[Federal Register Volume 66, Number 7 (Wednesday, January 10, 2001)]
[Notices]
[Pages 2043-2044]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-704]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

[Policy Statement No. ANE-1993-33.28TLD-R1]


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.

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SUMMARY: The Federal Aviation Administration (FAA) announces the 
availability of a proposed policy for the

[[Page 2044]]

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: [email protected]; telephone (781) 238-7164; fax: (781) 
238-7199.

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.
[FR Doc. 01-704 Filed 1-9-01; 8:45 am]
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