Advisory Circular (AC) No. 500-010 Issue 1

The purpose of this Advisory Circular (AC) is to provide a summary of the standards to be used for the approval of the design and installation of aircraft skis.

1.2 Guidance Applicability

This document is applicable to all Transport Canada personnel, delegates and industry.

1.3 Description of Changes

This document, formerly AMA No. 500/9A, is reissued as an AC. The reference documents and the content have been reviewed and updated.

1.4 Termination

This document does not have a terminating action. It will however, be reviewed periodically for suitability of content.

2.0 References

2.1 Reference Documents

It is intended that the following reference material be used in conjunction with this document:

(a) Part II, Subpart 1, of the Canadian Aviation Regulations (CARs) - Identification of Aircraft and Other Aeronautical Products;

(b) Part V, Subpart 11 of the CARs - Approval of the Type Design of an Aeronautical Product;

(d) Chapter 523-VLA of the Airworthiness Manual (AWM) - Very Light Aeroplanes;

(e) Chapter 523 of the AWM - Normal, Utility, Aerobatic and Commuter Category Aeroplanes;

(f) Chapter 525 of the AWM - Transport Category Aeroplanes;

(g) Chapter 527 of the AWM - Normal Category Rotorcraft;

(h) Chapter 529 of the AWM - Transport Category Rotorcraft;

(i) Chapter 537 of the AWM - Appliances;

(j) Transport Canada Engineering and Inspection (E & I) Manual, Part II - Requirements;

(k) Federal Aviation Administration (FAA) Technical Standard Order (TSO)-C28 - Aircraft Skis;

(l) Federal Aviation Administration Advisory Circular (FAA AC) 27-1 - Certification of Normal Category Rotorcraft;

(m) FAA AC 29-2 - Certification of Transport Category Rotorcraft;

(n) FAA AC 43.13-2A - [Large AC] Acceptable Methods, Techniques and Practices -Aircraft Alterations;

(o) National Aircraft Standards Specification National Aerospace Standards (NAS) 808 -Specification - Aircraft Skis;

(p) U.S. Military Handbook (MIL-HDBK)-5E - Military Standardization Handbook: Metallic Materials and Elements for Aerospace Vehicle Structures;

(q) MIL-HDBK 23A - Military Standardization Handbook: Structural Sandwich Composites; and

(r) U.S. Department of Defense, Subcommittee on Air Force-Navy-Civil Aircraft Design Criteria, Bulletin ANC - 18, 2d ed., 1951 - Design of Wood Aircraft Structures.

2.2 Cancelled Document

As of the effective date of this document, AMA No. 500/9A dated 29 October 1999 is cancelled.

3.0 Background

Prior to the publication of the Airworthiness Manual (AWM), the approval of aircraft skis and associated installations was primarily based on the standards specified in the Engineering and Inspection Manual (E & I), Part II, Chapter I, Section 1.1. These standards were developed mainly for small fixed-wing aircraft, but were also applied to large aeroplanes, excluding rotorcraft. The introduction of the AWM without rescinding the applicable section of the E & I Manual has generated some confusion with respect to the standards that should be applied for the approval of aircraft skis and their installation. The E & I Manual, Part II, Section 1.1 is now superseded. Pending the publication of specific requirements in the Airworthiness Manual these criterias and other information previously contained in the E & I Manual, including Restraining and Trimming Gear, Tail Skis and Propeller Clearance for fixed wing aircraft not found in other documents referenced herein, are repeated in this AC.

4.0 Skis

The AWM requires that each ski be approved following the procedures specified in Subpart 511 of the CARs. According to Chapter 537 of the AWM, the requirements for the approval of skis are contained in FAA Technical Standard Order (TSO) - C28. This order requires that skis comply with the strength and performance requirements of sections 4 and 5 of the National Aircraft Standards Specification (NAS) 808 - Specification - Aircraft Skis.

4.1 Material Specifications

The following material specifications are accepted:

(a) MIL-HDBK-5E - Military Standardization Handbook: Metallic Materials and Elements for Aerospace Vehicle Structures;

(b) MIL-HDBK-23A - Military Standardization Handbook: Structural Sandwich Composites; or

Any strength values used by the manufacturer pertaining to composite materials must be confirmed by test and presented to Transport Canada Aircraft Certification Branch for approval.

4.2 Identification of Skis

Each aircraft ski shall be suitably marked as specified in Section 201.10 of the CARs.

5.0 Aircraft

5.1 Fixed Wing Aircraft

In accordance with sections 523.737 and 525.737 of the AWM, the maximum limit load rating of each ski must equal or exceed the maximum limit load determined under the applicable ground load requirements specified in Chapters 523 and 525 of the AWM.

Supplementary conditions for skiplanes shall be determined as follows:

(a) Normal Category Aeroplanes - for normal category aeroplanes, these conditions are contained in section 523.505 of the AWM.

(b) Transport Category Aeroplanes - Chapter 525 of the AWM does not specify ground load conditions. This deficiency will be addressed by the issuance of Special Conditions (SCA) for each model and type.

5.2 Rotorcraft

The maximum limit load rating of each ski must equal or exceed the maximum limit load determined under the applicable ground load requirements of sections 527.737 and 529.737of the AWM. Supplementary ground load conditions for rotorcraft are contained in sections 527.505 and 529.505 of the AWM.

For additional information refer to section 305 of FAA AC 27-1 and FAA AC 29-2 for normal and transport category rotorcraft. Section 305 applies to the approval of "pads" or "bear paws" installed on skids or wheel landing gears.

6.0 Ski Installations

Ski installations can be approved either as part of the type design of the aircraft, according to Subpart 511 of the CARs, or as separate installations, in accordance with Subpart 513 of the CARs. Ski installations should meet the criteria contained in Chapter 5 of FAA AC 43.13-2A, except for the Restraining and Trimming Gear requirements specified in 6.2 for fixed wing aircraft.

For rotorcraft, ski installations shall be subject to flight and ground operation evaluations as specified in section 305 of FAA AC 27-1, or AC 29-2.

Note:

In the case of conflict between the instructions contained in the following paragraphs and approved manufacturers data for the specific installation, the latter shall apply, except in the case of the angular travel limits for the skis, specified below.

6.1Propeller Clearance

All ground and structural clearance requirements for the landplane shall be met, including propeller clearance when the ski is rotated within its rigging limits with the landing gear in the fully deflected position.

6.2Restraining and Trimming Gear

For fixed wing aircraft, the restraining gear shall meet the following Restraining and Trimming Gear criteria:

(a) Ski restraining and trimming gear attachments shall meet the requirements set forth in paragraphs (c) to (d) below. In addition, it shall be ensured that no interference can occur between the ski and any part of its attachments when the ski is in any position permitted by its restraining gear. Special stabilising devices will be examined on their own merits.

(b) An elastic trimming gear shall be provided to maintain the ski in an appropriate position during all normal flight conditions, and, be able to return the ski to that position when the nose is displaced by abnormal loads. In the absence of more adequate data the pitching moment about the pedestal bearing shall be taken as not less than 0.36 x 10^-5W V_ne² foot pounds, ultimate, when the nose of the ski is fully depressed to the limit of the restraining gear, where "W" is the weight in pounds of the aeroplane and "V_ne" is the never exceed speed in miles per hour. This pitching moment becomes less as the ski is returned to its normal flight position.

(c) A restraining gear must be provided which limits the angular travel of the ski to a nose down angle of -15° and a nose up angle of approximately 0° to +3° when the aeroplane is in the flying position, with no weight on the undercarriage.

(d) When the aeroplane is on the ground and the undercarriage compression leg is compressed to its static position, the restraining gear should allow the angular travel of the ski to accommodate the position assumed when the aeroplane encounters an up hill slope of 7½° when in a tail up attitude and a down hill slope of 7½° when in a tail down attitude.

(e) The restraining gear and the structure to which it is attached, should have sufficient strength to withstand the greater of the following, which are ultimate loads:

(i) The load in the restraining gear necessary to balance the pitching moment quoted in 6.2(b) of this AC.

(ii) The loads induced in the restraining gear by a vertical load equal to 0.8P ultimate, applied, firstly, at the fore end of the ski and, secondly, at the aft end of the ski.

7.0 Tail Skis

For tail skis, the criteria of either FAA AC 43.13-2A, or the following requirements of the E&I Manual may be used:

"Tail skis and pedestals do not need to be approved as components and will not be rated for strength by Transport Canada. It is recommended, however, that they be designed to meet the same strength standards as main skis on the basis of the maximum static load on the tail ski as installed in the aeroplane."

8.0 Flight and Ground Handling Requirements

When fitted with skis, the aircraft must continue to satisfy all the applicable requirements specified in its basis of certification. In the case of small aeroplanes certified to U.S. CAR 3, section 3.246: compliance with sections 523.51 and 523.75 of the AWM in lieu of the U.S. CAR 3 requirements is acceptable. This relieves the applicant of the requirement to determine take-off and landing distances.

9.0 Aircraft Flight Manual

Each operating limitation resulting from the installation of skis on an aircraft and the additional information necessary for safe operation must be developed and included in the Flight Manual Supplement.

10.0 Inspection Provisions

Adequate means shall be provided to permit a close examination of the skis when required, i.e. periodic inspection, adjustments for proper alignment and function, lubrication of moving parts etc. (Refer to NAS 808, paragraph 3.5).

11.0 Instructions For ContinuED Airworthiness

An applicant for the issue of a type certificate for skis must develop Instructions for Continued Airworthiness acceptable to the Minister.

In accordance with section 513.31 of the CARs, an applicant for an STC to install skis on an aircraft must develop Instructions for Continued Airworthiness for the complete ski installation. These instructions may include those prescribed by the ski type certificate holder.

The Instructions for Continued Airworthiness may be incomplete at the time of approval, provided a program exists to ensure their completion and acceptance by Transport Canada prior to the first time installation of these skis on an aircraft, other than for test purposes.

12.0 Headquarters Contact

For more information please contact:

Policy Standards Coordinator (AARDH/P)
Phone: (613) 990-3923
Facsimile: (613) 996-9178
E-mail: AARDH-P@tc.gc.ca

Original signed by Maher Khouzam

Maher Khouzam
Chief, Regulatory Standards
Aircraft Certification Branch

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