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Policy Statement With Respect to Part 25 Transport Category Airplanes Utilizing Displays With Geometric Altitude Labeled as a Mean Sea Level (MSL)

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Federal Aviation Administration (FAA), DOT.


Notice of proposed policy; request for comments.


The Federal Aviation Administration (FAA) announces the availability of proposed policy that clarifies current FAA policy with respect to part 25 transport category airplanes utilizing displays with geometric altitude labeled as a mean sea level (MSL).


Send your comments on or before December 23, 2002.


Address your comments to the individual identified under FOR FURTHER INFORMATION CONTACT.

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Ken Schroer, Federal Aviation Administration, Transport Airplane Directorate, Transport Standards Staff, Airplane and Flight Crew Interface Branch, ANM-111, 1601 Lind Avenue SW., Renton, WA 98055-4056; telephone (425) 227-1154; fax (425) 227-1320; e-mail:

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Comments Invited

The proposed policy is available on the Internet at the following address:​certification/​aircraft/​anminfo/​devpaper.cfm. If you do not have access to the Internet, you can obtain a copy of the policy statement by contacting the person listed under FOR FURTHER INFORMATION CONTACT.

The FAA invites your comments on this proposed policy. We will accept your comments, data, views, or arguments by letter, fax, or e-mail. Send your comments to the person indicated in FOR FURTHER INFORMATION CONTACT. Mark your comments, “Comments to Policy Statement ANM-02-111-05.”

Use the following format when preparing your comments:

  • Organize your comments issue-by-issue.
  • For each issue, state what specific change you are requesting to the proposed general statement of policy.
  • Include justification, reasons, or data for each change you are requesting.

We also welcome comments in support of the proposed policy.

We will consider all communications received on or before the closing date for comments. We may change the proposed policy because of the comments received.


This memorandum clarifies Federal Aviation Administration (FAA) certification policy with respect to installations that label Global Positioning System (GPS) derived geometric altitude as Mean Sea Level (MSL) altitude. The issue concerns the Terrain Awareness and Warning Systems (TAWS), Global Navigation Systems (GNS), and any other installation in which GPS derived altitude is presented as MSL altitude.

Regardless of the higher altitude accuracy that can be derived from GPS data, barometric altitude referenced to MSL remains the present standard used in the U.S. and internationally for vertical navigation. Even though there may be altitude errors while using barometric altitude, all aircraft within a particular sector are navigating (in principle) with the same error. Since there is a potential for large differences between barometric altitude and GPS derived altitude, labeling both as MSL may result in confusion and improper vertical navigation during high flightcrew workloads.

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Issued in Renton, Washington, on November 13, 2002.

Vi L. Lipski,

Manager, Transport Airplane Directorate, Aircraft Certification Service.

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[FR Doc. 02-29659 Filed 11-20-02; 8:45 am]