* Conducting air accident inquiry in war zone will be tough
* Access to site, rival accusations of blame complicate task
* Ukraine has legal authority, seeks international inquiry
* Black boxes may offer little insight into cause
* Beyond what happened, pressure to know who was responsible
By Victoria Bryan and Tom Miles
BERLIN/GENEVA, July 18 (Reuters) - As international investigators head to rebel-held eastern Ukraine to piece together what - and who - caused a Malaysian airliner to plunge into the steppe, securing evidence in the middle of a war zone is a major challenge.
Proving what happened beyond doubt and to the satisfaction of the warring parties may already be all but impossible, after local people and rebel fighters have spent 24 hours sifting and moving debris and bodies and Ukraine and Russia make detailed allegations against each other and argue over the black boxes.
In principle, all sides support a call, backed by Russia and other world powers in the U.N. Security Council, for an impartial international investigation. But even agreeing the Kiev government has jurisdiction in a region where separatists have declared their own republic poses difficulties.
“It is a national competence, and that is part of the problem in this case,” said Roland Bless, spokesman for the Swiss chair of Europe’s OSCE security body, referring to rebel claims to sovereignty in the eastern region of Donetsk.
The OSCE said some of its staff had visited the impact site on Friday, a day after the aircraft was lost with 298 aboard.
Separatists have said they have recovered both flight recorders from the Boeing 777 and are willing to cooperate, including by holding a ceasefire. But officials in Kiev accused them of trying to spirit the black boxes, and a missile launcher they used to shoot it down, across the nearby Russian border.
Russia, which under normal circumstances would have no obvious stake in the air accident investigation of a U.S.-made Malaysia Airlines plane flying from Amsterdam to Kuala Lumpur, has said it does not intend to take the recorders.
In a typical crash inquiry, it is up to Ukraine, on whose territory the plane came down, to secure the area and recover the flight data and cockpit voice recordings and liaise with the manufacturer to ensure their contents are downloaded correctly.
Ukrainian President Petro Poroshenko has already spoken with other world leaders about the running of an international investigation, which could allay some of the rivalries.
“It’s very important that unbiased international experts will be the first persons who get access to the black boxes,” said Ukraine’s U.N. ambassador in Geneva, Yurii Klymenko.
“The issue is who will ... open the boxes? We would like to have the true information, not the fake one.”
If another body obtains the recorders it must hand them over, otherwise it will run the risk of corrupting the data or being suspected of trying to destroy it, said London lawyer Jim Morris from Irwin Mitchell, a former British military pilot.
After a Soviet fighter shot down Korean Air Lines flight KAL 007 in 1983 when it strayed into Soviet air space, Moscow found the black box - but only handed it international investigators after the end of the Cold War nearly a decade later.
The United Nations air safety arm, the International Civil Aviation Organization, said it has made an offer to Ukraine to put together a team of international investigators.
Brian Alexander, an aviation attorney at New York law firm Kreindler and Kreindler, said that despite the “dicey” situation in the area, “with the international pressure, the community should be able to get a team to the site and allow an investigation to proceed as normally”.
“But trying to figure out who provided the training, the weapons, that’s a much thornier issue,” he said, adding that investigators would be looking for debris not part of the plane.
However, the flight data may offer little information on what caused the 777 to come down. An explosion by a heavy missile that blew the aircraft apart could show only as a sudden, catastrophic collapse of all the onboard systems.
If, as Ukraine alleges, MH17 was hit by an SA-11 missile, there is a good chance the pilots did not see it coming, leaving little or no informative trace on the cockpit voice recording.
The wreckage might show traces of explosives that could indicate the blast of a warhead. Somewhere in the debris strewn for miles across the steppe might be remnants of a missile. But finding them will be hard and proving their provenance after the confusion and mutual accusations of the first day will be tough.
A former British airman said: “Any recovered missile fragments could be analysed. But unless there is a stark difference in the exact type of arms both sides hold, differentiating is not easy.”
In fact, all sides use similar, former Soviet hardware.
Washington security expert Anthony Cordesman of the Center for Strategic and International Studies wrote in a report that while the use of an SA-11 or SA-17 radar-guided missile seemed likely, determining whether it was fired by pro-Russian rebels or by Ukrainian or Russian armed forces would be problematic.
Cordesman suggested that any of these three parties might have opened fire in an area of high tension, believing their target to be hostile rather than a civilian aircraft.
Noting in 1988 that the U.S. navy shot down an Iranian airliner that Washington said was mistaken for a warplane, he said: ”Human error does happen, particularly when both sides may be on the edge of overreacting and have virtually no real operational experience.
“The fact this is a horrible human tragedy should not lead to rushed judgment as to motive, guilt, or intent.” (Editing by Alastair Macdonald)