Pilots flying in fog are particularly vulnerable to disorientation but the black boxes will provide vital information about the aircraft’s flight
TRYING TO land an aircraft in bad fog is always fraught with uncertainty and investigators from the Air Accident Investigation Unit (AAIU) will try to understand why the pilot of the Manx2 Fairchild Metroliner tried to land after aborting two earlier attempts and circling for 20 minutes in a holding pattern hoping for conditions to improve.
There are no suggestions that conditions improved significantly, so it is unclear why the pilot attempted a third landing rather than divert in conditions in which earlier attempts were felt to have been unsafe.
Regulations require passenger aircraft to have sufficient fuel for both a hold and diversion to the nearest airfield, so shortage of fuel is unlikely to be an issue.
Fog is a capricious element and while one moment an approach appears clear, within seconds fog can swirl in and obstruct the runway. Flying through fog is also disorientating and can give rise to a condition known as vestibular disorientation, where the pilot’s natural balance organs convince him or her the aircraft is flying straight and level when in fact the opposite is the case.
At this early stage of the investigation there are no indications of any faults with the aircraft. It was produced by the Fairchild company which has in recent years specialised in continuing the production or operation of aircraft whose original manufacturer has ceased production.
The Metroliner is derived from a design originated in the 1960s and the aircraft which crashed in Cork was manufactured in 1992. An aircraft of that age would be designated an ageing aircraft and, while perfectly safe to continue flying, would be subject to extra maintenance checks to ensure its reliability.
The aircraft carries 19 passengers, a number contrived to avoid regulations such as the need to carry cabin crew. It is believed none was aboard the aircraft that crashed.
The aircraft’s “black box” flight recorders have been recovered, it emerged last night. The flight data recorder (FDR) will contain information on aircraft’s progress through the air, while the cockpit voice recorder (CVR), records conversations between pilots on the flight deck. The FDR will yield valuable information regarding the aircraft’s progress through 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 controls like ailerons, flaps and the rudder were operated by the pilots. But even the best FDRs have limitations. They may show what the aircraft did, but not why. And that is why the Cockpit Voice Recorder can prove invaluable. Very often the pilots have described the incidents leading up to the crash, and highlighted issues which 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 or not they were panicked, or if they were bewildered by something unusual happening to their aircraft. The conversation between the cockpit and the air traffic controllers at Cork will be important. Tapes of the radar returns from the aircraft will also be closely studied though this will be less reliable close to the ground. They will, at the very least, reveal the aircraft’s rate of descent and speed.
Investigators will first try to establish where the aircraft first impacted 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 there will be pressure on investigators to figure out how and why this happened.
One reason for inverted wreckage is that the aircraft came down heavily and at speed on its nose and that this caused it to somersault. However, photographs 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 or been forced up into the fuselage. 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 that caused the aircraft to flip over on to its back.
If there was a wing strike, could the fog have contributed to the pilot’s inability to keep his aircraft level? The US armed forces lose an average of between 20 and 30 aircraft annually because of vestibular disorientation.
Pilots flying in the dark, in fog or in cloud 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.
Investigators will try to establish if this happened to the Manx2 pilots. The 20-minute holding pattern they flew would have been circular or oval in shape and a prolonged period of constant banking in the same direction could easily give rise to a case of the leans.