In order to allow all airlines to electronically exchange information on a deviation from their basic schedule, standard message formats have been agreed. These formats also allow the airlines to submit these amendments to schedule aggregators.

The message formats have been designed to provide as much clarity as possible for the message users and the received message details can be processed either by computer or by manual methods.

Deviations from the basic schedules, such as an addition of a supplementary or an extra flight, change to a single operation of an existing flight in routing, timing, equipment or other data and cancellation of a flight are transmitted using the Ad-Hoc Schedules Message (ASM).

A message may consist of one or more Action sub-messages. Each sub-message will have its own Action Identifier to identify a specific change being made to the basic schedule.

The rules for the use and composition of this message, together with detailed specifications and examples, are explained in the following Sections of this Chapter.

Amendments to the basic schedule may be transmitted in the Standard Schedule Message (SSM).

The rules for the use and composition of this message, together with detailed specifications and examples, are explained in Chapter 4.

The Ad-Hoc Schedules Message (ASM) forms part of a complex system of timetable information exchange. The design of the message is based on the philosophy that a flight is recognised by the Flight Identifier, i.e. the combination of the Flight Designator and the Flight Identifier Date. The ASM applies to long term ad-hoc modifications of schedules (generally resulting from schedules or operational planning) as well as short-term operational decisions that affect flight schedules.

For reporting of operational events, such as delays and actual movements not affecting schedules, reference should be made to the procedures defined in the IATA Airport Handling Manual (AHM). In order to facilitate industry-wide acceptance of these standards, a range of optional features is included to ensure complete compatibility with the standards set in Chapter 7 for the exchange of computerized schedules and with the Standard Schedules Message set in Chapter 4. These optional features include such items as the use of local dates and times, leg and segment oriented traffic and sales information.