Name the one outstanding thing about registered aircraft N3977. Be specific, as the FAA Registration will not be of much specific help with this quiz, perhaps my most esoteric yet.

Alright... 1929 Travel Air 4000, owned by CAAA, displayed at Heidrick AG museum at one point, flew for the Precissi Flying Service in '45.

Dropped lots of sulfur on grapes, but that's not very unique.

I wonder if the engine was changed out when it was retrofitted...

I have it as a 1928 Travel Air 4000, but that is not the unique feature of the aircraft. Please keep trying.

5 days later

With over 250 views, here is the answer. This 1928 biplane aircraft converted to a cropduster is the OLDEST crop duster registered and working in the USA, based in northern California. Subject of a Television special, N3977 goes back to the era where ordinary available and suitable production aircraft were converted to have a chemical hopper and release system to dust field crops.

Purpose-design and build crop dusters such as the Piper PA-15 Pawnee of 235 Hp and larger PA-36 Pawnee Brave of 400 Hp (of 1960 and 1973 vintage, respectively), and others like the Air Tractor line with turboprop power are mainly low wing hard-working agricultural aircraft.

Nowadays, the term aerial applicators seems to prevail in this specialized field, and Aspen Helicopters, Inc. based at KOXR locally has been doing helicopter crop-dusting for many years. Less chemical waste and better accuracy are some of the features of a helicopter dusting farm crops and orchards.