AF 447 Search to resume

[mm43]

jimjim1 wrote:-

With the resources available on an airliner surely there is no problem at all to phone home with at least positional information every few seconds.

The technology is available and in place on many fleets. However, cost is still a huge problem, and the "every few seconds"option would currently not be considered commercially viable.

I would be surprised if phased array antennas were not available for non-irridium satellite work.

Phased arrays are commonly in use and can be used for both geostationary and low earth orbiting (sun synchronous) satellites.

In summary, the following non ATC position reporting and emergency beacon systems are available.

1. AOC/ACARS via VHF or Satellite.
2. Use ADS-B 1090MHz broadcast position data.
3. Monitoring of 406.025MHz ELT/EPIRB transmissions -

(a) By Geostationary satellites - GEOSAR,
(b) and Low Earth Orbiting satellites - LEOSAR

With reference to (1), AF447 was sending a basic AOC position report every 10 minutes to AF Operations/Maintenance by a commercial data link through a geostationary satellite. This same link provided the ACARS maintenance messages.

There are currently no geostationary satellites equipped with an ADS-B 1090MHz receive and forward package, as would be required for (2) to be of use in oceanic FIRs. Localized monitoring of ADS-B transmissions can and is made by suitably equipped ground stations subject to the aircraft being fitted with the mode. Reception range is dependent on the height of the aircraft and a suitable horizon at the receiving antenna. This is obviously not suitable for use in oceanic FIRs.

Emergency beacon transmissions (3) on 406.025MHz are monitored by a number of Geostationary (GEOSAR) and Low Earth Orbiting (LEOSAR) satellites operating as the Cospas-Sarsat international satellite-based search and rescue (SAR) distress alert detection and information distribution system.

Beacons detected by GEOSAR, provided they are transmitting position coordinates, can have SAR resources deployed quickly to their position. Beacons that do not transmit position coordinates will eventually be heard by a passing LEOSAR satellite and doppler shift techniques are used to establish that beacon's position.

NOTES::

• The LEOSAR system does have "holes" in its coverage - due to a lack of Local User Terminals in some remote parts of the globe. The southern polar regions are a notable void space.
• The GEOSAR system coverage is limited to latitudes of 70 degrees and less.

Any 121.5MHz signals emitted by the ELT/EPIRBs are no longer detected by satellite, but the signal is still used by ships/aircraft and land means to home in on the beacon.

But back to position reports. The most cost effective solution for fleets operating over oceanic FIRs is to implement a more frequent position reporting regime using the existing AOC/ACARS protocols. The costs will increase proportionately, but the costs of not doing so can be equated to those incurred in the search for AF447. The cost of the former as opposed to the later are minor in the extreme.

mm43