**THE TWENTY-SIXTH MEETING OF THE**

**INFORMAL PACIFIC ATC CO-ORDINATING GROUP**

**(IPACG/26)**

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

Agenda Item xx:

**Variations in True Airspeed Observed During the Operational Trial-Use
of 30-nm Lateral and Longitudinal Separation Standards in Oakland
Oceanic Airspace**

(Presented by the Federal Aviation Administration)

[Summary]{.underline}

This paper provides results of preliminary analysis used to examine
variations in aircraft true airspeed or Mach number evidenced in
periodic Automatic Dependent Surveillance (ADS) reports received at
Oakland Oceanic Area Center (OAC).

**1. Introduction**

1.  The Twenty-first Meeting of the Informal South Pacific ATS
    Co-ordinating Group (ISPACG/21) discussed variation in true airspeed
    upon reviewing the contents of reference 1. The Meeting also
    discussed the rule set forth in Annex 2 paragraph 3.6.2.2 b
    (reference 2), which requires Air Traffic Control (ATC) to be
    notified when the average true airspeed at cruising level between
    reporting points varies or is expected to vary by plus or minus 5
    per cent of the true airspeed from that given in the flight plan.

2.  The issue raised in reference 2 is related to the significant
    reductions experienced over the last decade in the longitudinal
    separation standard for aircraft equipped with ADS and CPDLC.
    Although the 30-nm and 50-nm longitudinal standards are now in use
    in various portions of oceanic airspace, the variation in true
    airspeed that pilots are permitted to undertake without notifying
    ATC has not been reduced in proportion and remains at 5 percent.

3.  Information received from some operators has indicated that recent
    increases in fuel costs have led to more widespread application of
    fuel optimal flight trajectories.

4.  This paper will present variations in true airspace observed during
    the operational trial-use of 30-nm lateral and longitudinal
    separation standards in Oakland oceanic airspace.

**2. Discussion**

1.  The Ocean21 oceanic automation system was introduced into full-time
    operation at the Oakland Air Route Traffic Control Center (ARTCC) on
    17 October 2005. On 22 December 2005, the FAA implemented 30-nm
    lateral and longitudinal separation standards on an operational
    trial basis in a portion of the Oakland Oceanic FIR, specifically
    oceanic sector 3 (OC3). In the remaining portions of the airspace,
    the FAA applies a 50-nm longitudinal separation standard to aircraft
    equipped with ADS and CPDLC. Figure 1 presents the geographical
    locations of the various oceanic sectors within the Oakland FIR.

![](media/image1.wmf){width="3.672222222222222in"
height="2.5805555555555557in"}

**Figure 1.** Oakland Oceanic Airspace

2.  As part of the operational trial, the FAA has formed a group of
    experts to evaluate performance of the various components of the
    system supporting the reduced separation minima. This group has been
    termed the "30-30 Scrutiny Group", more simply known as the scrutiny
    group. The scrutiny group is chaired by FAA Flight Standards
    Services and has representatives from various groups within the FAA,
    such as the Oakland and Anchorage ARTCC, Flight Standards Services,
    Aircraft Certification Service, Oceanic Enroute Procedures, FAA
    Technical Center, and support contractors.

3.  The scrutiny group has met five times since the start of the
    operational trial. During these meetings the group reviews pertinent
    data related to the operational trial. As part of the FAA's attempt
    to understand those factors affecting the reduced horizontal
    separation minima, the scrutiny group is in the process of examining
    variations in aircraft true airspeed or Mach number evidenced in the
    periodic ADS reports received at the Oakland Oceanic Area Center
    (OAC).

4.  Preliminary Observed Aircraft Speed Data

5.  The data used in this analysis are the aircraft filed flight plans,
    electronic coordination messages, and actual aircraft ADS reports
    collected from the Ocean21 system. The data sample time period
    includes 1 January through 31 March 2007.

6.  Comparisons between the filed and actual airspeed are made in the
    analysis. The sources of filed true airspeed or Mach number are the
    electronic coordination messages received by Oakland ARTCC from
    adjacent ATS providers and the original filed flight plans. When the
    true airspeed was provided, conversion to Mach number was completed
    using the Manual of the ICAO Standard Atmosphere (reference 3). The
    analysis utilized the instantaneous Mach number provided in the ADS
    periodic reports as the actual airspeed.

7.  Future work in this analysis will thoroughly investigate all
    electronic HF and CPDLC recorded messages with reported aircraft
    speed to verify the accuracy of the speed comparisons.

8.  The difference between the filed Mach number and the ADS-reported
    Mach number was computed for each ADS periodic report. Figure 1
    presents the sample mean and sample standard deviation for each day
    during the period 1 January through 31 March 2007. The grand sample
    mean of the data presented in Figure 1 is estimated to be 0.01 Mach.

![](media/image2.wmf){width="3.939583333333333in" height="2.49375in"}

**Figure 1**. Sample Mean and Standard Deviation of the Difference
between the Filed and ADS-reported Mach number

9.  The data presented in Figure 1 were further analyzed by operator,
    origin/destination city pair, and aircraft type. The preliminary
    results are presented in Figures 2-4.

![](media/image3.wmf){width="3.939583333333333in" height="2.49375in"}

**Figure 2**. Sample Mean and Standard Deviation of the Difference
between the Filed and ADS-reported Mach number by Operator

![](media/image4.wmf){width="3.939583333333333in" height="2.49375in"}

**Figure 3**. Sample Mean and Standard Deviation of the Difference
between the Filed and ADS-reported Mach number by Origin/Destination
City Pair

![](media/image5.wmf){width="3.939583333333333in" height="2.49375in"}

**Figure 4**. Sample Mean and Standard Deviation of the Difference
between the Filed and ADS-reported Mach number by Aircraft Type

10. The differences between the speed obtained from the filed flight
    plan and the ADS-reported Mach number appear to be well-behaved for
    most operators, city pairs and aircraft types. Future work in this
    analysis will further clarify the filed aircraft speed using the
    electronic HF and CPDLC messages contained within the Ocean21 data.

11. The magnitude of the difference between the filed speed and the
    ADS-reported Mach number was compared to the value equal to five
    percent of the filed Mach number speed. Any data points which were
    equal to or exceed the five percent threshold were recorded. Figure
    5 presents the proportion of ADS periodic reports which exceeded the
    five percent of the filed Mach number.

![](media/image6.wmf){width="3.952777777777778in"
height="2.5006944444444446in"}

**Figure 5**. Proportion of ADS Position Reports with the Difference
between the Filed Speed and ADS-reported Mach number was Observed to be
≥ 5 Percent of the Filed Speed

12. The data presented in Figure 5 were further analyzed by operator,
    origin/destination city pair, and aircraft type. The preliminary
    results are presented in Figures 6-8.

![](media/image7.wmf){width="3.952777777777778in"
height="2.5006944444444446in"}

**Figure 5**. Proportion of ADS Position Reports with the Difference
between the Filed Speed and ADS-reported Mach number was Observed to be
≥ 5 Percent of the Filed Speed by Operator

![](media/image8.wmf){width="3.952777777777778in"
height="2.5006944444444446in"}

**Figure 5**. Proportion of ADS Position Reports with the Difference
between the Filed Speed and ADS-reported Mach number was Observed to be
≥ 5 Percent of the Filed Speed by City pair

![](media/image9.wmf){width="3.952777777777778in"
height="2.5006944444444446in"}

**Figure 5**. Proportion of ADS Position Reports with the Difference
between the Filed Speed and ADS-reported Mach number was Observed to be
≥ 5 Percent of the Filed Speed by Aircraft Type

13. The proportions of ADS position reports with a difference between
    the filed speed and the ADS-reported Mach number greater than or
    each to the five percent threshold are not uniform across all
    observed sample days, operators, city pairs and aircraft types.
    Further investigation into the data will clarify the filed aircraft
    speeds against the available electronic HF and CPDLC messages
    contained within the Ocean21 data.

**3. Recommendation**

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

2.  The meeting is further invited to discuss the empirical experience
    with speed variation in Pacific airspace.

**[References]{.underline}**

1.  "Variation in True Airspeed", WP/25, Informal South Pacific ATS
    Co-ordinating Group (ISPACG/21), Auckland, New Zealand, 6-8 March
    2007.

2.  International Standards, Rules of the Air, Annex 2 to the Convention
    of International Civil Aviation, Ninth Edition, July 1990.

3.  *Manual of the ICAO Standard Atmosphere*, Third Edition,
    International Civil Aviation Organization, Montreal, 1993.

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