Aircraft Critical Surface Contamination

Question 1

Effects of Contamination on Performance

Answer 1

● This produces an increase in stall speed and a decrease in stall angle of attack
● It has been proven that a few millimeters of ice will increase the stall speed by as much as 20%

Question 2

Clean Aircraft Concept

Answer 2

● The Clean Aircraft Concept is an air regulation that does not allow the pilot to takeoff when frost, ice, or snow is adhering to any of the aircraft’s critical surfaces.
● If it is possible that frost, ice, or snow has collected on the aircraft, then an inspection is required before takeoff.
● This inspection is to be carried out by either the pilot or a crew member who is trained in what to look for

Question 3

Frozen Contaminants

Answer 3

● Ice accumulation with the thickness and roughness of a medium to coarse grit sandpaper will decrease the lift by as much as 30%, while increasing the drag by as much as 40%

Question 4

Cold Soaking Phenomenon

Answer 4

● Ice can form even when the outside air temperature (OAT) is well above 0°C (32°F).
● An aircraft equipped with wing fuel tanks may have fuel that is at a low temperature such that it lowers the wing skin temperature to below the freezing point.
● Liquid water coming in contact with a wing will freeze to the wing surfaces.
● Cold soaking can cause frost to form on the upper and lower wing under conditions of high relative humidity

Question 5

Practices for Pilots To Ensure a Clean Aircraft

Answer 5

● In any case, ice or frost formations on upper or lower wing surfaces must be removed prior to takeoff.
● The exception is that takeoff may be made with frost adhering to the underside of the wings provided it is conducted in accordance with the aircraft manufacturer’s instructions
➢ Must cool aircraft if precipitation is present
■ Fuel may hinder the cooling

Question 6

de icing fluid

Answer 6

● Type I
➢ Primarily for de-icing.
➢ Very limited anti-icing ability (short hold over time).
➢ Heated water with antifreeze (glycol) added at the nozzle.
➢ The exact percentage of antifreeze is adjusted depending on the air temperature.

● Type II
➢ More viscous (thicker) than Type I.
➢ Sticks to the wing.
➢ Absorbs falling precipitation to prevent freezing.
➢ Designed to shear off wings when airspeed reaches ~100 KT.

● Type III
➢ Similar to Type II but designed to shear off at slower airspeeds.
➢ Meant for some aircraft with Vr <100 KT. (With aircraft manufacturer approval)

Type IV
➢ Similar to type II but with a much longer hold over time.
➢ These fluids are dyed green so that they will not be mistaken for ice.
➢ These fluids do not flow off the wing as easy as type II fluids