by the National Transportation Safety Board

“ The two altimeters are served by separate static sources and there is no way in which the information on one altimeter can be displayed on the other. Any error that occurs in one system cannot be displayed on the other instrument thus providing a continuing cross-check capability for the crew. A review of the aircraft records revealed no history of altimeter malfunctions or problems. ”

“ While there is a possibility of an inflight catastrophic problem with this engine, there is no evidence such as fire damage or shrapnel damage to the recovered portions of the engine cowling to support this possibility. Catastrophic engine failures ordinarily make themselves known through fire damage and puncture damage to the surrounding structure and the engine cowling. Also, the crew was conducting a radio conversation with approach control until just before the accident and gave no indication that any problem existed with the aircraft or any of its systems. ”

“ A United Air Lines, Inc., Boeing 727-22, Flight 389 (UAL 389) was a regularly scheduled domestic passenger/cargo flight from LaGuardia Airport, New York to O'Hare International Airport, Chicago, Illinois. The aircraft had arrived at LaGuardia, on the date of the accident, following a trip from Los Angeles, California, with stops at Sacramento, California, Reno, Nevada, Denver, Colorado, and Chicago, Illinois. The flight crew of UAL 389 reported for duty at LaGuardia Airport one hour before scheduled departure where they prepared for the flight to Chicago. ”

“ Because the pawl is located in such a position as to be protected from damage during impact a possibility exists that the crew actuated the pawl to stop an unwanted nose up maneuver of the aircraft. It is also possible that the crew initiated an aircraft nose up maneuver just prior to impact and that impact forces caused a subsequent movement of the control column that activated the stabilizer brake and displaced the pawl. However, the position of the stabilizer jack screw in a 0.5 unit aircraft nose up at impact would indicate the pawl position was probably the result of impact. ”

“ This pawl is designed to stop stabilizer movement in the aircraft nose up direction. In this position the pawl was beyond the designed limit of its travel and could not function as a brake or stop device. The stabilizer trim brake system is actuated by operation of either pilot's control column to stop stabilizer out-of-trim motion. Should a runaway stabilizer cause a pitch in an unwanted direction, moving either pilot's control column in the opposite direction will stop the stabilizer from further movement in the out-of-trim direction, but will permit movement in the opposite direction. ”

“ All of the air carrier training and operations manuals reviewed stressed the fact that high rates of descent close to the surface of the earth should be avoided.
In addition to the above study, a review of Mechanical Reliability Reports on the B-727 was conducted to determine if there was any discernible trend in reports of static system problems or instrument problems traceable to the static system. No history of static systems or instrument problems was found. ”

“ At an altitude of approximately 16,000 feet the hash mark area is completely covered and the white arc is exposed to a point approximately halfway between the Nos. 1 and 2 on the face of the altimeter. As the altimeter is taken further up in altitude more of the white arc is exposed. As the aircraft descends the situation is reversed and the white arc is gradually covered up and at approximately 16,000 feet the hash marked area is again brought into view. For examples of altimeter presentations see Attachment #2. ”

“ Furthermore, the crew was in radio contact with the approach controller at this time in routine radio transmissions relating to their approach to the Chicago area. Included in this last transmission was a reference to the latest altimeter setting. Track K 047 is assessed as being associated with UAL 389 because there was no other known or observed radar traffic in the area where the track appeared plus its correlation with track A 039 which in turn can be associated with UAL 389 by comparison of the ARTCC controller's recollection of the flight path and positions of UAL 389 over known fixes. ”

“ When the broken sections of the control arm were matched, the control valve was in the reverse thrust position.
Several pieces of air distribution and air conditioning ducting were recovered. This ducting was installed overhead in the fuselage area. There was no soot or fire damage on these pieces of ducting. Both engine bleed air valves were found in the open position. The components which make up the cabin pressure control were recovered. The rate of climb indicator was intact in the panel but the pointer was detached from the shaft. The differential pressure gauge was intact. ”

“ If we assume the flight leveled off at 6,000 feet as their clearance required, and were at 6,000 at the time of their last radio communication with the approach controller, in order to proceed four miles at a speed of 240 knots and strike the water at 2120:38, the aircraft would have to average a descent rate of 9,430 feet per minute, and arrest it so as to strike the water in a nearly level attitude. ”

“ The mechanical linkage was in a 5 degree left aileron down position. The power unit was separated from the mechanical unit and the broken ends of the cable strands were necked down in the area of separation. The aileron trim indicator cable drum was in the neutral position. The elevator centering spring assembly was in the center position and could be moved to contact both stops. While the elevator control linkage was damaged, there was no evidence of pre-impact distress or failure. The elevator feel computer and feel control units were functionally tested and met all test requirements. ”

“ Examination of the recovered components of the hydraulic system reveal no evidence of pre-impact malfunction. The four anti-icing valves were recovered in the closed position which indicates the anti-icing system was "off" at impact. One pilot's directional indicator showed that the course selected, 251 degrees and the heading of 260 degrees, were in consonance with the inbound course of 254 and the wreckage distribution direction of 270 degrees. ”

“ The 100's pointer makes one complete revolution per 1,000 feet of altitude change, the 1,000's pointer makes one complete revolution per 10,000 feet of altitude change, and the 10,000's pointer makes one complete revolution per 100,000 feet of altitude change. ”

“ A United Air Lines, Inc., B-727-22, N7036U, Flight 389 crashed into Lake Michigan approximately 19.5 statute miles east of Lake Forest, Illinois, at approximately 2120 c.d.t., August 16, 1965. The 24 passengers and 6 crewmembers died in the crash and the aircraft was destroyed. ”

“ The pressurization switch and valve positions were those established for normal operation and both bleed air valves were open. In the event of fire, the checklist requires these valves be closed, as is also required in the event of a pressurization emergency. ”

“ A number of compressor blades on the front and rear compressors were bent opposite the direction of rotation and there was damage on the leading edges of many compressor blades and trailing edges of many stator vanes. Damage to the trailing edge of the stator vanes was in the direction of rotation. ”

“ The electrical stabilizer trim actuator was tested to stall torque specifications of 600-650 inch pounds in clockwise and counter clockwise directions. The unit stalled at 480 inch pounds clockwise and 456 inch pounds counter clockwise. Both the main stabilizer and autopilot cruise trim switches were found in the "on" position. ”

“ Furthermore, all altimeter settings given the crew were within one or two hundreths of the 29.92 setting and it is possible the crew did not reset the altimeter because the maximum difference in indicated altitude would be approximately 30 feet which would not be significant during a VFR approach and landing, particularly with an ILS glide slope available for the approach. ”

“ At 2119:36 the crew contacted ORD and was advised that radar contact had been established. At this time the aircraft target was 2-3 miles west of Sturgeon. UAL 389 was cleared to maintain 6,000 feet and to depart the Northbrook VORTAC on a heading of 240 degrees. The flight was advised that instrument landing system approaches were in progress on runway 14R at O'Hare and that the current O'Hare altimeter setting was 29.93. The pilot [3] read back the altimeter setting incorrectly, the controller corrected him, and the pilot repeated it correctly. ”

“ The target may be located anywhere within this rectangle. ↑ While there are potential errors in the height finding data experience has shown they are to a great extent self-cancelling. ↑ Time is expressed in hours, minutes and tenths of minutes and expressed as Greenwish Mean Time (Z) . ↑ "Heading" is actually the magnetic track being made good by the target. ↑ Ground speed is derived by continuously averaging the time vs location plot. ↑ All aircraft and pilot times are reported to the nearest whole hour. ”