Can Heated Pitot Tubes Be Repaired?

Captain Beak Palmer, in his book "Understanding Air French republic 447" has a section dedicated to answering that very question equally it pertains to AF447. Although there is no way to know for sure he puts forrard some possibilities.

He quotes a commenter on a website:

One commenter on the Weather Graphics website's AF447 article provided this interesting ascertainment: "I'k an shipping icing specialist and wanted to signal out a factor that hasn't been discussed much … loftier ice crystal concentrations. I've seen flight examination data from power rollbacks due to flight in high ice crystal environments … In our instance, the crystals collected within heated, aspirated Ram Air Temperature sensors, forming a 0 ° C slush…"

He notes that just before the pilot tubes clogged, the sound of water ice crystals hitting the windshield could be heard on the CVR.

Ice crystals bounce off the exterior of an plane and cause no visible ice accretion, only they can enter the probe inlets. When highly specific climatic conditions be in combination with certain combinations of distance, temperature, and Mach, the concentration of ice crystals inbound a probe tin exceed its capacity to melt and evacuate the wet through its drain holes. The result is that the water ice crystals course a physical barrier within the probe that disrupts the measurement of total pressure.

The item type of ice that may accept been responsible was a substance called graupel.

Graupel forms when tiny supercooled water aerosol adhere to snow crystals to the point that they engulf the snow crystal itself.

Graupel. Photograph from Wikimedia commons

Capt. Palmer notes factors that make graupel a possible suspect:

• No airframe icing. The supercooled water theory is discounted past the fact that the A330's icing detectors were not triggered.
• Graupel has large enough particles to exist aural on the voice recorder. It takes a particle with plenty mass and inertia (a given density) to hitting the fuselage with a audio, instead of flowing around it with the relative current of air, like snow.
• Graupel has plenty mass to temporarily overwhelm pitot anti-icing when concentrations are high enough. The pitot tubes are hot. Simply even if yous put a snowball on a hot skillet it does not melt instantaneously. If there is enough mass in the blockage, and in combination with new particles beingness added to the blockage as the kickoff ones melt, it may exceed the pitot tubes capability to cook the obstacle as fast equally information technology is introduced. Graupel is of significantly higher density than snow.
• Graupel has sufficient blocking properties to prevent efficient transmission of dynamic pressure within the pitot tube.For case, water tin flow and transmit pressure within the pitot tube, though it too can alter pitot-static readings, a physical non-fluid blockage could shield the force per unit area sensing port.
• The likely presence of snow or similar form, as evidenced by the St. Elmo's fire discussed by the crew. The accident report stated that the sound of ice crystals hitting the aircraft tin can be heard about twenty seconds before the airspeed loss and autopilot disconnect.

Information technology must be noted that the verbal crusade of icing issues on the A330 was never completely identified simply it was specific to the item make of pitot tubes originally installed. Airbus was in the procedure of replacing them all with pilot tubes from a different manufacturer.

Can Heated Pitot Tubes Be Repaired?,

Source: https://aviation.stackexchange.com/questions/24773/how-can-a-pitot-tube-freeze-when-its-heated

Posted by: lazarusfround.blogspot.com

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