NASA Ames Research Center SIERRA accident near Beaufort Sea, Alaska, July 27, 2013
On July 27, 2013 at about 2:15 am local time, a 2013 NASA Ames Research Center SIERRA, registered UNREG, was substantially damaged in an accident during maneuvering near Beaufort Sea, Alaska. It was an aerial observation flight under public-use (government) rules. No one was hurt. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
continued operation into engine intake system icing conditions resulting in a loss of power; due to schedule pressure and an insufficient risk management process.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 27, 2013 · about 2:15 am local time
- Place
- Beaufort Sea, Alaska · map
- Type
- Accident
- Injuries
- No one was hurt.
- Weather
- visual conditions (good weather)
- Aircraft
- NASA Ames Research Center SIERRA, built 2013
- Registration
- UNREG · no longer on the register · serial 1
- Damage
- Substantial damage
- Flight
- Aerial observation flight · public-use (government) rules
The NTSB's narrative final · quoted from the NTSB record
On July 26, 2013, approximately 18:50 Alaska Daylight Time, a National Aeronautics and Space Administration (NASA) Sensor Integration Evaluation Remote Research Aircraft (SIERRA) single-engine fixed wing unmanned aircraft system (UAS) was substantially damaged following an engine power loss and uncontrolled descent into the Beaufort Sea, 65 nautical miles north of Oliktok Point, Alaska. The flight was conducted as a non-military public aircraft operation under the provisions of Title 49 of the United States Code (U.S.C.) Sections 40102 and 40125, and a Federal Aviation Administration (FAA) Certificate of Authorization (COA). There were no injuries. The UAS was on it's maiden science flight for the Marginal Ice Zone Observations and Processes Experiment (MIZOPEX) and lost engine power 4.5 hours into the 6 hour scheduled flight. The UAS was powered by a 26 horsepower Herbrandson Dyad 290B 2-cycle carbureted engine with a belt driven pusher fixed pitch propeller. The flight crew noted a loss of engine RPM and electrical bus voltage on the CloudCap Piccolo Autopilot (AP) system display that was part of the ground control system (GCS). The UAS was beyond the range of the hand held radio and under the control of the Piccolo AP, upon losing power the GCS operator was unable to issue any commands to the aircraft. Telemetry data revealed that for a period of about 60 minutes prior to the accident, RPM and altitude fluctuated, and throttle demand increased, indicating the possibility of engine intake icing. Weather conditions at the time of the accident were included relative humidity (RH) from 85% to 95%, at 4 degrees C. The nearest observation sites to the accident were Deadhorse (62 km) and Nuiqsut (52 km). Both of these stations reported temperatures ranging from 9 to 14 degrees Celsius during the flight time. The National Center for Atmospheric Research examined the weather conditions and concluded a high risk for carburetor ice existed. The MIZOPEX Project was under significant time and budget constraints due to a change in project plan from a larger UAS platform requiring payload bay changes within the original funding timeline. A full NASA Mishap Investigation Team report of this accident is available in the public docket for this case.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
What happened, in order
- Loss of engine power (total) during maneuvering defining event
- Collision with terrain or object (not controlled flight into terrain) during emergency descent
The NTSB's findings
- cause Aircraft › Aircraft power plant › Engine (reciprocating) › (general) › Damaged/degraded
- factor Environmental issues › Conditions/weather/phenomena › Temp/humidity/pressure › Conducive to carburetor icing › Effect on equipment
- factor Organizational issues › Support/oversight/monitoring › Safety programs › Adequacy of safety program › Operator
- factor Organizational issues › Development › Design › Equipment design › Not specified
- factor Organizational issues › Management › Scheduling › Task scheduling/workload › Operator
Pilot
- Certificate: private
- Ratings: single-engine land
- Medical certificate: Class 2
- Seat: none
- Injury: no injuries
The aircraft
- Last inspection: inspection type not recorded
- Maximum gross weight: 400 lb
- Seats: 0
- Landing gear: fixed
- Engine: Herbrandson Dyad 290B (piston); 0 hours total
The flight
- Departed from: POLI Oliktok Point AK at 5:00 pm
- Destination: POLI Oliktok Point AK
- Flight plan: IFR
Weather at the time
- Light: daylight
- Wind: from 020° at 4 knots
- Visibility: 10 statute miles
- Sky: overcast at 4,000 ft
- Temperature: 54°F (12°C), dew point 45°F (7°C)
- Altimeter: 30.10 inHg
- Observation at 8:53 pm from PASC, 82 miles away
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
Other NTSB records under UNREG the same tail number, which may have belonged to a different aircraft at the time
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.