Home' RTCA Documents for Review : DO-213A Change 1 Contents 11
DO-213A Change 1
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Design radomes to tolerate rain impact with a repair/replacement life expectancy that will
result in an acceptable number of maintenance actions within an overhaul period. Unless
previously qualified through test or service history of the materials and construction in use,
test a sample of the radome wall with the finish coating on a rain erosion apparatus approved
by an appropriate governmental agency. Expose the sample at the maximum angle of impact
that the radome will experience in flight. Use a rain field with the mean drop size
(two millimeters in diameter) and intensity of a natural one inch per hour rainfall. Test the
sample at the average cruise velocity of the aircraft. Verify that the sample can withstand
the test for five minutes without delamination or fracture.
Incorporate construction features to render the radome as impervious to the impact of hail
as radome designs now in use. As an example, air transport radomes that have been
constructed with three plies of I 8I series glass fabric in an epoxy or polyester laminate on
each side of a core (two plies per facing in smaller commuter aircraft radomes) have a service
history with hail impacts of no known or very rare punctures to the radome. Damage local
to the point of hail impact (facing delamination and core crushing) is acceptable. Radomes
of this construction have shown that they do not break apart, which would result in pieces
possibly being ingested into an engine inlet downwind of the radome. Thus, the above
construction has rendered satisfactory service when subjected to hail impact.
New materials and designs should achieve the level of performance described in the
There are two means of radome protection from atmospheric electricity: lightning diverter
and anti-static systems. The aircraft manufacturer, operator, or governmental agency
determines the requirements for their application.
Lightning protection systems should prevent puncture of the radome wall during a lightning
strike to the nose of the aircraft. The lightning protection system's termination should be
grounded to the aircraft with a measured dc resistance of no more than 10 milliohms.
A lightning test procedure, which has been acceptable to the FAA for radome applications,
is in accordance with SAE ARP 5412B / EUROCAE ED-84A, Aircraft Lightning
Environment and Related Test Waveforms  and SAR ARP 5416a / EUROCAE ED-105A,
Aircraft Lightning Test Methods  for lightning strike zone 1A. Include wet environmental
conditions during the lightning test procedure, particularly when segmented diverter strips
An anti-static system may be used to bleed off static electricity. Anti-static coatings or paints
exist that provide a resistive path to bleed off static electricity. These coatings are used under
decorative paints and are sometimes applied to the surface over a portion of the radome. The
recommended surface resistance (ohms/unit area) can range from one (1) megohm/square to
500 megohms/square as measured with a 500-volt megohmmeter. To be effective, the anti-
static system must be grounded to the airframe. Test the anti-static system to ensure that the
system provides adequate p-static interference suppression. A high voltage p-static test set
may be used to test the radome's anti-static system.
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