A special military facility dedicated to testing the vulnerability of GPS installations to deliberate jamming is now open to corporate pilots whose operations take them into, over or even near troubled parts of the world where jamming is becoming increasingly common.

The USAF’s 746th Squadron–which has operated the USAF Center of Excellence for testing military navigation systems for all U.S. military services, government agencies, allied military forces and military navigation manufacturers since 1953–is conducting the tests over the White Sands, N.M. missile range at Holloman AFB. Today, the facility is renowned for its GPS jamming and anti-jamming expertise.

Every spring and fall, the 746th Squadron runs a week-long GPS Jamfest program, during which participants fly their aircraft, drive their vehicles or even march with portable GPS units over areas of the missile range while being exposed to a variety of GPS transmitters emitting jamming signals of varying complexity and power levels, in a closely controlled and instrumented test environment.

‘Real World’ Tests

The large, access-restricted, White Sands location allows a wide range of “real world” exposure to all types of jamming, as opposed to the confines of an enclosed test laboratory or the limitations of controlled airspace, and is particularly valuable in allowing a fully equipped aircraft and its avionics, including antennas, to be exposed to different GPS threat environments under normal operating conditions. The result is a clear understanding of the degree of vulnerability of each installation to different jamming threats, which could be extremely valuable to business aircraft crews.

Is GPS jamming something to be concerned about? Probably not for operators who fly only in the U.S. and Canada. But in less hospitable parts of the world, it is becoming a particularly insidious threat to civil air operations. Jammers today can be both cheap and easy to build–there are even do-it-yourself instructions available on the Internet–and they can run for long periods on a simple pen-light battery. They can also be quite small and easily concealed–inside, for example, an apparently discarded soft drink can and even, using slightly more advanced components, inside a cigarette pack.

Unfortunately, the GPS signals themselves are transmitted at extremely low power levels, with one comparison showing that by the time they reach the aircraft’s antenna, the satellite’s signals are, incredibly, one million trillion times less powerful than a 100-watt light bulb and easily overcome by the simplest jammer.

The reality is that GPS jamming is no longer the sophisticated electronic feat that it was several years ago, and this is one reason– others include inadvertent interruptions from certain tv frequencies and other sources, and even satellite failures–that operators are placing ever more emphasis on having some form of backup. It’s also why some have advocated loran for this role: during Jamfest’s exercise this spring, a station wagon equipped with commercial loran receivers drove through 746 Squadron’s custom-designed road “gauntlet” of 12 high-power GPS jammers and emerged totally undisturbed at the other end.

Jamfest Participation

Jamfest is arranged to cater to the requirements of a diverse group of surface and airborne participants, but each is assigned test procedures appropriate to its operational need and environment. After acceptance to enter the project and payment of the basic $5,000 participation fee, applicants attend a briefing conference at Holloman two to three months before the event.

The conference includes a description of GPS jamming in its various guises, and recognition cues to their onset, followed by individual reviews of aircraft GPS installations and associated avionics by Holloman technical staff. This review involves a discussion of the participant’s particular requirements, and how these can best be accommodated in the test flights.

Among other things, the technical review determines, for example, whether the aircraft already has a built-in data logging capability appropriate for detailed post-flight analysis or, if not, how an approved data logging device could be installed for the tests at minimum cost, since this would provide a clear record of system performance in a jamming environment.

The Holloman staff can usually provide and install any special equipment required, at the participant’s cost, or the participant can take the specifications of recommended units to his own facility for the temporary test installation. (Should the installation of additional equipment be involved, even for a brief period, a consultation with the local FAA FSDO would likely be a wise investment.) The desirability of having a Holloman technical specialist observer on board during the test flights might also be discussed during the Holloman briefing.

About one month before the tests, participants return to Holloman for a detailed briefing on the test plan, including individual dates and flight times during the five-day program. All flying is conducted at night, controlled by Holloman test range radar and other tracking facilities, and usually consists of a number of consecutive 45-minute sorties through the test range.

During each individual sortie, a highly calibrated 746 Squadron Beech 1900 flies in the test airspace, precisely recording the jamming signal environment for post-flight comparative analysis and determination of the participant aircraft’s jamming vulnerability thresholds. The report at the end of the test program includes these and other data.

Major David Hoey, commander of 746 Squadron, told AIN that he would particularly welcome the participation of corporate pilots, since they would bring fresh operational insights to the project. Hoey is clearly interested in drawing the attention of the civil community to the increasing threats of jamming– one of the growing realities of international operations but one that so far has mostly been paid only lip service.

The final Jamfest this year will be conducted from October 31 to November 4, and participants are already assigned. The next Jamfest will be held during the second week of May; inquiries should be sent to Robert.Blanchette @46tg. af.mil, telephone (505) 679 2828.