Fri, Mar 25, 2011
Terrain Awareness System Designed For Fixed Wing Aircraft
The FAA has issued a Special Airworthiness Information Bulletin
(SAIB) to inform owners and operators of rotorcraft equipped with
Garmin 400/500 series GPS Navigation Systems, with the activated
function of Terrain Awareness and Warning Systems (TAWS) designed
for use in fixed wing airplanes. There is an airworthiness concern
regarding operation of a rotorcraft with an alert system not
designed or intended for use on rotorcraft. At this time, this
airworthiness concern is not an unsafe condition that would warrant
airworthiness directive (AD) action under Title 14 of the Code of
Federal Aviation Regulations (14 CFR) part 39.
Controlled Flight into Terrain (CFIT) is an obvious safety
concern for all types of aircraft. Mandates to install TAWS systems
are regulatory for certain category and classes of aircraft,
typically transport airplanes and certain rotorcraft. The
installation of these potentially safety enhancing systems remains
non-required for the vast majority of smaller airplanes and
rotorcraft. The FAA has become aware of a number of installations
of Garmin 400/500 series GPS Navigation Systems, in rotorcraft,
with the airplane TAWS function activated. The TAWS function in
these systems was designed and certified for use in Part 23
airplanes (reference Supplemental Type Certificate (STC) SA01933LA)
and meets the requirements of Technical Standard Order (TSO) C151b
(TAWS for airplanes) but does not meet the requirements of TSO C194
(Helicopter Terrain Awareness Warning System or HTAWS).
Whereas the TAWS systems was not designed or intended for flight
below 1000 ft AGL, the HTAWS system requirements are better
optimized for operation at lower altitudes utilized by rotorcraft
in normal operations. Furthermore, the Garmin 400/500 TAWS
installation manuals clearly note that the TAWS function is not
designed nor approved for use in rotorcraft. The rationale driving
this safety concern is the number of nuisance warnings and cautions
that will be presented to the aircrew as a result of significantly
different algorithms in TAWS versus HTAWS systems. When operating
below 1000 ft AGL, these distractions to the aircrew and increased
workload could possibly decrease safety. Garmin has obtained an STC
for incorporating HTAWS functionality in the 400W/500W Navigation
systems on the Bell 206B model helicopter (STC SR02080SE),
effective September 23, 2010.
Garmin 500 HTAWS
The FAA recommends that operators incorporate an approved
installation of an approved HTAWS in your rotorcraft. It further
recommends that if the TAWS function is activated in your
rotorcraft, you deactivate that function by means of the options
selectable procedure described in the Garmin installation manuals
for the 400/500 series system until an approved HTAWS system can be
installed in your rotorcraft.
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