29 Jun 2014
Inmarsat, the company
that officially analyzed flight data from MH370, has confirmed the assessment
but says it does not know why the aircraft experienced a power failure.
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Inmarsat,
a empresa que oficialmente analisou dados de vôo do MH370, confirmou a
avaliação, mas diz que não sabe por que a aeronave experimentou uma falha de
energia.
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"It does appear
there was a power failure on those two occasions," Chris McLaughlin,
from Inmarsat, told The Telegraph. "It is another little mystery.
We cannot explain it. We don't know why. We just know it did it."
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"Parece
que houve uma falha de energia nessas duas ocasiões," Chris McLaughlin,
da Inmarsat, disse
ao The Telegraph.
"É mais um pouco de mistério. Nós não podemos explicar. Não sabemos o porquê. Só sabemos que foi isso. "
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The Australian report
released by Australian authorities has revealed that the Boeing 777 attempted
to log on to Inmarsat satellites at 2.25am, three minutes after it was
detected by Malaysian military radar.
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O
relatório australiano divulgado por autoridades australianas, revelou que o
Boeing 777 tentou fazer log-on nos satélites da Inmarsat às 02:25 AM, três
minutos depois que foi detectado pelo radar militar da Malásia.
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This was as the plane
was flying north of the Indonesian island of Sumatra. The aircraft had
already veered away from the course that would have taken it to its
destination of Beijing, but had not yet made its turn south towards the
Indian Ocean.
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Isto foi
quando o avião estava voando ao Norte da ilha indonesiana de Sumatra. A aeronave
já tinha se desviado para longe do curso que ele teria tomado para seu
destino Pequim, mas ainda não tinha feito a sua vez para o Sul em direção ao
Oceano Índico.
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The aircraft experienced
another such log-on request almost six hours later, though this was its
seventh and final satellite handshake and is believed to have been caused by
the plane running out of fuel and electrical power before apparently
crashing, somewhere in the southern Indian Ocean. The other five handshakes
were initiated by the satellite ground station and were not considered
unusual.
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A
aeronave experimentou outra solicitação de
log-on quase seis horas mais tarde, embora este foi seu sétimo e último
‘handshake’ com o satélite e é acreditado ter sido causado pelo avião ficar
sem combustível e energia elétrica antes de aparentemente se despencar, em
algum lugar ao sul do Oceano Índico. Os outros cinco ‘handshakes’ foram
iniciados pela estação terrestre de satélites e não foram considerados
incomuns.
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Asked whether the power
interruption could have been caused by a mechanical fault, Mr Gleave said:
"There are credible mechanical failures that could cause it. But you
would not then fly along for hundreds of miles and disappear in the Indian
Ocean."
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Perguntado
se a interrupção de energia poderia ter sido causada por uma falha mecânica, o
Sr. Gleave disse: "existem falhas
mecânicas críveis que causariam isso. Mas você não voaria depois ao longo de
centenas de quilômetros e desapareceria no Oceano Índico".
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Another aviation expert,
Peter Marosszeky, from the University of New South Wales, agreed, saying the
power interruption must have been intended by someone on board. He said the
interruption would not have caused an entire power failure but would have involved
a "conscious" attempt to remove power from selected systems on the
plane.
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Um
outro especialista em aviação, Peter Marosszeky, da Universidade de New South Wales, concordou, dizendo que a interrupção de energia
deve ter sido intencionada por alguém a bordo. Ele disse que a interrupção
não teria causado uma falha de energia inteira, mas teria envolvido uma
tentativa "consciente" para remover energia de sistemas
selecionados no avião.
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"It would have to
be a deliberate act of turning power off on certain systems on the airplane,"
he said. "The aircraft has so many backup systems. Any form of power
interruption is always backed up by another system.
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"Teria
de ser um ato deliberado de desligar a energia em determinados sistemas no
avião", ele disse. "A aeronave tem vários sistemas de suporte.
Qualquer forma de interrupção de energia é sempre sustentada por um outro
sistema.
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"The person doing
it would have to know what they are doing. It would have to be a deliberate
act to hijack or sabotage the aircraft."
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"A pessoa fazendo isso teria que
saber o que elas estvam fazendo. Issoteria que ser um ato deliberado para
seqüestrar ou sabotar a aeronave."
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Electrical
Power
There
are three individual power systems dedicated to the Primary Flight Control
System, which are collectively referred to as the Flight Controls Direct
Current (FCDC) power system. An FCDC Power Supply Assembly (PSA) powers each of
the three power systems. Two dedicated Permanent Magnet Generators (PMG) on
each engine generate AC power for the FCDC power system. Each PSA converts the
PMG alternating current into 28 V DC for use by the electronic modules in the
Primary Flight Control System. Alternative power sources for the PSAs include the
airplane Ram Air Turbine (RAT), the 28-V DC main airplane busses, the airplane
hot battery buss, and dedicated 5 Ah FCDC batteries. During flight, the PSAs
draw power from the PMGs. For on-ground engines-off operation or for in-flight
failures of the PMGs, the PSAs draw power from any available source.
Fault
Tolerance
‘‘Fault
Tolerance” is a term that is used to define the ability of any system to
withstand single or multiple failures which results in either no loss of
functionality or a known loss of functionality or reduced level of redundancy
while maintaining the required level of safety. It does not, however, define
any particular method that is used for this purpose. There are two major
classes of faults that any system design must deal with. These are
·
A failure which results in some particular
component becoming totally inoperative. An example of
this would be a loss of power to some electronic component, such that it no
longer performs its
intended function.
·
A failure which results in some particular
component remaining active, but the functionality it provides
is in error. An example of this failure would be a Low Range Radio Altimeter
whose output
is indicating the airplane is at an altitude 500 feet above the ground when the
airplane is actually 200 feet above the ground.
One
method that is used to address the first class of faults is the use of redundant
elements. For example, there are three PFCs in the 777 Primary Flight Control
System, each with three identical computing ‘‘lanes” within each PFC. This
results in nine identical computing channels. Any of the three PFCs themselves
can fail totally due to loss of power or some other failure which affects all
three computing lanes, but the Primary Flight Control System loses no
functionality. All four ACEs will continue to receive all their surface position
commands from the remaining PFCs. All that is affected is the level of
available redundancy.
Likewise,
any single computing lane within a PFC can fail, and that PFC itself will
continue to operate with no loss of functionality. The only thing that is
affected is the amount of redundancy of the system.
The
777 is certified to be dispatched on a revenue flight, per the Minimum
Equipment List (MEL), with two computing lanes out of the nine total (as long
as they are not within the same PFC channel) for 10 days and for a single day
with one total PFC channel inoperative.
Likewise,
there is fault tolerance in the ACE architecture. The flight control functions
are distributed among the four ACEs such that a total failure of a single ACE
will leave the major functionality of the system intact. A single actuator on
several of the primary control surfaces may become inoperative due to this
failure, and a certain number of spoiler symmetrical panel pairs will be lost.
However, the pilot flying the airplane will notice little or no difference in
handling characteristics with this failure. A total ACE failure of this nature
will have much the same impact to the Primary Flight Control System as that of
a hydraulic system failure.
The
second class of faults is one that results in erroneous operation of a specific
component of the system.
The
normal design practice to account for failures of this type is to have multiple
elements doing the same task and their outputs voted or compared in some
manner. This is sometimes referred to as a “voting plane.’’
All
critical interfaces into the 777 FBW Primary Flight Control System use multiple
inputs which are compared by a voting plane. For interfaces that are required to
remain operable after a first failure, at least three inputs must be used. For
example, there are three individual Low Range Radio Altimeter (LRRA) inputs
used by the PFCs. The PFCs compare all three inputs and calculates a mid-value
select on the three values; i.e., the middle value LRRA input is used in all
calculations which require radio altitude. In this manner, any single failure
of an LRRA that results in an erroneous value will be discarded. If a
subsequent failure occurs which causes the remaining two LRRA signals to
disagree by a preset amount, the PFCs will throw out both values and take
appropriate action in those functions which use these data.
Additionally,
a voting plane scheme is used by the PFCs on themselves. Normally, a single
computing lane within a PFC channel is declared as the ‘‘master” lane, and that
lane is responsible for transmitting all data onto the data busses for use by
the ACEs and other airplane systems. However, all three lanes are
simultaneously computing the same control laws. The outputs of all three
computing lanes within a single PFC channel are compared against each other.
Any failure of a lane that will cause an erroneous output from that lane will
cause that lane to be condemned as ‘‘failed” by the other two lanes.
Likewise,
the outputs from all three PFC channels themselves are compared. Each PFC looks
at its own calculated command output for any particular actuator, and compares
it with the same command that was calculated by the other two PFC channels.
Each PFC channel then does a mid-value select on the three commands, and that
value (whether it was the one calculated by itself or by one of the other PFC
channels) is then output to the ACEs for the individual actuator commands. In
this manner, it is assured that each ACE receives identical commands from each
of the PFC channels.
