PARIS — Aireon LLC, a joint venture of mobile satellite services provider Iridium and the air-navigation authorities of Canada, Ireland, Italy and Denmark to provide aircraft-location data to improve flight efficiency and reduce fuel consumption, plans to offer a free supplementary service for emergency tracking of aircraft in trouble.

McLean, Virginia-based Aireon was expected to announce the service, called Aireon Aircraft Locating and Emergency Response Tracking (ALERT), on Sept. 22.

Aireon Chief Executive Don Thoma said Aireon’s commercial business, which uses payloads on Iridium’s second generation of satellites scheduled for service in 2017, already includes ALERT’s capabilities and that the company has decided to make it available free of charge.

“We view this as a public service,” not a part of Aireon’s commercial business, Thoma said of the Aireon ALERT system. Satellite fleet operators Inmarsat of London and Globalstar of Covington, Louisiana, are planning similar services from their fleets.

Aircraft builders Boeing and Airbus have agreed to install Automatic Dependent Surveillance-Broadcast (ADS-B) transponders, whose position-location signals are relayed by the Aireon payloads, on their planes.. Aireon ALERT could be activated by any certified air-safety organization to request the last known location and flight path of any aircraft carrying an ADS-B transponder, even if the operator does not subscribe to Aireon.

Peter B. de Selding was the Paris bureau chief for SpaceNews.