Page:CAB Accident Report, Mohawk Airlines Flight 112.pdf/7

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At 1644, prior to Mohawk Flight 112 departure from the ramp, the siren on the fire house at the south ramp sounded. The crash equipment responded but upon being advised by the ground controller that the tower had not activated the siren, it was agreed that lightning must have struck the telephone wires and set it off. The crash equipment was returned to its quarters at 1648.

When the siren near the tower sounded the local Weather Bureau Observer was looking at the transmissometer graph to check on his visual measurement of existing visibility. While this instrument had not been formally commissioned it was recording a transmissivity which can be converted by reference to tables into runway visibility. This observer did not assess a visibility value to the transmissometer data at that time. The observer then called the control tower to inquire why the siren had sounded and was informed of the accident. At the same time he checked with the tower controller and both agreed that the visibility was then one-half mile. The Weather Bureau Observer continued taking the observation for a special report. As he walked outside he noted rain and 1/2 inch hail. He observed the wind to be east-southeast at approximately the same time Mohawk Flight 112 struck the ground. The special observation was completed at 1652. At 1649 the tower, by telephone, advised the Fire Department that Mohawk had crashed. Fire and crash equipment previously alerted by the spurious signal responded immediately. At 1651, the equipment was on the scene and by 1653 the fire was under control.

The aircraft contacted the ground 220 feet south of the centerline and 4,668 feet from the threshold of runway 28, and it came to rest 566 feet south of the centerline and 5,022 feet from the threshold of runway 28.

Contact with the ground was first made by the left wing tip. The aircraft then began to disintegrate in a left curving turn (see Attachment 1), cartwheeling, and came to rest on a magnetic heading of 280° in a drainage excavation approximately 6 feet deep adjavent to the takeoff runway. The aft section of the fuselage with empennage attached fractured around the circumference immediately behind the wing rear spar, pivoting approximately 90° coming to a stop in virtually an upright position against the remaining portion of the left wing and engine nacelle. The forward section was reduced to a mass of torn, twisted, and compressed metal. The center section remained intact and attached to the center wing panel, sustaining only interior damage. During and following the principal impact, all 20 double passenger seats were town free from their attachments. Most seats were thrown free of the wreckage. Both engines were torn free of the aircraft and were relatively intact. The propeller ground slash marks indicated that all propeller blades were intact prior to impact. Test of the propeller governors indicated that the engine RPM at impact were 2760 and 2830 for the left and right engines, respectively. Rated takeoff RPM is 2800. Propeller shim plate impact markings indicated that the left propeller blade angle was 34 degrees, and the right propeller blade angle was 33 degrees. Propeller performance data indicated that at this blade angle and RPM, the left propeller would have been absorbing 2440 BHP at 90 knots, and 2380 BHP at 100 knots. Similarly the right propeller power absorption would have been 2440 and 2360 BHP at these airspeeds, respectively. Wet rated takeoff power for this engine is 2400 BHP. Using left powerplant data as more representative because of impact conditions, the groundspeed at impact was calculated to be 92 knots.