Flight Numbering Alternatives

Alternative Options For Numbering Flights Have Become A Necessity

Because airlines are only allotted four-digit flight numbers in their flight-numbering scheme, some airlines are challenged with finding creative ways to number their flights as they near the 9,999 flight-number cap. Adding a fifth digit appears to be a quick fix; however, the associated costs in doing so outweigh the benefits. Therefore, alternative options have been identified for resolving the issue without enormous capital outlay.

Assigning numbers to flights may not be viewed as one of the more exciting or significant airline activities. It is not as scientific as fuel-tankering or block-time analysis. It lacks the mathematical complexity of fare-class alignment or fuel hedging. It does not carry the important safety implications flight-operations or line-maintenance processes do. It may not be as inherently interesting as marketing research or as highly anticipated as network planning.

That said, flight numbering is much more than a random process, and it is important. Many airlines put much consideration and effort into their flight-numbering processes. In doing so, they generally follow certain required rules and optional guidelines when assigning flight numbers. While flight numbering is an ongoing process, most of the work is done biannually and is driven by IATA’s designated summer and winter seasonal dates.

IATA’s two schedule seasons correspond to when Daylight Savings Time is or is not observed in European Union nations. Therefore, summer season begins on the last Sunday in March, while Winter season commences on the last Sunday in October.

While there are some airlines that develop specific schedules for as much as four seasons — and some do not have any seasonal differences — the majority of airlines around the world design specific schedules for at least the two IATA seasons. It is during these major schedule change periods where airlines typically make flight number modifications.

Four-digit Limit

IATA instated two rules by which airlines much comply when assigning flight numbers. They cannot repeat a flight number departing from the same airport on the same date, and flight numbers can have only four digits or less.

Numbering Requirements

When designing a flight numbering scheme, airlines must comply with two basic rules instated by IATA:

  1. An airline cannot repeat a flight number departing from the same station on the same date.
  2. Flight numbers can have no more than four numeric digits.

For example, a carrier may assign a single flight number, such as 0100, to a “through” routing of AAA-BBB-CCC-BBB-AAA. However, it cannot assign a single number to a routing of AAA-BBB-AAA-CCC because the routing involves two departures from AAA.

Airlines select their own flight numbers subject to these basic rules. However, air traffic management agencies, such as EUROCONTROL and the U.S. Federal Aviation Administration (FAA), may advise airlines to change flight numbers to avoid:

  • Multiple flights with the same number by the same carrier in the air simultaneously,
  • Multiple flights with the same or similar number (even if the carriers are different) that are scheduled to arrive at the same airport when the timing is expected to be close enough to potentially cause confusion,
  • Multiple flights with the same or similar number (even if the carriers are different) that would share proximate airspace during a similar time of day.

For example, assume American Airlines assigns flight number 0621 to a DFW-JFK route with a scheduled arrival of 11:25 a.m. Delta Air Lines then schedules a new ATL-LGA flight to arrive at 11:40 a.m. and assigns a flight designator of DL1621.

In this instance, the FAA would likely require Delta Air Lines to change its number to prevent confusion with the existing American Airlines flight that occupies proximate air space. Because airlines rarely anticipate such scenarios, they simply comply with change requests as received.

Historical Practices

In addition to compliance requirements, airlines also follow a set of internal optional guidelines designed to promote organizational consistency when assigning flight numbers. These guidelines vary by region and/or carrier, but commonly include:

  • Even numbers for northbound and eastbound flights and odd numbers for southbound and westbound flights,
  • Odd numbers for outbound flights departing from hubs and even numbers for flights returning to hubs,
  • Flight numbers that increase in sequence throughout the day in multiple-frequency markets,
  • Ranges by regional or other grouping (for example, international flights 0-199, domestic flights 200-999)
  • Ranges by connection carrier (such as 3000-3999 for the first regional carrier, 4000-4999 for the second regional carrier, etc.)
  • Ranges by codeshare partner (5000-5999 for one partner, 6000-6999 for another partner). Keep in mind:
    • Some codeshare agreements mandate use of a specified number range for certain partners.
    • Often marketing flight numbers add a multiple of 1000 (e.g., +3000 or +6000) to the corresponding operating flight number. For example, if AeroMexico codes on DL611, it might use the flight number AM*2611 (with the asterisk indicating that it is a codeshare).
  • Ranges by service type (for example, 8000-8999 for charters, 9000-9899 for freighters, 9900-9999 for ferry flights, etc.). In some cases, airlines designate specific ranges for peripheral or related services such as bus or train routes.
  • Retiring flight numbers involved in past incidents,
  • Avoiding numbers with cultural or symbolic connections, such as 13, 666, 1313, etc.,
  • Assigning numbers to specific routes with historical or symbolic significance, including 8, which has symbolic positive meaning in the Far East for Asian flights; 711, which represents luck for Las Vegas flights; and 1776, representing the year of America’s Declaration of Independence, etc.
  • Reserving flight No. 1 for an airline’s “flagship” flight.

By utilizing a consistent, predictable flight-number pattern, both airline employees and experienced passengers can more quickly and easily identify flight routes, types and departure terminals.

For example, a 3000-series flight number may indicate to interested parties that the flight is on a regional carrier and will, therefore, depart from a specific terminal or concourse.

However, changes to traditional numbering practices are taking place at some larger airlines. Optional fight-numbering practices routinely used by most airlines in past years are being modified or, in some cases, discarded as the industry evolves with the expansion of alliances and mega-mergers.

Avoiding Confusion

While airlines choose their own flight numbers, air traffic management agencies may direct carriers to modify flight numbers to avoid issues such as having several flights with similar numbers sharing proximate airspace within the same timeframe.

Trends And Obstacles

Many planning, operations and commercial systems currently used by airlines are based on IT infrastructure designed 30 or more years ago. Even though the systems and the technology have evolved, the logic behind these systems comes from a time when the industry environment was far different.

When these systems were developed, few codeshare agreements existed, and it was widely believed throughout the airline industry that four digits would be more than sufficient to cover any carriers’ flight- number needs. Even the largest airlines of the era operated fewer than 2,000 flights per day, and most in the industry could not have predicted that airlines would one day need more than 9,999 flight numbers.

Therefore, industry database and software designers built the infrastructure and subsequent technology with a hard-coded limit of four digits. Only in recent years has the four-digit flight-number limit become an issue due to the upsurge of codeshare flying driven by the expansion of alliances. In addition, recent mega-mergers of large airlines have resulted in consolidated networks with flights close to the 9,999 maximum.

Problem Resolution

To address the issue of insufficient flight numbers, some airlines have modified their flight numbering practices to “save” numbers, including:

  • Discarding the odd/even approach and assigning the same flight number to outbound and return flights (for example, AA2239 for ORD-DFW-ORD or DL1910 for ATL-DFW-ATL),
  • Applying “through” numbers to circuitous continuous routings (for example, same flight number for LAX-DFW-SFO),
  • Condensing flight-number ranges and limiting unused numbers within a range,
  • Abandoning the practice of adding a multiple of 1000 to partner operating flight numbers and simply assigning marketing flight numbers based on the first-available number to keep ranges smaller,
  • Routinely reviewing and modifying existing codeshare-partner flight-number ranges,
  • Discontinuing “blanket codeshares” in which an airline places its code on all its partners’ flights, in favor of selective coding on partner flights.

Unlike some of the more drastic changes recently adopted by the airline industry, such as charging fees for checked baggage or moving to paperless ticketing, flight-number modifications will have minimal impact on travelers.

However, these modifications are only “stop-gap” measures. As airlines continue to add alliance and codeshare partners and participate in mergers and acquisitions, some will soon reach the 9,999 flight-number ceiling, even with these measures in place. In all likelihood, a more fundamental change to the aviation industry regarding how flights are numbered is necessary.

Eliminating ATC Confusion

Multiple aircraft with the same or similar flight numbers that are scheduled to arrive at the same airport could become quite confusing to air traffic controllers and increase the chance of incident. Therefore, airlines must follow some rules established by IATA when assigning flight numbers.

Future Possibilities

Imagine a scenario in which SkyTeam and oneworld merge into a single alliance with all partners wanting to blanket code on all other partners and not be limited to only coding on a limited number of selected flights. Or, suppose large network carriers such as Delta Air Lines and United Airlines merge. What then? “Stop-gap” measures will no longer be sufficient to allow mega-carriers to remain below the maximum flight-number ceiling. In fact, that limitation will likely be reached even before these potential scenarios become reality.

So what is the next step for the airline industry?

On the surface, the easiest solution is to expand flight numbers to five digits. The idea was proposed several years ago by some major airlines during the biannual IATA Schedules Information Standards Committee meeting. IT providers were asked to analyze the impact of expanding to five digits. They examined the process necessary to recode and reformat commercial and operational systems, as well as update related infrastructure, and determined that the effort to implement such changes would be larger in scale than the Y2K transition had been for airlines, and the costs would be in the hundreds of millions of dollars with the potential to exceed US$1 billion.

While five-digit numeric flight numbers may not be the answer considering the excessive investment required, there are a few viable alternatives:

  • Add a letter to the four-digit flight numbers (e.g., UA1001X, BA950B, etc.); however, adding a non-numeric character is considered an operational suffix, and some commercial systems do not treat the operational suffix as part of the flight number, and some cannot even accept it.
  • Adding a letter to the four digits is an issue for some reservations systems (although it may be allowed in some operations systems). So this could be as difficult as adding a fifth numeric digit.
  • Provide larger carriers with additional airline codes for use on codeshare flights.
  • Allow smaller carriers to sell ranges of flight numbers with their flight-designator codes to larger airlines that no longer have enough numbers on their own designator codes.
  • Allow airlines to have multiple designator codes.
  • Leverage technology, such as Sabre® AirVision™ Codeshare Manager, that maximizes the use of flight numbers (especially codeshare flight numbers) to ensure numbers are not under used or wasted.

Such alternatives are more cost effective than moving to five-digit flight numbers, but they also require some investment and effort from both airlines and systems providers. Therefore, a thorough analysis of all options should be conducted to determine the best medium- and long-term approach.

Although additional alternatives are likely to be introduced and evaluated, it is becoming increasingly clear that a change in flight numbering is inevitable. However, in the interim, using tools to get the maximum usage of current flight number ranges is the best short-term alternative.

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