"the pilots on Flight TR996 had switched on a back-up power unit to prevent an overweight landing caused by excess fuel. This led to a slight loss of cabin pressure. While the safety of the flight was not compromised, the pilots decided to deploy the oxygen masks as a precaution"
https://www.straitstimes.com/singapore/sia-group-ceo-apologises-after-oxygen-masks-were-deployed-on-scoot-flight-to-taipei
