CEN18FA277

The pilot was conducting his second low-level aerial photography flight that day; the pilot would take the photographs through the left window of the airplane. A review of surveillance data showed the airplane depart from the airport and fly to the target areas for aerial photographs. After the pilot completed the photography work over the target areas, the airplane traveled over a river. The airplane then made several low-level turns over the river, most of which were to the left. The last recorded data point showed that the airplane at 1,700 ft. msl and a groundspeed of 49 knots. The airplane wreckage was found partially submerged in the river. The photographs from the pilot's camera were extracted, and the last several images showed a fish in the river. It was undetermined why the pilot was taking photos of the fish. Postaccident examination of the airplane and engine revealed no anomalies that would have precluded normal operation of the airplane. Given the temperature and dew point at the time of the accident, the airplane was susceptible to serious carburetor icing at glide power settings. The airplane was equipped with a carburetor temperature system that was installed on the right side of the cockpit. The system had an "ice zone" warning light that illuminated before carburetor ice could form. It is likely that, during the low-level turns to the left over the river, the pilot was focusing on taking photographs through the airplane's left window and did not see that the ice zone light had illuminated. After illumination of this light, a pilot was expected to apply carburetor heat. However, the airplane's carburetor heat was found in the off position. Thus, given the ambient conditions at the time of the accident, it is likely that carburetor ice formed and resulted in a loss of engine power. Because the pilot's attention was diverted while taking photos of a fish in the river, he likely did not notice the loss of airspeed, which resulted in the airplane exceeding its critical angle of attack, and a subsequent low-level aerodynamic stall. Before the accident flight, a mechanic who assisted the pilot with refueling the airplane observed that the pilot kept rubbing his eyes. The mechanic surmised the pilot was fatigued. The mechanic suggested that the pilot that take a nap before continuing flight operations and the pilot replied that he can't make any money if he isn't flying, and subsequently departed for the accident flight. Evidence does not suggest that the pilot had a reduced sleep opportunity or circadian disruption during the days preceding the accident. However, at the time of the accident the pilot had completed one photo flight in the morning and was about 57 minutes into a second photo flight when the accident occurred. Although the pilot's total flight time that day was not extreme, the single-pilot aerial photography flight required low level maneuvering and divided attention which could have been fatigue inducing from aworkload and time-on-task perspective. However, there was insufficient information from which to determine whether fatigue played a role in the sequence of events.

The carburetor icing probability chart from the FAA's Special Airworthiness Information Bulletin CE-09-35, Carburetor Icing Prevention, indicated a probability of serious icing at glide power at the temperature (86°F) and dew point (63°F) reported at the time of the accident. The Aircraft Owners and Pilots Association's Air Safety Foundation published a safety document titled "Maneuvering Flight: Hazardous to Your Health?" This document states that aerial work, including photography, "require a significant division-of-attention at low altitudes. Pilots performing aerial work are generally highly qualified and use excellent judgment. But, if something goes wrong, there is little time to recover." The airplane's tachometer time on the day of the accident indicated a total of about 4.5 hours of flight that day. Examination of the airplane's maintenance records revealed no evidence of uncorrected mechanical discrepancies. The airplane was equipped with an Electronics International carburetor temperature system on the right side of the cockpit, located to the right of the yoke on that side. The manufacturer's operating instructions states in part the following: When Carb. Temp. is selected on the Electronics International Carb. Temp. instrument, the carburetor temperature is continuously monitored and the "Ice Zone" warning light over the display is activated for that channel. The "Ice Zone" warning light is only active for the channel selected. At 39°F (before ice can form in the venturi of the carburetor) the "Ice Zone" warning light will light up. When this happens, apply carburetor heat, making small adjustments to bring the carburetor temperature above 39°F, thereby avoiding any possible carburetor icing condition…. If the carburetor temperature is below 10°F the "Ice Zone" warning light will go off. Below 10°F there is not enough moisture in the air to form ice in the carburetor. The "Ice Zone" warning light has the advantage of catching your attention without having to continuously monitor the unit. The carburetor temperature system provides a visual alert system and does not have aural alerts. Per the Pilot's Operating Handbook, the flaps up stall speed for the airplane at 45° bank is 43 kts. On July 17, 2018, about 1423 central daylight time, a Cessna 152 II, N24515, sustained substantial damage when it was involved in an accident near Fort Rice, North Dakota. The commercial pilot sustained fatal injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 aerial photography flight. The purpose of the flight was to take photographs of farms and ranches in Morton County, North Dakota. The pilot used a handheld digital camera and took photographs with the left window of the airplane opened. The pilot also used a kneeboard with a county map to locate the target areas. To photograph the targets, the pilot would set engine power between 1,800 and 2,200 rpm and fly at a 45° approach angle toward the target, positioning thecamera forward of the wing strut to not get the strut or the airplane's propeller in the photograph. On the day of the accident, the pilot conducted the preflight of the airplane at Mandan Municipal Airport (Y19), Mandan, North Dakota, and reported to a mechanic that he would return to the airport about lunchtime. The airplane departed from the airport about 0845 and returned at some point before 1330, after which the mechanic refueled the airplane. During the payment process for the fuel, the mechanic observed that the pilot "kept rubbing his eyes like he was tired." The mechanic suggested that the pilot take a nap before continuing flight operations, to which the pilot replied that he could not make any money if he did not fly. The accident flight departed about 1337. Federal Aviation Administration (FAA) surveillance data showed that the airplane followed the Missouri River on a southeast path toward Huff, North Dakota. Once established south of Huff, the airplane performed multiple turns throughout the area at an average altitude of 2,500 ft mean sea level (msl) before traveling east toward Fort Rice. The last segment of data showed that the airplane made several low-level turns over the Missouri River, as shown in figure 1. Most of the turns were to the left. The last recorded data point showed that the airplane at 1,700 ft msl and a groundspeed of 49 knots. About 1442, the Morton County Sheriff's Office received notification that a witness observed the airplane located in the Missouri River. Figure 1. Last segment of flight over the Missouri River. The image is oriented to the north. The times and locations of the last several aerial images captured by the pilot are shown. The North Dakota Department of Health, State Forensic Examiner, Bismarck, North Dakota, conducted an autopsy of the pilot. His cause of the death was blunt chest injuries. Toxicology testing performed at the FAA Forensic Sciences Laboratory was negative for carbon monoxide, ethanol, and tested-for drugs. The owner of the aerial photography company for which the pilot worked reported that the accident flight occurred during the pilot's second season (May/early June to October) with the company. The pilot's wife noted no concerns about the pilot's sleep schedule and activities during the 72 hours before the accident. The images from the pilot's digital camera were extracted. Most of the images were of farms and farm equipment taken at a low angle. Between 1421:57 and 1423:12, seven images of the river were captured at a high angle and an almost-straight-down orientation. The metadata associated with all of the recovered images did not contain any GPS data. The airplane was discovered nose down with its empennage elevated, in about 5 ft of water, and about 75 ft west of a sandbar in the middle of the Missouri River, as shown in figure 2. The front of the airplane was oriented about 190°. Figure 2. Aerial view of the airplane at the accident site. (Courtesy of the MortonCounty Sheriff's Office.) The airplane sustained substantial damage to the fuselage and aft crushing to the leading edges of both wings. The propeller spinner was crushed aft and showed no evidence of rotation. One of the two propeller blades was bent slightly aft. The carburetor heat was found in the off position (at both the cockpit and engine locations). The carburetor temperature system was found to be installed correctly from the cockpit to the carburetor. The switch for the carburetor temperature system was found in the "Carb Temp" position. No preimpact mechanical malfunctions or failures with the airframe and engine were found.