Posted by : Des Ross Friday, 25 July 2014

Although we have had a few disastrous months in 2014 with the loss of two Malaysian Airlines Boeing 777 aircraft, MH370 and MH17, followed this last week by the loss of the Taiwanese Trans Asia Airlines ATR72 Flight GE222 and the Air Algerie MD83 Flight AH5017, you still run a much greater risk of death or injury by driving your car to the supermarket than you do by flying across the World.

The difference, of course, is that car accidents usually claim 1 to 4 lives at a time whereas an air crash can account for 200 to 400 lives, hence making a much greater media spectacle and causing a great outpouring of grief across the World.

Flying on one of the World’s airlines in a modern jet aircraft is safe because of the immense international system which makes it so.  When an incident or an accident occurs it is thoroughly investigated by well trained and qualified aircraft accident investigators.  Except in the case of criminal intent, and MH17 appears to be a case of criminal / terrorist intent, then such investigations are conducted with the intention of learning lessons to avoid a recurrence rather than to apportion blame. 

So, part of the system is to record, as far as is practical, all the activities that occur in the air and to make all possible information for investigation when an accident occurs.

This is where the two recorders come in.  Someone in the media has dubbed the recorders as “black boxes” and this has been propagated by ignorance.  In fact they are bright orange and have always been bright orange.  They have never been black.  The orange colour is to make them as visible and easy to find as possible amongst the debris of an aircraft crash.

You have all seen the so called “pro-Russian rebels” carrying these orange boxes on the TV news during the last week.

There are two boxes.  One is the COCKPIT VOICE RECORDER (CVR) and the other is the FLIGHT DATA RECORDER (FDR).   So, what is their purpose?

The CVR, as its name implies, records all conversations and sounds on the flight deck (the cockpit) of the aircraft.  The recording continuously loops and overwrites the earlier content so that when it stops and is examined it will only contain the last two hours of the flight activities.  It will include all conversation between the pilots, all communications with Air Traffic Control, the sound of the flight attendant delivering a cup of coffee to the pilots and all gongs, warning bells, and other miscellaneous sounds.

In the case of MH17 it is possible that the last seconds of the tape may include the sounds of an explosion or other noises that may help to identify what occurred in the dying moments of the Boeing 777–200.  It may also record a discussion between the pilots and air traffic control which would explain the diversion north of the planned flight track which the Russian military now claims had happened.

The FDR orange box records the technical parameters of the aircraft and its operating systems.  It includes airspeed, altitude, heading, engine power settings, cabin pressure and temperature, the position of controls, and many other technical items.

In the case of MH17 and the other aircraft which have crashed these last days and months, the FDR should reveal technical details of the last moments of their flight. 

In the case of MH17, a very important measurement will be the cabin pressure and temperature.Most regular air travellers know that the aircraft cabin is set to simulate an altitude of 8,000 feet above sea level and a normal temperature around 22 C.  This is comfortable for us humans to breathe and relax.  This is vital to modern jet airline flight because the air on the outside will not sustain life!   When the aircraft is flying at 33,000 feet above sea level, the air does not contain enough oxygen for us to breath and the temperature is as low as -56 C.  Compare this to your home refrigerator which is normally about +3 C.  So, you simply could not survive without the pressurised cabin of the aircraft. 

Therefore, if the FDR shows that, at the end of the flight, there is a sudden loss of pressure rather than a gradual drop in pressure, it will confirm that there has been a massive explosion and break-up of the cabin structure.  If the pressure loss was slow it would suggest that only a relatively small hole was made in the aircraft body which allowed the air pressure to bleed off.   This finding will help to confirm what caused the explosion and destruction of the aircraft.

It is of little comfort to the relatives and loved ones of the lost passengers and crew, but if the decompression is sudden and instantaneous, it will also mean that they died almost instantly without pain.  It is not possible for the human body to survive the decompression from 8,000 feet to 33,000 feet and a temperature change from +22 C to -50 C within a matter of 2 or 3 seconds.  The traumatic effect of these changes will kill instantly.

So, whilst the readings on the FDR will provide vital information for the accident investigators, unfortunately it will not reveal who was responsible for the tragedy.

That becomes a job for the sleuths and police investigators on the ground.

There is much more to the accident investigation which includes the painstaking examination of the wreckage and identification of the explosives and missile that brought the aircraft down.

Of course, there is a problem in that the rebel forces which are in control of the area of the crash site have had several days to interfere with the wreckage and remove incriminating evidence which they might recognise.

This gross contamination of the crime scene and the removal of vital evidence is, in itself, a crime which should be punished by the full force of international law.

We can only hope that the investigation will also identify the missile and the perpetrators of this horrendous crime and that the individuals will be brought to justice.

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