Certain requirements (hereafter called triggers) have been set in the global reporting format (GRF) that urge the reassessment of the runway. Reassessment means the runway inspector must visit the runway, assess the runway and issue a new SNOWTAM if required. In this post, we explain the GRF requirements when the runway should be reassessed.
What are the regulatory criteria that trigger the reassessment of runway conditions?
Beginning of precipitation
The basic principle is that the reassessment should be carried out if the inspector assumes the runway condition code (RWYCC) is going to be changed. This situation occurs at the beginning of precipitation when runway third was previously reported to be dry, or the precipitation changes its form from water to snow and vice versa.
Contaminant type changes
Reassessment is required when the contaminant type changes on the runway. This often means that the runway condition code will also change. It is mandatory to give up-to-date contaminant information to the pilot.
Contaminant depth passes 3mm
According to Runway Condition Assessment Matrix (RCAM), contaminant depth 3mm is the limit value for different runway condition code classes. When contaminant depth passes 3mm, it requires immediate reassessment. Contaminant depth below 3mm normally represents runway condition code five. Depth over 3mm reflects runway condition codes three or two depending on the contaminant type.
Temperature passes -15°C
If compact snow has been reported and the temperature is passing -15°C (either increasing or decreasing), this means that the runway condition code changes from four to three and vice versa. In either case, it requires reassessment.
Contaminant depth passes regulatory step
GRF regulations set steps (see table below) about when to reassess the runway condition. These steps are compared to the previously reported contaminant depth.
Temperature <=3°C and dew point spread <=3°C
An important and fairly common situation is when the risk for frost build-up or runway freezing is imminent. To cover this risk, regulations state that when the temperature is equal or below 3°C and the dew point spread compared to the temperature is equal or below 3°C, an immediate reassessment is required. However, in addition to immediate assessment, a periodic reassessment should be also triggered as long as the risk exists.
AIREP below last reported RWYCC
When the aircraft is reporting any estimate of runway braking action which differs from the last reported runway condition value, an immediate reassessment should be carried out. This basic rule is described in two different specific cases in the GRF regulations. Aircraft reports braking action ‘less than poor’ equal to runway condition code zero means that an immediate reassessment is required. Using common-sense is also another one, of course, only if a runway condition code better than zero was previously reported. The regulations also state that if two consecutive landing aircrafts will report braking action ‘poor’ equal to runway condition one and if the last reported runway condition code was higher than one, an immediate reassessment is required. These rules can mean that if the aircraft report differs from the last reported value, a reassessment should be triggered.
After chemical treatment or use of sand
Another trigger for reassessment is after the use of chemicals, or so-called SPWR treatment on the runway (i.e. specially prepared winter runway). The duration of these treatments is limited. An airport should define a cycle as to when to reassess the runway condition. This cycle can mean periodic reassessment, number of operations, etc.
The same rule applies if the runway condition code upgrade has been applied. The upgrade is not valid forever and a periodic cycle should be declared to reassess the runway and determine whether the upgrade is still valid.
What are the other criteria that trigger a reassessment of runway conditions?
There are also other criteria that can trigger the reassessment of runway conditions and are not regulatory, but they are still important triggers:
Contaminant depth passes aircraft thin-thick limit
If the contaminant depth on the runway passes the aeroplanes’ thin-thick performance limit, it is quite obvious and important to publish a new SNOWTAM and runway condition report, since this has a dramatic effect on aeroplane performance calculation and V1 speed.
Airplane RWYCC differs from the last reported RWYCC
The aircraft can already behave as a sensor. During landing, some aircrafts are able to measure and calculate the runway condition code in case it is sensing a friction limited braking. If this code differs from the last reported runway condition code, this should trigger an immediate reassessment or maintenance action.
Global Runway Reporter (GRR) application alert module
All regulatory and non-regulatory triggers for a reassessment of runway conditions can effectively be handled by using the Global Runway Reporter Alert application, which gives targeted warnings when a new report needs to be done. The Alert module reacts to aircraft and weather sensor data (if available) and compares this data to the last reported runway status. The application improves cost efficiency due to better timing of maintenance and assessments efforts.