It's possible that your Uncle could have been killed in combat and the aircraft returned safely and landed without incident. If this was the case, there would not be a MACR (Missing Air Crew Report) or an Accident Report.
Here is a reported crash of a 491st BG aircraft on Sept. 09, 1944. I haven't found any other losses for that day so far.
09-09-44
"Bad weather restricted 8th AF operations during the first seven days of September although the 491st visited Karlsruhe on the 5th. It returned to the same target on the 8th, again without loss. Then it was Saturday, the 9th, and these entries were made in the Control Tower Log:
0400 Briefing.
0800 36 A/C on ops. 264 -K aborted.
0805 Crash 2 miles south of field. All notified.
0830 Notified by Bodney Flight Control that there were 3 survivors from crashed A/C.
0840 Notified by Capt. Barns at Station Hospital that A/C was ours. Survivors were Lt. Warczak (pilot), S/Sgt. Chaves and S/Sgt. Boling. A/C was #489 F. Notified by Watch officer that 489 crashlanded after #1 and #4 caught fire at 900 ft. Survivors escaped through slit in fuselage. Load of incendiaries exploded."
http://www.491st.org/491hist3.html
B-24 44-10489
http://www.aviationarchaeology.com/s...t2=Go&offset=0
http://www.8thafhs.com/db/get_one_ac...?acgroup_id=16