On October 23, 2014, about 1215 mountain standard time, a North American P-51D airplane, N351BD, sustained minor damage following a gear up landing at the Phoenix-Mesa Gateway Airport (IWA), Mesa, Arizona. The commercial pilot, who was also the owner of the airplane and the sole occupant, was not injured. Visual meteorological conditions prevailed for the local flight, which was being operated in accordance with 14 Code of Federal Regulations (CFR) Part 91, and a flight plan was not filed. The flight departed Stellar Airpark (P19), Chandler, Arizona, about 1117. In a statement provided to the National Transportation Safety Board investigator-in-charge, the pilot reported that after taking off and retracting the landing gear, he noticed a burning smell, either rubber or electrical, and the gear lights did not indicate a normal retraction. The pilot stated that he extended the landing gear and did a flyby of an accompanying helicopter that was filming him, and was informed that the right main landing gear was extended, and that the left gear was not. The pilot opined that he then flew into open airspace and began troubleshooting the gear malfunction, and performed the emergency procedures numerous times, but with no success; he then instructed the helicopter pilot to inform the IWA air traffic control tower operator that he would be doing a gear up landing here. The pilot reported that after he had burned off most of his fuel, the IWA controller cleared him to land on Runway 30R. The pilot stated that he performed a normal full stall, gear up landing, after which the airplane slid to a stop on the right center of the runway; only minor damage to the belly scoop was observed. The airplane was subsequently recovered from the runway to a secure location for further examination. On April 1, 2015, under the supervision of a Federal Aviation Administration (FAA) aviation safety inspector, a certified FAA airframe and powerplant mechanic who specializes in older warbird type airplanes performed an examination of the landing gear in an attempt to determine what precluded it from operating normally. The mechanic initially reported that after disassembly of the left main landing gear oleo strut, the only thing he could determine was that the chevron seals might have grabbed the strut, not allowing the oleo to extend on lift off. The mechanic further reported that he also checked the run out on the inner strut to see if it was bent, which it was not. He also opined that the strut gland nut might have been too tight, which could have compressed the seals against the inner strut, which could have caused the strut to extend too slowly, not giving it enough time to extend before the landing gear was retracted, which then may have caused the left main landing gear to get caught on the wheel well structure. However, after the mechanic performed further disassembly, inspection, and reassembly of the landing gear, he reported in an additional statement to the NTSB IIC, that he was unable to provide a definite cause that would explain why the landing gear became caught on the wheel well. The reason for the landing gear failing to operate in its normal extension and retraction modes could not be determined during the investigation.