* Black box used magnetic audio tape
* Crash inquiry continues; all theories still on the table
* Aircraft had lost speed and height before final plunge
(Adds details, expert on loss of control, background)
By Alexandria Sage and Tim Hepher
PARIS, Aug 7 Cockpit voice recordings from an
Air Algerie jet that crashed last month in northern Mali are
unintelligible, investigators said on Thursday, depriving them
of vital clues on what sent it into a sudden plunge that killed
all 116 passengers and crew.
The McDonnell Douglas MD-83 aircraft, en route to Algiers,
smashed into the ground on July 24 south of the Malian town of
Gossi, near the border with Burkina Faso.
Experts in Paris have been examining the two "black boxes"
retrieved from the wreckage. They have been unable to extract
information from one, Remi Jouty, president of France's BEA air
accident investigator, told a news conference.
The voice recorder on the 18-year-old aircraft used magnetic
audio tape, a system since replaced by digital methods. The tape
was broken or crumpled in places. Even after it was repaired,
the pilot conversations could not be understood.
"There is sound on the tape but it is unintelligible," said
Jouty, whose agency has been asked to support Mali's own
"The device seemed to be recording, but we don't yet know
why it did not work, except that this was not a result of the
crash itself," he told reporters, adding that first indications
were that it was a "simple technical problem".
French officials have said they believe bad weather was an
important factor in the crash of flight AH5017 but have not
ruled out other explanations.
"We're trying to avoid overly hasty theories," Jouty said,
adding all hypotheses were still on the table.
The pilots had asked for permission to alter their route
because of a storm as they flew north after taking off from the
capital of Burkina Faso, Ouagadougou.
The jet made a detour to steer around the storm cell, but as
it did so it gradually lost height and speed, according to data
from the other black box presented at the BEA's headquarters.
After largely resuming its original course, the aircraft
abruptly turned back on itself to the left and entered a
It hit the ground at high speed and the impact was
"extremely violent", Jouty said.
The strong concentration of debris in one spot on the ground
leads investigators to believe that the plane crashed rather
than disintegrating in the air.
Jouty said it was too early to explain the unusual pattern,
but experts said attention was likely to focus on what happened
in the crucial minutes as the MD-83 steered round the
Just two minutes before the detour, the aircraft had reached
its cruise height of 31,000 feet and cruise speed of 290 knots.
By the time it tipped leftwards into a sudden and spiralling
descent, its speed had fallen to 160 knots, the BEA said.
"It seems for some reason the aircraft became too slow and
may have stalled, after which control was lost," said Hugh
Dibley, a council member of the Royal Aeronautical Society, who
took part in industry work on "upset prevention and recovery".
Training to avoid loss of control and help pilots deal with
unexpected events, such as exceptional winds, has been one of
the aviation industry's top safety priorities in recent years.
Between 2001 and 2011, accidents resulting from a loss of
control in flight were the leading cause of deaths in commercial
aviation, according to a recent set of guidelines published by
the International Civil Aviation Organization.
"Training and knowledge of the reduced performance of
aircraft at high altitude are the most important ways of
preventing such accidents," Dibley said.
Without the voice recordings, however, experts face a
complex task in establishing what happened in the cockpit,
including whether the pilots had noticed a technical fault.
Jouty said investigators would continue to try to extract
useful recordings from the tape and meanwhile build up an
alternative picture of what the pilots may have been facing by
studying air traffic control recordings and other data.
Investigators are also trying to model the jet's performance
with the help of U.S. planemaker Boeing, which bought the
manufacturer McDonnell Douglas in 1997, as well as the U.S.
National Transportation Safety Board, Jouty said.
"Boeing is providing technical assistance to the (NTSB)
which is assisting authorities who are investigating the
accident," a Boeing spokesman said.
A first report into the crash will be published in
mid-September, said the head of the Malian investigating
(Editing by Andrew Roche, Larry King)