More than 80 per cent of Qantas maintenance workers are worried about safety standards at the airline, a poll has found.

The survey by the Australian Manufacturing Workers Union found 83 per cent were concerned about the safety of aircraft because of staff pressures and offshore maintenance.

About 200 union members across work sites in Melbourne, Avalon, Sydney and Brisbane were asked about the consequences of contracting out maintenance work.

Almost 70 per cent agreed work carried out offshore needed to be re-checked more often, 67 per cent agreed it had to be redone before it met standards, and 64 per cent agreed it was harder to ensure quality.

The safety of Qantas planes has been under scrutiny since late July, when a jumbo made an emergency landing in Manila after an oxygen tank exploded.

Qantas general manager of engineering David Cox said work carried out offshore was overseen by Australian-trained and based engineers.