曝光台 注意防骗
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static air temperature (SAT), speed, water or ice crystal concentration per
cubic metre of water, mean diameter of the water droplets, exposure time,
the probe’s local angle of attack are varied.
The set of icing tests to be performed to meet the Airbus specification includes
26 test points in all (10 for covering appendix C and 16 additional tests), thus
covering a wider envelope than that defined by the JAR25 regulations.
The Airbus specifications used for the certification of the probes are therefore
stricter than those of JAR 25 (annex 4).
1.18.5.2.3 Pitot probe conformity
Wind tunnel tests are performed by the equipment manufacturers (in this case
Thales and Goodrich) to demonstrate the conformity of the probes with the
specifications developed by Airbus.
There are many wind tunnels around the world in which this type of test
can be performed. Each wind tunnel nevertheless has its limits and its own
utilisation envelope in terms of speed, minimum temperature possible and
water or ice crystal concentration. It may therefore not always be possible to
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perform some of the requested tests. Equivalence laws are then used to define
similar conditions by varying the parameters in such a way that the amount of
water or of ice crystals received by the probe is identical to what is stipulated
for the test.
For example: a test must be performed at the speed of 190m/s with a water
concentration of 6.3 g/m3. The wind tunnel is limited to a speed of 161 m/s.
In this case the water concentration will be increased to 7.55g/m3 (190/161) x
6.3 = 7.55 g/m3) and the temperature of the test will be increased in order to
maintain a total temperature identical to the level of the probe.
This similarity method is used internationally and is accepted by the
certification authorities.
It is important to note that there are no wind tunnels capable of reproducing
all the conditions that the crew may be confronted with in reality.
Furthermore, some scientific studies to characterise the exact composition
of the cloud masses above 30,000 feet. They show in particular that not all
the phenomena are known with sufficient precision. This is particularly true
concerning the nature of ice crystals (size and density) as well as the dividing
level of super-cooled water and ice crystals.
The Goodrich 0851HL, Thales C16195AA and Thales C16195BA probes were
certified on Airbus A330 respectively in November 1996, April 1998 and April
2007 and meet all the requirements listed in § 1.18.5.2.2.
1.18.6 Earlier events associated with incorrect air speed indications
This section aims to qualify the number of events that meet the following criteria:
Those that occurred to A330 and A340 airplanes;
Those that occurred above FL 300 or in conditions described by the crew
as “icing”;
Those for which the crew testimony or the analysis of recorded data shows
erroneous air speed indications.
The list presented below cannot be considered to be exhaustive or definitive.
It should be noted that this approach is subject to numerous uncertainties,
such as:
the difficulty of identification and interpretation by crews of events that
are sometimes transitory or associated with additional phenomena such
as turbulence;
the existence and effectiveness of the feedback process within and between
organisations, from the crews to the manufacturer and the national and
international authorities involved;
the existence of programmes for flight data analysis and if applicable the
rate of flights really analysed (taking into account loss of possible data);
configuration of flight data analysis software;
archiving time limits for flight data.
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As of 3 November 2009, Airbus had identified thirty-two events that had
occurred between 12 November 2003 and 1st June 2009(18). According to Airbus
these events are attributable to the possible destruction of at least two Pitot
probes by ice. Eleven of these events occurred in 2008 and ten during the first
five months of 2009.
Twenty-six of these incidents occurred on aircraft fitted with Thales C16195AA
probes, two on aircraft with Thales C16195BA probes and one on an airplane
equipped with Goodrich 0851HL probes.
As of 1st June 2009 Air France had identified nine events that might meet
the above-mentioned criteria. After the F-GZCP accident the airline started a
targeted analysis of recorded parameters and identified six additional events
that occurred in 2008.
In addition, a foreign operator began a targeted analysis of recorded flight
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