Time for a New Approach

February 12, 2013

The world’s first commercial satellite based precision approach was completed by an AirBerlin flight into Bremen, Germany, using a Honeywell SmartPath Ground Based Augmentation System (GBAS) in February 2012. It was a milestone in Europe’s air traffic management history and a major step towards the reinvention of how to handle approach and landing guidance.

Traffic numbers continue to grow. In the Middle East and India, that growth is significant. That means the need to increase airport capacity and throughput at major hub airports is set to increase further. The arrival of satellite based precision landing is important and timely. The world’s major airports currently rely on tried and tested Instrument Landing System (ILS) technology to provide precision approach guidance down to the runway threshold in near-zero visibility (Category III). The ILS is effectively two sub-systems; a localiser, situated at the end of the runway providing lateral guidance, and a glide slope antenna, located at the side of the runway to provide vertical guidance. These antennas transmit radio beams that are received by ILS receivers onboard approaching aircraft and are used to determine whether the aircraft is off-centre, or approaching too high or too low.

This standard has remained the primary method of approach and landing guidance at commercial airports since the 1960s. However, it is based on principles dating as far back as the 1930s. While technology has evolved over time, the operating limitations of an ageing ILS concept continue to holdback airport growth, argues Honeywell Aerospace Senior Manager Pat Reines. Reines is business development leader for the company’s SmartPath GBAS precision landing systems. Reines argues that the ILS radio signal can be subject to interference and limits new ground infrastructure in the vicinity of an airport. Bad weather and terrain can have an adverse impact, for example sloping or uneven terrain can lead to signal reflections creating an uneven glide slope. Similarly, taxiway capacity can be limited by short-holding necessary to avoid taxiing aircraft from blocking and disturbing the ILS signal.

While these challenges restrict airport capacity from an infrastructure perspective, there are other issues with ILS says Reines. Due to the complex nature of the station and antenna arrays, installation and maintenance can be time-consuming and expensive, particularly as an ILS installation is limited to managing a single straight-in approach path at one end of a single runway. Aircraft are required to line up ahead of final approach and single-file down the ILS glide slope as though they were flying through the neck of a bottle.

Satellite-based solutions
GBAS is a relatively new alternative to ILS. GBAS augments Global Satellite Navigation Systems (GNSS) signals to make them accurate enough and safe to use for precision approach procedures. The ground equipment includes four GNSS reference receivers, a GBAS computing facility and a VHF data broadcast transmitter. This ground equipment is complimented by GBAS avionics installed on the aircraft. The GBAS ground facility receives positioning data from GNSS satellites, computes error corrections and satellite health information and broadcasts the necessary information out to all GPS Landing System (GLS)-equipped aircraft transitioning from en-route to terminal airspace twice a second. The result is positioning accuracy of less than 1 metre down to 200ft (Category I) regardless of terrain, obstacles and climatic conditions.

As well as the benefits of improved accuracy, a GBAS broadcast is omnidirectional, which means it is not subject to the same levels of interference as ILS. It also is capable of providing 26approaches, including final approach segments for Required Navigation Procedure (RNP) approaches and continuous descents, across all airport runways simultaneously. This adds to ATC flexibility and enhances airport capacity.

Honeywell’s SmartPath technology is the only certified GBAS available today, with operational certifications from the FAA since 2009 and Germany’s Bundesaufsichtsamt für Flugsicherung(BAF) since 2011. As well as the accuracy benefits and increased throughput GBAS brings, SmartPath can also yield economic savings for airports too. As a result of the reduced ground infrastructure and increased reliance on software, Honeywell argues SmartPath can bring maintenance savings of up to USD400,000 per airport, per year, over ILS.

Honeywell has demonstrated the benefits of GBAS for Category I precision approach guidance at more than 25 airports around the world. As well as the operation of SmartPath at Bremen, the system went live at Newark Liberty International, New Jersey in September 2012 while further SmartPath installations at Sydney International

Australia and Houston George Bush Intercontinental in the US are expected to become operational in 2013. GBAS is also in use in Latin America, where SmartPath is installed at Galeão–Antonio Carlos Jobim International Airport, Rio De Janerio, Brazil. The unit is currently undergoing tests to support operations in the unique Ionospheric conditions experienced in locations in very close proximity to the equator. Testing and certification of the Rio system is expected to be completed in 2014.As the momentum of SmartPath installations picks up at the airport, so too does GLS equipage onboard the aircraft. GBAS-compatible Multimode Receivers (MMR) are available for most mainstream commercial aircraft, and come as standard forward fit equipment on Boeing 787 and 747-800 aircraft and Airbus A380 - A380 hardware is equipped as standard, with activation optional for a fee.

A culture of change
According to Honeywell, one of the biggest hurdles facing GBAS is not one of technology or even financing, but of the difficulty in bringing together multiple stakeholders and pressing for a culture of change. For GBAS to progress from its current position as an early adopter technology, an acceptance of change is required among all stakeholders, not only up to the point of installation, but in the subsequent operational model. Airport authorities and ANSPs need to engage with regulators and primary airlines, with the help of their suppliers, to build a business plan for GBAS that defines objectives, timelines and metrics of success for all parties concerned. Only then can the desire to change be driven forward. In the meantime, Honeywell is working on developing its GBAS solution to provide sufficient integrity and accuracy to support Category II and III precision approaches, down to 50ft decision height. The company is confident it can extend the algorithms to meet the higher performance requirements within the next three or four years. With the first GBAS installations now certified and flying commercial traffic into major airports, Reines is confident the momentum will build to drive universal acceptance of a new approach at the world’s high growth airports.

First published in CANSO Airspace magazine January