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On June 25, 2015, about 1215 Alaska daylight time, a single-engine, turbine-powered, float-equipped de Havilland DHC-3 (Otter) airplane, N270PA, collided with mountainous, tree-covered terrain about 24 miles east-northeast of Ketchikan, Alaska. The commercial pilot and eight passengers sustained fatal injuries, and the airplane was destroyed. The airplane was owned by Pantechnicon Aviation, of Minden, Nevada, and operated by Promech Air, Inc., of Ketchikan. The flight was conducted under the provisions of 14 Code of Federal Regulations (CFR) Part 135 as an on-demand sightseeing flight; a company visual flight rules flight plan (by which the company performed its own flight-following) was in effect. Marginal visual flight rules conditions were reported in the area at the time of the accident. The flight departed about 1207 from Rudyerd Bay about 44 miles east-northeast of Ketchikan and was en route to the operator’s base at the Ketchikan Harbor Seaplane Base, Ketchikan.
TO THE FEDERAL AVIATION ADMINISTRATION: Implement ways to provide effective terrain awareness and warning system (TAWS) protections while mitigating nuisance alerts for single-engine airplanes operated under 14 Code of Federal Regulations Part 135 that frequently operate at altitudes below their respective TAWS class design alerting threshold.
Original recommendation transmittal letter:
Open - Acceptable Response
Ketchikan, AK, United States
Collision with Terrain Promech Air, Inc. de Havilland DHC-3, N270PA, Ketchikan, Alaska, June 25, 2015
Addressee(s) and Addressee Status:
FAA (Open - Acceptable Response)
Safety Recommendation History
The following is from the NTSB Aviation Accident Report “Collision with Terrain Hageland Aviation Services, Inc. dba Ravn Connect Flight 3153 Cessna 208B, N208SD, Togiak, Alaska October 2, 2016.” Report number AAR-18-02. Adopted on April 17, 2018 and published on April 26, 2018. 2.4.3 Routine Use of TAWS Terrain Inhibit Switch The Honeywell KGP 560/860 Pilot’s Guide for GA-EGPWS recommended that the TAWS alerts should not be inhibited during normal operations. The guide stated that the purpose of the terrain inhibit switch was to allow for operations without nuisance warnings at certain airports that were not in the system database. Although Hageland had no official published policy, Hageland allowed pilots to inhibit the alerts outside of the manufacturer’s recommendations because the alerts could be distracting to the crew during flights below the TAWS RTC. The chief pilot, DO, and a check airman each described scenarios in which pilots were allowed to inhibit the system when flying in VMC, including en route flight below 700 ft agl. The lack of specific guidance on TAWS use led to pilots routinely inhibiting a safety system important in CFIT prevention. The NTSB has investigated several other accidents in which pilots were involved in fatal terrain collisions in Alaska while conducting normal operations with their TAWS alerts inhibited.42 Research has shown that frequent nuisance alerts decrease user confidence in the alerts due to the “cry wolf” effect, motivating users to disable or otherwise disregard them (Sorkin 1988). As a result of these investigations, on May 9, 2017, the NTSB issued Safety Recommendation A-17-35, which asked the FAA to implement ways to provide effective TAWS protections while mitigating nuisance alerts for single-engine airplanes operated under Part 135 that frequently operate at altitudes below their respective TAWS class design alerting threshold (NTSB 2017a). On July 21, 2017, the FAA responded that it would review the issue and determine its next steps. Pending action from the FAA to address the recommendation, the NTSB classified Safety Recommendation A-17-35 “Open—Acceptable Response.” Due to the recommendation’s relevance to the circumstances of this accident, which also involved an operator allowed to conduct VFR flights at altitudes that could result in continuous TAWS alerts, the NTSB reiterates Safety Recommendation A-17-35. The NTSB notes that, since the FAA’s initial response, the FAA issued TSO-C151d, which required a FLTA en route alerting altitude of 500 ft agl (per DO-367) for new models of Class B TAWS equipment (for fixed-wing aircraft) identified and manufactured on or after August 31, 2017. (TSO-C151c, which applied to the TAWS installed in the accident airplane and specified a Class B minimum RTC of 700 ft, remains effective until February 28, 2019.) The NTSB looks forward to further updates from the FAA regarding any completed or planned action related to this safety recommendation.
We note that the General Aviation Joint Steering Committee (GAJSC) has assembled a working group to examine controlled flight into terrain (CFIT) accidents, including those involving aircraft operating under Part 135. Pending updates on the GAJSC’s efforts, and a plan that addresses the specific concerns outlined in Safety Recommendation A-17-35, the recommendation is classified OPEN--ACCEPTABLE RESPONSE.
-From Michael P. Huerta, Administrator: The Federal Aviation Administration (FAA) will review this issue and determine its next steps. However, we note that the accident that resulted in this recommendation involved Controlled Flight into Terrain (CFiT), which is of interest to the General Aviation Joint Steering Committee (GAJSC). The GAJSC has approved and assembled membership for a working group aimed at examining CFiT accidents, to include pa11 135 operations. The FAA 's goal is to begin the work of this group by late summer of 2017.
On April 25, 2017, the National Transportation Safety Board (NTSB) adopted its report concerning the June 25, 2015, accident in which a single-engine, turbine-powered, float-equipped de Havilland DHC-3 (Otter) airplane, N270PA, collided with mountainous, tree-covered terrain about 24 miles east-northeast of Ketchikan, Alaska.1 Additional information about this accident and the resulting recommendations may be found in the report of the investigation, which can be accessed at our website, http://www.ntsb.gov, under report number NTSB/AAR-17/02. As a result of this investigation, we issued 10 new recommendations, including 1 to the Cruise Lines International Association and the following 9 recommendations to the Federal Aviation Administration.
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