbus recommended back in 2006 that the original Thales pitot tubes (model - AA) be changed, either to a later version (model - BA). This was only a recommendation, not directive. Nevertheless, changing from original Thales - AA tubes to the - BA tubes would have made little or no difference, as a later assessment by Airbus said it had been determined that the - BA tubes were not better than the - AA.
The tubes built by Goodrich, however, were said by Airbus to have been better than the either the - AA or the - BA Thales tubes.
In 2009, following the AF 447 crash, the Air France pilots union demanded pitot tubes be changed, saying they would not fly the A330 unless the tubes were changed. According to http://www.segurancaaerea.coppe.ufrj.br/docs/aviation_week.pdf the pitot tubes where changed on all Air France Airbus planes.
Shortly thereafter, Airbus recommended all A330s and A340 have either three Goodrich tubes or two Goodrich tubes and one Thales tube in a specified third position. The Airbus recommendation did not extend to the A320.
At about the same time, the FAA required tube replacement on all A330s and A340. A pilot's message board says the pitot tubes have been replaced on all Delta A320s. See http://www.airliners.net/aviation-forums/general_aviation/read.main/4470008/
So, where do things stand?
- With the A330 and A340, the problematic Thales - AA and - BA tubes have all be replaced with Goodrich.
- Airbus has backup synthetic airspeed on the A380 and made it optional for other models
- Boeing planes have had little trouble with pitot tubes. Even when speed troubles arise on a Boeing airliner, natural feedback from the plane lets the pilot know what he or she needs to know to fly the plane. Even so, Boeing has installed synthetic airspeed on the 787.
- What about the A320? On the A320, the same Thales tubes have been problematic on the A330 have performed satisfactorily on the A320. This may be because the routes, altitudes, and shorter flights the A320 flies mean less exposure to pitot tube icing conditions. This AirAsia crash may be the exception, but if you look at the stats on the A320, there is no difference in safety between the A320 and the Boeing 737.
- My guess is that this will turn out to be a pitot tube accident and that a change of pitot tube will - at some point - be called for. But with no significant past pitot tube trouble with the A320, there is no reason not to fly it confidently. If the accident turns out to be due to some other cause, again, the record of the A320 gives us no reason not to fly it with confidence.



