In my article titled Would modern transponders have made the hijacked planes visible to radars on 9-11? about Mode-S and ADS-B usage I wrote:
According to an esteem by Flightradar24.com, around 60% of the civil airliners and only a small amount of business jets and military aircraft have an ADS-B transponder. This means that, although you will never spot a Stealth Helicopter nor Air Force One broadcasting its position, speed, altitude and route on the Web, you can still catch some extremely interesting planes. As the evasive US Air Force C-32Bs (a military version of the Boeing 757), operated by the Department of Homeland Security and US Foreign Emergency Support Team (FEST), used to deploy US teams and special forces in response to terrorist attacks.
I was wrong.
Although even the Flightradar24 FAQs confirmed that the Air Force One, the world’s most famous and important aircraft, should NOT be visible on their website, for a few seconds around 19.40UTC, the U.S. Air Force’s VC-25 (mil version of the B747), with registration 82-8000, transponder code 3614, advertised its position in the public domain while over Baltimore, descending through FL120 at 310 kts, heading towards Washington D.C. (for landing at Andrews AFB).
I don’t really know the reason for this quick appearance of the AF1 on FR24. A human error? A quick test? Hard to say. I’d expect the IFF Mode 5 with encrypted Mode-S and ADS-B to be paramount on the aircraft carrying the POTUS.
However, in the past I’ve witnessed some “doomsday planes” and other DoD flights shamelessly broadcasting on the Internet their position, altitude, track etc.
Let’s see what happens in the future. Maybe tracking Obama’s movements across the world will be possible. By means of a web browser….
Update Dec. 1, 2011: further investigation shows that the AF1 used genuine full ADS-B signal possibly triggered at the request of controllers for positioning purposes during descent to Andrews AFB.