Cessna 210N N4943U accident near Cincinnati, Ohio

Probable cause

The pilot's decision to operate the airplane with a "dead" battery contrary to guidance provided by the Pilot's Operating Handbook. An additional cause was the pilot's failure to verify that the landing gear was fully down and locked prior to landing. Contributing factors were the pilot's failure to properly service the battery prior to the flight and the subsequent loss of all electrical power, which rendered that normal gear extension system inoperative.

NTSB analysis

The pilot had not flown the airplane over the winter and the battery had lost its charge. The engine was started with the assistance of ground power. After engine start-up, the alternator output indicated 29 volts, battery voltage indicated zero, and the ammeter showed that the battery was charging.The pilot reported that upon raising the landing gear and flaps after liftoff, "immediately all electrical power went out." The pilot elected to remain in the traffic pattern and return for an immediate landing. He lowered the landing gear handle. However, due to what he perceived as an urgent situation and the attention required by other traffic in the vicinity, he did not use the emergency gear extension procedure to insure that the landing gear was fully down and locked. Upon landing, the main landing gear collapsed and the airplane departed the left side of the runway. The left horizontal stabilizer sustained skin and sub-structure damage. A post accident inspection revealed that the battery had little or no electrolyte in it. Battery output was 8.3 volts, with no indication of electrical current. The alternators and voltage regulators were tested. No anomalies with the function of the alternators or regulators were observed. The airplane was equipped with a 28-volt dual-alternator electrical system. The Pilot's Operating Handbook (POH) stated that "use of the ground service plug receptacle for starting an airplane with a 'dead' battery or charging a 'dead' battery in the airplane is not recommended." It added that a "failure to observe this precaution could result in loss of electrical power during flight." Landing gear extension and retraction is controlled by an electric motor, which provided hydraulic pressure to actuate the gear. Loss of electrical power prevented operation of the motor and required that the landing gear be extended manually. The pilot commented that the accident may have been prevented by inspecting the battery fluid level prior to the flight because the airplane had been tied down all winter.

Text from the NTSB. Open the NTSB docket for CHI08CA092 for the full record.