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The records indicate that the members of the flight crew were properly certified and qualified to operate the equipment, that they had had sufficient rest prior to originating the flight at Mexico City, and they had not exceeded the maximum allowable monthly flight time.
Company records indicate that the aircraft was within allowable gross weight and c. g. limits.
The takeoff was observed to be normal, and at 0202:38, when the flight was five miles north of the VORTAC, a radar handoff from Departure Control to the Center was effected. The recordings of transmissions from Flight 304 failed to reflect any apprehension on the part of the captain. At 0203:15 he acknowledged instructions to contact the Center, however, he never complied with this instruction. It is therefore believed that at approximately this time or very shortly thereafter an emergency occurred. The facsimile profile indicates that at this time the flight should have accelerated to or near en route climb speed, traveled approximately 12 miles, and reached an altitude of about 4,000 feet. The center controller stated that he last observed the radar target at eight miles on the 030-degree radial of the VORTAC. Since the aircraft was found 6.5 miles northeast of this position, it is obvious that there was a time lapse between this observation and his inquiry about the flight as 0205:40. At this time both controllers had lost radar contact. Allowing for controller recognition and time for the radar target to fade, it is probable that Flight 304 crashed at approximately 0205. While the time plot in Attachment B had been styled to an impact time of 0205, it is interesting to note that in developing this profile, any attempt to use 0205:40 as the end-point, associated with normal climb speeds, resulted in an excess of 35-to-40-seconds.
The recovery of all powerplants and portions of all extremities of the aircraft from a closely confined area indicates that the aircraft was structurally intact at the time of contact with the water. Based on the Board's observations over the years that the altitude of a diving aircraft tends to flatten between the times of the nose and wing contact, it can be assumed that N8607 struck the water at some dive angle in excess of the 20-degree indication in the damage pattern of the powerplants. The fact that the engines were being operated in the reverse thrust regime is in itself indicative of an attempt by the crew to recover from a diving upset into a steep dive, attributed to the successful recovery to the use of a previous thrust which, in addition to providing drag forces, produces a noseup pitching moment. Furthermore, it can be concluded from the symmetry of the powerplant damage pattern and from the small wreckage area that the aircraft was essentially level, laterally, at impact.
Examination of the horizontal stabilizer lower sprocket failure reflects that the sprocket rivets sheared during rotation of the sprocket in the sense of ANU. The Board can easily attribute the axial, non-rotational scoring of the sprocket shaft by the needle bearings, to impact damage. It cannot, however, accept the rotational pattern of rivet shear or the previously mentioned abnormal, displaced wear pattern of the unit as being associated with crash forces. These latter indications along with the discovered positions of the two irreversible-action stabilizer jackscrews reflect that the stabilizer drive unit had been operating in an abnormal condition over a period of time, then failed while being operated in an ANU direction from the full, or near full, AND position.
