File: Ethiopian authorities have promised to submit the preliminary report on Flight 302 by mid-April.
ADDIS ABABA - At the headquarters of the Ethiopian Civil Aviation Authority, a paper sign balanced above room 107 and a threadbare square of carpet welcome a stream of foreign visitors to the Accident Investigation Bureau.
This modest agency is under intense international scrutiny because the results of its investigation could have far-reaching consequences for the global aviation industry.
If the investigators highlight flaws in the 737 MAX 8 that echo a recent crash of the same model in Indonesia, their report could deal a major blow to Boeing, the world's biggest planemaker and a massive US exporter.
But if investigators find Ethiopian Airlines fell short in maintenance, training or piloting, that could damage one of Africa's most successful companies, a symbol of Ethiopia's emergence as a regional power.
Disagreements have broken out in Addis Ababa between Ethiopian authorities and foreign investigators over issues, including the handling of evidence and crash site management, according to several sources close to the investigation.
An 18-strong team of American investigators has been sent to aid the Ethiopians with the inquiry, including representatives from the US National Transportation Safety Board (NTSB), Boeing, and the Federal Aviation Administration (FAA), which certified 737 MAX planes as safe.
Some foreign officials are also unhappy about the prominent role Ethiopian Airlines played in the probe, suggesting a possible conflict of interests, they said.
Ethiopian Airlines' spokesman Asrat Begachew said the carrier was supporting the investigation. "We are not taking the lead," he added, declining to comment further.
Under global aviation rules, interested parties like airlines and manufacturers are discouraged from speaking publicly about the investigation.
Yet in the first days after the Flight 302 crash, Ethiopian Airlines made all of the public statements, including announcing the black box recorders would be sent overseas for data extraction.
It was not until six days after the tragedy that the Ministry of Transport began briefing the media and public.
Hours after the crash, Ethiopian Airlines tweeted a picture of its CEO Tewolde Gebremariam holding a piece of debris in the crater of the crash site, surprising aviation experts who said the site should have been preserved for investigators.
One of the two black box recorders of the Ethiopian Airlines 737 MAX which crashed minutes after taking off from Addis Ababa airport.
The cockpit voice and flight data recorders were recovered the day after the crash, but it took Ethiopian investigators three days to decide where to send them for the information to be extracted and decoded.
Like many fast-growing players, the Ethiopians do not have the technology to perform the task.
In a sign of the distrust between the parties, the Ethiopians turned down an American offer to perform the analysis in the United States, according to two sources.
US authorities declined to comment.
Ethiopian Airlines CEO Tewolde personally approached German authorities to request to send the black boxes to Germany to have the data extracted there, a separate source with knowledge of matter told Reuters. Airlines are not usually involved in such decisions, according to current and former investigators.
The airline could not comment on the investigation, a spokesman said in response to questions about the incident.
However German officials said they too did not have the most recent software needed to extract the data, so the devices were eventually sent to France.
Partial data from the flight data recorder was shared informally late on Monday with US and French investigators in Paris, but nothing from the cockpit voice recorder, three sources familiar with the matter said.
It is common for the host investigator to closely guard voice recordings to protect privacy but unusual for relatively little data to be available a week after being downloaded.
Ethiopia said on Thursday it had begun analysing cockpit data and was working with US and European experts.
File: More than 300 Boeing 737 MAX jets have been grounded worldwide after 346 people died in two crashes, one in Indonesia in October and one in Ethiopia last month.
Most crash investigations end up pinpointing a combination of factors.
For decades, reconstructions by independent investigators have been credited with reducing air accidents to record low levels.
The system of co-operation works by sticking to technical details and avoiding blame or other agendas.
Safety experts worry that too many turf battles can cloud the progress of an investigation.
"The sole purpose of an accident investigation is to reduce the chances of something ever happening again," said Paul Hayes, safety director at the Flight Ascend Consultancy.
The Flight 302 crash triggered the global grounding of Boeing's 737 MAX jets, wiping billions off the company's market value.
Also on the line are more than $500-billion worth of 737 MAX orders.
People stand near collected debris at the crash site of Ethiopia Airlines near Bishoftu, a town some 60 kilometres southeast of Addis Ababa.
Responsibility for leading the probe fell to Ethiopia because the crash occurred on its soil. Nairobi-bound Flight 302 went down into farmland minutes after take-off from Addis Ababa.
The crash killed people from 35 countries, all of which are also entitled to examine the crash site and join in the investigation. America, China, Kenya, Britain, Canada, Israel, France and other nations have sent investigators.
Some nations were unhappy that Ethiopia was using heavy earth-moving equipment at the site, potentially damaging evidence or human remains, although others said that was the only way to move heavy items such as engines.
Some foreign officials also complained of being unable to access the site in the days after the crash.
The European Union's aviation safety agency, EASA, waited more than a week to be allowed to join the crash investigation.
"The Ethiopian investigation body is very keen to keep a very, very closed circle around the investigation," EASA Executive Director Patrick Ky told the European parliament on Monday.
Musie Yehyies, spokesman for Ethiopia's Ministry of Transport, said the government had been quick to share information about the crash. He denied there was any mistrust between the Ethiopians and other parties.
The ministry did not respond to requests for comment on the airline's role in the investigation or any potential conflict of interest.
Ethiopia's Accident Investigation Bureau and civil aviation authority, which fall under the transport ministry, declined to comment on the investigation or any grievances of parties involved. Boeing, the FAA and the NTSB also declined to comment.
by Maggie Fick and Tim Hepher