Landing Performance Calculation on a Contaminated Runway (Including GRF Format)
1. Understanding Contaminated Runway and Depth of Contaminants
A contaminated runway is one where more than 25% of the surface is covered by:
• Water (more than 3mm)
• Slush (more than 3mm)
• Snow (compacted or loose)
• Ice (frozen or wet)
The depth of contaminants significantly affects the landing performance, particularly in terms of:
• Landing distance required (LDR)
• Braking efficiency (friction coefficient)
• Directional control (risk of hydroplaning/sliding)
Each type of contaminant has a different effect. For example:
• Standing water (>3mm) increases hydroplaning risk.
• Slush (>3mm) significantly reduces braking effectiveness.
• Wet ice or compacted snow provides very little friction.
2. Landing Performance Calculation on Contaminated Runways
The landing distance is calculated using:
• Aircraft Performance Data (from the AFM - Aircraft Flight Manual)
• Runway Surface Condition Reports
• Operational Landing Factors (e.g., wet/contaminated surface adjustment)
The general equation for landing distance:
\text{Landing Distance Required} = \frac{\text{Dry Runway Distance}}{\text{Braking Action Factor}}
Where:
• Braking Action Factor depends on the contaminant type, depth, and temperature.
• Reverse Thrust & Autobrakes improve performance but depend on runway conditions.
A common practice is using Landing Distance Factor (LDF) from aircraft manuals, which accounts for reduced braking on contaminants.
3. Global Reporting Format (GRF)
GRF is a standardized method introduced by ICAO (effective from November 2021) to assess and report runway conditions in a Runway Condition Report (RCR).
It standardizes how pilots, dispatchers, and controllers interpret runway conditions globally.
Key Elements of GRF
1. Runway Condition Code (RWYCC) – 0 to 6 Scale
• Describes braking action and performance impact.
2. Runway Condition Assessment Matrix (RCAM)
• Links contaminants, depth, and temperature to RWYCC.
3. Runway Condition Report (RCR)
• Issued by airport authorities and updated dynamically.
4. GRF & Contaminant Depth Consideration
• The depth of contaminants is reported in millimeters (mm) for precise performance adjustments.
• The GRF Runway Condition Code (RWYCC) is assigned based on the worst condition observed in each third of the runway.
Example RWYCC Based on Depth:
|
Contaminant |
Depth (mm) |
RWYCC (Typical) |
|---|---|---|
|
Dry or Wet (≤3mm) |
- |
6 (Good) |
|
Water/Slush |
3 - 12mm |
5-4 (Good-Med) |
|
Wet Snow |
3 - 12mm |
4-3 (Med-Poor) |
|
Ice |
Any depth |
2-0 (Poor) |
The pilot/dispatcher uses the RWYCC along with aircraft performance charts to determine the landing distance.
5. How GRF is Used in Landing Performance Calculation
• Step 1: Get the Runway Condition Report (RCR) from ATIS, NOTAM, or ATC.
• Step 2: Identify the RWYCC and contaminant depth.
• Step 3: Use AFM (Aircraft Flight Manual) charts for performance corrections.
• Step 4: Apply any operational landing distance factors (e.g., 1.15x for wet runways).
• Step 5: Ensure the calculated landing distance fits within LDA (Landing Distance Available).
6. Summary
• Contaminant depth affects braking action and must be factored into landing distance calculations.
• The GRF system standardizes runway condition reporting globally using RWYCC.
• Pilots use RWYCC & contaminant depth to adjust landing performance.
• Always apply corrective factors from AFM to ensure safe landing.
a sample calculation based on specific aircraft performance charts
Sample Landing Performance Calculation Using GRF
Let’s assume we are calculating the landing distance for a Boeing 737-800 on a contaminated runway using the GRF system.
Step 1: Get the Runway Condition Report (RCR)
Assume the following report from ATC:
• Runway: 26L
• Contaminant: Wet snow
• Depth: 6mm
• RWYCC: 3 (Medium Braking Action)
• Temperature: -2°C
• Wind: Calm
• Landing Distance Available (LDA): 2,400m
Step 2: Base Landing Distance on a Dry Runway
From the B737-800 AFM, at MLW (65,317 kg) and no wind, the landing distance required (LDR) on a dry runway is:
LDR_{\text{dry}} = 1,500m
Step 3: Apply Contaminated Runway Corrections
From the Boeing Contaminated Runway Chart, a Runway Condition Code (RWYCC) of 3 (Medium Braking) due to 6mm wet snow results in:
• Landing Distance Factor (LDF) = 1.47 (for RWYCC 3).
LDR_{\text{contaminated}} = LDR_{\text{dry}} \times LDF
LDR_{\text{contaminated}} = 1,500m \times 1.47
LDR_{\text{contaminated}} = 2,205m
Step 4: Compare with Landing Distance Available (LDA)
• LDR (Required): 2,205m
• LDA (Available): 2,400m
✅ Landing is feasible (2,205m < 2,400m), but with reduced safety margin.
Step 5: Adjust for Operational Safety
• If tailwind is present, increase LDR.
• If autobrakes are used, check if they reduce the LDR.
• Consider an additional 15% safety margin if regulations require it.
Final Decision
• Landing is possible but needs careful execution.
• Pilots should expect longer deceleration and possible directional control challenges.
• Alternate airport should be considered if conditions worsen (e.g., increasing snow depth).
detailed explanation on performance charts or safety margins
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