Sandel Avionics of Vista, Calif., has begun pre-certification flight testing of a helicopter-specific terrain avoidance warning system based on its fixed-wing class-A TAWS. The system, HTAWS, will meet or exceed performance for any current class-B TAWS for helicopters, company founder and president Gerry Block told NBAA Convention News. Initial flight testing is taking place at San Diego’s Montgomery Field using a Eurocopter AS 350B2 AStar. Sandel expects to roll out HTAWS in the first quarter next year.  

The panel-mounted HTAWS is form and fit interchangeable with existing 3-ATI indicators. Calling it “the only fully self-contained TSO C194- and TSO C151c-compliant HTAWS system,” Block observed that the FAA, responding to the NTSB’s suggested adoption of systems such as TAWS to address the helicopter CFIT problem, last December issued Technical Standard Order (TSO) C194. “That kicked off HTAWS’ final development. For the helicopter TAWS, the new TSO is not quite as definitive as for fixed-wing, so there will be a lot of performance differences between the types of systems. We spent a great amount of time on the whole fixed-wing nuisance-alert issue and we’ve tried to take that into the helicopter arena.”

Block said a major task has been to develop nuisance-alert reduction algorithms for both cruise and landing configurations. “This system is designed to be  accurate because the nuisance-alert rejection feature is quite refined. The TAWS really is alert-free until you do something wrong.” Block defined a valid alert as one that occurs only when a threat requiring pilot action is detected. “Eliminating invalid alerts is much more complicated in the helicopter.”

The HTAWS has a retail price of $18,950 with options for night-vision-goggle-compatible display lighting and provisions to allow the HTAWS to serve also as the primary TCAS or traffic advisory system display.

At Booth No. 3810 Sandel is also demonstrating, through a video simulation, what a charter helicopter crew would have seen on an HTAWS display immediately before striking a mountaintop after a night takeoff from a San Diego-area airport several years ago.

In addition to the HTAWS, Sandel is featuring the SG102 series of solid-state attitude-heading reference systems (AHRS) and its 3-ATI and 4-ATI high-resolution daylight-viewable navigation and attitude electronic displays. The SG102 AHRS, with a remotely mounted magnetic flux valve, is certified to provide primary heading and reversionary attitude. A high-vibration-tolerant version is available for helicopters. Sandel has certified a reversionary mode for its SN3500 and SN4500 navigation displays when driven by an SG102, which places both attitude and navigation guidance on the display if a primary attitude source fails.    
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