JPALS, Joint Precision Approach and Landing System

After many years of technology refinement, the Electronic Systems Center-led land-based increment of the Joint Precision Approach and Landing System is poised to progress to the system development and demonstration phase.

Known as JPALS, the system uses the Global Positioning System, or GPS, to enable accurate and reliable landing guidance for approaches, including those conducted in low-visibility conditions. It is, in fact, designed to provide precision approach and landing for all the military services in any weather and for virtually any mission, according to 1st Lt. Patrick Ris of the 853rd Electronic Systems Group. He is the ESC deputy program manager.

The Navy is the Defense Department's lead service for the joint program, and because of its specific needs, the sea service has fully funded and moved its maritime-based increment of the program forward. Now the Air Force seems ready to do the same, according to Brian Pierce, a contractor supporting the program.

"The technology is ready, and users are beginning to see all the advantages," Mr. Pierce said.

Those advantages include equipment and cost reductions. JPALS requires only one ground station per airfield, whereas the instrument landing system, which is now predominantly used, requires one ground station at each end of every runway on an airfield. The one JPALS ground station also may cover all other airfields within a 20 nautical mile radius.

The JPALS system uses datalink receivers on board the aircraft to connect with the ground station. The ground station, being in a fixed location, can constantly measure the ever-changing error factor inherent with GPS and transmit it to the aircraft. Navigation processing equipment onboard the aircraft incorporates the information to increase the accuracy of the aircraft GPS position.

JPALS then uses waypoints provided from the ground station to construct an approach path between the aircraft and touchdown point. The pilot can fly this approach using standard cockpit instruments, or JPALS can be coupled to the aircraft autopilot to perform "hands-off," auto-coupled landings, according to Mr. Pierce.

The system allows approaches to be changed easily. It also allows touchdown points to be moved.

"In a hostile environment like Iraq, it's easy to see what a huge advantage that would provide," Lieutenant Ris said.

To help Air Force operators realize the benefits of switching from ILS to JPALS, the 853rd team and contractors with ARINC Engineering Services set up a two-day informational event hosted by Boeing in Seattle earlier this year. There, roughly two dozen military observers boarded a new Qantas Airways Boeing 737-800 at Boeing Field for a demonstration of an advanced commercial satellite landing system that resembles JPALS.

During the flight, the Boeing 737 successfully completed 15 approaches at five different airfields in the Seattle region. A number of veteran Air Force pilots took turns in the co-pilot seat, Mr. Pierce said.

"People who came in with reservations came away sold," he said.

The demonstration was the latest in a series of events aimed at both wringing out and showing off the technology, according to Bob Norwood, who supports the program as a contractor.

In October 2007, the ESC group participated with many others in a field experiment held at the Federal Aviation Administration William J. Hughes Technical Center at the Atlantic City International Airport. There a so-called man-pack version of JPALS, integrated on the fly by ESC, MITRE and ARINC engineers, was tested.

Using just two backpacks worth of equipment set up not at the runway but at a nearby ball field and then in a salvage yard more than a mile from the runway, operators provided precision approach to Atlantic City airport, and later, to Ocean City airport, 12 miles away.

"There's lots of interest now," Mr. Pierce said, noting that, combined with an ever-clearer joint service need, that interest should help deliver successful results for the program.

JPALS began, more than a decade ago, as a program designed to meet the emerging needs of an aviation system perceived to be moving away from instrumentation-aided landing systems. It's still envisioned as the system of the future, and in fact such systems are being delivered at a far greater pace than ILS systems.

However, neither the FAA nor the International Civil Aeronautics Organization, which governs worldwide aviation, have yet mandated such a switch. Still JPALS' current value to the warfighter transcends any such mandate, according to the program officials.

"It just makes sense to do it," Mr. Norwood said.

And as for the extra time it has taken to reach the point where the Air Force is ready to adopt the system, it's only helped mature the technology, Mr. Pierce said.

"There's been a lot of work done on this, both here and at the FAA," he said. This is important because, when dealing with precision approaches and landing, the system accuracy has to be perfect.

"If you're using a GPS device while driving or hiking in the woods, and there's a momentary problem with one of the satellites, you can afford to wait a while for another to pick up," Mr. Pierce said. "But in precision approach, we don't have that luxury."

Therefore it's "been helpful in a way" that the system wasn't rushed into development and fielding.

"We've really been able to work at it and get a much better understanding of the system," Mr. Pierce said. "Now we're very confident that we're ready to go forward."