Page:CAB Accident Report, Northeast Airlines Flight 715.pdf/6

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operated at a low intensity Certain atmospheric debris may give the white lights an orange or brownish tint However, the red lights are not affected and the principle of color differentiation is still applicable

Following the acc1dent, Federal AViation Agency (FAA) Systems Maintenance personnel ground checked the ruuway 31 VASI installation for proper operation and approach slope alignment. All light Units, with the exception of the in- board unit on the right side doanind.bar, were within proper tolerances._ This unit was found at a setting of 2.5 degrees. However, it should be noted that one unit out of tolerance does not affect the overall Operation of the system.

Approximately six hours after the acc1dent the FAA conducted a flight check on the VASI in which the light intenSIty, glide slope angle, angular coverage, and obstruction clearances were inspected. The report of this check showed aid of these items to be satisfactory Wlth a computed glide slope angle of 2.90 degrees.

The on-glidepath corridor or wedge is 42 feet thick directly above the dike on the approach end of runway 31. The bottom of this wedge is 38 feet above the tap of the dike

The physical dimenSions of the DC-6B are such that the distance from the fusslage reference plane to the ground is 8 feet 10 inches, and the distance from the fuselage reference plane to the pilot's eye level is approximately 4 feet 6 inches. The total measurement from pilot's eye level to the bottom.of the main*Landing gear wheels is approximately 13 feet 4 inches.

The pertinent Federal AViation Regulation (EAR) relating to the utilisation of a.VASI system is FAR 91.87(d)3. It states, "an airplane approaching to land on a runway served by a visual approach slope indicator shall maintain an_aiti- tude at or above the glide slepe until a lower altitude is necessary for a safe landing."

1.9 Communications

All air/ground communications were conducted in accordance with applicable regulations.

1.10 Aerodrome and Ground Facilities

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LaGuardia Airport is bounded on three Sides by water. Because the surface of the airport is located at a height nearly level With the water, a dike has

i] The VASI glide slepe for runway 31 is attained by adjusting each light Unlt to a predetermined angular setting Settings are 3.13 degrees for the upwind units and 2.63 degrees for the downwind units These diverging angular settings produce a wedge-shaped band or lighrpath. The centerline of thelwedge is at a theoretically effective Visual approach angle of 2.38 degrees. Frmm any- where Wlthln this Wedge-shaped band the downwind lights appear white and the upwind lights appear red.