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Safety Recommendation Details

Safety Recommendation A-18-015
Synopsis: On October 2, 2016, about 1157 Alaska daylight time, Ravn Connect flight 3153, a turbine-powered Cessna 208B Grand Caravan airplane, N208SD, collided with steep, mountainous terrain about 10 nautical miles northwest of Togiak Airport (PATG), Togiak, Alaska. The two commercial pilots and the passenger were killed, and the airplane was destroyed. The scheduled commuter flight was operated under visual flight rules (VFR) by Hageland Aviation Services, Inc., Anchorage, Alaska, under the provisions of Title 14 Code of Federal Regulations (CFR) Part 135. The National Transportation Safety Board’s (NTSB) investigation determined that instrument meteorological conditions (IMC) were likely in the vicinity of the accident site at the time of the accident. The flight departed Quinhagak Airport, Quinhagak, Alaska, at 1133 and was en route to PATG. Data available for the accident flight showed that, after departure in visual meteorological conditions, the airplane proceeded along a generally direct route toward the destination at an altitude of about 1,000 ft mean sea level (msl), which resulted in terrain clearances between 500 and 700 ft above ground level (agl). During the last 4 minutes of the flight, the airplane climbed as it approached the mountain ridge that it eventually struck at an elevation of about 2,300 ft msl after having likely entered IMC. The airplane was equipped with a Class B terrain awareness and warning system (TAWS) that had an en route required terrain clearance (RTC) of 700 ft agl; flight at altitudes below the RTC (and not within 15 miles of an airport, given certain criteria) would result in TAWS terrain alerts. Hageland flights operated under VFR were allowed to fly as low as 500 ft agl, as was seen with this flight, which was flown en route below the TAWS alerting threshold. The system was equipped with a terrain inhibit switch that allowed the pilot to manually inhibit all TAWS aural and visual caution and warning alerts. A TAWS simulation that used an estimated flightpath for the accident airplane (assuming a level cruise altitude between known data points and a climb after the last data point to the accident elevation) showed that, if the alerts were not inhibited, the TAWS would have provided continuous alerts for most of the assumed flight. The investigation concluded that the TAWS alerts were likely inhibited for most, if not all, of the flight, eliminating a margin of safety.
Recommendation: TO THE FEDERAL AVIATION ADMINISTRATION: Modify the terrain awareness and warning system requirements in Technical Standard Order C151 such that, once the alerts are manually inhibited, they do not remain inhibited indefinitely if the pilot does not uninhibit them.
Original recommendation transmittal letter: PDF
Overall Status: Open - Acceptable Response
Mode: Aviation
Location: Togiak, AK, United States
Is Reiterated: No
Is Hazmat: No
Accident #: ANC17MA001
Accident Reports: Collision with Terrain Hageland Aviation Services, Inc. dba Ravn Connect Flight 3153 Cessna 208B, N208SD
Report #: AAR-18-02
Accident Date: 10/2/2016
Issue Date: 4/26/2018
Date Closed:
Addressee(s) and Addressee Status: FAA (Open - Acceptable Response)

Safety Recommendation History
From: NTSB
Date: 10/16/2018
Response: We note that you plan to work with manufacturers and operators to determine the standards, opportunities, and potential technical implementation paths for automatically uninhibiting alerts that were previously manually inhibited by the pilot. We believe this is a necessary first step toward addressing this recommendation. Pending updates on your progress and a plan for modifying the TAWS requirements in the TSO, Safety Recommendation A-18-15 is classified OPEN--ACCEPTABLE RESPONSE.

From: FAA
Date: 7/20/2018
Response: -From Daniel K. Elwell, Acting Administrator: The FAA plans to work with manufacturers and operators to determine the standards, opportunities, and potential technical implementation paths for automatically uninhibiting alerts previously manually inhibited by the pilot. Once the FAA completes this work. we will determine the best path forward to address the safety issues identified by this recommendation.

From: NTSB
Date: 4/26/2018
Response: On April 17, 2018, the NTSB adopted its report, Collision with Terrain, Hageland Aviation Services, Inc., dba Ravn Connect Flight 3153, Cessna 208B, N208SD, Togiak, Alaska, October 2, 2016, NTSB/AAR-18/02. The details of this accident investigation and the resulting safety recommendations may be found in the attached report, which can also be accessed at Among the Safety Recommendations, five are issued to Federal Aviation Administration (FAA) and can be found on page 71 of the report; eight are reiterated to the FAA and can be found on pages 72-73 of the report. The NTSB is vitally interested in these recommendations because they are designed to prevent accidents and save lives. We would appreciate a response within 90 days, detailing the actions you have taken or intend to take to implement these recommendations. When replying, please refer to the safety recommendations by number. We encourage you to submit your response.