quarta-feira, 19 de dezembro de 2007

Monovision Contact Lenses - for Pilots I

from "The Limits of Expertise"

R. Key Dismukes
Benjamin A. Berman
Loukia D. Loukopoulos

ASHGATE Studies in Human Factors for Flight Operations, 2007

Rethinking Pilot Error

Undershot Landing at LaGuardia, New York

Landing on Ranway 13

The plane struck the approach light system and runway deck structures. The main landing gear
separated on impact, and the airplane slid down the runway onits fuselage belly.

Of the 58 passengers and 5 crewmembers aboard, 3 passengers suffered minor injuries during
the ensuing evacuation. Both the captain and the first officer were highly experienced in the MD-88 aircraft and in the respective crew positions.

The NTSB determined that the probable cause of this accident was:

...the inability of the captain, because of his use of monovision contact lenses, to overcome his misperception of the airplane's position relative to the runway during the visual porpotion of the approach. This misperception occurred because of visual illusions produced by the approach over water in limited light conditions, the absence of visible ground features, the rain and fog, and the irregular spacing of the runway lights (NTSB, 1997b, p.vii).

1. The crew throughly discussed the challenging aspects of the approach and demonstrated good awareness of the changing weather conditions during the approach.

2. The aircraft departing ahead of flight 554's arrival rejected its takeoff, and the captain of flight 554 prepared for the possibility of a missed approach, resulting in a deviation above the glideslope.

3. The captain continued the approach, reducing pitch and power in an attempt to descend back onto the glideslope, and the airplane descended below the glidepath to the runway.

The use of monovision contact lenses may well have contributed to the accident by further imparing the captain's processing of visual information that was already substantiallly improverished and conducive to illusions; however, existing scientific knowledge is not sufficient to determine with certainty how much the contact lenses contributed to this accident.

Monovison contact lenses provide correct focus for far targets to one eye and correct focus for near targets to the other eye. This allows presbyopic individuals to discern both far and near objetcts without using bifocal or reading spectacles.

"Why the captain of Delta flight 554 was unable to land safetely?"

...resulted in his (unrecognized) degraded depth preception, and thus increased his dependence on monocular cues (instead of normal three-dimensional vision) to perceive distance. However, because of the degrade conditions encountered by flght 554, the captain was not presented with adequated monocular cues to enable him to accurately perceive the airplane's altitude and distance from the runway during the visual portion of the approach and landing. This resulted in the captain 's failure (during the last 10 seconds of the approach) to either properly adjust the airplane's glidepath or to determine that the approach was unstable and execute a missed approach ( NTSB, 1997b, p.59).

In this accident, an approach that was destabilized in response to a potential need to go around led to a snowball effect of rapidly changing events and pilot control inputs during the las seconds of the flight.

You can learn much more from the book "Limits of Expertise".

Teremos em breve a opinião do renomado médico brasileiro, Dr. Matta Machado

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