First Published 1 June, but inadvertently deleted. It has been edited and re-posted today along with the accompanying comments. Thanx. Paul Miller
The Weather Channel displayed an inter-tropical convergence zone (ITCZ) satellite shot of the area at the time of AF447 passage through the area. The Sat shot showed large areas of high cloud tops. This suggests ongoing convective activity. Routine meteorological knowledge of the troposphere in the tropics places the trop layer at about FL600.
In laymen terms, the thunder-boomers were likely topping out at 60,000 feet. The coverage for the area looked as if a flight would have to pick its way though and might not be able to “stay on the track of the course.”
If this metro estimation is relatively correct, the violent convection turbulence, hail, lightning and precipitation would make the transit of any cell or area of cells on this track or this course to be extremely hazardous.
Additionally, one other hazardous character of convection in the tropics is very rapid cell growth. Cells can grow at rates in excess of 6000 feet per minute. This means that a cell could literally grow right up in front of you in what may have appeared on radar to be a clear area. Pilots who fly to South America from various Miami airline domiciles can verify this amazing metro phenomenon when in the tropical inter convergence zone.
Three other safety things are troubling to me though: If the Weather Channel can have this data available for presentation to me, while I am sitting in my den in my house on my TV, why doesn’t airline’s flight control dispatch have this current data available for presentation to the flightcrew in the cockpit real time, while in flight? Remember that the preflight briefing occurred about 5 hours prior to the thunderstorm area transit, the transit was at night and this ITCZ is extremely dynamic both vertically and horizontally.
Why are Convective Sigments merely passed to flight crew, without flight control route hazard analysis, on the presumption that only the flight crew in flight, are to plot each weather report and compare it to the flight path to determine the hazard? Is not the company a stake holder in this issue? Should not flight control determine if the activity is in the flight’s path and recommend the safest path around the severe convection?
Why isn’t this done on the ground where more resources are available?
Next, does Air France have a procedure whereby flight crew are required to avoid convective cells by 20-30 miles? Do Air France flight crews actually comply with such a procedure? Is it a procedure or is it a policy? At your airline, is this avoidance a policy or a procedure?
Can an airborne radar with perhaps a good 80 mile range be expected to be sufficient equipment to circumnavigate an area 200 to 300 miles in width? Once in clouds, how capable is an airborne radar, in comparison to ground based hourly sat photos and infra red cloud top imaging?
Lastly, I suspect that there were other flights in the area at the time, heading to Europe and other points. What did they see in terms of weather? What did the official weather agencies report? Did any coordination transpire to assist the flight crews? Was there any chance of weather radar from Brazil being transmitted to flights in the area?
Let’s see, Antoine De Saint Exupery wrote about this in his 1931 novel “Night Flight.” ISBN 9780156656054
[Opps, I forgot, The Patagonian Weather services set up in the mid 1920’s, may not have changed much. I wonder if the same guy may still be working there with a sandwich, thermos of coffee, pack of cigarettes and a sharp pencil.]
How many times have pilots heard some version of this statement? “It is not our job to advise pilots about what they are supposed to do. It is our job only to observe and report the weather, the cloud covering and rain.”
Initially Posted by Paul Miller at 9:25 AM, June 1, 2009
Edited and re-posted 2 June.
Safety Forecast 
Paul…Some good questions.On transoceanic flights, where current weather data is minimal as compared to availability over land, it would seem that more can be done to keep those flights informed, through the use of current satellite information and computer projections of upper-air information and analysis from the most current soundings, when updated. That information could be incorporated with whatever current hourly ship and land weather and radar observations were available, along a given route. A dedicated analysis and forecast branch for transoceanic flights at NWS, or maybe even at the aircarrier, could keep a monitor of the enroute weather and weather hazards for immediate broadcast to the effected flights or as a continuous feed. The same way they do it over land, to emergency management facilities.Similar services are available to shipping (transoceanic ship routes), that forecast and update for ships, including warnings, advisories, and rerouting around hazardous weather and sea conditions.
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Air France already has a dispatch office with full access to all weather products published by every public source globally. The question now is, "how are they using that data?"If the data is not used to operationally steer flights clear of non navigable severe convective thunderstorm areas, then we have a problem. Once again this is a mishap that was 100% avoidable. First, Air France Flight Control should have been monitoring the weather in the flight path, as all scheduled airlines are required to do.Second, the Air France Flight Ops office should have noticed a large area of thunderstorms directly in the flight path of AF 447 with tops above FL500. In other words, the plane is not capable of flying over this weather.Third, AF Flight Ops should have plotted a new course for AF 447, coordinating with the Air Service Space Controlling Agency and diverted the course of AF447 around the storm areas.Fourth, this should be a routine standard operating procedure.Lastly, because it was not, the airline may have lost a plane valued over $120 million, 232 lives and all of the pain which accompanies a preventable loss.All of this was preventable. Future mishaps of this kind are also preventable.
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What are the costs that France, Brazil, Air France, Airbus and others are incurring related to this totally preventable disaster? Any guesses out there? My guess is about $500million.That money could pay for alot of weather diversions. I wonder if SOP at AF will change to send weather diversions to flights headed into areas with high %age thunderstorm coverage enroute?
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Let me say that thunderstorms are capable of producing turbulence which can literally rip the wings off of a modern jet airliner. How? Remember that manufacturer stress and strain testing is largely static testing, with perhaps cyclic and on some occasion dynamic testing. In a thunderstorm however, there is not only stress due to turbulence, there is rapid change in stress due to changes in turbulent wing loading. This could be called "jerk" or how rapidly stress forces are changed in acceleration. There is also a term called "snatch" where the acceleration of the jerk is variable. In a major storm, the stress, jerk and snatch will overwhelm the strongest of airframes. And I will tell you one other thing related to passenger travel. If by some miracle the plane survives one of these encounters, the people on the plane will be frightened to the most extreme. The chances of any of them ever getting on another airplane again voluntarily will be greatly diminished. So why fly through these thunderstorms?
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"OVER-MOMENT"A term called “over-momenting” is important to understand here. "Over-moment" occurs when the wing is snatched or jerked too fast. Application of g forces in a manner too quick for the wing to equalize stress over the entire wing area would be considered “over-momenting.” The term comes from the aerodynamic terms related to lift and stability. The aerodynamic force created on the wing, [from which lift is derived as the force perpendicular to the flight path and relative wind, while induced drag is the reverse facing horizontal component opposing thrust], is accompanied by a moment or a force acting at a moment arm or distance from where the force is created to the center of gravity of the wing and air frame. The moment arm is the distance between the center of gravity of the wing and the center of aerodynamic force along the wing. Typically on a straight wing, the moment is nose down along the longitudinal axis, because the aerodynamic force is aft of the center of gravity for many straight wings.However the moment to which the "over moment" to which may have broken up AF447 is referring, is acting along the horizontal axis, or out along the wing’s length. With “over moment” the lifting forces along parts of the wing onset so quickly and to such a large amount that the displacement of the wing and displacement of the fuselage wing box area are literally going in opposite directions. This is much like what would happen if you snapped a long piece of chalk or a long stiff thin stick.In the thunderstorm, the wings are subjected to both a magnitude of forces of massive dimensional proportions along with rapid departures of the direction of the force at the same time.A vector, which is a force with a direction, represents this. The vectors are changing in direction and dimension at the same time. In the case of an aircraft in a violent thunderstorm, with massive, violent and rapidly changing wind shafts, the changes of aerodynamic forces on the wing occur so rapidly that the dynamics of the airframe just can't keep up. It is not necessarily the g load per se that does the damage, but rather the rapid changes in the onset of the g loading that cause the damage. This again is called “jerk” or “snatch.” From a physics view point, it has to do with the derivative of force called acceleration and the derivative of acceleration commonly called “jerk” or “snatch.” By the way, roller coaster designers have to consider this in the track design to ensure that patrons don't sustain internal injuries or broken bones. I think that they came up with the terms “jerk” and “snatch.”In way it is very much related to momentum in the sense that everything is going one way and now is being force to go the other way!
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This is an excellent analysis of weather in the area at the time of the mishap. It is from a site called Weather Graphics, Tim Vasquez.http://www.weathergraphics.com/tim/af447/
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Paul…I read the Weather Graphics info you sent me. He did an excellent job. By definition, a thunderstorm that penetrates the tropopause IS a severe thunderstorm — as the one they apparently encountered was. With tops at or near 60,000 ft, in all probability, it was. From the graphics, it looks as if they penetrated the worst of the worst weather in that cluster. I can't possibly see how lightning wouldn't have been a formidable factor in that particular cell. Icing, probably the least of their worries. Turbulence — a given.I can't understand why they were routed through THAT cluster, especially on a long transoceanic flight with little or no alternatives if an emergency were to occur, to land, except the ocean. We're talking passengers…!Do buses try to beat trains through a railroad crossing? Are there not crossing gates?Thanks for your explanations of snatch, jerk, and "over-momenting". It's nice to know that physics has broken down and explained the forces that any kid might experience fearlessly riding a bike or racing a homemade race car. …Not a knock. Just an observation. LOL
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Paul…The first and most obvious question is, if the information that Tim used is available to him to use to analyse the incident, why isn't that same kind of information used to generate a safe flight route, before the flight leaves the ground?The Inter-Tropical Convergence Zone, the ITCZ (commonly called "the itch"), is essentially a frontal zone separating the northern hemispheric air masses from the southern hemispheric air masses, near the equator. It's where tropical storms and hurricanes are generated. Areas of convergence are prime for severe convective weather.Given an area of convective activity, along the ITCZ, in the flight path of a commercial airliner carrying passengers (200+ passengers), wouldn't the logical choice be to avoid it?Is it common practice, on continental passenger flights, to fly into possibly severe frontal system thunderstorms, approaching or penetrating the tropopause?
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The question now is this: "Is thunderstorm avoidance at AF a policy or a procedure?"A policy is an idea adopted as a goal, issued to guide actions.A procedure is a much more specific formula for action, the compliance with which is required and monitored.Did AF dispatch ofice have a procedure to avoid thunderstorms, or only a policy?
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Another question might be, how rigid are their computer-generated flight routes?Do they allow for deviation and if so, how much and under what circumstances?I've been party to rigid computer-generated transoceanic ship route forecasts, that didn't allow for deviation before consultation with the home forecasting facility and being granted permission to deviate.
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When I look at all of the money now being spent on search, rescue, recovery, public relations, investigations and when I look at all of the emotional pain being felt by so many people across the world, I find it very hard to hear arguments against safety based on money, time or effort.
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Good question. There is flexibility built into ocean crossing routes. I believe that route change procedures are routine enough, but that might not be the perception at AF and at other dispatch offices. Good point of discussion. Are route change procedures perceived to be routine by airline dispatch offices? Do airlines have route change procedures which are in use on a regular basis or only in the event of the most unusual circumstances? What does the record show?
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Paul…I read some points of speculation concerning the crash…1. A possible pitot tube problem. Air France is replacing the pitot tubes on its Air Bus 330s — apparently 3 on each plane — with a new, better designed version, better able to handle clogging during icing. AF Flight 447 hadn't received the modification. Although, like I said, I don't think icing was their issue.2. AF447 might have been deviating or returning to Brazil. Speculation based on where they've found the wreckage.3. First indications, based on sparse evidence from victims (I believe 28, so far) and wreckage, speculation that AF447 brokeup in the air.
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Funny thing though-if the pitot tubes malfunctioned, they seemed to have done so at about the same time the flight flew into 60,000 foot tall thunderstorms. My guess there were plenty of other components which began to malfunction at the same time.Here is a question: Did Airbus test and did the FAA or any other CAA certify the plane to operate within a 60,000 foot tall thunderstorms? If so, where is the data, when were the test flights? Who signed off on that certification? Where is the evidence that the plane is capable of performance within a storm such as this?
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Secondly, where is the FAA approved syllabus for operations within thunderstorms? Thirdly, have we not heard from the NTSB in more than a dozen airline mishaps that operation inside thunderstorms has been identified as one of the contributing causes of fatal mishaps?Why is there such an enormous disconnect between reality and what passes for "safe operation" by Air France?Who is the regulator? What value are the regulations which prohibit just such operations if the operators go ahead and operate in these storms?How is the flying public protected?
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I thought I read somewhere that information sent from AF447 during their last transmission, indicated electrical and equipment failures. That would seem to point to one or more lightning strikes.Couldn't that also lead to a fuselage breach?I've read about instances where plane parts have been blown off planes in flight by lightning strikes — one in particular, a nose cone.
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I agree. It makes absolutely no sense to deliberately fly into a hazard. There's a reason they call them "hazards."Flying into a thunderstorm's a hazard. If you fly into one deliberately, it's a gamble where the bet is your life and the lives of the people with you — along with a multimillion dollar plane.How could that kind of gamble possibly be justified?
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I wonder if anyone at AF will change the SOP?
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I guess we'll have to see… Here are a couple of links, one to Aviation Week and the other to The Aviation Safety Network, that might give additional info.They mention an Iberia Airline flight 7 minutes behind AF447 that had to divert around the same weather, to the East.Tim Vasquez's weather is referenced in the Aviation Safety Network article:http://aviation-safety.net/database/record.php?id=20090601-0Aviation Week:http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=comm&id=news/SPEED060509.xml&headline=AF447+Data+Suggests+Faulty+Speed+Data
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Bill, I don't know yet if the news has picked up on the costs involved in the recovery operation. I wonder if any news will surface on the victim compensation. It may have been the AF decision to delay retrofitting the newer pitot systems. Good to hear about the previous flights deviations. Again weather-based course deviations are common; what may not be common are deviations based on airline dispatch. But again dispatch is part of the operation run by the airline.
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Pitot failure is one of the dangers of entering into the severe weather of a thunderstorm. If this pitot system did fail, it is interesting that the failure occurred while within a severe thunderstorm. This is one of the reasons that flight training courses virtually universally recommend staying out of thunderstorms, especially when at cruising flight levels.
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The articles mention sequential computer generated downlinks of information of equipment failure warnings, as the occurred, from AF447 to Air France. I wonder if time/position/altitude information is included with each warning.I find interesting that the Iberia flight, behind AF447, saw the need to deviate around those convective clusters, but Air France didn't. AF447, according to the narrative, went through a smaller cluster before encountering the larger one.
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AF447 was cruising at FL350 — which should have been well above the freezing level, which should have be down around half their altitute, a least. That's why I question icing. The question is, were they still at cruising altitute in the second cluster of weather, if indeed, the pitot tubes were part of the problem?An article I read mentioned that Air France had already started retrofitting some of their fleet with new pitot tube systems. But, that AF447 hadn't been retrofitted yet.
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Here's a time line, including the infor that was transmitted by automated computer systems monitoring messages:From the Seattle Post-IntelligencerAerospace Newshttp://blog.seattlepi.nwsource.com/aerospace/archives/169986.aspTimeline of the disappearance of Air France flight 447 (updated)Timeline of the disappearance of Air France flight 447:All times are universal time, or Greenwich Mean Time. At this time of year, Seattle is seven hours behind GMT.May 31:22:03 — Air France flight 447 departs from Rio de Janeiro. (Brazilian Air Force says plane left at 22:30.)June 1:01:30 — Plane has last contact with Brazil air traffic control, where it is 351 miles from the city of Natal.01:48 — Brazilian Air Force has last radar contact. Plane appears to be flying normally.02:00 — Aircraft hits a zone of stormy weather with strong turbulence. The pilot sends a manual signal indicating that he is flying through an area of "CBs" – black, electrically charged cumulonimbus clouds that come with violent winds and lightning. 02:10 — Problems mount. The autopilot is disengaged, a key computer system is switched to alternative power and controls needed to keep the plane stable have been damaged, according to automatic messages. An alarm sounds, indicating that flight systems are deteriorating.02:13 — Automatic messages report the failure of systems to monitor air speed, altitude and direction. Control of the main flight computer and wing spoilers fail.02:14 — An automatic message was received from the aircraft as indicating a loss of cabin pressure and failure in the electric circuit. The plane is a long way from the coast. It is believed to be breaking up at this moment.02:20 — Plane fails to make previously scheduled radio contact with Brazil. Brazil notifies air traffic control in Dakar, Senegal.05:00 – 06:00 — Brazilian, African, Spanish and French air traffic control centers try to make contact with the flight, but are not successful. The French military air traffic control center cannot detect the aircraft.05:30 — Brazilian Air Force starts a search and rescue mission07:30 — Air France sets up a crisis center09:15 — Flight was expected to arrive in Paris11:31 — Air France announces the following: "Air France regrets to announce that it has lost contact with flight AF 447 from Rio de Janeiro to Paris-Charles de Gaulle, expected to arrive this morning at 11:15 local time."13:10 — Air France announces the following: "Air France regrets to confirm the disappearance of flight AF 447 flying from Rio de Janeiro to Paris-Charles de Gaulle, scheduled to arrive at 11:10am local time today, as announced to the press by Air France CEO, Pierre-Henri Gourgeon."13:59 — Air France reports that it has sent all of the information it has regarding the flight to the French Accident Investigation Bureau for civil aviation (BEA) and to Airbus 14:44 — By this time, the airplane is expected to have run out of fuel. Air France publicizes "its deepest sympathy to the relatives and friends of the passengers and crew who were on board AF flight 447 on 31 May 2009, which disappeared somewhere between Rio de Janeiro and Paris-Charles de Gaulle."Airbus also announces, "Airbus regrets to confirm that an Airbus A330-200 operated by Air France has been lost about 3.5 hours after departure."18:13 — Air France releases a list of the nationalities on board(Sources: Air France, Airbus, AP)
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Of note: A. 2203 is probably "block out," 2230 is probably the "off" time. B. 0214 probable flight demise til 0530 beginning of search. over 3 1/4 hours have passed.C. 0214 probable demise til 1130 when AF finally admits a problem, over 8 1/4 hours have gone by.D. 0214 probably demise until 1449 when AF admits the probable demise, 12 1/2 hours have gone by.The level of reluctance to admit an obvious problem is very high and very telling of AF management policy and procedures. This reluctance can be interpreted as part of the management style which made AF reluctant to move AF447 off of its originally planned and filed flight route when an obvious problem was dead ahead.Reluctance to adapt and change can be considered a very serious safety flaw and high hazard risk.
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On the AF safety problem horizon I would list reluctance to change and adapt operationally to serious safety hazards dead ahead. The forecast here is identifying serious flaws in AF safety policy, that is the ability to rapidly react to a safety hazard, until it becomes a mishap. For Plans I would suggest creation of a rapid response team to address real time safety hazards. What they seem to have now instead is a policy that the mishap has to occur first before the management will admit that there is a hazard. So in this case, AF philosophy is that the mishap caused the hazard to occur. They need to change that philosophy to the hazard can cause the mishap. This new philosophy will allow them to adopt a policy that hazard avoidance can improve safety. Too bad AF is not on my blog. They will never know what they could be doing to save themselves from so much disaster and tragedy.
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From the sequence of events, it seems as if things were going terribly wrong minutes before pitot tubes became an issue…from the sound of things, they might not have even had pitot tubes by the time their warning was transmitted.I can't even imagine the horror of experiencing these events as the occurred.How is it even humanly possible to handle all these occurrences all at once!Betcha they can't replicate this one in a flight simulator, to a good, safe outcome!
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great comment!
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Here's the latest from The Seattle Times. Not a revelation, but more evidence of the pointing to the supposed fate of AF447:http://seattletimes.nwsource.com/html/nationworld/2009352915_brazil18.html
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Like I said before, anyone who has ever been inside a thunderstorm knows that it will rip a plane to shreds. I just do not understand how manufacturers, airlines and regulators can not know this. My only conclusion is that the manufacturers, airlines and regulators are being run by people who do not fly.
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More evidence of an inflight breakup vs ocean impact today.
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Here's two articles with more recent info. They're still speculating Pitot Tubes:USA Today:http://www.usatoday.com/travel/flights/2009-06-28-crash-clues_N.htm?csp=34Wall Street Journal:http://online.wsj.com/article/SB124605948270463623.html
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Yes, good stuff, but it is kinda like breaking an axel when speeding through a desert wadi. the wadi might have something to do with it as well. but, the dang pitot tubes are known hazards, what were these people running AF and AB thinking? Did they consider this an admin change? With a known hazard, why was that flight not kept clear of icing conditions? None of this operation makes any logic. How many more mishaps are needed for FAA, AB and AF to take action? All of this is shocking!
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Did you note, one of the articles mentioned the possibility of the crew becoming overwhelmed with the total loss of the automated computer controls, and sparse simulator training addressing that issue?
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It's kinda like giving two guys a canoe with paddles and sending them towards a massive water fall. You will see two guys paddling to beat the band, but still going over. The comment might be, "They couldn't paddle fast enough to save themselves." Maybe some one would say, "They needed more paddle training."All true, but maybe they should not have been put on that course in the first place.The AF447 crew was overwhelmed by a known hazard. This was not a training issue. The hazard was known to be severe. Any certified airman has had metro training and tstorm severity is a well known part of the training and has been since a very long time ago.
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An article from "Bloomberg":http://www.bloomberg.com/apps/news?pid=20601209&sid=agpoS0u0a8rQHere's the latest from the French BEA:http://www.bea.aero/anglaise/actualite/actu.htm
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Why do I get this feeling of queasy skepticism from these latest findings and speculations?Some of what I read doesn't seem to be making much sense when compared to the auto-warning messages, and seemingly contradictory assessments by the BEA of the weather AF447 flew into.On one hand, they mention the severity of the storms. On the other, they suggest that storms such as those have been flown through before without consequence — but, that other flights immediately before and after AF447, successfully circumnavigated the weather, avoiding it.Also, now they're saying it landed flat in the water, when before they were saying, because of data on the messages and the condition of the passengers, they suspected it broke up in flight.Somehow, the speculation, that because the passengers were found with their clothes ripped off, suggesting in flight breakup; and new speculation, that none of the life vests were accessed or inflated; changed their opinions, based on passenger condition and actions, that the plane was intact when it hit the water! If the plane was intact when it hit the water, how did the passenger's clothes get ripped off? If they were unconscious because of loss of cabin pressure in flight, wouldn't that explain the life vests?Either I read it wrong, or there's something awry with the logic.I agree with your last post. I've long felt, that as competent as a flight crew might be, there are situations when human abilities in coping with failing computer-mechanical interfaces reaches a critical mass, and it becomes overwhelming. All the training in the world won't fix it. Timing is everything in an emergency, and you can't slow down the clock — at least not with current flying technology.
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Again what is remarkable is that no one, not the NTSB, BEA, AF nor AB is talking about the apparent complete lack of support provided to the flightcrew by the AF dispatch office, in avoiding a dangerous and large known area of thunderstorms. Either they did not have procedures for informing the crew and diverting the crew, or they did not have procedures for hazard avoidance of any kind. I have said this in my other blog- it is the "Safety Riddle:"Did the hazard cause the mishap or did the mishap cause the hazard?I think in the case of AF and their flight 447, they may believe the latter.Good to know. Now this provides an area where they can improve in safety.
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There's also the question of why Senegal delayed by six hours, informing Air France that they failed to achieve "handoff" when AF447 entered their airspace. Certainly pertinent in tracking the flight and the recovery. But, nothing to do with the cause of the accident.Also mentioned was, there was no "May Day". That might absolve those tracking the flight from taking immediate action when there wasn't a handoff, to some extent. But, it's no excuse. It's also testimony to the sudden, overwhelming circumstances resulting in the ultimate fate of AF447.Pitot Tubes, shmeeto tubes! They should never have been where they were when they flew into that weather!It was a gamble someone took who lost their bet — 228 lives and an airplane!
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Concerning Senegal: There is another one of the issues that pilots deal with everyday-poor and or non-existent communications from some countries.It is just my opinion but, some of these countries over which important aviation information flows, either could not care less, or have never invested in modern gear. Another troublesome radio agency is Kingston Radio, for LA/SA flights.
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I flew out of Montreal last evening. Even with radar, there are some storms which are hard to distinguish and discern when they are building and or diminishing. Airborne radar can be attenuated easily by moisture in the air, not in a cell. The help of groundbased radar and sat pix can help flight crew when in these circumstances.
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Does aircraft cockpit radar have a manual attenuation control, to manually adjust radar signal attenuation?
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No. Attenuation results from not having enough "penetrating power" in the radar beam. There are tilt, gain, display distance, motion, decibel differentiation and other screening controls on most airborne units. But to overcome attenuation, the radar needs to be moved out of the precipitation, so that the radar can "view the precip" from a distance.However once in the precip, the radar beam on most current day radars is not powerful enough to penetrate deeply into the rain field. So this is a very serious short coming.The problem is the result of band width and emitter power. In years past, longer wave radars were used with very powerful emitters. They could penetrate very well into precip fields. Today, a much higher frequency radar is used to get the signal to reflect over long distances. Frequency is part of the power formula for emitted radiation.But the higher freq waves are so good at making returns over distance that the current radars operate at much lower power emissions. The result of this lower emission power and higher frequency is that once in a moderate to high decibel field of precip, the radar runs out of penetrating power and the signal strength is drastically attenuated or absorbed by the precip field. If the radar is operating out side the rain field and looking at it from a distance, it can differentiate between light to moderate to heavy decibel returns quite well.But once inside the rain field, the radar return is highly limited. You can use various features such as tilt and gain and gain supression to try to get some differentiation, but you will not get enough information to be of safe use.What the radars need is alot more power, much more power, to be usable inside a rain field of moderate to heavy intensity.Ground based and ship board radars have the power to penetrate and certain airborne meteorological research radars have the necessary power. But most transport aircraft have a very modest power level J band weather radar. It is typed a radar to help the pilot avoid precip, but not navigate though it. That is clearly stated as a limitation in the operating manual of the all of the manufacturers of which I am aware.
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The old AN/FPS-41 weather radar, the civilian WSR-57, had an attenuation knob for adjusting attenuation — adjusting it upward would show only more intense precip; downward, included lighter precip. It also included an iso-echo feature, with echoes of differing intensity showing up in differently shaded band patterns. It also included my favorite, an AZ-EL scope, showing a vertical depiction.But, of course, all those features might not be practical for onboard use in an aircraft. Aircraft radar seem more geared to collision avoidance, than weather phenomena.
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Yes, that is correct. The aircraft weather radar on transport category aircraft is intended for weather avoidance and not for picking a navigating path through an area of thunderstorms.Was the AN/FPS-41 weather radar, the civilian WSR-57, a "C" band radar? Do you happen to know or can you find out?Many older and more powerful radars used the technology of the C band transmission (wave length of C band is longer and therefore less powerful than J band. As a result the C band emission power lever was much higher. This much higher power level allowed the radar signal to penetrate deeper into a rain field and thunderstorm. That is why the radar had the ability to adjust attenuation up or down with a knob. As you said, "for adjusting attenuation — adjusting it upward would show only more intense precip; downward, included lighter precip.The C band radars require more electrical power, but they sure could burn through just about any precip and remain strong over a long distance.
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The radar uses a wavelength of 10.3 cm.[11] This corresponds to an operating frequency of 2890 MHz. This frequency is in the S band, which is also used by today's weather radar network. WSR-57 radars had the following interesting statistics:[11] Dish diameter: 12 feet Power output: 410,000 watts [11] http://weather.cod.edu/sirvatka/radar.htmlMaximum range: 915 km (494 nm)
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Bill, great info. These radars are very powerful; and with the 10 cm beam width, they pick up and discriminate better than the 1 cm beam width in transport category airborne radar. The airborne weather radar on transport category aircraft is much different and much less capable. Again this is another reason to supplement info from airborne radar with the beefier ground based weather radar. I think that this huge differential has not been well enough explained and understood in the aviation community, nor by the FAA.
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I think I see what the problem is. If you read the below linked FAA criteria for transport category weather radar, there does not appear to be any criteria set to avoid rain attenuation. http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/22763
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Paul:Here's the latest…Note the mention of, "…the airline was reviewing procedures for radar use…" From "The Times Online"July 10, 2009Air France pilots blame safety agencies for crash of Flight 447http://www.timesonline.co.uk/tol/news/world/europe/article6675343.ece?token=null&offset=0&page=1
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A related article from "ATW [Air Transport World] News":Air France reviewing 'every factor' that could have caused AF447 crashhttp://www.atwonline.com/news/story.html?storyID=17193
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