By Chris Yates
IHS Jane's aviation analyst
Questions have been raised about the transmission of the flight plan
Poor air traffic communication contributed to a delay in the launch of a search and rescue mission for Air France 447 which crashed in the Atlantic on 1 June.
According to the French air accident investigation agency BEA, AF 447 attempted automated contact with Dakar Air Traffic Control (ATC) three times before it crashed, but these three contact requests were refused by the control system since no flight plan existed.
Neither Brazilian nor Senegalese air traffic control authorities noted the loss of the airliner and the alarm was only formally raised several hours later when the aircraft failed to appear in Spanish and, latterly, French airspace.
Specifically, BEA highlighted poor shortwave communication between aircraft crossing the area between the southern and northern hemispheres and ground based ATC centres.
BEA also singled out inadequate liaison between the relevant centres as a cause of the delay in raising an alarm.
Typically, an airline raises a flight plan with an appropriate agency some time before departure of a flight.
Air traffic control lost contact with the flight after it took off from Brazil.
The flight plan is then transmitted to all control agencies along the planned route its aircraft intends taking.
Importantly, the flight plan generated and sent by Brazilian air traffic control authorities did not include the address code for Dakar ATC.
During the course of the flight, the aircraft flight deck crew communicates by voice and data transmission with the control agencies to pass vital information including position and altitude.
Separately, automated systems will communicate from time to time with the airline's maintenance base.
BEA initial findings state that Brazil only passed information about AF 447 after a voice request from Dakar, less than thirty minutes prior to its estimated time at the Tasil reporting point - which marks the boundary between Brazilian and Senegalese-controlled oceanic airspace.
Although Dakar then generated a virtual flight plan for AF 447, the centre had no radio or data contact with the flight.
Crucially, the Dakar centre did not appear to follow standard operating procedures when contact with an inbound aircraft cannot be made.
These procedures state that if contact is not made within three minutes following the estimated time of passing above a transfer point, then the receiving sector should inform the exiting sector so that adequate measures can be taken.
The Dakar shift supervisor only informed Dakar Rescue Control Centre that AF447 was missing at 0741, some 6 hours after generating a virtual flight plan and 5.5 hours after the aircraft should have entered Senegalese controlled airspace.
ATC service within the Africa and adjacent Oceanic regions has long been a source of significant consternation for airline pilots.
Over recent years the International Civil Aviation Organisation (ICAO); the International Air Transport Association (IATA) and L'Agence pour la Securite de la Navigation aerienne en Afrique et a Madagasar (ASECNA) have taken steps to improve both voice and data communications between aircraft and ground within the region.
These steps have included establishing satellite voice and data channels between air traffic control centres, a significant upgrade of ground-to-air communication systems and enhanced operational procedures to improve the safety of flight.
Nevertheless, the loss of this aircraft and the delay in mounting a search and rescue operation, clearly shows that much more must be done to improve the lot for air carriers and their passengers.
As the investigation into the loss of AF 447 progresses, stern questions need to be asked of both the Brazilian and Senegalese air traffic control agencies over their inter-agency communication capability and procedures.
Specifically these agencies must be taken to task as to how a civil airliner could simply fall out of the sky on their watch and go unnoticed for several hours until other air traffic control agencies along the planned and filed route raised the alarm.