On March 9, 2021, about 1215 central standard time, a Cessna 170A, N9515A, was substantially damaged when it was involved in an accident near Poplar Bluff, Missouri. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.
The pilot stated that he departed Shawnee Regional Airport (SNL), Shawnee, Oklahoma, about 0900, for the cross-country flight to Poplar Bluff Regional Business Airport (POF), Poplar Bluff, Missouri. The airplane was equipped with a communication radio, but it was not equipped with very high frequency omni-directional range (VOR) equipment or a transponder. Although he had access to a handheld Garmin GPSmap 396 device, the pilot did not use it to navigate during the flight. The pilot stated that he navigated via dead-reckoning and following roads. He occasionally referenced a mobile phone application to verify the airplane’s position on a digitized visual flight rules (VFR) sectional chart. The pilot acknowledged that he did not have traditional paper VFR sectional charts to navigate with if his mobile phone’s battery became depleted during the flight.
About 15-20 minutes before reaching Poplar Bluff, Missouri, the pilot’s mobile phone powered off after its battery became depleted. The pilot stated that he then inserted the Garmin adapter into the airplane’s cigarette-lighter socket, but the GPS device did not power on. The pilot continued flying his current heading, which took him directly over the city of Poplar Bluff, Missouri. The pilot did not see the airport to the east of the city, so he turned and flew a couple miles south of the city before he made a 180° course reversal and flew over the city northbound.
After flying several miles north of the city, he decided to locate a suitable field for a precautionary landing due to the airplane’s low fuel status. The left fuel tank gauge indicated “empty” and he estimated that the airplane had about 10 minutes of fuel remaining in the right fuel tank. He turned the airplane into the wind and landed in what he believed to be a suitable field. The pilot stated that the engine was still running throughout the precautionary landing. After touchdown, the airplane rolled about 200-300 ft before the main landing gear dug into the soft terrain and the airplane nosed over. The airplane sustained substantial damage to the vertical stabilizer and the engine mounts.
During a telephone interview, the National Transportation Safety Board investigator asked the pilot to connect the Garmin GPSmap 396 device to his vehicle’s 12-volt direct current (DC) cigarette-lighter socket by means of the Garmin cigarette-lighter adapter. The GPS device automatically powered-on when connected to the power source, with and without the device’s battery installed. When disconnected from the power source, the GPS device did not power-on with battery installed. The last known position displayed on the GPS device was from a flight completed two days before the accident.
The airplane wreckage was recovered to a secured location where it was examined by two Federal Aviation Administration (FAA) airworthiness inspectors. The airframe battery was removed from the airplane during wreckage recovery. The 12-volt battery was not an aviation-certified battery and was consistent with a motorcycle battery. Without any electrical load, the battery had 12.45 volts when tested with a digital multimeter. The battery had 11.8 volts when it was connected to an automotive battery tester that subjected the battery to a 5-second electrical load. The battery was then reconnected to the airplane and, when the master switch was turned on, the communication radios powered on and the cigarette-lighter socket had 12.45 volts when measured with a digital multimeter. The FAA inspector inserted his personal USB charger adapter into the cigarette-lighter socket and confirmed that there was sufficient power to charge his mobile phone.
Additional bench testing of the alternator, voltage regulator, and battery did not reveal any anomalies that would have prevented normal operation of the airplane’s electrical system.