[Federal Register Volume 64, Number 233 (Monday, December 6, 1999)]
[Notices]
[Pages 68194-68195]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-31523]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration


Terrain Awareness and Warning System

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of publication of Technical Standard Order (TSO)-C151a, 
Terrain Awareness and Warning System.

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SUMMARY: The FAA has issued TSO-C151a, Terrain Awareness and Warning 
System, and canceled TSO-C151. The FAA has taken this action to clarify 
and correct certain paragraphs and tables that appeared in TSO-C151. 
The FAA has determined that the changes to TSO-C151a are of a 
clarifying and corrective nature, and that these changes do not alter 
the original intent of the airworthiness requirements of the paragraphs 
or tables being changed. Therefore, the FAA has taken this 
administrative action without using public comment process. However, 
the FAA will accept any comments about TSO-C151a and will consider them 
in any future revision to TSO-C151a. The changes are discussed below 
under the section titled SUPPLEMENTARY INFORMATION.

FOR FURTHER INFORMATION CONTACT: Michelle Swearingen, Federal Aviation 
Administration (FAA), Aircraft Certification Service, Aircraft 
Engineering Division, Avionic Systems Branch, AIR-130, 800 Independence 
Avenue, SW, Washington, DC 20591, Telephone: (202) 267-3817, FAX: (202) 
267-5340.

SUPPLEMENTARY INFORMATION:
    Table 3.1, Appendix 1: The FAA has modified table 3.1 of appendix 1 
to make it clearer and easier to use. These modifications include new 
notes to table 3.1 and appropriate modifications to the related test 
conditions in appendix 3. The specific modifications are described in 
the following discussion.
    In table 3.1 the column titled TAWS(RTC) was changed to TAWS(RTC) 
DESCENDING. A new column titled TAWS(RTC) LEVEL FLIGHT was added 
between the column titled TERPS(ROC) and the column now titled 
TAWS(RTC) DESCENDING. The new column contains the following parameters: 
for enroute the parameter is 700 feet; for terminal, 350 feet; for 
approach, 150 feet; and for departure, 100 feet.
    Note 2 was modified and corrected by retaining the ability to use a 
linear slope but by deleting the reference to a specific design 
criteria that does not meet the requirement of table 3.1. The note now 
reads as follows: As an alternate to the stepped down reduction from 
the terminal to approach phase in Table 3.1, a linear reduction of the 
RTC as the aircraft comes closer to the nearest runway is allowed, 
providing the requirements of Table 3.1 are met.
    Two clarifying notes were added, note 3 and note 4. Note 3 reads as 
follows: During the visual segment of a normal instrument approach 
(typically about 1 NM from the runway threshold), the RTC should be 
defined/reduced to minimize nuisance alerts. Below a certain altitude 
or distance from the runway threshold, logic may be incorporated to 
inhibit the FLTA function. Typical operations below Minimum Descent 
Altitude (MDA), Decision Height (DH), or the Visual Descent Point (VDP) 
should not generate nuisance alerts. Note 4 reads as follows: The 
specified RTC values are reduced slightly for descending flight 
conditions to accommodate the dynamic conditions and pilot response 
times.
    The related test conditions in appendix 3 were modified to be 
compatible with the modified table 3.1 of appendix 1. In paragraph 1.3, 
appendix 3, 700 replaced both 500 parameters. In paragraph 1.5, 
appendix 3, 350 replaced both 300 parameters. In paragraph 1.7, 
appendix 3, both 100 parameters were replaced with 150. In table B, 
appendix 3, for the 250 and 300 ground speed test runs, both 6000 
parameters were replaced with 5800. In the same table B, all five 5500 
parameters were replaced with 5700. In table D, appendix 3, all four 
1300 parameters were replaced with 1350. In table F, appendix 3, all 
four 500 parameters were replaced with 550.
    Section 3.3, Appendix 1: The FAA has modified the first paragraph 
of section 3.3 by clarifying when the GPWS functions may be adjusted or 
modified and by deleting general language that paraphrases FAA 
deviation policy. Deviations are addressed in paragraph 3.f of the 
basic TSO, and the use of deviations is applicable to the entire TSO 
document. The first paragraph of section 3.3 now reads as follows: In 
addition to the TAWS Forward Looking Terrain Avoidance and PDA 
functions, the equipment shall provide the GPWS functions listed below 
in accordance with TSO-C92c. Some GPWS alerting thresholds may be 
adjusted or modified to be more compatible with the FLTA alerting 
functions and to minimize GPWS nuisance alerts. However, it is 
essential to retain the independent protective features provided by 
both the GPWS and FLTA functions. In each case, all the following 
situations must be covered. The failure of the TSO C92c equipment 
functions, except for power supply failure, input sensor failure, or 
failure of other common portions of the equipment, shall not cause a 
loss of the FLTA, PDA, or Terrain Display.
    Section 10.0, Appendix 1: The FAA has modified section 10.0 to 
clarify the use of alternate definitions for various phases of flight. 
The FAA also has removed reference to TSO-C129 and RTCA/DO-229. These 
documents are for GPS navigation operations and are not appropriate for 
TAWS operations.

[[Page 68195]]

Section 10.0 now reads as follows: The TAWS equipment search volumes 
and alerting thresholds should vary as necessary to be compatible with 
TERPS and other operational consideration. For that reason, a set of 
definitions is offered for Enroute, Terminal, Approach and Departure 
Phases of Flight. Other definitions for enroute, terminal and approach 
may be used by TAWS provided they are compatible with TERPS and 
standard instrument approach procedures and will comply with the test 
criteria specified in Appendix 3.
    Tables A, C, and E; Appendix 3: The FAA has modified these tables 
by correcting certain parameters. Note 4 to table A, note 2 to table C 
and note 2 to table E state that the values are based upon 20 percent 
of the airplane's vertical velocity. However, a few values were 
calculated using a 20-second criteria instead of the 20 percent 
criteria. The corrected values are as follows: In column F of table A, 
the 2111 value was replaced with 1800. In column F of table C, the 1036 
value was replaced with 900, and the 1456 value was replaced with 1100. 
In column F of table E, the 639 value was replaced with 550.
    How To Obtain Copies: A copy of TSO-C151a may be obtained via 
Internet (http://www.faa.gov/avr/air/airhome.htm) or on request from 
the individual listed under the section titled FOR FURTHER INFORMATION 
CONTACT. REFERENCED DOCUMENTS: TSO-C151a references several RTCA, Inc. 
documents that contain specific requirements related to the TSO. RTCA 
Document No. DO-161A, ``Minimum Performance Standards--Airborne Ground 
Proximity Warning Equipment,'' dated May 27, 1976; DO-160D, 
``Environmental Conditions and Test Procedures for Airborne 
Equipment,'' dated July 29, 1997; DO-178B, ``Software Considerations in 
Airborne Systems and Equipment Certification,'' dated December 1, 1992; 
and DO-200A, ``Preparation, Verification and Distribution of User-
Selectable Navigation Data Bases,'' dated November 28, 1988, may be 
purchased from the RTCA Inc., 1140 Connecticut Avenue, NW., Suite 1020, 
Washington, DC 20036.

    Issued in Washington, DC, on November 29, 1999.
James C. Jones,
Manager, Aircraft Engineering Division, Aircraft Certification Service.
[FR Doc. 99-31523 Filed 12-3-99; 8:45 am]
BILLING CODE 4910-13-M