APPROACHES & LANDINGS

GLS grows in popularity

Ground-based augmentation system isn’t ILS or WAAS but it does provide precision approach at low cost.


Dash 8 cockpit. Universal Navigation obtained the TSO for installation of the GLS 1250 GPS land­ing system in the Dash 8. Widerøe Airlines will have all 19 Dash 8s so equipped by 2010.

The RNP approaches, which require quite an investment in equipment and training, curve almost 180° to avoid overflying New York City. One advantage of GLS approaches is that they too can be constructed with curves.

GLS approaches will soon supplement the Rwy 29 RNP approaches, but with lower minimums. The Port Authority of New York & New Jersey is negotiating with Honeywell for the certified Beta 4000 GPS ground base, which will serve all EWR’s runways, not just Rwy 29.

Another US airport that will soon have GBAS—and perhaps even by the time you read this—is MEM (Intl, Memphis TN), the home of FedEx. Here again, the ground station vendor will be Honeywell. FedEx has an obvious need for precision approaches to all runways at MEM.

One might object that there’s no need to bother with GLS, since ILS approaches already exist to all the runways at MEM, but the reason lies in the other advantage of GLS that was hinted at earlier—one that will arrive in the near future.

Next advantage

Right now, GLS approaches around the world operate as Special Category 1 (SCAT 1) approaches to as low as 200 ft AGL. However, in the future, after necessary development and demonstration, GLS/GBAS will be able to support Cat II and III autoland.

Currently, only Rwys 36L, 36C and 36R at MEM have Cat II and III mins. FAA Spokesman Tammy Jones says the agency is presently planning the activities required for GBAS Cat II and III R&D at MEM. One GLS ground station can support approaches at multiple runways.

(In theory, it can even support approaches at multiple airports, provided they are close enough and line-of-sight VHF transmission to approaching aircraft is assured.) Therefore, one GBAS ground station at MEM or EWR can, obstacles and runway lighting permitting, potentially support Cat II and III autoland at any of the runways at the airport for a relatively small initial investment and less maintenance cost than ILS.

Because ILS is a transmitted beam of electromagnetic energy, installing it in areas near manmade structures or steep nearby terrain won’t work. The beam is distorted by reflection, and airports in mountain valleys around the world often cannot use ILS for this reason.

Airports located in the fjord regions of Norway cannot abide ILS, placed as they are between steep mountain walls. Unfortunately, too, these locations suffer many days of restricted visibility. While Europe will eventually have EGNOS—equivalent to WAAS/SBAS—it is not yet operational.

Widerøe Airlines Dash 8 service in Norway relies on Universal Navig­ation GLS receivers in order to fly GLS approaches into difficult destinations surrounded by mountains.

The largest regional airline operating in Scandinavia, Norway’s Widerøe Airlines, was driven to improve the precision of its approaches by a fatal CFIT accident in 1988. Widerøe found what it needed in GLS. The airline is equipping its fleet of Bombardier DHC8 turboprops with Universal Navigation’s GLS 1250s.

In Jun 2006, Universal received the European TSO (ETSO) for the GLS 1250, and Field Aviation subsequently obtained an STC for this installation in a Widerøe Dash 8. Six DHC8-100s are equip­ped now, and Widerøe will have all 19 equipped by 2010.

In Oct 2007, BNN (Brønnøysund, Norway), 500 miles north of Oslo, became the first airport equipped with a Park Air Systems GLS ground station. GLS certification followed at HFT (Hammerfest, Norway), and Avinor, the owner/operator of Norway’s STOL airport network, will have all 9 airports in Finnmark County equipped by 2010. Another area of the world where airports and airlines are exploiting the advantages of GLS is down under.

Airservices Australia (ASA) has sponsored Honeywell in the installation and certification of a GLS ground station at SYD (Kingsford Smith, Sydney NSW, Australia). Qantas began operational trials with GLS approaches at SYD in 2006.

Initially, the airline equipped 9 Boeing 737s with GLS-capable Rockwell Collins GLU 925 multimode receivers. Eventually, it plans to equip nearly 40 Boeing 737-800s in this way. Qantas was the launch customer for the GLS-equipped Airbus A380.

Eventually the airline will have 20 of the type, all equipped with GLS. Interestingly, one motivation for installing GLS at SYD in the first place was the sheer size of the A380. That, and the fact that Qantas plans to operate so many of them, may mean interference with the ILS beams in Sydney’s tight peninsular spaces.

The vertical tail alone of the A380 is a terrific ILS reflector! GLS is an option on A380s worldwide, as it will be on the Airbus A350 XWB. GLS will come standard on all Boeing 787s and on the new 747-8.

Considering that Boeing already has 1000 787s on order, this is significant for the worldwide promulgation of GLS. In the near future, use of GLS will expand slowly in parts of the world where SBAS or WAAS does not exist and may not exist in the future.

However, it’s possible that in the long term GLS may replace Cat II and III ILS facilities wholesale across the planet, simply because of economies of purchase and maintenance. After all, FAA’s goal is an eventual nationwide transition to a completely satellite based navigation system.

For that to happen, something will have to replace ILS! WAAS can provide for minimums as low as 200 ft but cannot provide for Cat II or III. GLS, on the other hand, has the potential to provide Cat III autoland.

Once this has been demonstrated satisfactorily, and operations have proved robust and reliable, we can expect to see much wider use of GLS. Don Witt was a USAF McDonnell F4 aircraft commander in Vietnam and is a former Airbus A320, Boeing 737 and 757/767 captain with United. He has also worked as a meteorologist and is currently an FSI Learjet instructor and training/check airman in Tucson AZ.

Don Witt was a USAF McDonnell F4 aircraft commander in Vietnam and is a former Airbus A320, Boeing 737 and 757/767 captain with United. He has also worked as a meteorologist and is currently an FSI Learjet instructor and training/check airman in Tucson AZ.

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