Hoar Frost?

[ops_guy]

Hi Guys,

I am doing my CPL Meteorology exam in 2 days time and one particular question (that I now remember I got wrong in the PPL theory exam). In the text book that I am using it specifically says " Hoar Frost has very little effect on aircraft performance". At the end of the same book in the practice exam it gives the answer as it being " Hazardous to aircraft performance as it increases the stall speed". Now I know in general that Frost is detrimental to performance - i am just confused because this text book contradicts itself!!!

It says Hoar Frost forms as white crystalline deposits when a cold soaked aircraft descends in to warmer, more humid air (dpeosition occurs) and that it can also happen on a calm, clear night with a high relative humidity. SO what do you reckon - a silly mistake by the books publisher and that Hoar Frost is indeed detrimental to aircraft performance (getting it wrong in the PPL test confirms this for me)?

Cheers guys,

Opso

[redsnail]

Hoar frost on top of the wings and thick enough on the fuselage to be unable to read labels etc must be removed.

Hoar frost underneath the wings were the fuel tanks are and within a specified boundary is ok.

[captain_quagmire]

And there was me thinking it was some sort of STD;)

[paco]

Having hoar frost on the surface is like having it covered with fine sandpaper. In my opinion, all of it should be removed.

Phil

[EGBKFLYER]

From our SOPs, says that the Commander has final say on what gets de-iced, but this is the minimum:

Take-off with light coatings of frost, up to 1/8 inch (3mm) in thickness on lower wing surfaces due to cold fuel, is permissible; however, all leading edge devices, all control surfaces, tab surfaces, upper wing surfaces and balance panel cavities must be free of snow or ice.
Thin hoar frost is acceptable on the upper surface of the fuselage provided all vents and ports are clear. Thin hoar frost is a uniform white deposit of fine crystalline texture, which usually occurs on exposed surfaces on a cold and cloudless night, and which is thin enough to distinguish surface features underneath, such as paint lines, markings or lettering.

[EpsilonVaz]

It's what you get on a cold night layover in Amsterdam :ouch: