PARIS/HAMBURG (Reuters) - Airbus is mobilizing staff from outside Germany to assist with a tricky production ramp-up of A321 passenger jets at its plant in Hamburg, industry sources said.

FILE PHOTO: The Airbus logo is pictured at Airbus headquarters in Blagnac near Toulouse, France, March 20, 2019. REUTERS/Regis Duvignau

The planemaker has faced a string of industrial problems at the plant, which is responsible for the in-demand A321 model - the largest member of the best-selling single-aisle A320 family.

Although single-aisle jets are increasingly standardized, manufacturing has been complicated by the fact that planes like the 180-240-seat A321 are in demand for long-range trips of up to eight or nine hours as airlines test out new markets.

Such long trips require new multi-class cabins, compared to short- or medium-range trips for which the A321 was originally designed, and Hamburg is the Airbus factory responsible for handling this type of work on the company’s important cash cow.

Airbus is moving workers from other locations to help in the industrial recovery and to prepare for higher production.

“There are staff shortages in Hamburg,” a person familiar with the matter said.

“The long-range variant has three-class seating. This is a completely different technique and requires a lot more work... The management has miscalculated the number of hours required for the aircraft,” a union source told Reuters separately.

Airbus is offering redeployment to some of the 3,500 staff who face losing jobs as output of the A380 superjumbo ends in 2021. It is upgrading some temporary workers to permanent contracts to work on the complex A321 “Cabin Flex” variant.

“The A320 production generally, and especially in Hamburg, is ramping up,” an Airbus spokesman said.

“A321 Head of Versions (the first edition of a new cabin design) are exclusively built in Hamburg. To address the above challenges, attention and resources are shifting to Hamburg.”

Hamburg has felt the brunt of a race to meet growing jet demand because it is introducing new versions of the A321 just as overall production is running faster than ever.

Production has however improved compared to last year, the company’s new operations chief told reporters last week.

Airbus aims to increase production of single-aisle jets to 63 a month in 2021 from about 60 now and has been studying the possibility of 71 a month. Airbus says it will decide in the second half on any future output hikes.