Capitalizing on the success of its new, more efficient approach procedure at Wantachee, Wash., which reduced weather delays and cancellations at the airport, Horizon is now deploying a Head-up Guidance System (HGS) at Great Falls using Great Falls International Airport’s new Category III (CAT III) landing minima to increase reliability and the often fog-shrouded airport. Horizon Air received Federal Aviation Administration (FAA) approval earlier this month, to use the new minima for aircraft equipped with the Head-up Guidance System (HGS) – informally called the “fogbuster” – to land in lower visibility than previously allowed.
HGS-equipped aircraft landing on Great Falls’ CAT III designated runway need only 600 feet of runway visibility to land, as opposed to the 1,800 feet required for other aircraft. Horizon is the only passenger carrier serving Great Falls that operates HGS-equipped aircraft. The lower minima have paid off, reducing cancellations from 45 a year ago to 14.
At Wanatchee, Horizon uses Wenatchee's Special Instrument Landing System which offers much lower landing minima than those currently in place. Pilots can now land when they can see a mile in front of the aircraft and the ceiling is as low as 300 feet above the ground, a reduction from four miles visibility and 1,300-foot cloud ceilings previously required. The airline estimated in November 2006 the new approach will allow the airline to land an average of 50 more flights during the winter months that would otherwise have been diverted in poor weather. That equates to an 80 percent reduction in the number of flights that would have been prohibited from landing, according to Vice President Marketing and Planning Pat Zachwieja.
Horizon, and its parent, Alaska, are at the forefront of exploiting new technologies to increase reliability in the rugged Northwest weather. They have developed Required Navigation Performance (RNP) at Portland and Seattle, according to an Avionics, RAN’s sister publication, which posted a cover story on the systems in August.
Considered by some as the ultimate breakthrough, allowing the transition from ground-based to aircraft-based navigation, Required Navigation Performance (RNP) has had a slow evolution, according to Author James Ramsey.
He reported that Naverus, this year, became the first FAA-authorized company to provide RNP approach and departure procedures to airlines, airline operators and airports. The company designs RNP procedures — it has developed more than 350 "tailored" procedures — and "leases" them to its customers. FAA-developed RNP procedures are deemed "Public Approaches," available to a broad range of operators.
Meanwhile, Horizon Air, building on the decade-long experience of its parent. Alaska Airlines, is an industry leader in developing and proving RNP approaches into its Portland hub, and it plans to add RNP approaches at six more airports. RNP is a type of area navigation (RNAV) that uses GPS with inertial reference system backup and sometimes DME (distance measuring equipment) navigation, allowing aircraft to fly predetermined paths loaded in their flight management computers. Accuracy is ensured through on-board performance monitoring, with a crew alerting system, if necessary.
FAA had authorized a total of 37 RNP procedures at 17 airports. In 2006, the agency published 28 Special Aircraft and Aircrew Authorization Required (SAAAR) RNP approaches at 14 airports; it planned to publish at least 25 more RNP approach procedures in FY 2007. In addition to Alaska and Horizon airlines, Delta and Continental have been approved to fly RNP approaches in the United States. Alaska Airlines and Horizon Air have developed RNP approaches for Sun Valley and for Palm Springs, Calif.
Southwest is developing RNP since it discovered can be used for more than just terrain-challenged airports."By using it everywhere we’ll unlock the tremendous capabilities of modern avionics, maximizing our investment in new aircraft and equipment," said Mike de Ven, Southwest executive vice president and chief of operations.

Turboprop RNP
As the lead carrier at Portland, one of five airports identified for initial RNP implementation by a FAA/industry task force, Horizon helped develop and test RNP procedures. Since they were approved by FAA for operation in August 2006, Horizon has been flying the procedures in revenue service on its Q400s into Portland. Horizon was developing its Palm Springs approach, which requires a software update for the aircraft’s FMS. Other candidate airports that Horizon serves are Medford and North Bend, Ore., and Butte, Missoula, and Helena, Mont.
Horizon began testing RNP in 1997 when, according to Perry Solmonson, the airline’s manager of flight operations-technical, "most of the FAA we spoke with didn’t understand what RNP was, let alone how to approve it."
Key to the Q400s ability to perform RNP are dual FMS with the latest software, dual GPS, a single Litton IRS, and Thales EFIS displays that can show curved path RNP approaches. RNAV provides aircraft with better access and flexibility for point-to-point operations. FAA has authorized 155 RNAV procedures at 38 airports and planned to publish an additional 42 procedures by the end of FY 2007.
"The real difference between RNAV and RNP is the integrity and continuity of the procedure," Solmonson said. "Integrity is the certainty that the system is functioning properly and providing good information. Comparing integrity requirements of the two, RNP SAAR operations are 100 times more stringent than RNAV operations."
Continuity is the ability to continue an operation even though a failure may occur. "With RNAV there is no continuity — if a RNAV procedure is dependent upon GPS, and GPS fails, the only option is to ask for radar vectors," Solmonson said.
To date, RNP is being used for approaches, but it can work well for departures as well, Solmonson said. However, criteria for RNP-based departures will take another five years.
For the complete Avionics report, including flying a Portland approach, click here.