Jeppesen has recently changed charted racetrack procedures. Until now, pilots could expect to find charted racetrack patterns in the FMS database, as procedures coded for coupled entry. Those codes were Jeppesen’s attempt to emulate the racetrack procedure using defined ARINC 424 “path-terminator” codes (explained later in this article). However, it was discovered that unsafe maneuvers could arise because of this coding if the racetrack procedure was entered at certain angles.
Now, Jeppesen has removed the coding completely, concluding no other solution can be identified. This article will discuss and define racetrack procedures, as well as provide a better understanding of the coding challenge faced by Jeppesen.
The term racetrack procedure refers to procedures used where “sufficient distance is not available in a straight segment to accommodate the required loss of altitude and when entry into a reversal procedure is not practical. Racetrack procedures may also be specified as an alternative to reversal procedures to increase operational flexibility.” (PANS-OPS Volume II, Part 1, Section 4, Paragraph 3.4.1).
This is very similar to how a “hold-in-lieu of” procedure turn is used in the U.S. “The racetrack procedure has the same shape as a holding pattern but with different operating speeds and outbound timing. The inbound track normally becomes the intermediate or final segment of the procedure.” (PANS-OPS Volume II, Part 1, Section 4, Paragraph 3.4.2). See Figure 1 for the general design of a racetrack procedure.
The ICAO definition is as follows: “A procedure designed to enable the aircraft to reduce altitude during the initial approach segment and/or establish the aircraft inbound when the entry into a reversal procedure is not practical.” (ICAO Doc 8168: Aircraft Procedures, chapter 3)
Figure 1: Racetrack Procedures Illustrated From 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.