曝光台 注意防骗
网曝天猫店富美金盛家居专营店坑蒙拐骗欺诈消费者
At an altitude of 8,000ft: approx. 3/4 atmosphere (approx. 11.03psi, 760hPa)
At an altitude of 18,000ft: approx. 1/2 atmosphere (approx. 7.35psi, 507hPa)
At an altitude of 34,000ft: approx. 1/4 atmosphere (approx. 3.68psi, 253hPa)
2.8.2 Investigation of the communications of the said aircraft’s air to ground data link
system
The said company’s ground facility automatically received and recorded downlink data
from the said aircraft’s ACARS (Aircraft Communications Addressing and Reporting
System) air to ground data link system. The following information on warnings had been
recorded:
(1) 11:45: SAFETY VALVE OPEN
(Safety valve not fully closed)
(2) 11:46: EXCESS CAB ALTX
(Cabin altitude exceeded 9,550 ft±350 ft)
(3) 11:48: LO DIFF PRXX
(Loss of cabin pressure)
9
2.8.3 Investigation of the cabin pressure system of the said aircraft
On December 28, 2001, the cabin pressurization system and structure of the said aircraft
were investigated at the hanger of the said company at Osaka International Airport. The
set of two safety valves was installed in the aircraft, serial numbers 9632127 (S/N127) and
9632129 (S/N129). It was found by a positive differential pressure test (Positive Relief Test)
that the gate of the safety valve (S/N129) opened at 5.16psi. The Aircraft Maintenance
Manual (AMM) specifies that the gate opens in the range 8.52–8.67psi. No other anomalies
were found except for this safety valve.
The history of this safety valve is as follows.
The set of two safety valves in question, S/N127 and S/N129, had been installed in
another aircraft of the same model belonging to the said company since manufacture in
1997.
The maintenance program manual of the said company specifies a functional test of the
safety valves as a required inspection item to be accomplished during the “4C” aircraft
maintenance check (carried out at 60-month intervals). On November 8, 2001, during the
aircraft’s first 4C Check, these valves were found to be outside operating tolerances (the
gate valve should not open at the specified maximum positive differential pressure), and
they were removed from the said aircraft.
Thereafter, the differential pressure at which the safety valves should operate (the actuation
differential pressure) was adjusted at an Approved Repair Station (ARS) certified by the Civil
Aviation Bureau of Japan. The Component Maintenace Manual (CMM) prescribes the limit at
which the gate should open as 8.55–8.60psi. At that time, S/N127 and S/N129 were adjusted
to approximately 8.59psi and approximately 8.57psi respectively. Subsequently, they were
tagged with “Authorized Release Certificate” in accordance with Civil Aviation Regulation
Operating Standard Article 41, and were stored as serviceable spare parts of the said
company.
During the first 4C Check of the said aircraft, it was found that the safety valves
fitted at that time were out of tolerance (they should not have opened when the differential
pressure reached the positive maximum pressure specified). They were removed and
replaced with S/N127 and S/N129, which had been stored as spare parts, on December 25,
2001. After that, the said aircraft made three flights before the occurrence of this serious
incident, and the maximum cruising altitude reached during that period was 25,000ft
(maximum differential pressure: 7.37psi).
There were no maintenance records on S/N127 and S/N129, apart from the above-mentioned
adjustment of the differential pressure.
2.8.4 Detailed Investigation of the Safety Valves
The set of two of safety valves installed in the said aircraft at the time of the incident
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was removed and subjected to functional and other tests at the ARS. The results of these
tests were as follows:
(1) Functional test of S/N129
① A visual check revealed no abnormalities.
② In functional test for positive differential pressure, the valve could not support a
pressure differential of more than 0.39psi, a worse condition than when it had been
installed in the aircraft.
③ The stem assembly (an internal part of the control valve) was assembled into a good
safety valve (S/N127) and the positive differential pressure functional test was repeated.
As a result, the gate opened at 0.44psi. The focus of the search for the abnormal
operation therefore shifted elsewhere.
④ The parts of the control valve apart from the stem assembly were substituted with
parts from a good safety valve (S/N127) and the positive differential pressure functional
test repeated. As a result, the gate has opened at approximately 9.01psi, nearly the
specified limit, and the anomalous behavior was not exhibited.
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AIRCRAFT SERIOUS INCIDENT INVESTIGATION REPORT ALL NIPPON AI(4)
