On September 21, 1997, at 1910 central daylight time (cdt), a Cessna 172G, N4375L, piloted by a private pilot, was substantially damaged when its left wingtip struck the side window of an airline crew bus while taxiing at O Hare International Airport, Chicago, Illinois. There were no passengers on the crew bus. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 personal flight was not operating on a flight plan. The pilot reported no injuries. The bus driver reported minor injuries. The flight departed Midway Airport, Chicago, Illinois, at 1835 cdt. According to the pilot's written statement, he "...was taxiing past [an] American Airlines bus near A-18 and D taxiways." The pilot said the airplane "...was almost completely past [the] stationary 40' bus when the driver moved it... ." He said the left rear section of thebus struck the airplane's left wingtip. The on-scene investigation revealed the airplane had landed on runway 22R. After exiting the runway, the pilot was instructed to turn onto taxiway A-17. The pilot turned the airplane onto a service road the airline crew bus was using. Shortly after turning, the airplane's left wingtip struck the left rear side window of the crew bus as it was turning to the right. Inspection of N4375L revealed its left wing rear spar was bent aft and cracked about 18-inches out from the wing root. The left wing tip had separated from the wing. The upper wing skin was buckled aft of the left wing main fuel tank.