Aircraft Certification Policy Letter (ACPL)

ACPL No.: 18
Issue No.:  1
Issue Date:  1999-10-18
AARD File:  5009-0-18

Aircraft Certification Policy Letter (ACPL)

Subject: Terrain Awareness and Warning System

Table of Contents

1.0 Purpose

2.0 Reference Documents

2.1 Regulatory References
2.2 Regulatory Material

3.0 Background

4.0 Policy

4.1 First Time Transport Canada Certification
4.2 Aircraft Certification Headquarters Specialist Support
4.3 Transport Canada Ground and Flight Test Requirements
4.4 Requirement for a Terrain Situational Awareness Display
4.5 Self Test Functions
4.6 Vertical Accuracy
4.7 Aircraft Flight Manual Information

5.0 Termination Date

1.0 Purpose

1.1 The purpose of this Aircraft Certification Policy Letter (ACPL) is to provide Transport Canada Aircraft Certification personnel, including delegates with guidance for the certification of Terrain Awareness and Warning System (TAWS) and Enhanced Ground Proximity Warning System (EGPWS) on Canadian registered aircraft. This policy is provided with the consideration that there is no firm TSO standards or advisory material for the certification of TAWS at the present time.

1.2  For the purpose of this Policy Letter, the term EGPWS is meant to be used interchangeably with TAWS. This Policy Letter is not intended for the certification of conventional Ground Proximity Warning System (GPWS).

2.0 Reference Documents

2.1 Regulatory References

2.1.1 FAA draft TSO C-151, "Terrain Awareness and Warning System", draft 24/5/98 (accessible from Web site: www.faa.gov/avr/air/airhome.htm (TSOs/Proposed TSOs));

2.1.2 FAA TSO C-92c, "Airborne Ground Proximity Warning Equipment", dated 3/19/96 accessible from Web site: www.faa.gov/avr/air/airhome.htm (TSOs/Current TSOs));

2.1.3 FAA Notice N 8110.64, "Enhanced Ground Proximity Warning System (EGPWS)", dated 10/22/96 (accessible from Web site: www.faa.gov/avr/air/air100);

2.1.4 Notice of Proposed Rulemaking (NPRM), Terrain Awareness and Warning System, [Docket No. 29312; Notice No. 98-11], Issued August 19, 1998 (accessible from Web site: www.faa.gov/avr (Rulemaking(ARM)/Final Rules &NPRMs)

2.1.5 FAA Advisory Circular AC No. 25-11, Transport Category Airplane Electronic Display Systems, dated July 16, 1987.

2.2 Regulatory Material

2.2.1 TSO C-151 will prescribe the minimum operational performance standards for TAWS. All TAWS equipment approved to TSO C-151 standards will require a Forward Looking Terrain Avoidance (FLTA) and Premature Descent Algorithm (PDA) function.

2.2.2 Under the TSO, TAWS will be classified as Class A or Class B TAWS, each having different requirements. Class A TAWS will require basic GPWS modes 1-5 and a five hundred foot callout. Class B TAWS will require two specific GPWS modes and a five hundred foot callout.

2.2.3 The particular FAA operating rules mandating the installations of TAWS, will dictate the class of TAWS required. Class A TAWS will be intended for FAA Part 121 operations and Part 135 operations with more than nine (9) passengers. Class B TAWS will be intended for other Part 135 and Part 91 operations.

2.2.4 Certifications done by the FAA to date have been accomplished in accordance with guidance material contained in FAA Notice 8110.64, titled "Enhanced Ground Proximity Warning System", (EGPWS) dated October 22, 1996. This notice provides guidelines and criteria for the certification of Allied Signal EGPWS meeting TSO C-92C standards.

2.2.5 The FAA is currently developing an Advisory Circular (AC) providing guidance for the installation of TAWS meeting TSO C-151 requirements. This AC is not yet available for public viewing. FAA Notice 8110.64 is expected to be superseded by the forthcoming AC on TAWS.

2.2.6 It is expected that Transport Canada will be accepting the TSO C-151 and the FAA AC as regulatory material for the certification of TAWS. In the meantime, FAA Notice 8110.64, (and FAA AC 25-11 for terrain awareness displays) may be used as guidance material.

3.0 Background

3.1 An FAA Notice of Proposed Rulemaking ( NPRM 98-11) for Terrain Awareness and Warning Systems (TAWS), applicable to U.S registered aircraft, has been issued by the FAA. The NPRM proposes operational rules that require the installation of FAA approved TAWS for specific operations. The TAWS equipment will be required to meet the forthcoming TSO C-151, and certain operations will require the installation of a terrain situational awareness display.

3.2 Transport Canada is also developing operational rules, mandating the installation of TAWS on Canadian registered aircraft, for specific operational approvals. It is expected that the forthcoming Canadian rules will require that TAWS meet TSO C-151 and require a terrain situational awareness display, similar to that specified in the FAA NPRM 98-11.

3.3 Most TAWS certifications to date have been conducted by the FAA under the Type Certificate (TC) and Supplemental Type Certificate (STC) process. The majority (if not all) of the equipment certified has been the Enhanced Ground Proximity Warning System (EGPWS) equipment manufactured by Allied Signal.

4.0 Policy

4.1 First Time Transport Canada Certification

4.1.1 Transport Canada will conduct an evaluation of a particular make or model of TAWS equipment on the first time installation on a Canadian registered aircraft. The majority of these evaluation are expected to be for TAWS systems previously certified on an aircraft by another airworthiness authority. At the present time, all of the EGPWS systems certified by Transport Canada have had previous FAA TC/STC certifications. Transport Canada Headquarters Flight Test and/or Avionics divisions should be contacted to determine if a particular TAWS system had been prior evaluated by Transport Canada.

4.1.2 The following documentation, as a minimum, should be submitted by an applicant to Transport Canada in support of an application for the certification of a particular TAWS system:

  1. Initial certification document (TC/STC);
  2. Approved data contained in initial TC/STC;
  3. Installation drawings;
  4. Aircraft specific installation configuration parameters;
  5. Failure analysis;
  6. Ground and flight test plan;
  7. Ground and flight test results;
  8. Compliance program;
  9. Pilots guide;
  10. Draft flight manual or flight manual supplement (as applicable); and
  11. Any other documentation deemed necessary by Transport Canada Aircraft Certification
4.2 Aircraft Certification Headquarters Specialist Support

4.2.1 Transport Canada Aircraft Certification Headquarters specialists shall normally conduct an evaluation of a particular TAWS system installed for the first time on a Canadian registered aircraft.

4.2.2 Subsequent certifications will normally be conducted by the Regional Aircraft Certification Engineers, unless there are significant deviations to the first time Transport Canada certification. Transport Canada Headquarters Avionics and/or Flight Test specialists should be consulted if any of the following deviations are present, to determine the requirement for and extent of any Headquarters specialist participation:

  1. Major software changes;
  2. Installation of a terrain situational awareness display, if not previously certified (or vice versa);
  3. Terrain situational awareness display or interface significantly different;
  4. Significant change and/or relocation in visual and aural alerting scheme, annunciators and controls;
  5. Navigation source input significantly different.
4.3 Transport Canada Ground and Flight Test Requirements

4.3.1 First time Transport Canada certification of a specific TAWS system may require Transport Canada Aircraft Certification Flight Test participation. The extent of any testing will normally be determined by the degree of familiarity required for the particular TAWS system, the complexity of the installation interface and the characteristics of any terrain awareness display.

4.3.2 Regional Aircraft Certification Engineers will normally witness installation, ground and flight tests for TAWS systems already accepted by a first time Transport Canada certification. Test witnessing may be conducted by appropriate Transport Canada delegates or appropriately qualified individuals.

4.3.3 The Aircraft Certification Flight Test division should be consulted for installations, which have significant deviations as described in para 4.2 above. Draft test plans or applicant's test data should be submitted prior to the conduct of any required Transport Canada certification flight testing.

4.4 Requirement for a Terrain Situational Awareness Display

4.4.1 There is no current certification or operational requirement mandating the installation of a terrain situational awareness display. TAWS may be certified without a terrain situational awareness display, if all required functional and installation requirements are met.

4.4.2 Applicants should be made aware that forthcoming operational rules will likely require a terrain display for aircraft operated in accordance with specific operational approvals. This may require the installation of a terrain display at a future date, if not installed currently.

4.5 Self Test Functions

Any self test function, which prevents TAWS alerting functions during flight, must be inhibited during flight.

4.6 Vertical Accuracy

4.6.1 Most existing TAWS systems rely on barometric altitude inputs as a means to derive true altitude for correct functioning. Barometric altitude may deviate significantly from true altitude in non-standard atmospheric conditions, or if incorrect altimeter settings are entered. These errors may cause TAWS to fail to alert the crew when required, or cause nuisance alerts. Extreme cold temperatures normally experienced in Canada are a potential source for errors in true altitude.

4.6.2 Appropriate Aircraft Flight Manual (AFM) information, to enhance crew awareness, should be provided for systems that are not able to derive an accurate true altitude. This AFM information is not required for more recent EGPWS systems able to derive an accurate true altitude (e.g. Allied Signal EGPWS having "Geometric Altitude").

4.6.3 An accurate true altitude derivation, independent of the above noted errors, will likely become a Transport Canada certification requirement, when Canadian operational rules for the installation of TAWS become mandatory.

4.7 Aircraft Flight Manual Information

4.7.1 The AFM information provided during a first time Transport Canada certification shall typically serve as the basis for the AFM information to be used in subsequent Transport Canada certifications. Flight manual information describing vertical source errors, as described in para 4.6 above should be provided, unless the system has an automatic self correcting capability.

4.7.2 The Transport Canada Aircraft Certification Flight Test division should be consulted, if necessary, for appropriate AFM information required for a TAWS certification.

5.0 Termination Date

This ACPL shall be revised with the publication of the applicable FAA Advisory Circular and TSO for TAWS. This ACPL shall ultimately be rescinded with the publication of a pertinent AMA.

Original signed by:

Maher Khouzam
Chief, Regulatory Standards
Aircraft Certification Branch

 

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