A young fly-in, fly-out worker has combined his imagination, weed killer and a light plane to win the heart and hand of his girlfriend in Western Australia's Great Southern.

Braden Smale, 31, sprayed the message 'WILL U MARRY ME' in eight-metre-high letters with herbicide on his block at Kendenup, before waiting two weeks for the chemical to take effect.

The drill and blast operator, who also holds a private pilot's licence, then hired a Cessna 172 from Albany Aero Club to take his girlfriend Cassandra Pope on a fly-over of his property.

Mr Smale said he disguised the flight as an opportunity to check his crop.

However once they were 1,000 feet over the property, he asked Ms Pope to look down at the runway where he had sprayed the marriage proposal.

"As we were flying over the block she says 'oh the crop looks good and the dam's still got heaps of water in it'," Mr Smale said.

"And I was like 'Oh yeah, what's that over there on the runway?'

"She looked over, and then she didn't say anything to me for a while, and then she looked back and she had tears coming out of her eyes.

"And then she was laughing and in between then I sort of pulled out the ring, sort of in a bit of hysterics you know ... and I said 'Will you marry me?'

"And she said 'Yes, of course I will.'"

Braden Smale and new fiancee Cassandra Pope celebrated by taking a selfie in the aeroplane before flying to Margaret River for lunch. ( Supplied: Braden Smale )

Mr Smales, who works fly-in, fly-out at the Brockman Four mine in the Pilbara, said he had thought hard about how to pop the question to Ms Pope, having seen other examples of proposals writ large with hay bales, smoke trails and on beaches.

"I have heard of people doing something similar and thought that would be a good way to do it," he said.

"It's raised the bar at work, with a few guys at work thinking I've made it a bit hard for them to top that proposal."

Mr Smale said after Ms Pope said yes, the pair celebrated by taking a selfie in the aircraft before flying to Margaret River for a celebratory lunch.