04/12/2011

A balloon or a UFO?

According to the press, the hot-air balloons flew over Geneva last Sunday. Unlike previous festivals, they seemed not to have active transponders, but there was one possible intruder.


On some previous occasions when hot-air balloons have flown from Geneva, they have operated with an active transponder, meaning that they were broadcasting who they were to everyone. Thus, other aircraft would know about them, and radar would enable them to be located.

Having read that they were flying from Geneva last Sunday, 10 April, I looked into the daily record of flying objects recorded by the ARAG aircraft movement detection system. To my slight surprise, I found none at all. On reflection, it is possible that Skyguide air traffic controllers asked the pilots to switch them off, as they seem to do for helicopters crossing the main aircraft runway, to avoid other aircraft getting confused by possible collision warnings.

What I did find was an unidentified flying object which said nothing about what it was : almost all aircraft give out some call sign giving some information (though sometimes a bit confusing, as for an Air France aircraft that gave out the call sign "CANCEL"). All that it gave as identification was a 32-bit (8 hexadecimal characters) identifier "565000".

These identifiers are normally one of a consecutive range of identifiers allocated to different countries. For Switzerland, the range is from 4B0000 to 4B7FFF, with the sub-range 4B7000 to 4B7FFF reserved for the military aircraft. I have a list of all these allocations, which is used to list the country of any detected identifier.

So what was detected for 565000? Nothing: my list does not include any match for this identifier. Of course, my list may be out of date, and the ICAO may now have an allocation for this (to be checked). All that I can see is that the identifiers near to it are from various eastern europe states, some of them quite new following the break-up of the USSR.

Another possibility is that the identifier is incorrect. The ICAO, in one of its published documents, recognises that such errors can happen (errare humanum est) but states that it can be rather dangerous. An extract from the actual text of the ICAO is as follows :-

Instances occur of incorrect 24-bit aircraft addresses being installed/hard-wired on individual aircraft. This has happened not only on first installation of a Mode S transponder but also when a major modification has been made to the Mode S equipment, and following a change of State of Registration. Incorrect installation, such as setting the address to all zeros, or, inadvertent duplication of an address can pose a severe risk to flight safety. In particular, the airborne collision avoidance system, ACAS II, performs on the assumption that only a single, unique 24-bit aircraft address per airframe exists. The performance of ACAS II can be seriously degraded and in some instances disabled if an incorrect or duplicate address is installed on an aircraft.

All that I know of this mystery aircraft is that it was first detected at 4h03 pm flying at 3200 feet altitude. It then rose slowly to 7900 feet at 4h16 pm, before gently descending to 2400 feet at 4h44 pm. I have no idea where it was: maybe quite a distance away and taking off or landing somewhere hidden behind some mountains.

The Tardis or a flying saucer? Ask Skyguide.

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