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safely land, even given the actual condition of the runway at Irkutsk
airport (covered with water).
8. This scenario shows that, after the co-pilot had reported that “the
RPM’s are increasing” if the crew had moved the TCL of the left
engine back to idle and applied the reverser again (in this case the
spoilers would also have been released automatically), then the
overrun speed would have been around 70 kph.
Also the very last occasion when the crew would have been able to stop
the airplane on the runway was determined by moving the left throttle lever back
to idle and applying the reverse thrust of the right engine once again. This
occurred et 22:44:16, which means that the crew had more then 25 seconds to
diagnose the irregular situation (from the moment the throttle control lever of
the left engine started to be moved).
1.16.3. Analysis of materials from previous research work to
determine the friction coefficient of a runway with various
surface conditions
This series of investigations was conducted in 1986 when analyzing the
reasons why an Il-86 overshot as it landed on a runway covered with water. The
investigations were carried out at the State Scientific and Research Institute of
Civil Aviation (SSRICA). Report No 1.01.02.189 was drawn up and approved
on Sept. 17, 1986 based on the results of the investigations.
The results of these investigations showed that with a layer of water on
the runway the measured ATT-2 friction coefficient did not typify the actual
runway surface friction. It was established that during landings of an Il-86 on a
runway covered with water, the average friction coefficient was approximately
four times lower than that measured by corresponding airport instruments, and at
speeds of 100-200 kph these differences could even be 5-6 times higher.
The above-mentioned magnitudes correlated well with the results of
investigations carried out to study the accident in question. Given a measured
friction coefficient of 0.5 and the good braking conditions reported, based on
this coefficient, the simulation of the emergency landing showed that the actual
friction coefficient for speeds of 150-180 kph was ~0.1, which corresponds to
braking conditions on a runway "covered with water".
1.16.4. Assessment of forces needed to move the throttle control
lever
Final Report
INTERGOVERNMENTAL AVIATION COMMITTEE
58
As part of the commission's work the forces required to move the TCL of
engines on some A-310 airplanes with P&W and GE engines were measured.
The investigations showed that, in GE engines that had a fully mechanical
control linkage, the magnitude of forces was no less than 2 kg for every TCL.
The picture was significantly different on P&W 4000 engines equipped
with FADEC computers. The mechanical part of the control cable for these
engines (before FADEC) is short enough and has its own friction of the order of
350-400 grams for every TCL. The standard magnitudes according to section
76-11-00 of the А-310 airplane maintenance guide lie in the 1.17 – 1.54 kg
range, and the difference in forces between the left and right TCLs should not
exceed 110 grams. To adjust the forces, the control cable has an additional
friction unit. The forces are adjusted by changing the tightness of the friction
unit. Existing technical maintenance documentation (MPD) does not provide for
the periodic inspection and adjustment of the forces. This work is carried out
irregularly upon requests of flight crews whenever they feel uncomfortable in
controlling throttles. There was no such record found in the log book of the
airplane involved in the accident.
The table below shows the results of the control measurements made on
the fleet of the Uzbekistan Havo Yullary airline:
According to the logbooks of these airplanes, no inspection or correction
of the friction forces was carried out on them before the investigations following
the F-OGYP accident. It should be noted that the friction forces decreased on the
"old" airplane in this fleet (1991) to a level corresponding to the inherent friction
on the mechanical part of the control linkage for engines (without the friction
unit). The commission does not have other official information on actual friction
forces of other airplane because in the course of the investigation Airbus failed
to comply with the relevant request to carry out a one-time inspection of its fleet
of airplane.
Note: According to EASA regulations a complete fleet
inspection is launched when there is a continuous
airworthiness concern, but low friction forces in
REG.
SER
№
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