snow pellets vs. snow grains

[Rank&File]

After reading the article in this month's ALPA magazine, Operations in Conditions of Light Ice Pellets or Light Snow Pellets, I asked myslef these simple questions: what is the difference between a snow pellet and a snow grain? What is the difference between freezing drizzle and ice pellets? Unfortunately, I don't know the answers. Do you?

Type I and Type IV holdover times exist for snow grains and freezing drizzle, but not ice pellets or snow pellets. Hmmm. I wish I knew how to tell one from another. Can someone clue me in?

Anyway, ALPA reccommended that crews not depart when snow and ice pellets are falling from the sky because studies have shown that the types of fluids we use today do not adequately protect vital surfaces against such precip. They showed a picture of a wing that had been treated, and within the holdover time, the stuff was sticking. Scary stuff.

 

[N632SP]

Snow pellet: A small white ice particle that falls as precipitation and breaks apart easily when it lands on a surface.
Snow grain: Precipitation consisting of white, opaque ice particles usually less than 1 mm in diameter.
Ice crystals: Precipitation in the form of slowly falling, singular or unbranched ice needles, columns, or plates. They make up cirriform clouds, frost, and ice fog. Also, they produce optical phenomena such as halos, coronas, and sun pillars. May be called "diamond dust."

 

[Kaman]

Hello,
I read a similar article in the USAirways flight operations safety magazine discussing the same topic. Research has found that ice pellets may cause a high incidence of fluid failure as you discussed, so operations are prohibited in intensities of greater than light ice pellets. Apparently, ice pellets because of their structure and weight can penetrate into the Type IV fluid and decrease it's effectiveness as a FPD. Fluid will take on a opaque appearance if this phenomena takes place. Drop me a line if you want me to scan a copy of the article for you.

Regards,

ex-Navy Rotorhead

 

[Secret Squirrel]

I remember reading an article that Ice pellets are a good indication of freezing rain above (Temperature inversion). What I read was that they were saying shortly after takeoff you could enter freezing rain which may degrade your takeoff performance while at a criticle phase of flight. It was not only the problem of the ice pellets adhearing to an aircraft w/out deice/antiice.

SS

 

[FN FAL]

I remember reading an article that Ice pellets are a good indication of freezing rain above (Temperature inversion). What I read was that they were saying shortly after takeoff you could enter freezing rain which may degrade your takeoff performance while at a criticle phase of flight. It was not only the problem of the ice pellets adhearing to an aircraft w/out deice/antiice.

SS

Yea, but at least you're not taking off with a contaminated airplane.

Depending on what weather lies above, you may be going into more than what your plane can handle or less.

 

[Secret Squirrel]

Are you following me?

 

[Flyin2low]

The official weather observer determines what the type of precip is and then you reference your Deice chart for the holdover. You don't need to know how to tell the difference between all those precip types. That's why those guys go to special training.