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AAL CDM Message Sending Process. CDM A&D Meeting January 24-25, 2001 Presented by: Roger Beatty - Operations Coordinator American Airlines - System Operations Control. CDM Message Sending -Technical.

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Aal cdm message sending process

AAL CDM Message SendingProcess

CDM A&D Meeting

January 24-25, 2001

Presented by: Roger Beatty - Operations Coordinator

American Airlines - System Operations Control

Cdm message sending technical
CDM Message Sending -Technical

  • The Flight Operations System (FOS) is our mainframe process that records and communicates ALL operational changes to all AAL departments.

  • A PC application (XPE) downloads the schedule and all schedule updates from FOS (once a minute).

  • A CDM data collector program creates and manages CDM data and FAA message files.

  • A PC communications program sends The FAA message files via AOCnet to Volpe center.

  • Error and Warning messages received from Volpe are logged and periodically reviewed by IT staff.

Cdm message sending procedural
CDM Message Sending - Procedural

  • The CDM sender runs continually in the background. Short of pulling the power plug, it cannot be turned off by operations personnel (but can be modified).

  • A rolling daily download is performed. Whenever a flight’s departure time comes within 18 hours of “now” an FM, FC or FX message is sent.

  • Cancellations, diversions, etc. are sent as soon as they are known (less than 60 seconds after entry).

  • Delays of 1 minute or more are sent immediately.

  • For more details see Appendix A

Cdm message sending personnel
CDM Message Sending - Personnel

  • Flight create, cancel and diversion events are always entered into FOS by Dispatch/SOC personnel.

  • Most gate delay predictions are entered by airport personnel as they have the best knowledge of local events or when gate space may be next needed.

  • Some gate delays such as crew legality or airport curfew violations may be entered by SOC/Dispatch

  • Updates of “OFF” times are entered by the flight crew (via ACARS into FOS) or by CDM sender automation applying “Time Out” logic. (see Appendix A)

Delayed gate departure predictions issues
Delayed Gate Departure Predictions Issues

  • A gate delay prediction failure is considered differently for passengers than it is for ATC-TFM.

  • That propagation delays and local event delays are different in the prediction of gate departure.

  • How important is the stability of the prediction versus its ultimate accuracy?

  • Can different predictions of gate departure be sent to different users?

  • If a less public version of departure time is sent, how can that information be properly secured?

Appendix A

AA CDM processing consists of the XPE/XPF Downloader, the CDM Data Collector (labeled above as CDM) and the Communications Program. All three execute once per minute.

The CDM Data Collector processing rules are:

Daily download:

A rolling download is performed. Whenever a flight reaches the number of hours prior to scheduled departure as set by a parameter, an initial FX or FM will be sent. Currently the parameter is set to 18.


Upon receipt of a cancellation from FOS, an FX will be sent.

Reinstatement of a cancelled flight:

When a cancellation is reinstated, an FC will be sent.

Diversion after takeoff:

An FM is sent for the diverting leg to change the destination station to the new station.

An FC is sent to create the continuation leg from the destination station to the original destination. This will have the same flight number as the diverting flight.

Undiverting a flight after takeoff:

An FX is sent to cancel the continuation leg. An FM is sent to change the destination station back to the original destination station.

Diversion prior to take-off:

An FX is sent to cancel the leg.

Two FCs are sent, the first to create the leg from the origination to the station into which the flight will divert. The second FC will create the leg from the station into which the flight diverts to the original destination.

Undiverting prior to take-off:

Cancel (FX) the two legs created by the diversion, and then send an FC to create the flight from the origin to the original destination.

Change of flight number (Stub):

If a flight is stubbed, an FM is sent to change the flight number. All FMs or FXs after this will be sent using the new flight number.

Reinstate the flight number to the original (unstub):

An FX is sent to cancel the flight with the stubbed number. Then an FC is sent to create the leg with the original flight number.

Air Interrupt (Diversion after take-off to the originating station):

AA cannot handle this properly as AA creates the continuation leg with the same scheduled departure time as the original leg. Thus when the FC is sent to create the continuation leg, Volpe rejects it saying that this flight has already occurred. To differentiate the legs within FOS it is necessary to enter the actual (latest) time as well as the scheduled departure time.

Changes to departure time:

Prior to a flight taking-off, whenever any of the T1, T2, T3 or 4 times change from the prior time that was sent to Volpe by more than the number of minutes based on a parameter, an FM is sent to Volpe. Currently this parameter is set to one minute; thus any change in these times results in an FM.

Change of equipment:

An FM is sent if the equipment change results in the change of fleet as sent to Volpe. If the equipment is a tail number change within fleet, no FM is sent.

Prevention of time-outs:

This is governed by a "time-out minutes" which is currently set to 60. During each cycle, if a flight is:

Not yet OFF

Past the latest Off Time by the "time-out minutes" minus 15

The actual equipment is equipped with ACARS

Not already flagged to be sent to Volpe in this cycle

The flight becomes a time-out candidate and will have an FM sent to prevent time-out cancellation. If a time-out candidate is not yet OUT, the latest departure time for OUT will be set to time now and the other times adjusted accordingly. If a flight is OUT but not OFF, the estimated OFF is set to time now and the estimated ON and IN adjusted accordingly. At no time is the enroute time or taxi in minutes adjusted.