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Gerry Byrne: Cork crash has chilling echoes of Polish tragedy

Yesterday's fatal crash of the Manx2 has chilling parallels with the crash of a Polish Air Force passenger jet carrying the Polish president Lech Kaczynski and 95 other senior Polish officials and relatives at Smolensk last year.

Both occurred in heavy fog. In the Smolensk crash the pilot felt under pressure to land, even though air traffic controllers advised against it.

Fog is a capricious element and, while one moment an approach looks clear, in seconds it can swirl in and obstruct the runway. Flying through fog is also extremely disorienting and can give rise to a condition known as vestibular disorientation, where the pilot's natural balance convinces him the aircraft is flying straight and level when the opposite is the case.

At this early stage of the investigation there are no indications of any faults with the airliner. It stems from a design that originated in the 1960s and the aircraft that crashed in Cork was manufactured in 1992. Such an aircraft would be designated as 'ageing' and, while perfectly safe to continue flying, would be subject to extra maintenance checks.

There have been about 16 serious accidents involving the Metroliner. In 2005 a New Zealand Post Metroliner crashed, and a week later another crashed in Queensland, Australia, killing 15. No connections were found between the two.

The aircraft carries 19 passengers, a number contrived to avoid regulations such as the need to carry cabin crew. It may also be below the size threshold for the installation of 'Black Box' flight recorders, the Flight Data Recorder (FDR), which records the aircraft's progress though the air, and the Cockpit Voice Recorder (CVR), which records conversations between pilots on the flight deck.

Last night both the recorders were recovered from the wreckage. The FDR will yield valuable information regarding the aircraft's progress though the air although many recorders of the aircraft's vintage supplied limited information, especially if they were manufactured for US operators. For example, older FDRs could show parameters like the aircraft's heading, altitude and speed but might not reference issues such as what happened with controls like ailerons, flaps and the rudder.

But even the best FDRs have limitations. They may show what the aircraft did, but not why. And that is why the CVR can prove invaluable.

Very often the pilots have described the incidents leading up to crash, and highlighted issues that might not be recorded on the FDR.

Even grunts and the rate at which they speak can tell investigators a lot about their state of mind, whether they were panicked, or if they were bewildered by something unusual happening to their aircraft.

In the case of USAir Flight 427, which crashed on approach to Pittsburgh in 1994, investigators were able to demonstrate that the rudder pedal had jammed because of the unusual laboured grunts emitted by the co-pilot flying the aircraft.

Shortcomings in the Black Boxes may be compensated to some degree by the conversations between the cockpit and the air traffic controllers at Cork. These are always recorded. Tapes of the radar returns from the doomed aircraft will also be closely studied although this will be less reliable close to the ground. They will, at the least, reveal the aircraft's rate of descent and speed.

But initial probes will take place on the runway as investigators sift through the wreckage. They will first try to establish where the aircraft first hit the ground and will carefully look for scrapes on the tarmac, or furrows in the grass verge and attempt to relate them to parts of the aircraft. The aircraft was found upside-down and investigators must figure why this happened.

One reason for an inverted wreckage is that the aircraft came down heavily and at speed on its nose and that this caused it to somersault.

However, pictures of the wreckage show the nose wheel is still in position: in a heavy nose down impact the nose-wheel would more than likely have snapped off.

A second, more likely explanation is that there was a wing strike, where the aircraft wings were not level and one wingtip forcibly struck the ground in a manner which caused the aircraft to flip over onto its back.

If there was a wing-strike, could the fog have contributed to the pilot's inability keep his aircraft level?

Because of vestibular disorientation, the US armed forces lose on average between 20 and 30 aircraft annually, the Federal Aviation Administration lists it as the leading cause in 15pc of fatal small aircraft crashes and it was blamed for the crash of seven Dutch F-16 jet fighters.

It can occur when pilots lose visual clues to their surroundings and, either because they misread, mistrust or ignore their instruments, allow the aircraft to wander off course, develop an excessive bank and eventually spiral out of control with the pilot often not realising until too late.

Experiments conducted more than 20 years ago by the University of Illinois demonstrated that, with the autopilot switched off, a pilot can lose control in as little as 20 seconds if he is denied sight of his instruments. The human body has its built-in spirit level in the inner ear which controls our balance. Also known as the vestibular system it consists of the semi-circular canals of the inner ear plus a system of small fluid-filled sacs containing sensitive hairs, which respond to gravity.

Pilots flying "blind" are particularly vulnerable to a phenomenon known as the "leans". This occurs when the vestibular system of the inner ear gives a false reading after a long period of being banked at an angle, or in a turn, such as a prolonged period in a holding pattern, and they imagine they are flying level. When they level their aircraft according to their artificial horizon, they often mistrust the instrument because their vestibular system has fooled them.

A confused pilot will often apply the wrong controls and precipitate a fatal spin. Closer to the ground it could result in a wing-strike.

Investigators will try to establish is this, or something similar happened to the Manx2 pilots. The 20-minute holding pattern they flew would have been more or less circular or racetrack shaped and a prolonged period of constant turns in the same direction could give rise to a case of the leans.

Irish Independent