曝光台 注意防骗
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Two icing envelopes are defined:
the “continuous maximum” envelope corresponding to an average cloud
17.4 nautical miles long, with low water concentrations, rising up to 22,000
feet and with a temperature as low as - 30°C;
the “intermittent maximum” envelope corresponding to an average cloud
2.6 nautical miles long, with high water concentrations, rising up to 30,000
and with a temperature as low as - 40 °C.
F-GZCP - 1st June 2009
62
1.18.5.2. Pitot probe certification process
1.18.5.2.1 General
Based on these regulatory requirements, the aircraft manufacturer draws
up equipment technical specifications for the equipment manufacturers for
each piece of aircraft equipment. For the Pitot probes, these specifications
include the physical (shape, weight, resistance to shocks, etc.) and electrical
characteristics, the degree of reliability sought along with the environmental
conditions (behaviour in icing atmospheres, for example). The development
of the probe by the equipment manufacturer consists of several phases:
definition/design of the equipment;
development of a prototype;
tests in the laboratory and tests intended to qualify the product with
respect to the required specifications;
Failure Modes, Effects and Criticality Analysis (FMECA).
FMECA is an inductive approach – as exhaustive as possible – that consists of
identifying the potential failure modes, their causes, effects and probability at
the level of a system or of one of its subassemblies.
The manufacturer systematically performs tests in the laboratory and in
flight to verify that the Pitot probe behaves correctly in as real as possible an
environment. The purpose of these tests is to check the interfaces (electrical,
mechanical, aerodynamic) between the Pitot probe and the other aircraft
systems.
The certification authority is associated with all these tasks.
All these operations and the documents drawn up at the time of each
development phase make up the certification dossier which is sent to the
certification authority.
Note: The privileges associated to the manufacturer’s design agreement allow the
authority to rely on the manufacturer’s internal processes for checking the justifi cations
produced and thus not receive and examine the whole of the certifi cation dossier.
One of the elements making up this certification dossier is a summary
document: Declaration of Design and Performance (or DDP).
This document certifies that the equipment meets the requirements of the
certification regulations as well as of the specifications requested by the
manufacturer and identifies the main substantiating documents.
When they have been manufactured, and before being put on the market,
each probe produced is submitted to an in-depth quality inspection (physical
appearance, inspection of the finish, resistance and performance tests, etc.).
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1.18.5.2.2 Anti-icing certification of the probes
In order to cover all the super-cooled water icing conditions specified in
appendix C of JAR 25, Airbus has developed a ten-point test table with
different static air temperatures (SAT), speeds, total air temperatures (TAT),
water concentrations per cubic metre of air, mean diameters of the water
droplets, exposure time, Pitot heating electrical power supply and the probe’s
local angles of attack in order to cover the aircraft’s flight envelope under the
following conditions:
All the tests are performed with reduced de-icing power (106 VAC instead
of 115 VAC);
The water concentration values are multiplied by an installation factor (1.5
or 1.7 or 2 according to the speed chosen for the test) with respect to the
values in appendix C of JAR 25 in order to take into account the effect of
the probe’s installation on the aircraft (boundary layer effect). Airbus then
applies an additional factor of 2 (design margin coefficient).
In addition to these points, whose aim is to meet the minimum regulatory
requirements, Airbus specifies test points aiming to cover additional criteria
defined by:
STPA specifications CIN3 n°42067 developed by Direction Générale de
l’Armement (DGA);
a set of specifications developed by Airbus from 1995 onwards and
designed to improve the behaviour of the Pitot probes in icing conditions
including, in particular, ice crystals, mixed conditions (ice crystals plus
super-cooled water) and rain conditions. The diameter of the ice crystals is
set at hypothetical 1mm. These specifications include 10 tests in which the
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