On 21 May 1921 they ordered three aircraft for $48,000 each.

It ordered 187 aircraft with the last received by early Q2 2012.

Originally 12 aircraft were ordered but the company went on to build more than 80 Short 184s.

The trials were successful and the aircraft was ordered into production.

A total 40 aircraft were ordered with deliveries beginning in 2005.

With a load of 60 troops it was expected that 50 aircraft would be ordered.

"I estimate that 309 commercial aircraft worth about $21 billion were ordered last year," he said.

Three further aircraft had been ordered and allocated service numbers, but it is not known whether any of these were built.

Another concern for United is that it has fallen behind in ordering new aircraft.

Two aircraft were ordered, but only one was built.