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Newer Wx radar vs. older units

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Newer Wx radar vs. older units

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Old 8th Jan 2010, 20:00
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Newer Wx radar vs. older units

An interesting incident report here on how newer wx radars operate differently than older units. Has anyone noticed significant differences in their own experience.

http://www.cad.gov.hk/reports/main3.pdf

It is recognized that all airborne weather radars do
operate in a similar fashion and on broadly the same
principles. However, there are significant differences
between modern, ‘flat-plate’ antenna radars, such as the
RDR-4B, and older, parabolic antenna radars. These
older radars, on which many senior pilots gained
experience, have up to 15 times the power of modern
radars, are able to detect close-in weather at lower
altitudes relative to the aircraft due to large side lobes
and generally require less ‘effort’ to interpret a radar
picture. In comparison, the RDR-4B radar focuses
radar energy in a narrow ‘pencil’ beam, the power of
which is greatest at the centre and reduces as the
angular distance from the centre of the beam increases,
with little energy emitted as extraneous side lobes. The
narrow beam and loss of side lobes make tilt and range
control more critical. The beam width of the RDR-4B
radar is nominally 3 degrees. The radar energy is
focused at the middle of the 3-degree beam, reducing to
half power at the edge of the beam. Thus while radar
targets having good reflectivity may produce returns
from the 3 degree periphery, targets with less
reflectivity may not ‘paint’ at all.


The Honeywell RDR-4B Forward Looking Windshear/Weather
Avoidance Radar System User’s Manual gives a very detailed
description of the operating procedures for the weather radar, with
particular emphasis on range selection and antenna tilt management.
Adopting the procedures in this document, or alternatively, those
described in FCOM 3.04.34, would have adequately established a
protection zone ahead of the aircraft. Both documents stress that it
is important for the antenna tilt angle to be lowered progressively
as the aircraft approaches weather to maintain a clear radar picture
of the weather ahead. This will help to ensure that a deviation will
clear any weather hazard by a safe margin. However, there was no
evidence that these procedures were adopted prior to the
occurrence. Although the Honeywell RDR-4B radar has a feature
that provide an automatic increase in gain above 25,000 feet to
compensate for the lower reflectivity of the ice crystals in the upper
levels of a storm cell, the radar remains limited by the reflectivity
characteristics of the target being scanned and the available gain. It
is for this reason that the RDR-4B Users Manual stated repeatedly
that effective tilt management is the single, most important key to
more informative weather radar displays.
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Old 9th Jan 2010, 03:47
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I won't answer your question directly, PL, but will provide some info. Thanks for the link.

Newer is a relative term. The RDR-4B is RDR-4A with forward looking windshear circuitry added in about 1995. The 4A went into service in 1982 on the new 767. That's 27 years, which was well before the FO on that flight was born.

It doesn't matter which WX radar; if the pilots don't get trained, they won't use it correctly. I have never known any airline to provide more than laughable WXR training, other than United A/L. It's criminal.

The accident report spelled out the major operational differences between the old magnetron radar and Arinc 700 radar (RDR-4, WXR-700). But the pilots weren't trained on the old radar, either. Further, the report didn't mention the shortcoming of the RDR-4 having a single tilt control, yet with split ranges available. The WXR-700 has full dual tilt, mode and range available. At altitude, to use split ranges adequately, you need split tilts.

AF-447 had WXR-700, but pilots apparently untrained in its use, from what I read on that thread. Has AF done anything about that?

The state of the art WX radar is the Collins WXR-2100 (and HNWL equiv), which provides automatic mode, tilt and range, reducing pilot workload, and ostensibly reducing the amount of pilot training needed. AF could have bought that radar when the 447 ship was delivered new, or could have retrofit the fleet at any time.

Some airliners continue flying Grandpa's radar, because the authorities lack incentive to require upgrades.

GB
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Old 10th Jan 2010, 09:28
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The details of operating the transitional systems to current simply require the operator to be proficient with the MACHINE. They are just as good if not better as long as you know how to operate them. Any lack of is certaintly complancy on the operators part.
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Old 10th Jan 2010, 11:21
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Couple of PPRuNe threads on tilt management:

http://www.pprune.org/tech-log/48016...technique.html
hmmm .. seems the other one has been lost.
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