Landing with satellite navigation

Updated: Mar 16, 2016

Satellite navigation offers a means of global navigation, available 24/7 in all weather conditions. Although GPS was designed for military purposes, these features rapidly attracted the attention of the civil aviation community. They saw its potential for navigating and approaching any runway around the globe compared to fully relying on an airport’s local ground infrastructure.

GPS was therefore rapidly welcomed and used for en route navigation, or at least as a complementary means of navigation.

Issue

For landing aircraft, the situation was quite different. System requirements are far more stringent. The system has to be particularly accurate and reliable. For example the pilot has to be informed within in a few seconds when system performances are degraded and must not be used for navigation.  Such satellite navigation aviation requirements are defined by the International Civil Aviation Organisation (ICAO) as seen in the table below.

As the performance of GPS is not fixed, the service cannot be guaranteed and there is no feature to alert the user in case of a failure that impacts the quality of the positioning measurement and consequently the safety of the user. This restricts the use of GPS as is as an instrument to assist in aircraft landing operations by imposing important safety buffers to compensate for the lack of precision.

GNSS requirements

ICAO Standards and Recommended Practices Appendix 10 – Nov 2006

Phase of flight

Accuracy
(m)

Availability

Alarm Limit

Time to Alert

Integrity Risk

Continuity

En Route

H : 3.7 km

0.99 to 0.99999

H : 7.4 km or 3.7 km (continental)

5 min

10-7 /h

10-4 / h to 10-8 / h

Terminal

H : 0.74 km

0.99 to 0.99999

H : 1.85 km

15 s

10-7 /h

10-4 / h to 10-8 / h

NPA

H : 220 m

0.99 to 0.99999

H : 556 m

10 s

10-7 /h

10-4 / h to 10-8 / h

APV I

H : 220 m
V : 20 m

0.99 to 0.99999

H : 40 m
V : 50 m

10 s

2x10-7 / 150s

8x10-6 for each 15 s

APV II

H : 16 m
V : 8 m

0.99 to 0.99999

H : 40 m
V : 20 m

6 s

2x10-7 / 150s

8x10-6 for each 15 s

Cat I

H : 16 m
V : 6-4 m

0.99 to 0.99999

H : 40 m
V : 15-10 m

6 s

2x10-7 / 150s

8x10-6 for each 15 s

 

The EGNOS solution

The EGNOS ground infrastructure continuously monitors GPS performance for all of the European Union and beyond and provides the user with error corrections, considerably increasing the navigation accuracy of the signal. In addition, EGNOS is able to detect GPS satellite faults, to assign a confidence level to the data transmitted to a user and to provide timely warnings when GPS or its data should not be used for navigation. 

Satellite navigation therefore becomes within reach for Instrument Flight Rules. To formalise it, EGNOS was certified by civil aviation authorities and was officially declared as appropriate for civil aviation landing (APV) in 2011. The first commercial operation using a final approach with EGNOS was the Trislander aircraft operated by Aurigny Air Services, a regional airline operating connection flights between the Channel Islands and the UK and France, from December 2011 onwards. The US WAAS system provides similar capabilities for the North American region.

The impact is therefore sizable. Aircraft will be able to land in all locations where adequate procedures are published, without requiring a huge investment in airport equipment and maintenance.

Approach operations will be less constrained by ground equipment features; they will be more precise, increasing airport runway capacity and overall airport efficiency.

General aviation, business jet services and regional airlines have rapidly identified the benefits of such use of the technology.  Avionics equipment manufacturers are already proposing EGNOS-enabled equipment and the retrofitting of GPS equipment with EGNOS capability.

The commercial aviation sector is also joining the club. For example Airbus is equipping its A350 XWB with a satellite-based augmentation system (SBAS) receiver, providing their customers with the capability of landing without navigation ground infrastructure and providing a geometric vertical guidance, free of temperature and barometric setting errors.

 

What is needed to make EGNOS a reality in the aviation sector?

  • EGNOS compatible avionics need to be installed in aircraft, in line with EASA AMC20-28, published in Sept 2012
  • Approach procedures must be written and approved by the National Supervisory Authority (NSA) of each Member State. The list of actual published procedures can be found here
GNSS market segment: