Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
SW-11-24
March 18, 2011
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin is 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.
Background
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, HTAWS). Whereas the TAWS
systems was not designed or intended for flight below 1000 ft. Above
Ground Level (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.
Recommendations
We recommend if you seek the safety benefit a terrain awareness systems
offers, you work to incorporate an approved installation of an approved
HTAWS in your rotorcraft. We further recommend 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.