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position reports passing each waypoint along the route, a report about every 15 minutes, as well as warning messages if an airplane’s altitude changes by 200 feet, route by 10 miles, or the absence of an expected position report.
    The crew also has an emergency setting which will force the sending of position reports every minute. This would be appropriate if a flight was diverting to an alternate airport due to an on-board emergency as they might not pass any of the planned waypoints along the way. Setting the Emergency ADS to ON, requires making selections in the communications-system menu. It is not a one-button item and not at the top of the list of things to do when control of the airplane is in question. It would be something a crew would get to once their diversion was initiated.
    CPDLC (Controller Pilot Data Link Communications) is a text messaging system. With it, pilots and controllers exchange formatted text messages to exchange requests, clearances, and messages. The messages are formatted such that key content can be interfaced with the flight management system so that it can, for example, load a transmitted clearance directly into the system, or remind the crew of instructions that take effect at a given time. Pilots can also send position reports, but if ADS is in use, it is rarely necessary. A typical use of CPDLC en route would be for the crew to request a different altitude, or a lateral offset from their planned route for a weather deviation.
    CPDLC also requires a logon, which is done concurrent with the ADS logon. Like ADS, an agreement between the airline and the ATC facility has to be in place before the facility will accept the logon and provide service via this method. After all, the airline is billed for this service, so the system does not accept a logon from just anyone.
    Currently, the North Atlantic air traffic control agencies are initiating a program of reduced lateral and in-trail separation on routes dedicated to aircraft with ADS and CPDLC (also referred to collectively as FANS 1/A). This initiative is expected to generate greater efficiency and flexibility for both individual aircraft and the system as a whole.
    AF447 was not able to log on with CPDLC or ADS that night. An error in entering the flights data into the ATC computer prevented the system from matching up the identification data transmitted from the airplane with what was erroneously typed in to the computer. So when the crew was approaching the oceanic portion of the flight and tried to log on, the logon was unsuccessful, and the crew reverted to using only HF voice communications.
    The night of the accident, AF447 was in radar and VHF radio contact with the Recife controller as they left the coast of Brazil. The controller instructed the crew to contact Atlantico over the INTOL waypoint (the boundary between Recife and Atlantico), and Dakar over TASIL waypoint (the boundary between Atlantico and Dakar) and issued the frequencies for each.

    At 01:34 the crew contacted Atlantico and successfully completed a SELCAL check, which verified that the controller could call the flight. That was the last radio voice contact with Air France 447.
    At 01:35 the Atlantico controller asked the crew three times for its estimate for passing TASIL. The crew did not answer, nor was the call noted on the voice recording.
    One disadvantage of both HF with SELCAL, and CPDLC is that you cannot hear what the pilots of other aircraft are doing and saying. To somewhat make up for that, pilots will often communicate on a designated air-to-air frequency to exchange such information. The night of the accident other flights along the route were diverting around the worst areas of weather, but no air-to-air calls are in the transcript. The crew of AF447 was on their own to determine if a deviation around weather was warranted.

Chapter 4: Intertropical Convergence
    As the flight progressed north of the Brazilian coastline, it entered a band of weather