01-704. Policy for Time Limited Dispatch (TLD) of Engines Fitted With Full Authority Digital Engine Control (FADEC) Systems

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Notice of proposed policy statement; request for comments.

SUMMARY:

The Federal Aviation Administration (FAA) announces the availability of a proposed policy for the time limited dispatch (TLD) of engines fitted with full authority digital engine control (FADEC) systems. This proposed policy would revise the current policy to clarify it; the basic intent of the policy would not change.

DATES:

Comments must be received by February 9, 2001.

ADDRESSES:

Send all comments on the proposed policy to the individual identified under FOR FURTHER INFORMATION CONTACT.

FOR FURTHER INFORMATION CONTACT:

Gary Horan, FAA, Engine and Propeller Standards Staff, ANE-110, 12 New England Executive Park, Burlington, MA 01803; e-mail: [e-mail]; telephone [phone]; fax: [phone].

SUPPLEMENTARY INFORMATION:

Comments Invited

The proposed policy statement is available on the internet at the following address: http://www.faa.gov/​avr/​air/​ane/​ane110/​hpage.htm. If you do not have access to the Internet, you may request a copy by contacting the individual listed under FOR FURTHER INFORMATION CONTACT. The FAA invites interested parties to comment on the proposed policy. Comments should identify the subject of the proposed policy and be submitted to the individual identified under FOR FURTHER INFORMATION CONTACT. The FAA will consider all comments received by the closing date before issuing the final policy.

Background

The FAA Engine and Propeller Directorate (EPD) issued a policy on time limited dispatch (TLD) on October 28, 1993. The purpose of this policy is to assure uniformity in applying TLD to engines fitted with FADEC systems. The objective of the TLD approach is to preserve suitable FADEC system integrity while minimizing dispatch delays and cancellations by allowing dispatch of the FADEC system with faults present. The control system is allowed to continue to operate with faults present, provided the resulting system operation and overall average reliability are adequate, and operating exposure in this less redundant state is appropriately limited.

The dispatchable configrations for the FADEC system and their associated dispatch intervals are an engine airworthiness limitation specified in the FAA-approved Airworthiness Limitations Section (ALS) of the Instructions for Continued Airworthiness (ICA) for the engine. Although TLD is not a requirement for engine certification, entries in the ALS become part of the engine type design. In addition, the type certificate data sheet (TCDS) notes that the engine model has TLD approval and references the ALS for detailed dispatch interval information. In this revision, the FAA recommends that an applicant for engine type design approval include appropriate TLD information in the engine installation manual.

The applicant must submit a statistical TLD analysis to substantiate that the overall average reliability of the control system resulting from the applicant's proposed TLD approach meets the integrity requirements in the FAA TLD policy. The applicant is also required to establish a formal, auditable reporting system that provides periodic reports to the FAA office that oversees the engine type certificate. This system compares in-service experience with the analysis on which the TLD approval is granted.

The proposed revision to the TLD policy:

1. Clarifies where the manufacturer must include the TLD approval statements.

2. Adds a fourth category of faults, for manufacturer/operator defined dispatch intervals that have no impact on the loss-of-thrust-control (LOTC) analysis and whose repair time is not specified through the TLD analysis.

3. Clarifies the engine-aircraft interface regarding the fault recording means required for TLD.

4. Clarifies that the provision for a temporary extension of the dispatch interval must be substantiated in the TLD, analysis; also clarifies the authority of the FAA Principal Maintenance or Avionics Inspector (PMI/PAI) to temporarily extend the dispatch interval based on the TLD analysis.

5. Clarifies descriptions of the full-up and single-fault system models used in the TLD analysis.

6. Clarifies the maintenance strategies, including eliminating the use of the maintenance terms “On-Condition” and “Condition Monitoring.”

7. Modifies Table 2 to specify both the short time and long time fault limitations in terms of the maximum operating time in flight hours only; to accommodate the addition of a fourth dispatch category.

8. Adds Table 3 to show the time limitations for both the short time and long time fault conditions associated with the maintenance approach used to address those fault categories.

9. Adds Figure 1 to show the typical graph used to substantiate the analysis for compliance with the requirement for equivalent or better reliability than the hydromechanical technology of early systems.

10. Adds Figure 2 to show a typical aircraft avionics system associated with FADEC system maintenance information and displays.

(Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44704.)

Issued in Burlington, Massachusetts, on January 2, 2001.

David A. Downey,

Assistant Manager, Engine and Propeller Directorate, Aircraft Certification Service.