Ask CIOs what keeps them awake at night and legacy mainframes rate high on the priority list.

In a frank admission to ICT Outlook Forum delegates last week, Qantas CIO Fiona Balfour said porting Cobol script from the airline's Unisys Univac was a challenge haunting her waking hours.

In a stern warning to banks, carriers and the government, Balfour said she was not alone and there are plenty of CIOs in the same predicament.

Describing it as a huge, deep and often unaffordable challenge, she said the problems associated with migrating legacy systems in IT shops more than 30 years old is one which the large banks, Telstra and government agencies share.

"They won't be able to see [the problem of legacy migration] yet with the clarity I see it, but that is because I am in a 50-year-old IT shop," Balfour said.

"There are very limited options once you get down to the pointy end of the systems age ... we have had very good business value from them and we forget we invested in something with a relatively short timeframe and we always intended to replace it with something, but then the system gets deeply embedded.

"It gets connected to 250 other systems like our engineering and maintenance systems, so the problems of changing get harder."

Balfour said the airline's engineering and maintenance systems are in Cobol and sit on a Unisys Univac (Sperry) environment.

"We cannot run an airline without them, because they are our client system for the aircraft and as we buy more aircraft we have huge data sets (in terms of volume) that we have to keep online," she said.

"Now these systems are very old, and of the original architects and designers of the system - three of the guys who worked on the system have retired and one of them died two years ago - yet we have had three attempts in the last decade to try and build a business case to get this onto a Unix environment.

"I can cope with Cobol on an EVS (Enterprise Vision System, a business rule and extraction tool) environment, but the overall cost of replacing these systems is huge."

She estimated the cost to be more than $100 million, adding that the business risk is extraordinary.

"If we have one error in data conversion then the fleet has to be grounded," Balfour said.

In the last four years alone, she said Qantas has changed the reservation system, the inventory system and the human resources system.

"We are in the middle of a project to change the general ledger and schedules system; all of these are embedded systems and the options available are to get all Cobol on Univac ported onto an IBM system in order to get the mainframes to run the code. Or we can recompile the data onto Unix," she said.

Balfour said the airline would be lucky to extract business rules from the code and if they were exceptionally lucky they could normalize the data and get it onto a different database.

"But that is probably something we couldn't do in Australia. To do this economically, we have to do it offshore, but then you have risks involved in doing that," Balfour said.

"There is no shortage of Cobol programmers, but my point is, on the assumption that nothing else changes, the time will come [when it has to be done] and I think you have between five and 10 years depending on what happens in the Australian marketplace."