Advisory Circular (AC) No. 500-008 Issue 1

Induction System Snow Protection

File No. 5009-6-500 AC No. 500-008
RDIMS No. 528255-V2 Issue No. 01
Issuing Branch Aircraft Certification Effective Date 2004-12-01

1.0 Introduction

1.1 Purpose
1.2 Guidance Applicability
1.3 Description of Changes
1.4 Termination

2.0 References

2.1 Reference Documents
2.2 Cancelled Document

3.0 Background

4.0 Acceptable Means of Compliance

4.1 Methods
4.2 Acceptance Criteria
4.3 Test Witnessing
4.4 Test Results

5.0 Rotorcraft Flight Manual

6.0Headquarters Contact

1.0 Introduction

1.1 Purpose

The purpose of this Advisory Circular (AC) is to provide guidance material for acceptable means, but not the only means, for conducting a test program to demonstrate compliance with the requirements of Chapters 527 and 529 of the Airworthiness Manual (AWM) dealing with the operation of helicopter engines in snow conditions.

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. 500/7A, is reissued as an AC. With the exception of minor editorial changes and updated references, the content is unaltered.

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 materials be used in conjunction with this document:

(a) Chapter 527 of the Airworthiness Manual (AWM) - Normal Category Rotorcraft;
 
(b) Chapter 529 of the AWM - Transport Category Rotorcraft;
 
(c) Part 27 (FAR 27) of the Federal Aviation Administration (FAA) Title 14, Code of Federal Regulations (CFR ) - Airworthiness Standards: Normal Category Rotorcraft;
 
(d) Part 29 (FAR 29) of the FAA CFR - Airworthiness Standards: Transport Category Aircraft;
 
(e) Federal Aviation Administration Advisory Circular (FAA AC) 27-1, Change 1 - Certification of Normal Category Rotorcraft; and
 
(f) FAA AC 29-2A - Certification of Normal Category Rotorcraft.

2.2 Cancelled Document

As of the effective date of this document, AMA No. 500/7A dated 27 January 2000 is cancelled.

3.0 Background

The U.S. Federal Aviation Administration amended their rules applying to ice and snow protection in engine air induction systems so that snow is now treated differently than ice (FAR Part 27, Amendment 27-23, and Part 29, Amendment 29-26). Based on the new rules and their associated advisory material (FAA AC 27-1 Change 1 and FAA AC 29-2A), it is clear that the FAA no longer requires a demonstration of any capability for flight in snow if this flight condition is prohibited in the Rotorcraft Flight Manual (RFM).

From the Canadian perspective, this situation was considered unacceptable. It is inconceivable that a helicopter being operated in the Canadian climate will not, at some time, inadvertently encounter snow while in flight. The aircraft will have to have at least some basic capability to fly out of, or through, the snow conditions.

For this reason, Transport Canada did not adopt FAR Amendments 27-23 and 29-26, but amended the requirements of paragraphs 527.1093(b)(1) and 529.1093(b)(1) of the AWM to stipulate that each engine and air induction system shall demonstrate a tolerance to falling, blowing, and re-circulating snow, as a minimum. If certification for flight in snow is being requested, the requirements are effectively the same as those of FAR Parts 27 and 29.

The Canadian amendments (Changes 527-1 and 529-1) introduce two levels of capability for Canadian approved helicopters for operations with respect to engine air induction systems in snow. This situation is parallel to that required by the requirements for engine operations in icing conditions of subparagraphs 527.1093(b)(1)(i) and 529.1093(b)(1)(i) of the AWM. These requirements stipulate that a capability must be demonstrated, by all rotorcraft certified under these rules, for inadvertent encounters with in-flight icing conditions regardless of the RFM limitations.

The two levels of capability called up in these requirements are:

(a) Basic subparagraphs 527.1093(b)(1)(iii) and 529.1093(b)(1)(iii) of the AWM:
At this level, the aircraft will not be cleared for flight in any type of snow. In fact, the RFM shall contain a limitation statement prohibiting flight in snow, excluding brief encounters with blowing and re-circulating snow during normal take-off and landing (limited exposure).
 
(b) Snow Clearance subparagraphs 527.1093(b)(1)(ii) and 529.1093(b)(1)(ii) of the AWM:
 
At this level, the rotorcraft will receive full clearance for flight in snow.

4.0 Acceptable Means of Compliance

4.1 Methods

Acceptable methods, that may be used to demonstrate compliance with induction system snow protection requirements, are those described in FAA AC 27-1 Change 1 or FAA AC 29-2A, as is appropriate. The Canadian variation is limited only to the Acceptance Criteria. At the "Basic" level the demonstration conditions are less demanding and the operation times are shorter than those at the "Snow Clearance" level.

4.2 Acceptance Criteria

There are two levels of acceptance criteria:

(a) Basic Level:
For each rotorcraft type that is to be approved for operation in Canada, it must be demonstrated that operations can be conducted in falling, blowing and re-circulating snow under the following conditions:
 
(i) Visibility - one mile, or less, in falling snow.
 
(ii) Temperature - minus 4 to plus 1.5 degrees Celsius (as in FAA AC 27-1 Change 1 and FAA AC 29-2A) unless other temperatures are deemed more critical.
 
(iii) Operations:
 
1) Ground operations - five minutes;
 
2) IGE hover - one minute;
 
3) Level flight - 10 minutes; and
 
4) Descent and landing.
 
(b) Snow Clearance Level:
When a snow clearance is requested the demonstration criteria will be identical to those of FAA AC 27-1 Change 1 or FAA AC 29-2A, as appropriate.

4.3 Test Witnessing

Where practical, the demonstration should be witnessed by Transport Canada or a delegated representative.

4.4 Test Results

A report of the flight test results should be submitted to Transport Canada for review.

5.0 Rotorcraft Flight Manual

The RFM limitations section shall state clearly the snow conditions in which flight is not permissible. If compliance with the criteria for a snow clearance has been satisfactorily demonstrated there should be no snow related limitations. Visibility restrictions for falling and blowing snow operations and time limitations, except perhaps for ground and hover, are not appropriate.

Aircraft which have only demonstrated to the Basic Level conditions shall be prohibited from flight into falling and blowing snow, and also from flight in re-circulating snow, except for take-off and landing.

If compliance with the Basic Level criteria has not been achieved, a statement will be required in the Limitations Section prohibiting flight in ambient temperatures less than, or equal to, +5 degrees Celsius.

6.0 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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