Selection and Use of Time and Frequency Sources for all Systems, Services, and Applications Supporting NAS Operations

1770.68 · FAA

Public domain · FAAOrders & Notices

Overview

The Selection and Use of Time and Frequency Sources for all Systems, Services, and Applications Supporting NAS Operations (1770.68) is a public-domain FAA order, republished here as a free chaptered HTML edition with a linked table of contents and the official PDF.

Publisher: FAA
Document: 1770.68
Pages: 7
Chapters: 2

Key points

This Order establishes the FAA policy for selecting and using time and frequency sources for NAS operations.
All NAS systems must transition away from GPS and GNSS-dependent time sources to NIST or USNO traceable sources by FY 2025.
The FAA will create an Enterprise Time and Frequency Service (ETFS) to provide networked time and frequency services for NAS systems.
Use of non-US GNSS systems for time and frequency is prohibited for NAS systems, which must utilize only US GNSS systems until connected to ETFS.
An Office of Primary Responsibility (OPR) will be established to implement and oversee compliance with the time and frequency policy.

Frequently asked questions

What is the purpose of this Order?

The purpose of this Order is to establish the policy for selecting, modifying, upgrading, implementing, and using time and frequency sources for systems supporting NAS operations.

What is the deadline for NAS systems to transition to new time sources?

All NAS systems must migrate away from GPS and GNSS-dependent time sources by FY 2025.

What is the Enterprise Time and Frequency Service (ETFS)?

ETFS is a resilient networked source providing precise time and frequency references for all NAS operational users, ensuring compliance with National Resilience Policy.

What happens if a NAS system is not connected to the FAA network?

NAS systems not connected to the FAA network must demonstrate that their standalone time and frequency sources meet or exceed required performance and resilience.

Who will oversee the implementation of the time and frequency policy?

An Office of Primary Responsibility (OPR) will be established to implement and ensure compliance with the time and frequency policy.

Appendix A

11/03/2020 1770.68 Appendix A Appendix A. Definitions Enterprise Time and Frequency Service (ETFS): The ETFS is a resilient networked source or sources providing precise time and frequency references for all NAS operational users. The ETFS will provide safe, trustable time and frequency traceable to UTC (NIST or USNO).

Frequency stability: The rate of change of a repetitive event defined in Hertz (Hz) per hour; required to maintain synchronization within and across networks.

Network Time Protocol (NTP): A networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in current use.

Primary Holdover and Integrity Capability: Provides a primary means for maintenance of time and/or frequency in accordance with application requirements independent of external inputs for a specified duration of time that depends upon application needs. This function provides continuity in the event of EFTS disruptions or delays and enables consistency cross - checks to reject any erroneous inputs that might be received from EFTS or other sensor inputs.

Precision Time Protocol (PTP): A protocol used to synchronize clocks throughout a computer network. On a local area network, it achieves clock accuracy in the sub-microsecond range, making it suitable for measurement and control systems.

Time-of-day: Reference time that is traceable to Coordinated Universal Time (UTC); provided in hours, minutes, and seconds and often includes the date. This is the most common use of time information in NAS systems and is used to timestamp data.

Time difference: Supports determining the time duration of an event or between different events from start to finish. In the future, additional precision may be required.

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Next: Appendix B →

Appendix B

11/03/2020 1770.68 Appendix B Appendix B. References Executive Order on Strengthening National Resilience through Responsible Use of Positioning, Navigation, and Timing Services, February 12 2020, https://www.whitehouse.gov/presidential - actions/executive-order-strengthening-national - resilience-responsible-use-positioning-navigation- timing-services/ , accessed on July 8 2020.

National Airspace System Enterprise Architecture NAS Timing Study , FAA Office of NAS Systems Engineering & Integration, July 9 2019, https://sep.faa.gov/includes/documents/FAA_NAS_TimingStudyReport_07092019-508.pdf , accessed on July 8 2020.

Presidential Policy Directive 21 , Critical Infrastructure Security and Resilience, February 12 2013, https://obamawhitehouse.archives.gov/the-press-office/2013/02/12/presidential-policy - directive- critical-infrastructure-security-and-resil , accessed on July 8 2020.

Target NAS Requirements Document (TNRD) 2018, Version 2.9, December 2018, https://sep.faa.gov/file/get/3221 , accessed on July 8 2020.

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