**THE TWENTY-SIXTH MEETING OF THE**

**INFORMAL PACIFIC ATC CO-ORDINATING GROUP**

**(IPACG/26)**

(Anchorage, Alaska, USA, May 14-18, 2007)

Agenda Item 6: Air Traffic Management (ATM) Issues

**Status of the Operational Trials and Demonstrations for 10 Minute
Longitudinal Separation Without Mandatory Mach Number Technique (MNT) in
the Anchorage Flight Information Region (FIR)**

(Presented by the Federal Aviation Administration)

[Summary]{.underline}

This paper describes the operational trial and the data requirements
needed to demonstrate the 10-minute longitudinal separation without Mach
Number Technique (MNT) conducted within the Anchorage FIR. This paper
also describes the data sources and the safety assessment methodology to
be used in the implementation of the 10 minute longitudinal separation
without MNT within the Anchorage FIR. A preliminary analysis on observed
longitudinally proximate pairs of aircraft is provided.

**1. Introduction**

1.  The operational trial for the use of 10 minute longitudinal
    separation without Mach Number Technique (MNT) within Anchorage FIR
    began on 12 April 2007. The purpose of the operational trial is to
    obtain data for analysis and to acquaint controllers with the
    operational aspects of its application. A similar operational trial
    in the adjacent Oakland Flight Information Region (FIR) was
    initiated in September 1998. Reference 1 contains the analysis
    conducted to support the operational trial in the Oakland FIR.

2.  The application of the 10 minute longitudinal separation without the
    use of MNT applies only to eastbound turbojet aircraft operating at
    or above FL290. The 10 minute longitudinal separation without the
    use of MNT can be applied to these aircraft upon entry into the
    Anchorage FIR and is applicable until either the aircraft is under
    radar coverage or leaves the Anchorage FIR.

3.  This paper will describe the data sources and the safety assessment
    methodology to be used in the implementation of the 10 minute
    longitudinal separation without MNT within the Anchorage FIR. It
    also provides a preliminary analysis on observed longitudinally
    proximate pairs of aircraft.

**2. Discussion**

1.  Data Collection Process

    1.  On 1 March 2007, the Ocean21 system was introduced in the
        Anchorage FIR in oceanic sectors 10 and 11. Figure 1 illustrates
        the location of these sectors within the Anchorage FIR.

![](media/image1.wmf){width="5.360416666666667in"
height="2.522222222222222in"}

**Figure 1.** Location of Anchorage Oceanic Sectors 10 and 11

2.  The data collected through the Ocean21 system provide the positions
    (latitude, longitude (or fix) and flight level and associated times
    of all aircraft regardless of reporting method (HF, CPDLC, or ADS)
    in the sectors of interest. These data are processed and aircraft
    pairs in which the longitudinal separation minimum has been applied
    are identified. These aircraft pairs are referred to as proximate
    aircraft pairs. A proximate aircraft pair fulfils the following
    criteria: both aircraft were operating at the same flight level,
    following the same route, and pass the same airspace fix within 15
    minutes of each other.

3.  These proximate aircraft pairs are "followed" until the time of
    release of separation and final estimate of their times over a
    common position are also derived. The difference in the
    inter-aircraft separation over that time period, if any, is then
    recorded as the pairwise estimate of gain or loss of the separation.
    The samples are accumulated and, since many of the aircraft will
    have the separation applied over varying time periods, the
    observations will be normalized. The resulting data will be the
    distribution of gain-loss for the sampled aircraft pairs. This will
    be examined relative to previous studies.

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2.  Safety Assessment Methodology

    1.  The investigation of 10 minute longitudinal separation without
        the use of MNT revolves about the examination of the gain-loss
        probability distribution for aircraft pairs. The analysis
        centers on the description of aircraft pair-wise separation and
        their combined ability to maintain a separation, once it has
        been applied. The premise is that newer aircraft control
        mechanisms and sensors are better able to hold speeds and that
        the operating characteristics of the fleet of aircraft in
        general result in more similar cruise speeds than those observed
        during previous Pacific studies. Thus, the gain-loss probability
        distribution will be such that, all other factors remaining
        unchanged, the risk of collision will be at least equivalent to
        previous studies. Therefore, it will be unnecessary to control
        the speed by the assignment of Mach number when applying
        longitudinal separation.

    2.  The safety assessment methodology used in the investigation of
        the 10 minute longitudinal separation without MNT will follow
        the guidelines set forth in ICAO Doc 9689 (reference 2).
        Reference 2 contains detailed information pertaining to the
        required analyses needed to justify the application of the 10
        minute longitudinal separation without MNT in Anchorage oceanic
        airspace.

3.  Preliminary Data Analysis

    1.  As mentioned earlier, the start of the operational trial was 12
        April 2007. At the time this paper was written, three weeks have
        past since the start of the operational trial. In order to
        complete a safety assessment to support the implementation of
        the 10 minute longitudinal separation without the use of MNT, a
        sufficient number of proximate aircraft pairs must be observed.

    2.  A preliminary analysis was performed on the aircraft position
        data available from the Anchorage oceanic airspace from 16 April
        through 1 May 2007. All pairs of turbojet aircraft operating
        above FL290 were considered in this preliminary analysis. In
        this 16-day data sample, a total of 31 longitudinally proximate
        aircraft pairs were observed. As stated in paragraph 2.1.2, a
        longitudinally proximate aircraft pair is two aircraft observed
        at the same flight level, on the same route, and observed
        passing the same airspace fix within 15 minutes of each other.
        The geographic area in which the data were examined includes the
        airspace between the Anchorage/Fukuoka boundary and 170E within
        the Anchorage FIR.

    3.  Of these 31 aircraft pairs, 27 aircraft pairs were observed
        travelling westbound. The estimated longitudinal spacing for the
        27 westbound aircraft pairs ranged between 10 and 15 minutes. It
        is very likely the assigned Mach number for these aircraft was
        delivered via VHF radio while the aircraft were under radar
        coverage of the Shemya radar. The estimated average change in
        longitudinal separation for these aircraft pairs was a gain in
        separation equal to 0.22 minutes (or about 13 seconds).

    4.  Only 4 of the 31 aircraft pairs identified as longitudinally
        proximate were observed travelling eastbound. The estimated
        longitudinal spacing for the 4 eastbound aircraft pairs ranged
        between 12 and 15 minutes. The estimated average change in
        longitudinal separation for these aircraft pairs was a decrease
        in separation equal to 0.10 minutes (or about 6 seconds).

    5.  Based on this preliminary analysis and the numbers of eastbound
        aircraft pairs observed participating in the operational trial,
        the best estimate for the length of time needed to collect a
        sufficient number of proximate aircraft pairs is 6 months. This
        estimate is subject to change based on the observed number of
        proximate aircraft pairs.

**3. Recommendation**

3.1 The meeting is invited to note the information provided in this
paper.

**[References]{.underline}**

1.  "Status of Operational Trials and Demonstrations for 10 Minutes
    Longitudinal Separation Without mandatory MNT in the Oakland FIR",
    IP/3, Review of the General Concept of Separation Panel (RGCSP),
    Working Group A Meeting, St. Petersburg, 17-28 May 1999.

2.  *Manual on Airspace Planning Methodology For the Determination of
    Separation Minima*, First Edition, Doc 9689-AN/953, International
    Civil Aviation Organization, Montreal, 1998.

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