Page:CAB Accident Report, American Airlines Flight 383.pdf/11

– 10 – in the ATC Manual of Air Traffic Control Procedures. The manual defines "visual approach" as follows: "An approach wherein an aircraft on an IFR flight plan, operating in VFR conditions and having received an Air Traffic Control authorization, may deviate from the prescribed instrument approach procedures and proceed to the airport of destination by visual reference to the surface."

A visual approach clearance does not constitute cancellation of the flight's ITR clearance and ATC is required to provide appropriate minimum aircraft separation standards. In this case cancellation of the clearance was not requested and ATC minimum aircraft separation requirements remained in effect.

1.10 Aerodrome and Ground Facilities

Runway 18, 8,600 feet long and 150 feet wide, is equipped with high intensity runway lights and a standard configuration type "A" approach lighting system with sequenced flashing condenser (strobe) lights. All lights were on their highest intensity setting and operating satisfactorily at the time of the accident. The published airport elevation is 890 feet above sea level.

1.11 Flight Recorder

The aircraft was equipped with a United Data Control model F-542 series flight recorder which scribes traces of inflight pressure altitude, indicated airspeed, magnetic heading and vertical acceleration as a function of time. Examination of the flight recorder record for that portion of the flight from takeoff at LaGuardia to the initial descent into Cincinnati area revealed no abnormalities or unusual occurrences. In order to more closely examine the final portion of the flight, a large scale plot of the recorded parameters was prepared for the descent from 7,000 feet m.s.l. to impact, encompassing the last six minutes of flight (see Attachment #2). The plot shows that a continued descent from 7,000 feet to 2,000 feet was maintained on a heading of approximately 305 degrees with a brief level off at 5,000 feet m.s.l. During this descent the airspeed was reduced from 350 knots to 250 knots with descent rates ranging from 2,800 to 3,000 feet per minute. Level off was made at 2,000 feet (1,110 feet a.f.l.) and the aircraft remained at this approximate altitude for 1 minute 20 seconds while the airspeed was further decreased to 190 knots. While maintaining this altitude the aircraft turned to a northerly heading on the downwind leg and subsequently initiated a left turn toward the base leg. At 1859:57 a descent from 2,000 feet (1,110 feet a.f.l.) commenced. It was noted that a relatively steady descent averaging about 800 feet per minute was maintained for approximately 70 seconds and that the airspeed was further reduced to 160 knots. At this point the aircraft was holding a west-northwesterly heading on the base leg. The readout shows that at 1900:53 a left turn was initiated toward the final approach course for runway 18 and at 1901:07, (20 seconds before impact) at an altitude of 1,100 feet (210 feet a.f.l.), the descent rate increased to approximately 2,100 feet per minute. This rate of descent was maintained for about 10 seconds to an altitude of approximately 725 feet (165 feet below published field elevation) with the airspeed holding at 160 knots. The descent rate then decreased to about 625 feet per minute for approximately the last 10 seconds of flight with the airspeed decreasing to 147 knots at impact. The last readable heading point obtainable from the recorder was 270 degrees at time 1901:12. However, and individual engraved mark of the heading trace was found