Page:CAB Accident Report, Frontier Airlines Flight 32.pdf/6

- 6 - establish surface visibility at night. The FSS observer used only one reference point, the obstruction lights at the end of Runway 4 which were one mile distant, when he determined the one mile visibility. This did not allow him to ascertain the visibility prevailing through one-half of the horizon circle, as prescribed in the Manual of Surface Observations (Weather Bureau, Air Force, Navy) Circular N.

The VOR approach procedure prescribes that the aircraft starts a descent from an altitude not below the minimum en route altitude (6,000 feet) to 4,500 feet outbound on the 211-degree radial of the VOR and executes a procedure turn not below that altitude. Upon completion of the procedure turn further descent to 3,500 feet is authorized while inbound to the station on a 031-degree course. After crossing the VOR on final approach, descent to 3,100 feet is authorized until passing Fort Intersection (a 300-degree hearing from the MLS radio beacon). Further descent to minimum altitude is then authorized. The night weather minima for this approach (circling) were ceiling 400 feet and visibility one mile for any runway. The procedure as depicted on both the U.S. Coast and Geodetic and Jeppesen approach charts provides that final approach is not authorized from the holding pattern at the VOR and that a procedure turn must be made.

Following this accident Board investigators requested FAL to instruct certain Flight 32 crews to execute VOR instrument approaches to the MLS Airport for the purpose of ground witness observations. The company complied and flights were so made on March 15 and 17, 1964. The first flight landed on Runway 30 and the second simulated a landing on Runway 30 before using Runway 12. During both flights, investigators were present at certain witness locations, With the Witnesses to compare what they saw and/or heard with their observations on the night of the accident.

The elapsed time between the reported positions of these latter flights were substantially the same as those reported by Flight 32 of March 12. During the second flight, engine r.p.m. and manifold pressure were increased to maximum limits when directly above the crash site in an attempt to duplicate the sound heard by one witness immediately prior to the crash of Flight 32 of March 12. This witness, an experienced pilot, remarked that the noise on the night of the accident was much louder, seemed to be lower in height, and was followed by complete silence.

Other witnesses recalled that what they saw and/or heard on the night of the accident seemed to be much closer or louder to them than what they saw and/or heard during these tests.

Analysis

The investigation revealed no improper procedures and/or malfunctions of the following: dispatch, ground-air communications, aircraft components, power-plants, and pertinent navigational airport aids to landing. Therefore, it is indicated that the causal factors of this accident are related to either the manner in which the aircraft was flown or to the prevailing severe weather conditions, or to a combination thereof.