Aircraft Accident/Incident Report

Prudhoe Bay, Alaska 99734
Friday, July 26, 2013 18:15 AKD

On July 26, 2013, about 1815 Alaska daylight time, a Sensor Integrated Environmental Remote Research Aircraft (SIERRA) Unmanned Aircraft System (UAS), referred to as Ship 1, is believed to have sustained substantial damage after impacting ocean ice approximately 90 miles north of Prudhoe Bay, Alaska. While in domestic airspace, the aircraft was being operated by the NASA Ames Research Center as a public use flight under the provisions of a special Certificate of Operation (COA)issued by the Federal Aviation Administration (FAA). In international airspace,the aircraft is operated as a state aircraft. There were no injuries as a result of the accident. Visual meteorological conditions prevailed in the area at the time of the accident. Mission flight following and autonomous return to base procedures were implemented for the flight which originated from Oliktok Point, Alaska about 1400. The SIERRA is a medium-class UAS, that can perform remote sensing and atmospheric sampling missions in isolated and often inaccessible regions, such as over mountain ranges, the open ocean, or the Arctic/Antarctic. Designed by the U.S. Naval Research Laboratory and developed at NASA's Ames Research Center, the SIERRA is well suited for precise and accurate data collection missions because, with a maximum takeoff gross weight of 400 pounds, it is large enough to carry up to 100 pounds of scientific instruments for up to 600 miles yet small enough not to require a large runway or hangar. The aircraft was being utilized as part of the Marginal Ice Zone Observations and Processes Experiment (MIZOPEX). The purpose of the experiment is to assess ocean and sea ice variability during the melt season within a key marginal ice zone region. The project also has goals to demonstrate potential for geophysical research using multiple UAS in polar regions, and to determine best practices for collaborating with FAA regarding flight requirements and limitations for UAS operations. On the morning of the accident, the SIERRA UAS conducted it's first checkout flight of the MIZOPEX mission. The flight lasted 1.3 hours, and included landing pattern optimization, and a transit to international airspace and back. The flight was uneventful and aircraft behavior appeared normal. The accident flight was the first science mission for the aircraft. The 6 hour flight was slated to fly to international airspace over the arctic sea ice, and complete a mapping pattern over the sea ice edge. About 4 hours into the mission, there was a momentary loss of the Iridium satellite communications link with the aircraft. The Ground Control Station (GCS) operator was recording this event when the Iridium system reacquired the signal after approximately one minute (note that loss of Iridium is expected and had been occurring occasionally during the flight with reconnect times ranging from 1-4 minutes). Upon reacquisition of the Iridium link, the RPM and Alternator warning lights were illuminated on the GCS display. The RPM display was at zero RPM and the battery bus voltage was 24 Volts, indicating the aircraft was operating solely from batteries, and that the engine-driven alternator was not charging them. The aircraft entered a controlled glide at an autopilot commanded airspeed of 56 knots. The aircraft continued this glide until impact with the surface at which time the Iridium link went down at 1815 local. There is a high probability that the SIERRA impact occurred on ice, and there are no plans to attempt a recovery of the aircraft.

Not Yet Reported