HTAWS to be mandated on all EMS helicopters
FAA says only TSO'd equipment meets required specs.
Honeywell Aerospace EGPWS/HTAWS is based on a proven fixed-wing platform. The system entered airline service in 1996 and was adopted for rotorcraft ops in 2001. Combined, both systems will soon pass 1 billion hours of service.
Sandel Avionics HeliTAWS is the only self-contained multihazard terrain system that protects against terrain, obstacles and transmission lines. The system has been installed on helicopters such as the AgustaWestland A109, Bell 412EP, Eurocopter AS350 and Sikorsky S76.
HEMS operator users include Metro Aviation, North Memorial Medical Center and New Zealand's Northland Emergency Services Trust. Sikorsky recently selected Sandel HeliTAWS as standard equipment on export S70i Blackhawks.
HeliTAWS is optimized for flight below 500 ft AGL, far exceeding the RTCA DO309 MOPS. TruAlert algorithms are designed to trigger only valid alerts and reduce or eliminate nuisance alerts.
Low-altitude operations are enhanced by a reduced-sensitivity mode that changes system logic to recognize pilot intent. By selecting off-airport mode, the pilot indicates the intent to land off airport, and the system calculates the flightpath from present position to landing zone, ensuring a safe, obstruction-free approach.
Maryland State Police Trooper 2—Analysis of a HEMS accident flight
One fatal HEMS accident highlighting the need for HTAWS occurred on Sep 27, 2008. A Eurocopter SA365N1 Dauphin operated by Maryland State Police (MSP)—call sign Trooper 2—had picked up 2 automobile accident patients in Waldorf MD destined for Prince George's Hospital Center in Cheverly MD. While enroute, the pilot of Trooper 2 reported to DCA Tower personnel that he'd "just run into some heavy stuff [a cloud layer at 900 ft MSL]." Then he said, "I don't think we're gonna make it all the way to the hospital. I'd like to continue... If I don't see a hole, I'd like to go IFR to ADW (Joint Base Andrews, Camp Springs MD)."
Trooper 2 continued on a northerly heading at 900 ft MSL and 1/4 mile from Prince George's Hospital made a 180° turn and advised DCA Tower of his intentions to climb to 2000 ft and divert to Andrews. Following a handoff to Potomac Approach, ATC vectored Trooper 2 to an ILS Rwy 19R at ADW. Trooper 2 joined the localizer approximately 1 nm outside the FAF.
On initial contact with ADW Tower, Trooper 2 reported difficulties with the glideslope and requested an ASR approach. Due to the controller's qualification levels, an ASR approach was not approved. Within 27 sec, the aircraft's descent rate increased from 500 fpm to 2000 fpm and Trooper 2 impacted terrain 3.2 nm north of the runway threshold. The aircraft was destroyed and 4 of the 5 occupants were fatally injured. One patient survived with serious injuries.
Post-accident analysis revealed no difficulties with airborne or ground-based ILS equipment or components. In addition, according to the NTSB report, a TAWS manufacturer concluded through its analysis that the pilot of Trooper 2 would have received 3 aural terrain alerts at 7, 4 and 2 sec prior to impact and a glideslope warning 24 sec prior—if there had been a valid glideslope signal. The flightpath profile analysis suggested an intentional deviation from the glidepath. If the aircraft had been HTAWS equipped, the terrain alerts "Caution—terrain," "Warning—terrain" and "Pull up" would have been provided prior to the accident.
Sandel Pres & CEO Gerry Block stated in reference to the MSP accident and his company's HeliTAWS, "Unquestionably, the system would have alerted the pilot and saved the aircraft if it had been on board. The system's GPWS function would have generated most of the alert... [It] goes beyond the enroute protection required by TSO C194."
During an off-airport takeoff, a similar assessment is made to ensure the path is clear of terrain, obstacles or wires. Another low-altitude feature reduces the sensitivity for operations below 300 ft AGL.
HeliTAWS provides all Class A GPWS alerting modes with the exception of Mode 2 (terrain closure rate). WireWatch is another unique feature of HeliTAWS which alerts pilots of power lines along their flightpath. Wire strikes are the leading cause of rotorcraft fatalities over the past 10 years.
In flight, power lines are nearly invisible. WireWatch identifies these threats day or night. Sandel uses a database of wire locations which is updated continuously by power generation and distribution companies and HeliTAWS users.
Mandating HTAWS equipment on HEMS aircraft is a safe bet to improve rotorcraft safety. While this new rule will only cover those operators under direct FAA oversight—namely, Part 135 HEMS operators—other operators (commercial, public use or other nongovernment organizations) should not hesitate to install this lifesaving equipment.
Airlines around the world have demonstrated for nearly 2 decades the effectiveness of advanced TAWS equipment. Today, CFIT accidents are very rare in TAWS-equipped transport category aircraft.
All signs point to adopting HTAWS as a use of proven technology to save lives. Indepth accident analysis from both government (NTSB and FAA) and industry (IHST, FSF and manufacturers) support this rule change. This is one case where FAA needs to be applauded for acting on good, solid information and persevering with the rulemaking "process" that wears us all down.
Stuart Lau is a consultant. He leads the IHST HFDM Working Group and acts as an IHST liaison to the Global HFDM Steering Group. He is also a pilot for a large international airline and a safety and accident investigation committee member. Lau has been associated with Pro Pilot since 1996.