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[Federal Register Volume 77, Number 23 (Friday, February 3, 2012)]
[Notices]
[Pages 5616-5617]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2012-2464]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

Proposed Technical Standard Order (TSO)-C151c, Terrain Awareness 
and Warning System (TAWS)

ACTION: Notice of availability and request for public comment.

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SUMMARY: This notice announces the availability of, and request for 
public comments on a second draft of Technical Standard Order (TSO)-
C151c, Terrain Awareness and Warning System. Comments received from the 
initial June 2011 release, resulted in changes to the proposed document 
significant enough to require this public comment offering.

DATES: Comments must be received on or before March 5, 2012.

ADDRESSES: Send all comments on the proposed technical standard order 
to: Federal Aviation Administration (FAA), Aircraft Certification 
Service, Aircraft Engineering Division, Avionics Systems Branch (AIR-
130), 470 L'Enfant Plaza, Suite 4102, Washington, DC 20024. Attn. Ms. 
Charisse Green. Or you may hand deliver comments to 470 L'Enfant Plaza, 
Suite 4102, Washington, DC 20024.

FOR FURTHER INFORMATION CONTACT: Ms. Charisse Green, AIR-130, Federal 
Aviation Administration, 470 L'Enfant Plaza, Suite 4102, Washington, DC 
20024. Telephone (202) 385-4637, fax (202) 385-4651, email to: 
Charisse.Green@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

    You are invited to comment on the proposed revised TSO by 
submitting written data, views, or arguments to the above address. 
Comments received may be examined, both before and after the closing 
date at the above address, weekdays except federal holidays, between 
8:30 a.m. and 4:30 p.m. The Director, Aircraft Certification Service, 
will consider all comments received on or before the closing date.

Background

    The initial public offering of the draft TSO-C151c offered the 
following changes:
    a. Clarification of the 500 foot altitude call out requirement for 
Class A TAWS equipment.
    b. Addition of Localizer Performance with Vertical guidance (LPV) 
and Global Navigation Satellite System (GNSS) Landing System (GLS) 
glidepath alerting to the Ground Proximity Warning System (GPWS) Mode 5 
glideslope alert.
    c. Elimination of the provision to adjust or modify the GPWS 
envelopes to minimize nuisance alerts based on Forward-Looking Terrain 
Avoidance (FLTA) and Premature Descent Alert (PDA) functionality 
without a deviation.
    d. Allowances for eliminating GPWS nuisance alerts (Appendix 1, 
paragraph 3.4).
    e. Requirement for the primary horizontal position source to be 
GPS, to ensure utilization of the most accurate and consistent 
horizontal position data.
    f. Addition of velocity and vertical GPS reporting requirement to 
inhibit alerting when GPS position is invalid, unless a backup position 
source is in use.
    The FAA received numerous comments on: (1) The 500 foot altitude 
call out; (2) the elimination of the GPWS envelope modification 
allowance; (3) the GPS horizontal position source requirement; and (4) 
the position source requirements. A summary of those public comments 
and the FAA's resolution are included with the second draft of TSO-
C151c.
    This announcement requesting comments to the revised proposed TSO-
C151c, contains the following significant changes:
    a. Alert suppression for Required Navigation Performance (RNP) 
requirements are added to Appendix 1, Paragraph 3.1.4.
    b. The allowance in TSO-C151b to adjust or modify the GPWS alerting 
thresholds is restored in the current version of TSO-C151c. (We provide 
clarifying language that deviations need to be accomplished in 
accordance with Title 14 of the Code of Federal Regulations (14 CFR) 
21.618.)
    c. The requirement in the initial proposal of TSO-C151c, requiring 
the Class A 500 ft voice call out on all approaches is changed to the 
TSO-C151b requirement, for the Class A 500 ft voice call out on non-
precision approaches only.
    d. TSO-C151b and the first offering of the proposed TSO-C151c, both 
allowed for the 500 ft callout to be made based on radar altimeter 
height above terrain, or by a comparison of current altitude 
(barometric or GNSS) above the runway threshold height. This revised 
proposed TSO-C151c allows the 500 ft voice call out to be the current 
altitude (barometric or GNSS) above the runway threshold height. Note 
that in the current proposal, the allowance to make the voice callout 
based solely on a radio altimeter height above terrain is removed. The 
rationale is that all TAWS equipped aircraft will annunciate the 
altitude call referenced to the runway

[[Page 5617]]

threshold height, allowing for consistency in the altitude call out.
    e. Clarification of TAWS position requirements (See Proposed 
Paragraphs 5.0 through 5.6).
    f. All GPS requirements are unchanged from the TSO-C151b 
requirement.

How To Obtain Copies

    A copy of the proposed TSO-C151c may be obtained via the 
information contained in the section titled FOR FURTHER INFORMATION 
CONTACT, or from the FAA Internet Web site at: http://www.faa.gov/aircraft/draft_docs/.

    Issued in Washington, DC, on January 31, 2012.
Susan J. M. Cabler,
Assistant Manager, Aircraft Engineering Division, Aircraft 
Certification Service.
[FR Doc. 2012-2464 Filed 2-2-12; 8:45 am]
BILLING CODE 4910-13-P
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