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parts of the mid-spar balance weight. The rudder PCU, the lower hinge and actuator
fittings, as one unit, were recovered from the river and found to be severely damaged.
Vertical stabilizer (Figure 10.g) - All the vertical stabilizer spar terminal fittings and the
fin trailing edge hinge fittings were accounted for at the crash site, indicating that the
vertical stabilizer structure was intact at impact. Damage to the vertical stabilizer
precluded a full accounting of the front spar and interspar structure. The rudder upper
hinge showed evidence of over-travels in the left and right directions. Other hinges
exhibited twisting damage consistent with excessive rudder movement in the clockwise
direction (looking forward). However, it could not be determined when the twisting
damage was incurred.
Rudder (Figure 10.h) - The rudder hinge fittings were complete except the ones at rudder
station 194, which was found with the aft portion of the attachment missing. The rudder
auxiliary actuator fitting was not recovered. Fifty percent (by area) of the rudder
honeycomb skin panels were found on land.
1.12.2 Power plants
The aircraft was delivered on 14 February 1997 with two new CFM 56-3B-2 engines
(Serial numbers 858-480 and 858-481) manufactured by CFM International. There were
no reported problems with engine number one 90 days prior to the accident. According to
the aircraft technical log serial number D 20608 there was only one maintenance action
reported on the number two engine within a 90-day period preceding the accident. On 2
October 1997 it was reported that the ground idle fan and core speeds (N1 and N2) were
higher than those of the number one engine. The number two engine ground idle speeds
were adjusted to match those of the number one engine.
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The engine hardware was recovered from the river. Both engines were severely damaged
by the impact. It was estimated that about 85 percent by weight of both engines was
recovered. All the major rotating components from both engines were accounted for. The
recovered engine hardware include the fan disks and blades, compressor blades and
vanes, turbine blades and vanes, variable stator vane (VSV) actuators, and main engine
control (MEC) units.
1.12.2.1 Engine
The engines were severely fragmented. The inspections indicated that the operating
conditions of the engines at the point of impact were as follows:
• The three recovered Variable Stator Vane (VSV) actuators have impact witness marks
on the actuator rods indicating that both engines were running at high engine speed
setting at impact.
• The high pressure compressor case fragments showed that VSV platforms were
locked in an open (high speed) position - consistent with the impact witness marks on
the actuator rods.
• All major rotating engine hardware, i.e. fan, compressor, high pressure and lowpressure
turbine disks were recovered with no indication of disk failure.
• Disassembly and inspection of the two recovered MEC systems at the Woodward
Governor Company, Rockton, Illinois, showed that the remaining servos and valves
were in a high flow, high engine speed position.
• The recovered high-pressure compressor blades were bent in a direction opposite to
the engine rotation, indicating that the engines were operating at the time of impact.
• The recovered engine casings were very fragmented and did not show any evidence of
high energy uncontained rotating engine hardware.
• No evidence was found of pre or post impact engine fire. (There was no melted or
soot-covered engine hardware recovered.)
1.12.2.2 Main Engine Control (MEC) / Governor
The disassembly and inspection at the Woodward Governor Company of the two
recovered MEC systems indicated that:
• The recovered servos and valves were in a high flow, high engine speed position.
• The fuel valve rotor was found in an open position suggesting a high fuel flow.
• The governor servo piston appeared to be within approximately 0.25 mm of the
maximum fuel flow stop screw.
• The tang from the coupler was found in a position of rotation suggesting that the
power lever was at a high angle (i.e. near the full forward stop).
• The pump unloading and shutdown rotor was in a position of rotation indicating a
run/open position.
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1.12.2.3 Throttle Box
The throttle box was found with the engine thrust levers in forward thrust (i.e. high
power) and the fuel shut-off levers were in the “run” position (see Section 1.12.3.3.j). It
could not be determined to which of the two engines the throttle box belonged. These
thrust lever positions are consistent with information derived from evidence found in
　
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本文鏈接地址：NTSC Aircraft Accident Report SILKAIR FLIGHT MI 185 BOEING B(12)