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#82
7th June 2009, 05:09 PM
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Freezing pitot theory
Although one would not expect pitot tubes to be blocked by ice at 35,000 feet (because there's no freezable moisture that high up) it is possible that the unusually severe weather conditions did result in that condition, which could lead to conflicting air speed data being fed to the avionics, which could lead to auto pilot disconnect and flight crew disorientation, especially if accompanied by a lightning strike and wing icing.
I do hope the subs headed to the crash zone this week find the CVR and FDR boxes. The location of a wing, other debris and bodies at least confirms the crash area has been located. Aircraft breakup at 35,000 feet usually results in most bodies being dismembered from the free fall at terminal velocity. That may explain why officials are refusing to discuss the state of the recovered bodies.
__________________
Philip 
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#83
7th June 2009, 05:59 PM
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Philip,
It is quite possible for pitot tubes to be iced up at FL350. The type of ice that can be found at that level is Rime Ice, which is supercooled water droplets that freeze on impact. If a surface is left unheated, rime ice can form on the surface, which in the case of a Pitot Head, would block the opening. On an ISA day (International Standard Atmosphere), you wouldn't expect to find any freezable moisture at that level. However, I've been flying for close on 10 years and 3,000hrs, and I've never seen ISA temperatures at any level. Normally sits anywhere between ISA -10 to ISA +30, depending on the level. Thunderstorms can be known to reach levels of up to 50-60,000ft. So there is freezable moisture up there,  .Mick Last edited by Mick F; 7th June 2009 at 07:09 PM.
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#84
7th June 2009, 07:24 PM
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Gents, the pitot/static systems, along with the alpha vanes are all heated on all jet transport aircraft, alleviating the possibility of icing to which you allude.
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#86
7th June 2009, 08:02 PM
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Mick and Hugh are correct. I'm exploring more the avionics programming that isn't adequately tested in my opinion for unexpected or "impossible" concurrent conditions.
__________________
Philip
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#87
7th June 2009, 08:14 PM
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So coming from a non aviation background here, if one of the systems that heated this device failed when everything else did and the pilot took control of the plane, the device could give the computer a incorrect speed and stall the plane? Hence the messages that were transmitted before it disappeared?
And secondly, if it was as faulty as Air France make out amoung their fleet of 330s then surely airbus will have to pocket some of the blame?
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#88
8th June 2009, 08:47 AM
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Quote:
What caused the multiple failures is for investigators to determine and hopefully either aircraft manufacturers to fix or provide advice to aircrew on how to deal with such an extreme situation. The system failures that have been reported are below. 02:10Z: Autothrust off Autopilot off FBW alternate law Rudder Travel Limiter Fault TCAS fault due to antenna fault Flight Envelope Computation warning All pitot static ports lost 02:11Z: Failure of all three ADIRUs Failure of gyros of ISIS (attitude information lost) 02:12Z: ADIRUs Air Data disagree 02:13Z: Flight Management, Guidance and Envelope Computer fault PRIM 1 fault SEC 1 fault 02:14Z: Cabin Pressure Controller fault (cabin vertical speed) Looking at that sequence, it appears there was other problems occurring on that flight on top of air data information disagreements. The loss of all attitude information (i imagine the standby attitude indicator is serviceable however) on top of all air data information in dark, unfavourable weather conditions would have made flight extremely difficult I’d imagine. If all of the aircrafts pitot sensing tube/s failed it would be almost impossible for either a 'computer aircraft' or 'analogue aircraft' to accurately display aircraft speed or thus for aircrew to fly the aircraft within flight limits. If one fails/becomes blocked then you will get a mismatch in airspeed and possibly altitude. Aircrew then need to identify that and utilise the redundancy system and swap sensors to either the captain or first officer, depending on whose system is affected. All THREE ADIRU’s (Air Data Inertial Reference Units) are shown to have failed on flight AF447. Two of the ADIRU’s are electronic and utilise software and digital components and are the prime ADIRU’s onboard an A330. The third ADIRU is a mechanical sensing device utilised as a backup. It is designed to get around any electrical ‘glitches’ and provide backup airspeed/altitude information. If, however all of the sensors have become invalid as seems to be shown above through blockage or some other fault, then no ADIRU will be able to provide valid airspeed, vertical speed or altitude information. This seems to be what has occurred on this particular flight. It has happened before and is why Airbus had initiated a pitot tube replacement program, which unfortunately the aircraft involved had not received. The fact that all three Attitude Gyro’s failed the autothrust and autopilot systems had been turned off and numerous other failures have occurred seems to indicate it’s more than just a pitot static system fault that caused the loss of this aircraft. As has been shown in many accidents however, if one sequence had been broken, then the aircraft would not have been lost. Would a 'mechanical' (flight control cables, not fly by wire) flight control aircraft managed to have stayed in the air and allowed the crew to reach a safe airfield?
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#89
8th June 2009, 12:03 PM
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More bodies and Debris retrieved.
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Linear Mode
