On February 14, 2023, about 0800 Hawaii-Aleutian standard time, a Cessna C337H airplane, N5KR, sustained substantial damage when it was involved in an accident in Kona, Hawaii. The pilot had minor injuries and four passengers were not injured. The airplane was operated by the pilot as a Title 14 Code of Federal Regulations Part 135 sightseeing flight. The pilot completed the preflight inspection and engine run-up with no anomalies noted. The airplane departed from runway 35 at the Kona International Airport (KOA), Kona, Hawaii. During takeoff, after an indicated positive rate of climb, the pilot retracted the landing gear. As the landing gear retracted, the airplane had significantly less performance. The pilot performed an emergency landing to the runway overrun area with the landing gear retracted. The airplane sustained substantial damage to the fuselage. The operator’s weight and balance for the flight showed a takeoff weight of 4,681.5 lbs. with an allowable maximum gross weight of 4,700 lbs. An engine examination was performed by Federal Aviation Administration inspectors after the accident. The rear engine started normally, accelerated smoothly, and ran continuously without interruption. The front engine spark plugs were removed from the engine and no anomalies were observed with their electrodes. The crankshaft was rotated by hand and valvetrain continuity was confirmed to the rear accessory section. Thumb compression was attained on all cylinders. Magnetos were checked and timing was correct and both magnetos were operational. The examination of both engines revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation. Review of recorded engine monitoring data revealed that, about 4 minutes after both engines were started, the rear engine’s cylinder head temperatures (CHT) and exhaust gas temperatures (EGT) began to decrease, the engine oil pressure dropped from 69 psi to 1 psi, the fuel flow rate dropped to 0 gph, fuel pressure decreased from 6.9 psi to 1.3 psi, and the horsepower dropped from 32% to 0%. About 7 minutes after both engines were started, the front engine rpm increased and the airplane began to takeoff. Placards on the instrument panel stated, “Do not initiate single engine take-off” and, “Lead with rear engine power check RPM and fuel flow.” The owner’s manual indicated that, during takeoff, it was recommended to advance the rear engine throttle ahead of the front engine throttle and to periodically monitor fuel flow and rpm throughout the takeoff. If either of these indicators was below normal, the takeoff should be discontinued immediately while sufficient runway remained. The owner’s manual also indicated that full throttle checks on the ground were not recommended. The owner’s manual stated that the airplane drag with the landing gear doors opened and the gear partially extended is greater than the drag with the landing gear fully extended. Corresponding rate-of-climb penalties are 240 fpm and 110 fpm, respectively. Therefore, since there is a drag increase with the initiation of gear retraction, it should not be attempted unless adequate airspeed and altitude margins exist for sustained flight. This is especially important under the conditions of weight, altitude, and temperature that result in little or no single-engine climb.