Gravel Runway Maintenance and CBR Testing
A gravel runway changes with every thaw, rainfall and season. We help mine airstrips and northern and regional airports keep theirs strong, smooth and reported, so the aircraft that serve the mission can keep landing. We help you accomplish the mission.
Who Is It For?
Mine airstrips, from the first construction flights to production and crew rotations. Northern airports and community airstrips where gravel is the runway surface. Regional airports with a gravel runway, taxiway or apron.
See the mine project stages. Construction air logistics.
What Does Cirrus Do?
Gravel Runway Maintenance
We inspect slopes, drainage, frost heave and surface defects, then plan the grading, compaction, gravel replacement and ditch work that keep the runway in shape. Spring thaw and fall are the key windows. Dust control uses products that will not corrode aircraft, so road salt and calcium chloride stay off the airside.
Source: AC 300-004, sections 7.0, 8.0 and 8.3.
CBR Testing
We test the runway's surface strength in place and report it the way Transport Canada asks for unpaved surfaces: the CBR number, the surface type and the evaluation method. You get a clear picture of what the runway can carry and where it is weak.
Sources: TP312, as quoted in AC 300-004, section 3.0; AC 300-004, section 6.2.
Geotechnical Work and Resurfacing
We look below the surface: soil type, frost susceptible material, drainage and permafrost. That tells us whether regular grading is enough or the runway needs new gravel or resurfacing, and where to start.
Source: AC 300-004, sections 4.0, 5.0 and 8.1.
Runway Condition Reporting
In winter, a gravel runway often becomes a compacted snow surface. We inspect it and prepare condition reports in the format Transport Canada sets for gravel runways, by full runway length, and make sure your Canada Flight Supplement entry describes the winter surface.
Sources: CAR 302.417; AC 300-005, section 7.0; AC 300-019, section 5.11.
Ice Runways
Planning a seasonal ice runway instead? That is part of our aerodrome design work. Aerodrome design and feasibility.
Getting ready for certification? See TP312 compliance.
From Our Projects
At one mine, the question was simple: could the gravel runway carry the planned aircraft? We ran a series of penetrometer tests on the runway and analysed the results. The runway was found adequate as tested. See our projects.
Who Does the Work?
Our runway team, who have tested gravel runways at mine sites and kept them in shape through the seasons, with our airport managers for condition reporting. The work is done by qualified personnel, and every report names the method used. If you need it, the report can be sealed or certified on request.
How Does a Runway Program Work?
- Runway and mission review. We start with the aircraft you plan to use, what their flight manuals require, the runway's history and any past CBR reports.
- Condition inspection. We inspect the runway, taxiways and apron and record slopes, drainage, frost heave, ruts, soft spots and large stones.
- CBR testing. We test along the wheel paths and at any soft areas, ideally soon after spring thaw, when the runway is at its weakest.
- Report and maintenance plan. You get the results with the method, surface type and conditions on test day, plus a plan for grading, compaction, new gravel, drainage and resurfacing, in order of priority. Carriers can compare the results with their flight manuals.
- Through the seasons. We retest after construction work, when ruts or pilot reports suggest the runway is weakening, or after a season without use. In winter, we keep the condition reports going. The procedures go into your airport operations manual.
Runway findings can feed your safety management system.
Frequently Asked Questions
What is a CBR test on a runway?
CBR stands for California Bearing Ratio. It expresses the surface strength of an unpaved runway as an index compared with crushed limestone. Transport Canada's standard for certified airports says the strength of a gravel or grass surface is found with a recognized CBR method and reported with the CBR number, the surface type and the method.
Sources: TP312; AC 300-004, sections 2.3, 3.0 and 6.2.1.
When should a gravel runway be tested?
Normally soon after spring thaw, when the surface is at its weakest. Transport Canada also suggests testing after construction work on the surface, when there are signs the runway is weakening, such as ruts or pilot complaints, and after a season without use or maintenance. How often depends on the runway, the aircraft and how busy it is.
Source: AC 300-004, section 6.2.6.
Which test method do you use?
The one that fits the runway and the aircraft. ASTM D4429 is the field standard for CBR in place, and ASTM D1883 the laboratory one. Penetrometer methods, including the dynamic cone penetrometer under ASTM D6951, are faster but give an estimate of CBR, so results differ from one method to another. That is why every report names the method, and why it should match the method behind the minimum CBR in the aircraft's flight manual.
Sources: AC 300-004, sections 6.2.1, 6.2.3 and 6.2.7; AC 700-011, sections 10.0 and 10.4.
Does a CBR test tell us which aircraft can land?
It tells you how strong the runway surface is. The carrier compares that with the minimum surface strength in its aircraft flight manual or supplement, measured the same way, and decides. Cirrus does not operate aircraft; we give the carrier and the airport the data to make that call.
How do you maintain a gravel runway?
With regular inspections and grading. The runway is graded and compacted as soon as possible after spring thaw and preferably again in the fall before winter, with gravel added where material is lost and ditches kept clear so water drains away. In summer, dust control may be needed, using products that will not corrode aircraft.
How is a gravel runway's condition reported in winter?
Under the Global Reporting Format used in Canada, a gravel runway is reported by full runway length, not by thirds, and gets no runway condition code. The report describes the surface, and can note that the runway was graded or packed. Transport Canada also asks airports to say in the Canada Flight Supplement when the surface is a compacted snow and gravel mix in winter. At certified airports, CAR 302.417 requires movement area inspections and these reports.
Sources: CAR 302.417; AC 300-005, sections 5.2 and 7.0; AC 300-019, sections 5.3 and 5.11.
Do you also work on ice runways?
Yes, as part of our aerodrome design work. We plan seasonal ice runways and compare them with other ways to bring freight in. See Aerodrome design and feasibility.
Official Sources
- TP312, Aerodrome Standards and Recommended Practices
- AC 300-004, Unpaved Runway Surfaces
- AC 700-011, Operations on Runways with Unpaved Surfaces
- AC 300-005, Changes to Runway Surface Condition Reporting
- AC 300-019, Global Reporting Format for Runway Surface Conditions
- CAR 302.417, movement area inspections and reports
Is Your Gravel Runway Ready for the Season?
Tell us about your runway and the aircraft you plan to use. We will tell you what the work involves.
Talk to usOr email info@cirrusintelligence.ca