Racetrack Procedures

Figure 1: Racetrack Procedures IllustratedFrom ICAO Doc 8168 Chapter 3

Holding vs. Racetrack Patterns

Generally speaking, a Holding Pattern is very similar to a Racetrack pattern. However, they are not entirely the same. Therefore, it is important to understand the differences. A Holding Pattern is an FAA defined procedure, used in the United States. A Racetrack Pattern is an ICAO defined procedure, used internationally. Both procedures start at a designated facility or fix.

Racetrack patterns (ICAO Defined)

• Customizable to allow for descent and airspace constraints
• The outbound leg of racetrack procedures can be anywhere from 1 to 3 minutes, specified on the chart in 30 second intervals
• Maximum airspeeds are aircraft category specific
• Typically have a procedure segment (intermediate or final) imbedded into the inbound leg of the pattern. For these the start of the procedure segment would be defined as intercepting the inbound course of the racetrack pattern (similar to a procedure turn in the US)
• “The length of the outbound track of a racetrack procedure may be limited by specifying a DME distance or radial/bearing from a suitably located facility.” (PANS-OPS Volume II, Part 1, Section 4, Paragraph 3.4.6)

Holding patterns (FAA Defined)

> Standard pattern is defined

  Leg length (1 or 1 ½ minutes)   Max airspeed (based on altitude)

> Exceptions to the standard are explicitly charted

  Leg length based on distance   Non-standard maximum airspeed

> Holding-in-lieu of a procedure turn

Figure 2 demonstrates both how holding and racetrack patterns are depicted on an approach chart, and how the Honeywell FMS had been depicting racetrack patterns as part of flight plans.

Figure 2: Holding Pattern vs. Racetrack Procedure

As described above, racetrack procedure design standard does not exist. This creates several challenges for coding standardization organizations, such as ARINC 424 and commercial data suppliers like Jeppesen, to standardize entry procedures for FMS coupling.

There is also no coding standard for racetrack procedures. So, what does that mean for pilots? It means that pilots should not expect to see the racetrack pattern as an option in the FMS database for a coupled entry, meaning they can expect to manually fly the procedure as depicted on the chart. The attempt at coding this type of procedure had been found to potentially result in unsafe aircraft maneuvers. This is explained in more detail and illustrated in Figure 3.

To better explain the challenges with coding and translating text to FMS databases, it is important to understand the process of how data is translated from aeronautical charts. For a procedure to be used in a navigation database, it first involves translating The Aeronautical Information Publication (AIP) text and charted procedure into ARINC 424 text files. This is accomplished using strict formatting standards by commercial data suppliers, such as Jeppesen. Next, an avionics OEM (e.g. Honeywell) compiles and converts the ARINC 424 files into binary datasets tailored to a specific FMS for loading.

Table 1 and 2 below demonstrate the ARINC 424 coding definitions and constraints.

Table 1 defines the codes, which result in the maneuver type combinations shown in Table 2. The Table 1 Path and Terminator columns refer to how the course is to be defined (the Path), and how the Path ending will terminate (“Terminator”). Those columns define the constraints, using the ARINC 424 Coding Standards.

Table 2 is a list of coding constraints (Path and Terminator) which can be combined to use for coding a maneuver. As described earlier, racetrack procedure design is intended to be customizable. This means that one coding standard may not cover all the conditions under which a pilot can safely enter a racetrack pattern. As stated in the beginning, Jeppesen had attempted to code the procedure. Using the Course to a Fix (CF-CF) option, it soon became evident this couldn’t cover procedure turns correctly in all instances. Since the CF leg entry method turns the aircraft in the direction of turn requiring the shortest route, this can result in a turn towards the non-protected side of the racetrack pattern, when approaching the fix from certain angles.

This coding issue was first brought to the attention of Honeywell’s Global Customer Committee where a viable solution was researched to no avail. Due to the lack of a viable coding solution, Jeppesen has since removed these coded transitions from the navigation databases. After thorough assessment of options, ARINC 424 has determined that coding entries for racetrack patterns is not currently possible.

Please contact Honeywell Flight Technical Services with any questions or operational issues.