Yankee AA1
Flight Crew Commercial; Flight Crew Multiengine; Flight Crew Sea; Flight Crew Instrument
Flight Crew Last 90 Days 50; Flight Crew Total 840; Flight Crew Type 480
Situational Awareness
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Aircraft Aircraft Damaged; Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action; General Flight Cancelled / Delayed
Aircraft; Manuals; Human Factors
Heard a pop and felt a jolt forward of the firewall. Engaged electric fuel pump; suspected fuel flow fluctuation. Five minutes later; fuel pump turned off; engine instruments normal. Five minutes after that I smelled something burning and noticed an oil colored streak had appeared on the cowling moving aft. I initiated the Engine Fire in Flight Checklist and landed the aircraft on a US Highway; northbound. The fiberglass nose cowling attach points failed and the cowling slid forward and came into contact with the propeller and the rear of the flywheel. The propeller and flywheel melted and wore through the fiberglass; causing the smell and the streak running up the cowling turned out to be fiberglass dust. I called my local Mechanic that does all the work on my airplane to come down and we secured the cowling for the flight back to the home base of ZZZ. I do not see how this could have been avoided. The cowling felt secure when I checked it during preflight. I do believe I took the correct action by putting the airplane on the ground while I still had control over the situation.
Reporter stated the nose cowl; also called a 'Nose Bowl' is a one piece fiberglass cowling just aft of the propeller. The Nose Bowl has two attach points on the top side that attach to the left and right engine cowl upper surfaces with latches on the side. Countersunk screws attach the lower half of the Nose Bowl to both engine access cowlings. Reporter stated the fiberglass Nose Bowl on their Grumman was at least 43 years old. The two upper attach fasteners and washers had worn through the fiberglass and allowed the Nose Bowl to slide forward from its own weight into the back side of the propeller. There is no actual support structure for the Nose Bowl. Their local Mechanic repaired the nose cowl by rebuilding the worn out section of fiberglass. He has not heard of anyone else experiencing the same type of attach point failure. There is a Supplemental Type Certificate (STC) available that allows for a split type (two pieces) Nose Bowl installation. The STC allows for removal of the Nose Bowl without having to remove the propeller.
A pilot reports he heard a pop; felt a jolt forward of the firewall; smelled something burning and noticed an oil colored streak had appeared on the cowling moving aft while flying his Grumman AA-1 aircraft. Suspecting an engine fire; he landed on a Highway. The fiberglass nose cowling had slid forward; contacting propeller and aft side of the flywheel.