Advisory Circular (AC) No. 700-011

Subject: Operations on Runways with Unpaved Surfaces

Issuing Office:	Civil Aviation, Standards
Document No.:	AC 700-011
File Classification No.:	Z 5000-34
Issue No.:	02
RDIMS No.:	20574731-V19
Effective Date:	2026-06-05

1.0 Introduction
2.0 References and requirements
3.0 Background
4.0 Runway surfaces
5.0 Climatic and wear effects
6.0 Effects of unpaved surface operations on aeroplanes
7.0 Protection and certification of aeroplanes for unpaved surface operations
8.0 Regulatory requirements
9.0 Minimum required surface strength
10.0 Measurement of surface strength
11.0 Information management
12.0 Document history
13.0 Contact us

1.0 Introduction

(1) This Advisory Circular (AC) is provided for information and guidance purposes. It describes an example of an acceptable means, but not the only means, of demonstrating compliance with regulations and standards. This AC on its own does not change, create, amend or permit deviations from regulatory requirements, nor does it establish minimum standards.

1.1 Purpose

(1) The purpose of this document is to provide guidance to operators (air operators and private operators) for the safe operations of aeroplanes on runways with unpaved surfaces in accordance with the applicable Canadian Aviation Regulations (CARs) and Standards.

1.2 Applicability

(1) This document is applicable to all Transport Canada Civil Aviation (TCCA) employees, to individuals and organizations when they are exercising privileges granted to them under an External Ministerial Delegation of Authority. This information is also available to the aviation industry for information purposes.

1.3 Description of changes

(1) Due to the number of changes incorporated into this Issue, readers should review the content of the entire document. The major changes are:
- (a) Section 2.0 References and requirements
  - (i) Subsection 2.1 References documents updated
  - (ii) Subsection 2.2 Cancelled documents updated
  - (iii) Subsection 2.3 Definitions and abbreviations updated
- (b) Section 3.0 Background – revised
- (c) Section 4.0 Runways with unpaved surfaces – New section with new content to describe and relate unpaved runways
- (d) Section 5.0 Climatic and wear effects – Section renumbered
- (e) Section 6.0 Effects of unpaved surface operations on aeroplane performance and handling – Section renumbered, title changed, and content revised
- (f) Section 7.0 Protection and certification of aeroplanes for unpaved surface operations – Section renumbered, title changed, and content revised. Content from former Section 6.0 Protection of aeroplanes for unpaved surface operations, and 7.0 Certification of aeroplanes for unpaved surface operations, merged into Section 6.0 of Issue 02 of this AC
- (g) Section 8.0 Regulatory requirements – Section renumbered, title changed, and content revised
  - (i) Subsection 8.1 CAR subpart 704 requirements – subsection revised to reflect change in CAR subpart 704 gravel runway operational requirements being moved from the former CASS 724.44(3) to CAR subpart 704 Division IV – Aeroplane Performance Operating Limitations. Examples provided for maximum weight calculations
  - (ii) Subsection 8.2 CAR Subpart 705 Requirements – new subsection
  - (iii) Subsection 8.3 CAR Subpart 702, 703 and 604 Requirements - new subsection
  - (iv) Subsection 8.4 Frozen Unpaved Runways - Subsection renumbered and content revised
  - (v) Subsection 8.5 Dispatch Limitations - Subsection renumbered
- (h) Section 9.0 Minimum required surface strength – Subsection renumbered, and content on runway strength classification revised
- (i) Section 12.0 Document history – Subsection renumbered, and content revised to reflect Issue 02 of this AC
- (j) Section 13.0 Contact us – Titled changed and content revised

2.0 References and requirements

2.1 Reference documents

(1) It is intended that the following reference materials be used in conjunction with this document:
- (a) Aeronautics Act (R.S.C., 1985, c. A-2)
- (b) Part V Subpart 21 of the Canadian Aviation Regulations (CARs) — Approval of the Type Design or a Change to the Type Design of an Aeronautical Product
- (c) Part V Subpart 71 of the CARs — Aircraft Maintenance Requirements
- (d) Part VI Subpart 2 of the CARs — Operating and Flight Rules
- (e) Part VI Subpart 4 of the CARs — Private Operators
- (f) Part VII of the CARs — Commercial Air Services
- (g) Advisory Circular (AC) 300-004 — Unpaved Runway Surfaces, Issue 04, Effective Date 2017-12-05, or later issue
- (h) AC 302-011 — Airport Pavement Bearing Strength Reporting Issue 02, Effective Date 2016-01-04, or later issue
- (i) AC 300-021 — Thin Bituminous Surface Runways, Issue 01, Effective Date 2022-06-10, or later issue
- (j) AC 521-004 — Changes to the Type Design of an Aeronautical Product, Issue 01, Effective Date 2012-03-16, or later issue
- (k) AC 521-005 — Supplemental Type Certificates, Issue 01, Effective Date 2012-03-16, or later issue
- (l) AC 525-006 — Operations from Unpaved Runway Surfaces, Issue 01, Effective Date 2004-12-01, or later issue
- (m) Canada Flight Supplement; Effective 0901z 12 June 2025, or later edition; Canada and North Atlantic Terminal and Enroute Data; Published by NAV CANADA in accordance with ICAO Annexes 4 and 15 of the Convention on International Civil Aviation
- (n) Transport Canada Publication (TP) 312 — Aerodrome Standards and Recommended Practices, Land Aerodromes, 5th Edition, Effective date: September 15th, 2015, or later issue

2.2 Cancelled documents

(1) Not applicable.
(2) By default, it is understood that the publication of a new issue of a document automatically renders any earlier issues of the same document null and void.

2.3 Definitions and abbreviations

(1) The following definitions are used in this document:
- (a) Aircraft Classification Number (ACN): a number expressing the relative structural loading effect of an aircraft on a pavement for a specified pavement type and a specified standard subgrade category (former International Civil Aviation Organization [ICAO] pavement strength reporting format).
- (b) Aircraft Classification Rating (ACR): A number expressing the relative effect of an aircraft on a pavement for a specified standard subgrade category ICAO pavement strength reporting format).
- (c) Aircraft Load Rating (ALR): A number expressing the relative structural loading effect of an aircraft on a pavement (Transport Canada strength reporting format).
  
  Note: Transport Canada no longer uses ALR and PLR as an Aircraft/Pavement Load Rating system.
- (d) California Bearing Ratio (CBR): A measure of the load bearing capacity of a given sample of soil expressed as a ratio relative to the load bearing capacity of crushed limestone.
  
  Note: The load bearing capacity of crushed limestone is expressed as a CBR of 100.
- (e) Gravel Runway: A runway with an unbound granular surface composed of sand, clay, crushed stone or other soil materials, or a bound surface composed of a thin layer of binding material atop a runway pavement structure.
  
  Note: Arunway with a thin layer of bituminous binding material is a Thin Bituminous Surface (TBS) Runway. A TBS Runway with Class 1 or Class 2 treatment is a Surface Treated runway (i.e., gravel runway).
- (f) Operator: In respect of an aircraft, it means the person that has possession of the aircraft as owner, lessee or otherwise.
  
  Note: In the context of this AC the term operator applies to an air operator under Part VII of the CARs or a private operator under Part 604 of the CARs.
- (g) Paved Runway: An asphalt cement concrete (flexible), Portland cement concrete (rigid), or thin bituminous surface.
  
  Note: Guidance on acceptable thin bituminous surfaces is contained in Advisory Circular (AC) 300-021 – Thin Bituminous Surface Runways.
- (h) Pavement: The combination of sub-base, base course, and surface course placed on a subgrade to support the traffic load and distribute it to the subgrade (as per ICAO definition in the ICAO Aerodrome Design Manual). For the purposes of this Advisory Circular (AC), a pavement can be defined as the total construction built upon natural soil to produce a load carrying structure or surface.
- (i) Pavement Classification Number (PCN): a number expressing the bearing strength of a pavement for unrestricted operations (former ICAO pavement strength reporting format).
- (j) Pavement Classification Rating (PCR): A number expressing the bearing strength of a pavement (ICAO pavement strength reporting format).
- (k) Pavement Load Rating (PLR): a number expressing the bearing strength of a pavement for unrestricted operations (former Transport Canada strength reporting format).
  
  Note: Transport Canada no longer uses ALR and PLR as an Aircraft/Pavement Load Rating system.
- (l) Surface Definition: A definition of the surface for which the aircraft has been certified to operate from, normally provided in the Aircraft Flight Manual (AFM) or applicable supplement. Each type of surface should be defined so that it can be recognized, controlled and maintained in service. The definition should include specification and characteristics of the surface as necessary for safe operation.
- (m) Surface Treated Runway: An unpaved runway with a gravel surface covered by a thin layer of binding material, to prevent the penetration of water and facilitate drainage.
  
  Note: Surface Treated Runways are gravel runways and may also be referred to as Chip Seal Runways (referred to as “GRVL/chip seal” in the Canada Flight Supplement) or Seal Coated Runways.
- (n) Thin Bituminous Surface (TBS) Runway: A runway pavement structure meeting the criteria of a Class 3 Thin Bituminous Surface as defined by the Transportation Association of Canada. The structure is comprised of a double sealed granular surface layer, and one or more granular base layers. Thin Bituminous Surface Runways are distinct and separate from Surface Treated Runways.
- (o) Unpaved Runway: A runway pavement constructed with an unpaved surface.
- (p) Unpaved Runway Surface: A runway surface comprised of gravel, turf, clay or hard packed soil mixtures. Unpaved runway surface can be on manually constructed pavements or on naturally occurring unprepared surfaces.
- (q) Unprepared Runway Surface: An altered, unaltered, or naturally occurring surface without an underlying pavement structure used as a runway.
(2) The following abbreviations are used in this document:
- (a) AC: Advisory Circular
- (b) ACN: Aircraft Classification Number
- (c) ACR: Aircraft Classification Rating
- (d) AFM: Aircraft Flight Manual or Aeroplane Flight Manual
- (e) ALR: Aircraft Load Rating
- (f) ASTM: American Society of Testing Materials
- (g) CAA: Civil Aviation Authority
- (h) CARs: Canadian Aviation Regulations
- (i) CASS: Commercial Air Service Standard
- (j) CBR: California Bearing Ratio
- (k) CFS: Canada Flight Supplement
- (l) C.G.: Centre of Gravity
- (m) COM: Company Operations Manual
- (n) ICAO: International Civil Aviation Organization
- (o) PCN: Pavement Classification Number
- (p) PCR: Pavement Classification Rating
- (q) PIC: Pilot In Command
- (r) PLR: Pavement Load Rating
- (s) POI: Principal Operations Inspector
- (t) STC: Supplemental Type Certificate
- (u) TBS: Thin Bituminous Surface
- (v) TP: Transport Canada Publication

3.0 Background

(1) This Advisory Circular (AC) applies to the operation of aeroplanes on runways with unpaved and unprepared surfaces.

4.0 Runway surfaces

4.1 Runways with unpaved surfaces

(1) Runways with unpaved surfaces are referred to as unpaved runways and may have surfaces of bound or unbound materials overlying a runway pavement structure. Gravel runways are a form of unpaved runways.
(2) Unpaved runways may be referred to in the Canada flight supplement (CFS) aerodrome facility directory/RWY data as:
- (a) Clay
- (b) crushed rock
- (c) Grass
- (d) GRVL
- (e) GRVL/chip seal
- (f) Sand
- (g) Snow
- (h) Turf
Note 1: Unpaved runways may be referred to by industry as unimproved runways.

Note 2: Surface treated gravel runways may also be referred to as chip seal runways (referred to as “GRVL/chip seal” in the Canada Flight Supplement) or seal coated runways.
(3) Thin bituminous surface (TBS) runways, as defined in subsection 2.3 (above), are categorized by the Transportation Association of Canada into three main structural categories: Class 1, Class 2, and Class 3. Classes 1 and 2 are considered surface treated runways and may appear in the Aerodrome facility directory of the Canada Flight Supplement (CFS) under RWY data as GRVL or GRVL/chip seal. Class 3 TBS pavements are distinct paved runways and are identified in the CFS as “paved - TBS.”

Note 1: Refer to Advisory Circular 300-021 – Thin Bituminous Surface Runways for guidance respecting TBS runways.

Note 2: Refer to AC 300-004 – Unpaved Runway Surfaces for guidance respecting surface treated runways.

4.2 Runways with paved surfaces

(1) Class 3 TBS pavements are distinct and separate from surface treated runways and meet the definition of a thin bituminous surface runway as defined in AC 300-021 – Thin Bituminous Surface Runways.
(2) Class 3 TBS pavements are paved runways and are identified as “paved – TBS” in the CFS. The operation of aeroplanes on Class 3 TBS pavements (paved runway operations) is outside the scope of this AC.

4.3 Unprepared runway surfaces

(1) Unprepared runway surfaces may be temporary or permanent surfaces constructed for specific operations and are not published in the CFS. Examples of Unprepared Surfaces include unprepared natural surfaces, clay, sand, gravel, turf etc. surfaces without an underling pavement structures or frozen lakes. The guidance of this AC may be applied to unprepared surface operations.

5.0 Climatic and wear effects

(1) Unpaved runways can be subject to wide variations in their strength and surface characteristics because of climatic effects and the effects of aircraft operations. Unpaved runways can achieve their design strength and surface characteristics when maintained properly and are not subjected to excessive moisture.
(2) Conditions of excessive moisture, such as heavy precipitation, poor drainage or spring thaw can result in a significant degradation in runway surface strength. The degradation in surface strength may be enough to limit or completely restrict operational use.
(3) During periods of extended and deep frost, unpaved surfaces such as gravel runways can have strength characteristics similar to those of paved hard surfaces. (Refer to subsection 8.4 of this AC.
(4) The following is a list of possible adverse climatic and wear effects on unpaved runways:
- (a) Loss of material resulting in bare spots and sub-grade material appearing on the surface;
- (b) Accumulation of loose, non-cohesive aggregates on surface because of material segregation;
- (c) Formation of rutting in wheel paths;
- (d) Persistence of damp or wet areas because of poor surface drainage;
- (e) Soft areas during spring thaw or wet conditions;
- (f) Differential heaving or depressions because of frost action;
- (g) Runway roughness or longitudinal unevenness (waviness); and
- (h) Vegetation growth.
(5) An unpaved runway such as a gravel runway may be restored to its nominal conditions by grading, compaction and rolling, the addition of material, improvement in drainage and the removal of vegetation.

6.0 Effects of unpaved surface operations on aeroplanes

6.1 Performance and handling

(1) The AFM performance information (or data) is valid for only the type of surface the aeroplane has been certified to operate from, which is normally a paved, smooth, hard surfaced runway.
(2) Operations on unpaved surfaces may result in a degradation of the certified aeroplane performance, resulting in increased take-off and braking distances.
(3) Take-off and accelerate-stop distances may increase due to factors such as increased rolling resistance, the installation of protective equipment and changes in operating procedures.
(4) Braking distance (affecting landing and accelerate-stop distances) may increase due to lower braking effectiveness on unpaved surfaces and brake anti-skid systems that are optimized for paved hard surfaces.
(5) The interaction of tires with the reduced strength and surface characteristics of unpaved surfaces can result in degradation in the handling qualities of the aeroplane during take-off, landing, ground manoeuvring or braking. Aircraft steering and anti-skid braking performance may be degraded.

6.2 Damage from debris and dust

(1) Operations on unbound unpaved surfaces expose an aeroplane to hazards caused by the impingement and ingestion of stones, dust and debris. Debris can be raised from propellor or jet wash, or from wheel rotation which may strike the airframe, become wedged in flight controls, damage propellors or be ingested by engines or inlets with adverse effects.

6.3 Structural loads

(1) The operation on rough unpaved runway surfaces can cause dynamic loading that may damage the aircraft structure or landing gear or invalidate fatigue life assumptions.

7.0 Protection and certification of aeroplanes for unpaved surface operations

7.1 Protective equipment

(1) Protective systems to mitigate the hazards from the impingement of stones, dust and debris may include various shields, deflectors, filters, engine intake vortex dissipators, and abrasion resistant finishes.

Note: The installation of protective equipment is a modification under Subpart 571 of the CARs and may require design approval under Subpart 521 of the CARs.

7.2 Revised operating procedures

(1) Special procedures may be required to minimize the adverse effects of unpaved surface operations, which may include pre-flight inspections, thrust/power handling techniques, use of reverse thrust, use of nosewheel steering, etc.
(2) The application of special procedures may have adverse effects on aeroplane performance.

7.3 Tire pressure

(1) Reducing tire pressure may reduce tire rolling resistance and reduce the adverse effects on aeroplane performance on unpaved runway surfaces. The reduction in tire pressure may be limited by the tire design, associated tire pressure limitations, and the necessity to avoid excessive deflection of the tire under load. It may be necessary to reduce aircraft weights if operating under reduced tire pressures. Some aircraft are modified with oversize, floatation or balloon type low pressure tires for operations on soft unpaved surfaces.

Note: Any alterations of tire pressure, or types of tires used are modifications under Subpart 571 of the CARs and may require a design approval under Subpart 521 of the CARs, which would be carried out in accordance with AC 521-004 or AC 521-005.

7.4 Aircraft certification requirements

(1) Aeroplanes designed and certified for operations on smooth paved hard surfaced runways may not require design approval under Subpart 521of the CARs, to operate on unpaved runway surfaces, unless they are modified with the installation of protective equipment.

Note 1: Any modifications should be evaluated in accordance with Subpart 571 of the CARs and may require design approval under Subpart 521 of the CARs, which would be carried out in accordance with AC 521-004 or AC 521-005.

Note 2: Anyone meeting the applicable eligibility requirements of Subpart 521 of the CARs may apply for a design approval to allow an aeroplane to operate on unpaved surfaces, if needed.
(2) TC Advisory Circular AC 525-006, Operations from Unpaved Runway Surfaces, provides the guidance and criteria for the certification of transport category aeroplanes for operations on unpaved surfaces. Section 5.0 of the AC, Acceptable means of compliance provides the aircraft certification requirements, which are summarized in the following:
- (a) Surface Definition, which requires the definition of each type of unpaved runway surface that are valid for operational use. The surface definition includes the surface and pavement bearing strength requirements to be published in the AFM supplement.
- (b) Take-off, Landing and Accelerate-Stop Performance including the effects of protective equipment and revised procedures on aircraft performance.
- (c) Aircraft Handling Characteristics, including weight, C.G. limits and special procedures and techniques.
- (d) Aircraft systems (e.g. brake anti-skid, and nosewheel steering) must continue to perform their intended functions. In addition, the aeroplane should operate on the defined unpaved runway surfaces without any hazard from the impingement of stones, dust and debris.
- (e) Structural considerations that include limitations and revisions to weight limits and C.G. ranges, fatigue life limits on landing gear and other structural elements, and the effects of likely impingement of debris on the structure.
- (f) Maintenance requirements associated with unpaved runway operations.
- (g) MMEL requirements for dispatch with inoperative protective equipment such as anti-skid, nosewheel steering etc.
- (h) Aircraft Flight Manual or supplement information to include:
  - (i) Limitations including runway surfaces the aeroplane may operate on, runway inspection requirements, weight and C.G. limitations, tire pressure limitations, approved aircraft configurations, and thrust/power limits.
  - (ii) Procedures including normal, non-normal and emergency procedures associated with unpaved runway surface operations.
  - (iii) The aeroplane performance in the form of guidance information, that accounts for any special procedures and the surfaces the aeroplane may operate on. The performance information should include a statement that the performance information does not constitute an operational approval.

7.5 Operation of aeroplanes not certified for unpaved runway surface operations

(1) Operators intending to operate aeroplane(s) on unpaved runway surfaces not certified for such operations, should consider the adverse effects of such operations as described in the preceding and establish appropriate mitigations. The criteria of AC 525-006 should be considered when establishing mitigations. Operators should submit amended procedures and limitations with appropriate substantiation to the Operator’s POI for review and approval.
(2) Operators may choose to use manufacturer’s guidance for aeroplane operations on unpaved runway surfaces (referred to as Manufacturer’s Data) or AFM supplements approved by other Civil Aviation Authorities (CAAs). Operators should consider the criteria of AC 525-006 when considering the adequacy of such information. Operators should submit the use of Manufacturer’s Data or foreign CAA AFM supplements with appropriate substantiation to their POI for approval.

8.0 Regulatory requirements

(1) Section 602.07 of the CARs requires aircraft to be operated in accordance with limitations contained in the AFM or applicable supplement. All limitations for unpaved runway operations including the limitations concerning the minimum runway surface strength for which operations are certified must be complied with.
(2) For operations under Part VII of the CARs, sections 704.44 and 705.55 of the CARs require that any determinations made for the purposes of these sections shall be based on approved performance information (or data) as set out in the AFM. Air operators must therefore respect minimum runway surface strength requirements and surface description/characteristics when provided as performance information in an approved AFM or AFM supplement.
(3) While there are exception provisions for operations on gravel for sub-part 704 propeller-driven aeroplanes (see section 8.1, below), these exceptions do not apply to operations under subpart 705, or turbojet aircraft under subpart 704. Therefore, compliance with the limitations and performance information found in the AFM or AFM supplement is mandatory for these types of operations.

8.1 CAR Subpart 704 requirements

(1) Section 704.44 of the CARs requires that any determination made for the purposes of sections 704.45 to 704.51 shall be based on the approved performance information specified in the AFM. Section 704.46 (subsections 704.46(5) and 704.45(6)) provides take-off and landing weight limitations applicable to gravel runways. Section 704.51 provides operational requirements for gravel runway operations.
(2) Subsection 704.46(5) of the CARs requires that the maximum weights for a take-off on a gravel runway or landing at a destination or alternate aerodrome shall be in accordance with gravel runway performance specified in the AFM. Gravel performance information in an AFM is normally in the form of an approved supplement to the AFM.
(3) Subsection 704.46(6) of the CARs provides similar maximum weights as subsection 704.46(5) for take-off from a departure aerodrome and landing at a destination or alternate aerodrome for propeller driven aeroplanes, which do not have gravel runway performance in the AFM (Approved AFM supplement for gravel runway operations). Instead, these maximum weights are to be determined based on information specified in the AFM as follows:
- (a) Calculations must be based upon a dry, paved hard-surface runway that does not exceed 1, 524 m (5,000 feet) in length. An air operator may not use a runway longer than these values for the purpose of calculating maximum weights,
- (b) No credit may be taken for reverse thrust to reduce stopping distances,
- (c) No credit may be taken for the use of a clearway to determine the maximum take-off weight,
- (d) The corresponding length of dry, paved hard-surface runway used to determine the required take-off distance, accelerate-stop distance and landing distance (to calculate maximum weights) shall be obtained by dividing the length of a gravel runway by a factor of:
  - (i) 1.10 in the case of an aeroplane with a MCTOW of not more than 5,700 kg (12,566 lb.) (small aeroplane) or,
  - (ii) 1.15 in the case of a large aeroplane.
    
    Note 1: The performance factors of paragraph 704.46(6)(c) of the CARs are only valid if the ratio of the aeroplane’s tire pressure in Pounds Per Square Inch (psi) divided by the CBR of the runway as measured by the Boeing Penetrometer is 5 or less. An air operator should ensure that the runway has a minimum CBR, or the maximum tire pressure of the aeroplane is limited (within required limits) to satisfy this ratio. For example, if an air operator is intending to operate on a gravel runway with an aeroplane that has a tire pressure of 125 psi, the minimum runway bearing strength as assessed by the Boeing Penetrometer must have a surface CBR of no less than 25. (125 psi divided by 5 = 25.)
    
    Note 2: These performance factors are also valid for a minimum surface CBR value of 8 as measured by the Boeing Penetrometer. For example, the maximum allowable tire pressure for the performance factors to remain valid for a CBR of 8 would be 40 psi. (CBR of 8 times 5 = 40 PSI).
    
    Caution: A CBR value of 8 represents a gravel runway with a very low surface strength and would likely be practical only for very small aeroplanes or aeroplanes with low pressure tires, considering the maximum associated tire pressure of 40 psi. An air operator should exercise caution when operating on such low strength unpaved runway surfaces.
    
    Note 3: The ratio of tire pressure (PSI) divided by CBR is based upon CBR derived from the Boeing Penetrometer. This CBR value may differ from that derived by other methodologies such as the ASTM method or a Shock Penetrometer. The CBR values derived from the Shock Penetrometer may be less than those of the Boeing Penetrometer by a factor of 2 to 4 for the same surface. Although this may result in a conservative minimum CBR, care should be taken to account for the measuring devices used to establish a minimum CBR value. (Refer to sub-section 10.2 The Sliding Weight Shock Penetrometer)
(4) The following cases provide three examples of maximum weight calculations for propeller driven aeroplanes taking off from gravel runways to comply with subsection 704.46(6) of the CARs:
- (a) Example 1: An air operator of a small aeroplane with a MCTOW weight of 10,000 lb (4,536 kg) is calculating the maximum take-off weight from a gravel runway that is 4,000 feet (1219 m) in length.
  - The air operator may use a paved hard-surface runway from the AFM of 3,636 feet (1108 m) (4,000 feet (1219 m) divided by a factor of 1.10) as the basis to calculate the maximum take-off weight.
  - No credit may be taken for any clearway or reverse thrust in the calculations.
- (b) Example 2: An air operator of a large aeroplane is calculating the maximum take-off weight from a gravel runway that is 5,000 feet (1524 m) in length.
  - The air operator may use a paved hard-surface runway from the AFM which equals 4348 feet (1325 m) (5,000 feet (1524 m) divided by a factor of 1.15) as the basis to calculate the maximum take-off weight.
  - No credit may be taken for any clearway or reverse thrust in the calculations.
- (c) Example 3: An air operator of a large aeroplane is calculating the maximum take-off weight from a gravel runway that is 6,000 feet (1829 m) in length. The air operator determines the paved hard-surface runway from the AFM that is 5217 feet (1590 m) in length (6,000 feet (1829 m) divided by a factor of 1.15).
  - The air operator must not use the 5217-foot (1590 m) value as the basis for calculating the maximum take-off weight.
  - The operator may use 5,000 feet (1524 m) for the maximum take-off weight calculations, with no credit to be taken for any clearway or reverse thrust in the calculations.
(5) Section 704.51 of the CARs requires that no air operator shall authorize a flight from or to a gravel runway in an aeroplane unless the Company Operations Manual (COM) sets out procedures for take-offs and landings from gravel runways. In addition, Section 704.51 sets out gravel runway training and experience requirements, and the need for a person to be certified by the chief pilot as being competent to conduct take-offs and landings on gravel runways.
(6) Section 704.52 of the CARs applies to take-off or landing on Unprepared Surfaces in a propeller driven aeroplane for which the AFM does not set out any information relating to unprepared surface operations. Section 704.52 also provides Pilot In Command (PIC) training and experience requirements, and the need for a PIC to be certified by the chief pilot as being competent to operate on unprepared surfaces.

8.2 CAR Subpart 705 requirements

(1) Section 705.55 of the CARs requires that any determination made for the purposes of sections 705.56 to 705.61 shall be based on the approved performance information specified in the AFM. This means that any operations (take-off or landing to or from) a runway surface that differs from that the performance information (or data) contained in the AFM is based upon, must be in accordance with approved AFM information for that runway surface.

8.3 CAR Subpart 702, 703 and 604 requirements

(1) Subparts 702, 703 and 604 of the CARs do not have the Aeroplane (Subpart 704) and Aircraft (Subpart 705) Performance Operating Limitation requirements that subparts 704 and 705 of the CARs have. Section 602.07 of the CARs requires that no person shall operate an aircraft unless it is operated in accordance with the operating limitations as set out by this regulation. This means that unpaved or gravel runway operations shall be conducted in accordance with the applicable operating limitations which have been established for such operations.
(2) Where no operating limitations have been established pertaining to unpaved or gravel runway operations, an operator (under subparts 702, 703 and 604 of the CARs) may conduct operations to or from or on such surfaces without any additional requirements.

8.4 Frozen unpaved runways

(1) During periods of extended and deep frost, unpaved surfaces such as gravel runways can have strength characteristics similar to those of runways with paved hard surfaces. Operational experience has indicated that two weeks of ambient temperatures of –20°C or lower may be necessary for an unpaved runway to achieve strength similar to a paved hard surfaced runway. Once frozen solid, the runway will remain in this state, until ambient temperatures increase to above freezing.
(2) While the frozen unpaved runway may have the same surface strength as a paved hard surfaced runway, it is still considered to be an unpaved runway, and all applicable Aircraft Flight Manual (AFM) performance operating limitations remain valid for the unpaved runway. It is also necessary to consider the surface characteristics of the frozen unpaved runway to ensure the correct operational considerations are applied.
(3) Pursuant to sections 704.44 and 705.55 of the CARs, all applicable AFM performance information should be applied for frozen unpaved runway operations.
(4) If the frozen runway is covered with frozen contaminant such as compacted snow, the operator should consider the effects of the contaminant when calculating take-off and landing performance in accordance with the TALPA-based methods (runway surface descriptors and runway condition codes) contained in AC 700-057 – Global Reporting Format for Runway Surface Conditions: Guidance for Flight Operations.

8.5 Dispatch limitations

(1) Sections 704.49 and 705.60 of the CARs require the application of dispatch factors for landing at destination and alternate aerodromes. These factors should be applied to the required unpaved runway landing distance for the runway(s) being dispatched to. The wet runway dispatch limitations for turbo-jet powered aeroplanes as required by Sections 704.50 and 705.61 of the CARs need not be applied, unless specifically required by the applicable AFM or the surface is observed to be wet enough to adversely affect braking performance.
(2) Air operators should exercise caution when dispatching to unpaved runways where the regulatory dispatch limitations do not apply. The unpaved runway landing distances are based upon AFM landing distances with no additional distance margins. The AFM landing distances are derived from landing distance demonstrations that employ more aggressive landing techniques than that used during normal operations. The possibility of a runway overrun or excursion may increase when landing on an unpaved runway under limiting conditions. Air operators should consider using operational landing distances or using the landing distance factors provided in AC 700-057, Appendix E.4, Table 6, where manufacturer-provided operational landing distance data is not available.

9.0 Minimum required surface strength

(1) The surface strength of an unpaved runway needs to be established for unpaved runway operations. The required performance information for a specific set of conditions as published in an AFM or supplement for a specific type of unpaved runway (e.g., gravel) will not be assured unless the unpaved runway meets or exceeds the AFM strength requirement. The strength of a gravel runway for operations in accordance with subsection 704.46(6) of the CARs should be measured to ensure that a Tire Pressure to CBR (as measured by the Boeing Penetrometer) ratio of 5 is not exceeded.
(2) Many aircraft manufacturers have adopted CBR as an expression of unpaved runway surface strength. CBR is the ratio of the load bearing capability of a given sample of soil compared to that of crushed limestone. The CBR of a given soil test is expressed in a percentage ranging from 0 to 100% or a whole number ranging from 0 to 100. When the CBR of the actual unpaved runway is greater than or equal to the minimum CBR value published in the AFM or supplement, the published AFM performance should be achievable.
(3) CBR has been accepted as the most common index of expressing unpaved runway surface strength. CBR should be considered an index of runway surface strength as opposed to an absolute or true value of shear strength, because of the dependence of the CBR value on the measuring device used. For this reason, it is essential an operator know and understand the measuring device used to establish a required CBR value published in an AFM or supplement.
(4) Most manufacturers identify the required CBR for operations in the AFM or associated supplement. Foreign AFMs supplements may express required surface strength requirements in terms of International Civil Aviation Organization (ICAO) Aircraft Reference (ACR) instead of CBR to establish the required gravel runway strength for operations. The operator of this type of aircraft should ensure that the corresponding Pavement Classification Reference (PCR) of the runway is sufficient to satisfy the ACN requirements respectively.

10.0 Measurement of surface strength

(1) The standard for CBR measurement is that of the American Society of Testing Materials (ASTM), which has standards for the laboratory and on site (Field In-place) testing of CBR. The ASTM D4429 standard applies to Field In-Place testing and consists of measuring the deflection of a piston (through a flat plate) into the soil against a large reactive load. The ASTM method also specifies soil conditions including moisture content for which CBR results are valid.
(2) The ASTM method has proven to be impractical for the CBR measurements on unpaved runways because of the relatively laborious set-up required for this measurement method. Some aircraft manufacturers have developed simpler CBR measurement methods for unpaved runway operations.

10.1 The Boeing High Load Penetrometer

(1) This measurement device is commonly used in North America. The test apparatus consists of a hydraulic cylinder to provide a large penetration force at a test probe. The test probe is driven into the unpaved surface to a specified depth (typically 4 inches (10 cm)) by increasing hydraulic pressure within the cylinder. The hydraulic cylinder is normally positioned against the frame of a heavy vehicle, which serves as a large reactive load.
(2) The Boeing High Load Penetrometer is similar to the ASTM method in set-up except a probe rather than a piston is applied against the surface. A CBR value is derived from the pressure required to drive the probe to the specified depth. The CBR values derived from the Boeing High Load Penetrometer are approximately 10% less than the values derived from the in-field ASTM method for a piston penetration of 0.5 inches. (The ASTM method requires readings to be taken at 0.1 and 0.2 inches). The Boeing High Load Penetrometer is more practical than the ASTM method for operational use, because of its simpler set-up and reasonably close CBR values to the ASTM method.

10.2 The Sliding Weight Shock Penetrometer

(1) Several European aircraft manufacturers use a device called a Sliding Weight Shock Penetrometer. This device uses a sliding weight which is repeatedly raised to a specified height and dropped along a long rod to drive a probe into the surface to a specified depth. A CBR value is derived from the number of drops of the sliding weight required to drive the probe to a specified depth.
(2) The force available to drive the probe into the surface is relatively small in comparison to the hydraulic force available by the ASTM method and Boeing High Load Penetrometer. The CBR derived from a Shock Penetrometer may under-read the CBR derived from the Boeing penetrometer on the same surface by a factor ranging from 2 to 4. The presence of small stones as small as one-half inch (12.5 mm) in diameter may result in artificially high readings. Shock penetrometer values may only be valid for relatively softer surfaces because of the lower penetration forces available from this device.
(3) Operators should be aware that any surface CBR values derived from a Shock Penetrometer can underread a CBR value derived from another strength measuring device such as the Boeing High Load Penetrometer by a significant factor.

10.3 Dynamic Cone Penetrometer

(1) The Dynamic Cone Penetrometer is similar in principle to the sliding weight Shock Penetrometer. The Dynamic Cone Penetrometer follows the ASTM D6951/D6951M, 2009—Standard Test Method for the Use of the Dynamic Cone Penetrometer in Shallow Pavement Applications. The forces capable from the Dynamic Cone Penetrometer are similar to those of the Sliding Weight Shock Penetrometer. Caution should also be exercised when establishing the strength of an unpaved runway in terms of CBR when derived from this device.

10.4 Operational use of California Bearing Ratio values

(1) As stated in subsection 9.0 (3) above, the CBR value derived from other than the ASTM method should be treated as an index of surface strength rather than an absolute value of CBR. The method used to measure an unpaved runway for operational use should be the same method used to derive the minimum CBR published in the AFM or supplement. For example, if the CBR value published in the AFM or AFM supplement was derived using the Boeing High Load Penetrometer, the runway intended for operational use should be assessed using the Boeing High Load Penetrometer.

Caution: Many AFM’s do not identify the measuring device used to establish the minimum or required CBR for operational use.
(2) Hazardously misleading results may occur if a Boeing High Load Penetrometer is used to measure the surface strength of an unpaved runway to comply with a minimum required CBR established using a Sliding Weight Shock Penetrometer. For example, the CBR derived from a Boeing High Load Penetrometer would have to be in the range of 30 to 60 to satisfy an AFM requirement for a CBR of 15, if based on the Shock Penetrometer (based on an error factor of 2 to 4 between the two devices).
(3) It is the responsibility of an operator to clearly understand the basis of a required CBR value, required by the AFM or supplement for unpaved runway operation. The operator should determine from the aircraft manufacturer or other sources, the CBR device used in establishing the required CBR as published in the AFM or AFM supplement.
(4) The operator should reconcile strength values if different devices are used between the required and measured CBR for operational use.It may be necessary to apply conversion or correlation factors if the methods used to derive CBR for the AFM or supplement differ from those used to assess an unpaved runway for operational use. The operator may need to conduct an engineering analysis or contact an aircraft manufacturer for this information.

10.5 Measurement of unpaved runway surface strength

(1) The manufacturer’s instructions of the measuring device for gravel runway strength measurements should be followed. Measurements are normally taken along the length of the runway in the anticipated main landing gear wheel paths and at specific intervals (normally 100 - 200 feet (30-60m)). The measurement locations should be evenly staggered between the two wheel paths. Spot measurements should also be made along taxiways and aprons, or other areas suspected to be soft.
(2) A minimum of 20 measurements should be taken when measuring the surface strength of an unpaved runway to account for the non-uniform strength characteristics of an unpaved runway. The published runway surface strength CBR value should be the average of all the measurements taken on the runway minus one standard deviation (i.e., $C B R = Χ - σ$ ).
(3) The strength of an unpaved runway will vary with moisture and time of year. When the strength of an unpaved runway is measured during its weakest annual condition, normally soon after spring thaw, it is likely the strength of the runway will be sufficient during the remainder of the year, unless exposed to prolonged precipitation. The operator should continually monitor the condition of the unpaved runway to ensure that strength requirements continue to be met for operational use.
(4) Measurements may also be required at additional depths if required by the AFM supplement or by the specific test methodology applicable to the measuring device.

11.0 Information management

(1) Not applicable.

12.0 Document history

(1) Advisory Circular (AC) 700-011, Issue 01, RDIMS 6331431 (E), 6831058 (F) dated 2012-03-16 — Operations on Runways with Unpaved Surfaces.

13.0 Contact us

For more information, please contact:
Commercial Flight Standards (AARTF)
E-mail: AARTFInfo-InfoAARTF@tc.gc.ca

We invite suggestions for amendment to this document. Submit your comments to:
Standards Branch Documentation Services
E-mail: AARTDocServices-ServicesdocAART@tc.gc.ca

Original signed by

Jamie-Lee MacDermid
Executive Director
Standards Branch
Civil Aviation

AC 700-011 - Operations on Runways with Unpaved Surfaces
(PDF, 480 KB)