FAQ’s

It is possible to calculate the conditions of runway turnoff ramps, taxiways and parking ramps.  AST anticipates developing future product releases which can provide these reports.

Airports will benefit from having a periodic, objective measure of braking action conditions, as well as developing braking action trends. Whether operating in inclement weather with snow and ice, or hydroplaning conditions caused by winds and rain, airport operations can optimize runway closure and maintenance decisions. At the most active airports, braking action reports will occur within minutes of each other. This data pattern should enable an airport to monitor runway conditions during periods of high activity and limit the need to shut a runway down for an exploratory ground based measurement test. Such tests can take 15 to 25 minutes each and can place dozens of aircraft in holding patterns. In addition, at large airports, it can take 30 minutes or more to move maintenance equipment in place to clean a runway. Having visibility of developing trends will improve safety, airport operations and flow control decisions. AST believes airport operations will realize cost savings, operational efficiencies and improve customer service benefits which are multiples of the cost to utilize AST reports.

Air carriers will benefit from having insight into current landing conditions and developing trends at the airports from which they operate, which will contribute significantly to safety and schedule reliability. The benefits will include improved safety and flight operations’ decisions, visibility on pilot and crew sequencing issues, better fuel and cargo weight management, and cost savings from reduced holding patterns and optimized landing and taxiing sequences. Customer service should also improve across the network for all participants.  Overall annual carrier savings from deploying the AST system in the US are projected to be several hundred million dollars.

Working with DFDAU / FDIMU avionics vendors, AST develops an ACMS report script for each participating aircraft type. Upon touchdown, the FDAU box captures the required data from the main data bus for between 35- 45 seconds. At the end of the rollout period, the report is sent to AST’s server via ACARS, wireless gatelink or other communications means. Depending on the latency of the communications network, a braking action report is generally available less than one minute after rollout.

The reports’ outputs cannot be used to criticize a pilot’s landing. All reports are de-identified, and only express runway conditions, not airplane handling metrics. AST does not retain the flight data file once the runway friction report is produced. Otherwise, AST manages the data file transfers within accepted FOQA or other air carrier data management policy protocols.

Pilots derive several safety and operational benefits from AST reports.  If upon approach, a pilot receives an objective measure of current landing conditions, he can be better prepared to set the aircraft up for landing.  Pilots must factor aircraft weight, surface conditions, runway type, differences in braking action measurement standards (domestic, international, military), among other things, in planning a landing sequence.  In addition, the ability for the aircraft to provide a pilot runway condition report post landing frees up the pilot to concentrate on other aspects of taxiing and removes the liability of misreporting braking conditions.

The measurement of runway surface friction employs redundancy at many levels.  Whenever possible, multiple measurements are used to determine the runway surface conditions.  As landings proceed on a given runway, all landings within a meaningful time span are used to calculate a weighted average that is reported as the runway braking conditions.

Redundancy also figures into the computations of the runway conditions for any given landing.  As the aircraft decelerates through its landing roll, data is calculated along the entire path of the roll and these data points are averaged to report summary values for touchdown, midpoint, and rollout segments of the runway.  Likewise, these three summary values are used to compute a single overall summary value for the runway as a whole.  Finally, these summary values for each of the active runways at an airport are used to compute a single weighted summary value that represents the overall condition of the airport as a whole.

The advantage of these various summary values is that they afford a quick representation of the conditions that can be read at a glance, as well as an ability to drill down to specific runway section condition analysis.

As one of the materials and surfaces involved in the generation of frictional forces in a braking action the importance of the runway surface cannot be neglected.  The actual contact between the aircraft tires and runway (actual contact area, contact pressure, tire stretching etc.) depends to great extent on the runway surface characteristics.  Surface material as well as surface texture, grooving and other parameters can heavily influence braking action.

Different environmental factors such as precipitation, ground contaminants like snow or slush or water influences braking and friction significantly.  The introduction of side forces on the landing gear tires due to cross winds has a profound effect on the ability of the tires to develop braking friction.  The very strong and non linear interdependency of the braking friction and lateral friction on a tire makes cross wind component and other dynamic effects initiating side forces a serious issue that can not be neglected.  In general the generation of lateral forces during aircraft braking initiated by crosswinds will reduce the possible maximum frictional forces in a nonlinear way that depending on braking maneuver and the magnitude of initiated cornering forces can be seriously limiting braking action.

During landing depending on aircraft minimum equipment list, landing speeds and other parameters aircrafts can heavily depend on tire friction especially at a lower airspeed portions of the landing maneuver.  Frictional forces are developed by the interaction of the aircraft tire and the runway surface or runway contaminant (water, snow, ice etc.).  These frictional forces are heavily dependent on the tire properties and therefore tire parameters and the interaction of developed tire forces (side force, loading force, frictional force).

The AST algorithms are capable of delivering normalized runway condition reports independent of aircraft, tire and other parameters. As the model takes into account the relevant tire parameters as well as computes the different aircraft dependent dynamic forces it is able to account for variations and deliver a normalized and meaningful runway friction condition report independent of the aircraft type, tire variations and runway surface types.

The model has been tested in operational, scientific and accident investigation contexts over the past twelve years.  It has been tested in scientific research within the Joint Winter Runway Friction Program (sponsored by NASA, FAA, JAA, Transport Canada and other research organizations).  The model was used in aircraft testing in the US, Japan, Germany and Canada.  The model also has been used in aiding accident and incident investigations where it was cross-checked against the results from proprietary simulations and models of the involved airframe manufacturers.  The reporting system has been successfully tested on several models of aircrafts from Boeing, Airbus, Bombardier, and other airframe manufacturers. In 2011, a prototyping exercise with commercial carriers, involving several different airplane types, further validated the reliability and accuracy of the computational models used in SafeLand.

Pilot reports, visual observations and ground based measurement systems are used today to estimate runway braking conditions.  All three methods are highly subjective and have proven to be inaccurate in post accident investigations.  In addition, the effect of crosswinds, temperature, type of contamination, runway surface material, aircraft design and tires dramatically impact braking conditions and are not factored into the current measurement methods.  AST is not proposing that industry participants stop using any of the existing methods.  There will be a need for these measurements at airports with infrequent landings and for the “first plane in” at the start of operations.

To our knowledge, the patented AST model is the only aircraft runway friction and braking action calculation model that takes into account the three dimensional interdependent nature of frictional, loading, and side force (cornering force) of the aircraft tire.  This is the only model that is capable to account for the differences in frictional behavior of tires based on rolling and true ground speed and calculating the interaction between the changes in tire load, cornering forces and other relevant parameters.

Modern aircraft tires are very complex, made of rubber compounds that are viscoelastic in nature, operate at high pressure with geometric and construction designs that add to their complexity.  The interaction between the tires and the rolling surface is dependent on literally hundreds of parameters including surface material type and construction, ambient temperature, tire pressure, tire material, tire design and dimensions as well as runway condition, aircraft ground speed, tire rolling speed, tire load and many other parameters.  Added to these complexities are the dynamic forces developing on the bodies of a landing aircraft effecting braking action including residual lift on the wings effecting tire loads, loading/unloading and dynamic momentum caused by the thrust/reverse-thrust of engines, side forces caused by cross winds and many others.  The combination of these two highly non-linear processes causes the calculation of the true effective braking action of landing aircraft to be a very complex and highly non-linear process.

The AST algorithm for the calculation of true available runway friction and cornering friction coefficients is based on the combination of a total energy based aircraft dynamic simulation and a proprietary non-linear frictional tire contact model.  The total energy based model aircraft simulation uses data recorded within the data management systems of the landing aircraft and effectively computes all relevant forces acting on the aircraft including aerodynamic drag; engine thrust forces, wind side loads, lift and many others.  The computed forces are used to back calculate actual generated forces acting on the aircraft tires.  These forces are used in a complete three dimensional non-linear tire model to compute the friction, cornering, rolling resistance, contaminant drag and other relevant braking condition parameters.