Prediction and Measurement of Surface Friction During Winter Operations

In case you need prediction in Winter Operation solutions, iJET operation specialists are ready to assist. To ensure smooth flight operations in harsh winter conditions, our expert team examines the necessary instructions.

A Study was initiated by the Accident Investigation Board Norway (AIBN) in 2006 following the investigation of a number of accidents and serious incidents involving reduced wintertime road surface friction.  Based on the AIBN mandate, the Findings and generic Safety Recommendations are specific to the Norwegian context. There are, however, many issues in the Report that may be of interest to those based in other countries where runway surface condition assessment and their correlation with actual aircraft braking are also unresolved.

Uncertainty In Friction Measurements Due to Weather Conditions

Water combined with contaminated runways plays a more significant role in ‘slipperiness’ than previously thought. In certain meteorological conditions, the difference between measured/estimated runway friction coefficients (FC) and airplane braking coefficients (ABC) is especially great. There are many factors that contribute to sanding success, including layers of contaminants, moist and wet conditions, air temperature, dew point temperature, sanding, and strong crosswinds.

• In the case of dry compact snow or ice, the correlation between the friction coefficient (FC) and the experienced airplane braking coefficient (ABC) is of the order of 0.5.
• Based on the temperature, dew point, precipitation, and their historical values, friction coefficient should be calculated. When assessing runway friction, these factors can serve as practical safety indicators.

Friction measurement devices lack the necessary scientific basis for their validity ranges. Even when the same surface is being measured by different friction measurement devices, the results vary. There is no friction measurement device that is reliable for all types of contamination, regardless of how it is constructed internationally.

Treatment For Runways

Friction-improving means – both sanding and chemical use – have received limited scientific research and forecasting model approval from authorities. When it comes to loose layers of snow on top of compact snow or ice, sanding is not very effective. This includes sanding on wet and compact snow or ice. When used on such surfaces, friction measurement devices measure excessive friction values. It has been found that chemicals may reduce friction by causing wet and mixed contamination caused by melting snow and ice. This is due to the fact that wet and mixed contamination causes friction to decrease until the contaminant is completely melted. A chemical liquid is further diluted by water melted from ice and snow, so when it freezes, it forms invisible ice.

Effects of Functional Friction on Aircraft Operation

The effects of rolling, slipping, and skidding on an aircraft:

1. Aircraft/Runway Interaction

The critical tire/ground contact area determines the mechanical interaction between aircraft and runways. For the largest aircraft in service, this small area (approximately 4 square meters) drives the roll and braking characteristics, as well as the directional control of the aircraft.

2. Lateral Forces

At speeds where flight controls are less effective, these forces facilitate directional control on the ground operations. The operational manuals recommend taking special precautions (for example, reducing maximum allowable crosswind for takeoff and landing, reducing taxi speeds) if contaminants are present on the runway or taxiway surface and reduce friction characteristics.

3. Longitudinal Forces

As a result of rolling and braking friction forces, these forces can be classified along the speed axis of the aircraft (affecting acceleration and deceleration). An aircraft facing a slippery runway surface is subject to additional drag forces when it is covered with a loose contaminant (e.g., slush, snow, or standing water)

Reporting Format for Global Transactions

In order to determine aircraft performance for takeoff and landing as accurately as possible, runway state conditions must be reported in a standardized manner. In order to communicate runway state data effectively, aircraft performance charts supplied by the manufacturer must be used in conjunction with the terminology and values reported on the runway state.

In order to make this commonality of terminology and values work, manufacturers, aerodrome personnel, flight operations officers and flight dispatchers, as well as air traffic controllers and aeronautical information specialists, all of whom transmit the data, must use the same terminology and values.

The reporting of runway conditions requires a common understanding of definitions and processes. Considering the possibility of merging the following initiatives into one new format is proposed:

• ICAO SNOWTAM 52
• ICAO NOTAM
• Canadian CRFI
• Initiative between the FAA and the TALPA ARC

iJET Ground Handling Services in Winter Conditions

When it comes to flight support in winter conditions, every minute counts. The iJET team is here to help you achieve smooth flight operations in winter conditions.