It's not that hard. Basic salary for year 1 F/O is $81,292. Annual increment is c.$2,000 per month. Plus Hourly Duty Pay (up to 10% if you work a full 84 hr month (unlikely on 747)). Plus 15.5% by way of pension. Plus $14,000 'housing allowance' (paid as cash). Plus some school fees. Plus cash allowances in outports. Plus overtime if above 84 hrs in a month. Plus 13th month salary in december...probably. Hong Kong dollar is pegged to US dollar at 7.8. Income tax is max 15%.
Suitably qualified S/Os had the opportunity to apply for the F/O positions. Some did.
Hong Kong is really expensive. Schools can be hard to get into, depending on age.