By Allison Lampert, Gabriel Araujo and Valerie Insinna
SAO PAULO/MONTREAL (Reuters) -Russia has informed Brazil's aircraft investigation authority that it will not probe the crash of the Brazilian-made Embraer jet that killed mercenary boss Yevgeny Prigozhin under international rules "at the moment", the Brazilian agency told Reuters on Tuesday.
Prigozhin, two top lieutenants of his Wagner Group and four bodyguards were among 10 people who died when the Embraer Legacy 600 crashed north of Moscow last week.
He died two months to the day after staging a brief mutiny against the Russian defense establishment that posed the biggest challenge to President Vladimir Putin's rule since he rose to power in 1999.
Brazil's Center for Research and Prevention of Aeronautical Accidents (CENIPA), in the interests of improving aviation safety, had said it would join a Russian-led investigation if it were invited and the probe held under international rules.
Russia’s aviation authority was not obligated to say yes to CENIPA, but some former investigators said it should, as the U.S. and other Western governments suspect the Kremlin of being behind the Aug. 23 crash of the Embraer Legacy 600, which has a good safety record.
The Kremlin denies any involvement. Prigozhin was publicly critical of Moscow's prosecution of its invasion of Ukraine. The Wagner mercenaries fought battles there on Russia's side.
According to the Montreal-based United Nations International Civil Aviation Organization (ICAO), the flight from Moscow with a destination of St Petersburg was domestic, so it is not subject to international rules known throughout the industry by their legal name "Annex 13."
NO OBLIGATION TO ACCEPT INTERNATIONAL RULES
"They are not obliged, only recommended to do that," CENIPA head Air Brigadier Marcelo Moreno told Reuters after the agency sent an email last week asking Russia whether it would open such a probe.
"But if they say they’ll open the investigation and invite Brazil we will participate from afar."
U.S. aviation safety consultant and former investigator John Cox said an internal Russian investigation would always be questioned without the participation of Brazil, the country where the plane was manufactured.
"I think it’s very sad," Cox said after being told of the Russian response. "I think it hurts the transparency of the Russian investigation."
CENIPA said in an emailed statement it got the response from the Interstate Aviation Committee - Commission on Accident Investigation (IAC) on Tuesday, with the Russian authority saying it would not open for now a probe under Annex 13.
In air crash investigations, experts work to improve aviation safety without assigning blame, but probes are often tainted by political interests.
CENIPA and manufacturer Embraer want to prevent future accidents but face challenges in getting information from the investigation due to sanctions on Russia and Moscow's reluctance to allow outside scrutiny.
Some 802 Embraer regional jets with 37 to 50 seats, built on the same platform as the Legacy 600 corporate aircraft, are in service, underscoring Brazilian interest in the probe.
Embraer declined comment.
Jeff Guzzetti, a former U.S. air crash investigator, said Russia should accept assistance from Brazil, even if CENIPA can only participate remotely.
"If they don't, well, then that's a sure sign that it's not going to be a transparent investigation."
Drawing their name from an annex to the Convention on International Civil Aviation - commonly known as the 1944 Chicago Convention - the rules represent a low-key but effective form of international cooperation that has rarely been challenged.
By promoting unusually close technical co-operation across political frontiers and steering clear of issues of blame, Annex 13 has been credited with improving air safety dramatically since it was first introduced, safety officials said.
(Reporting by Allison Lampert in Montreal, Gabriel Araujo in Sao Paulo and Valerie Insinna in Washington; editing by Denny Thomas and Grant McCool)