Copyright © 2016 Boeing. All rights reserved. 47
7.6 GLS Growth
Airlines, airports and air navigation service providers are exploring the applicability of RNP to GLS
operations to support their future plans to increase capacity, efficiency and enable cost effective precision
approaches. Aircraft avionics and airport equipage are reaching a tipping point as GLS CAT I capability is
becoming standard on new aircraft models. Both domestically and internationally, RNP to GLS procedures
are considered a necessary technology to support future operational needs.
Major airports in the United States including John F. Kennedy International Airport, LaGuardia Airport,
Chicago O’Hare International Airport, Hartsfield-Atlanta International Airport, and Seattle-Tacoma
International Airport are considering GLS operations in the next five years. Internationally, many nations
have proposed GLS implementation plans in the near term. China views GLS as a way to “leapfrog” ILS
at new airports. In 2015, China’s aviation authority published a Performance Based Navigation
Implementation Roadmap, which included GLS and other advanced satellite capabilities, to enhance
efficiency and airport access. GBAS and GLS trials and research in Europe, including Frankfurt, Zurich
and Toulouse, are supported in part by Single European Sky Air Traffic Management (ATM) Research
(SESAR), a public-private partnership to overhaul the air traffic in Europe. GLS studies are underway in
the UK, Norway, Poland, Switzerland, Sweden and France. In Germany, there are GBAS units operational
at Frankfurt Airport (FRA) and Bremen Airport (BRE). Bremen published the first public European RNP to
GLS procedure in early 2016. GBAS installations at Houston (IAH), Newark (EWR), Sydney (SYD), and
FRA provided valuable insights into the operational benefits of GLS. During Winter Storm Jonas, in January
2016, ILS guidance was unavailable at EWR due to snow accumulation. The GBAS continued providing
GLS service allowing United Airlines to continue landings with GLS capable aircraft.
ILS is the predominant precision approach capability at airports today. However, there are limitations to
these systems: they require periodic flight checks which can impact airport operations as each ILS
procedure must be flown in its entirety. ILS requires large, unobstructed areas to prevent signal
interference from terrain or structures, and a single ILS provides only one glideslope and touchdown point
per single runway end. On the other hand, GBAS flight checks are less invasive as they only require a
single flight check to confirm that the system is operational, and a single GBAS supports multiple
approaches with different glideslopes and touchdown points, and does not have critical areas like ILS.
Simultaneous parallel operations, like SOIA and CSPO, are key enablers to maintain capacity and
efficiency in low ceiling and visibility conditions. Wake turbulence mitigation for parallel runway operations
with different glideslopes is in place today, however the additional flexibility provided with GBAS offers
many more approach alternatives with a single facility. Maintaining wake turbulence separation criteria are
essential for safety. Lastly, it is critical that all landing aircraft be stabilized on the lateral and vertical
guidance towards an aiming point on the runway. With existing precision approach capability, meeting
stabilized approach criteria requires longer, straight-in, final segments to allow sufficient time for ILS signal
capture and stabilization.
RNP procedures alone can provide community noise and emissions reduction. By overflying unpopulated
areas, like industrial zones or natural waterways, noise is moved away from the general public. While both
RNP and GLS can be used separately, the most operational benefits are achieved when an RNP approach
terminates in a GLS final segment. With RNP to GLS approaches enabled by a GBAS, it is possible to
provide precision approach capability to runways near to natural or man-made obstruction, differing
glideslopes, and different displaced thresholds. The added flexibility from RNP to GLS procedures allows
added capability for wake turbulence mitigation. In addition aircraft require less time to meet stabilized
approach criteria which in turn allows for a shorter final segment which can reduce track miles flown, and
therefore reduce fuel burn and emissions. Airports and airlines are likely to press for increased RNP to
GLS operations. The demonstration flights by Delta and United on August 27
th
, 2016, highlighted the
potential of RNP to GLS capabilities.