This IndiGo aircraft used Gagan satellite system instead of ground radio to land; Here's how it did it

An IndiGo Airbus A320 approaching Udaipur on June 27 completed a landing that looked routine from the cabin but marked a first for Indian aviation.

Instead of relying on the conventional radio-based landing aids installed at major airports, the aircraft used Gagan, India’s satellite-based navigation augmentation system. The Directorate General of Civil Aviation confirmed that this was the first time a full-sized passenger jet had landed in India using the indigenous technology.

Smaller turboprop aircraft had previously carried out similar approaches, but a commercial narrow-body jet had not.

What is Gagan?

Gagan, or GPS Aided GEO Augmented Navigation, was developed jointly by the Indian Space Research Organisation and the Airports Authority of India.

The system broadcasts signals through the GSAT-8 and GSAT-10 communication satellites, which remain in fixed positions over the equator and provide continuous coverage across Indian airspace.

Gagan is often mistaken for NavIC, but the two systems serve different purposes.

NavIC is an independent satellite-navigation network that determines location. Gagan, by contrast, does not provide navigation on its own. It improves the accuracy and reliability of GPS signals already being received by an aircraft.

In effect, Gagan checks GPS data, corrects errors and tells the aircraft whether the resulting signal is safe enough to use for aviation.

Why can ordinary GPS not guide a precision landing

A smartphone’s GPS can usually locate a user within a few metres, which is adequate for road travel. Aviation requires far greater accuracy, especially when an aircraft is descending through clouds or poor visibility.

GPS signals can be distorted as they pass through the ionosphere, an electrically charged region of the upper atmosphere. The signals may slow down or bend, creating errors in the position reported to the receiver.

These disturbances are particularly difficult over India because the country lies under the equatorial ionisation anomaly, a region where ionospheric conditions can change rapidly and produce larger positioning errors.

That makes uncorrected GPS unsuitable for guiding a large aircraft close to a runway.

How the correction system works

Gagan relies on a network of 15 reference stations located across India.

The exact position of each station is known with centimetre-level accuracy. These stations continuously receive GPS signals and compare the location reported by GPS with their actual fixed position.

Since the stations do not move, any difference between the two readings can be identified as an error in the GPS signal.

A central processing facility calculates the necessary correction and sends it to the geostationary satellites. The satellites then transmit the updated information to aircraft operating in the region.

The aircraft’s onboard receiver applies the correction automatically.

The system also monitors the integrity of the signal. If the corrected information is no longer considered reliable, the flight crew receives a warning within seconds.

What happened during the Udaipur approach

The IndiGo aircraft carried out an LPV, or Localiser Performance with Vertical Guidance, approach.

An LPV approach gives pilots both horizontal and vertical guidance while descending towards the runway. It can offer precision comparable to a conventional Instrument Landing System, or ILS, without requiring the same equipment to be installed on the ground at the airport.

That is the main significance of the Udaipur landing.

ILS installations require specialised equipment, regular maintenance and substantial investment. Extending such infrastructure to every regional airport would be costly and time-consuming.

Gagan can provide similar guidance using satellites and ground stations that already cover a large part of the country.

Why it matters for regional airports

India is rapidly expanding air connectivity to smaller cities, but many regional airports do not have advanced precision-landing systems.

Satellite-guided approaches could allow more of these airports to support safer operations during poor visibility, without the expense of installing a full ILS.

The technology could also reduce diversions caused by weather, improve access to airports with limited infrastructure and lower the cost of expanding aviation services.

For airlines, it could mean more reliable schedules. For airports, it could reduce dependence on complex ground-based navigation equipment.

Gagan’s wider role in Indian aviation

Isro has identified two main purposes for Gagan.

The first is to provide the accuracy, reliability and signal integrity required for civil aircraft to conduct safe approaches in difficult weather.

The second is to support more efficient flight paths and improve the management of traffic across Indian airspace.

Gagan has also been designed to work alongside similar satellite-augmentation systems operated by other countries. This allows compatible aircraft to move between different regions without losing enhanced navigation support.

India is among a small group of countries to have built such a system. Its performance is particularly important because of the challenging atmospheric conditions found near the equator.