A Pilot's Guide to Ground Icing
Module I - Risks
How ground icing can hurt you
Section: Module Summary
Start This SectionModule Summary Risks
Make sure that your aircraft’s critical surfaces are clean prior to beginning the takeoff roll. Each contamination situation is unique – how thick, how rough, how and where it is distributed all play a roll in the effect it may have. Contamination may:
- reduce maximum lift available at rotation
- decrease the stall angle, possibly without triggering the stall warning system
- reduce the rate of climb
- lead to a roll or pitch upset
- flame out the engines
- break off and get ingested into the engine
- cause faulty and confusing airspeed, altitude, AOA or engine indications
Keep your aircraft clean. Don't think twice, de-ice.
Further Information
In this course, we will use "clean" instead of "frozen contaminants are not adhering”" for simplicity. Here is how the partner regulatory agencies define the term.
Canadian Aviation Regulations (CAR 602.11) prohibit persons from conducting or attempting to conduct a take-off in an aircraft that has frost, ice or snow adhering to any of its critical surfaces.
By "clean" we mean a wing that is free of frozen contaminants other than those permitted by the AFM. A wing that has been properly de-iced and subsequently coated with de/anti-icing fluids is considered to be a clean wing up to the point of fluid failure.
FAA regulations prohibit the take off of an aircraft that has frost, ice, or snow adhering to any propeller, windshield, wing, stabilizing or control surface, to a power plant installation, or to an airspeed indicator, altimeter, rate of climb, or flight attitude system, or other critical surfaces of the aircraft.
Kurt Blankenship, NASA Research Pilot, reflects on the Birmingham, UK Challenger accident
Related Information
BIRMINGHAM, ENGLAND
JANUARY 4, 2002
CHALLENGER 604
Immediately after takeoff from Runway 15 at Birmingham International Airport the aircraft began a rapid left roll, which continued despite the prompt application of full opposite aileron and rudder. The left winglet contacted the runway shoulder, the outboard part of the left wing detached and the aircraft struck the ground inverted, structurally separating the forward fuselage. Fuel released from ruptured tanks ignited and the wreckage slid to a halt on fire; the Airport Fire Service was in attendance less than 1 minute later. The accident was not survivable.
Numerous possible causes for the uncontrolled roll were identified but all except one were eliminated. It was concluded that the roll had resulted from the left wing stalling at an abnormally low angle of attack due to flow disturbance resulting from frost contamination of the wing. A relatively small degree of wing surface roughness had a major adverse effect on the wing stall characteristics and the stall protection system was ineffective in this situation. Possible asymmetric de-icing by the Auxiliary Power Unit (APU) exhaust gas during pre-flight preparations may have worsened the wingdrop tendency.
N90AG's pilots should have been aware of wing frost during pre-flight preparations but the aircraft was not de-iced and the ice detector system would not have alerted them. It was considered that the judgement and concentration of both pilots may have been impaired by the combined effects of a nonprescription drug, jet-lag and fatigue.
Possible contributory factors were; the inadequate warnings on the drug packaging, Federal Aviation Administration (FAA) guidance material suggesting that polished wing frost was acceptable and melting of the frost on the right wing by the APU exhaust gas.
The investigation identified the following causal factors:
- The crew did not ensure that N90AG's wings were clear of frost prior to takeoff.
- Reduction of the wing stall angle of attack, due to the surface roughness associated with frost contamination, to below that at which the stall protection system was effective.
- Possible impairment of crew performance by the combined effects of a non-prescription drug, jetlag and fatigue.