Inmarsat leveraged a “groundbreaking but traditional mathematics-based process” to analyze data from other flights that use its satellite network and establish a pattern that helped investigators nail down Malaysia Airlines Flight 370’s (MH370) final flight path as traveling south over the Indian Ocean, an Inmarsat executive explains.

Inmarsat’s initial analysis, handed over to investigators on March 11, helped investigators establish the now-famous northern and southern arcs as possible flight corridors for MH370 after it dropped off radar on March 8 over the Andaman Sea.

Inmarsat VP External Communications Chris McLaughlin says the company continued to analyze its data, and concluded on March 23 that the aircraft’s last known position was in the middle of the Indian Ocean, well southwest of Perth.

“What we discovered and what we passed to the investigation ... is that the southern path predicted fits very well with the path that’s been indicated by our pings,” McLaughlin says. “To all intents and purposes, there’s no way [the aircraft] went north.”

A key calculation done by Inmarsat was determining the “Doppler shift” in the ping, or the slight change in the frequency of the signal caused by the movement of the aircraft relative to the satellite in space.

“From that process – a compression or an expansion of the wavelengths – you can determine whether the aircraft is getting closer or farther away,” McLaughlin explains. “It’s been a groundbreaking but traditional mathematics-based process that was then peer-reviewed by others in the space industry, and indeed contributed to by Boeing.”

The data analyzed was generated by pings from MH370 to one of Inmarsat’s 10 satellites. McLaughlin likened the Inmarsat avionics and antenna on an aircraft to a mobile phone, while the applications that use the satcom link, including the Aircraft Communications and Reporting System (ACARS), are “apps.” On MH370, “the apps were turned off, but the handset wasn’t,” he explains.

Since MH370 was not sending routine communications, the Inmarsat satellite was sending hourly “polling signals” to the Boeing 777. So long as the aircraft was operating, acknowledgement signals came back. “This includes its unique identification code, and confirmation the aircraft satcom is still operating and available for communications, if required,” Inmarsat explains on its website.

Inmarsat used these signals to establish that MH370 was in the air for about 6 hr. after it lost contact. The deeper analysis helped the company and U.K. Air Accidents Investigation Branch investigators narrow down the final ping to a remote area over the southern Indian Ocean, in the vicinity of where search teams have been working for more than a week.

So far, sightings of debris have not been linked to MH370’s disappearance. However, the more detailed analysis was enough to convince Malaysian officials that the aircraft went down in the area where the recent search efforts has been focused.

“Based on the new analysis, Inmarsat and AAIB have concluded that MH370 flew along the southern corridor, and that its last position was in the middle of the southern Indian Ocean, west of Perth,” Malaysian Prime Minister Najib Razak said March 24.

The location is both “remote” and “far from any possible landing sites,” he continued. “It is therefore with deep sadness and regret that I must inform you that flight MH370 ended in the southern Indian Ocean.”